在 Android 中使用 Firebase 实时数据库进行用户身份验证和 CRUD 操作

Firebase 是谷歌的著名产品，许多开发人员使用它为他们的网站和应用程序添加后端功能。 Firebase 将使您的后端数据库和处理数据库的工作变得更加轻松。在本文中，我们将看看 Firebase 实时数据库在 Android 中的实现。在本文中，我们将在我们的应用程序中添加电子邮件和密码身份验证，同时我们将使用 Firebase 实时数据库在我们的应用程序中执行CRUD（创建、读取、更新和删除）操作。

我们将在本文中构建什么？

在本文中，我们将构建一个简单的 Android 应用程序，我们将首先使用他们的电子邮件和密码对用户进行身份验证。之后，我们将在回收站视图中显示 Geeks for Geeks 上可用的课程列表。我们将能够对这些课程执行 CRUD 操作。在下面的视频中，我们将看到我们将在本文中构建的内容。

分步实施

第 1 步：创建一个新项目

要在 Android Studio 中创建新项目，请参阅如何在 Android Studio 中创建/启动新项目。请注意，选择Java作为编程语言。

第 2 步：将您的应用连接到 Firebase

创建新项目后，导航到顶部栏上的“工具”选项。在里面点击 Firebase。单击 Firebase 后，您可以在屏幕截图中看到下面提到的右列。

在该列中导航到 Firebase 实时数据库。单击该选项，您将看到“将应用程序连接到 Firebase”和“将 Firebase 实时数据库添加到您的应用程序”这两个选项。单击立即连接，您的应用将连接到 Firebase。之后单击第二个选项，现在您的应用程序已连接到 Firebase。

将您的应用连接到 Firebase 后，您将看到以下屏幕。

之后验证 Firebase 实时数据库的依赖项是否已添加到我们的 Gradle 文件中。现在导航到app > Gradle Scripts并在该文件中检查是否添加了以下依赖项。如果您的 build.gradle 文件中未添加以下依赖项。在依赖项部分添加以下依赖项。下面是完整的依赖项部分，其中有身份验证和数据库的依赖项。

dependencies {
    implementation 'androidx.appcompat:appcompat:1.3.0'
    implementation 'com.google.android.material:material:1.4.0'
    // dependency for picasso for loading image from url 
    implementation 'com.squareup.picasso:picasso:2.71828'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    // dependency for firebase database. 
    implementation 'com.google.firebase:firebase-database:20.0.0'
    implementation platform('com.google.firebase:firebase-bom:28.2.1')
    // dependency for firebase authentication. 
    implementation 'com.google.firebase:firebase-auth'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

添加此依赖项后，同步您的项目，现在我们已准备好创建我们的应用程序。如果您想详细了解如何将您的应用连接到 Firebase。请参阅本文以详细了解将 Firebase 添加到 Android 应用程序。

第 3 步：创建 4 个不同的空活动

导航到应用程序 > 您的应用程序包名称 > 右键单击它 > 新建 > 活动 > 选择空活动并创建新活动。下面是我们在创建新活动时必须传递的四个不同活动的名称。

• AddCourseActivity ：我们将使用此活动添加新课程。
• EditCourseActivity ：此活动将用于编辑我们的课程以及删除我们的课程。
• LoginActivity ：此活动将用于现有用户登录的登录目的。
• RegisterActivity ：此活动用于注册新用户。

主要活动。 Java文件将已经存在，我们将在其中显示 RecyclerView 中的课程列表。

第 4 步：使用 AndroidManifest.xml 文件

导航到app > AndroidManifest.xml文件并为其添加 Internet 权限。下面是 AndroidManifest.xml 文件的完整代码。在此文件中，我们还将启动器活动更改为登录活动。代码中添加了注释，以便更详细地了解。

步骤 5：更新 colors.xml 文件

导航到app > res > values > colors.xml并将以下颜色添加到其中。

XML

    #296D98
    #296D98
    #296D98
    #FF03DAC5
    #FF018786
    #FF000000
    #FFFFFFFF
  
    #0e2433
    #1C4966
  
    #22252D
    #296D98
  
    #296D98
    #424242
    #ffa500
    #0D2162
    #17388E
    #12B2E6
  

第 6 步：更新我们的 themes.xml 文件

导航到app > res > values > themes.xml并将以下代码添加到其中。

XML

第 7 步：为我们的按钮和自定义进度条背景创建自定义背景

导航到应用程序 > res > drawable > 右键单击它 > New Drawable Resource 文件并将其命名为button_back并向其添加以下代码。代码中添加注释，详细了解。

导航到应用程序 > res > drawable > 右键单击它 > New Drawable Resource 文件并将其命名为progress_back并将以下代码添加到其中。代码中添加注释，详细了解。

步骤 8：使用 activity_register.xml 文件

导航到app > res > activity_register.xml并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

第 9 步：使用 RegisterActivity。 Java文件

导航到应用程序 > Java > 您应用程序的包名称 > RegisterActivity。 Java文件并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
  
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputEditText;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
  
public class RegisterActivity extends AppCompatActivity {
  
    // cretaing variables for edit text and textview, 
    // firebase auth, button and progress bar. 
    private TextInputEditText userNameEdt, passwordEdt, confirmPwdEdt;
    private TextView loginTV;
    private Button registerBtn;
    private FirebaseAuth mAuth;
    private ProgressBar loadingPB;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
          
        // initializing all our variables. 
        userNameEdt = findViewById(R.id.idEdtUserName);
        passwordEdt = findViewById(R.id.idEdtPassword);
        loadingPB = findViewById(R.id.idPBLoading);
        confirmPwdEdt = findViewById(R.id.idEdtConfirmPassword);
        loginTV = findViewById(R.id.idTVLoginUser);
        registerBtn = findViewById(R.id.idBtnRegister);
        mAuth = FirebaseAuth.getInstance();
  
        // adding on click for login tv.
        loginTV.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // opening a login activity on clicking login text. 
                Intent i = new Intent(RegisterActivity.this, LoginActivity.class);
                startActivity(i);
            }
        });
          
        // adding click listener for register button.
        registerBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // hiding our progress bar. 
                loadingPB.setVisibility(View.VISIBLE);
  
                // getting data fro =m our edit text. 
                String userName = userNameEdt.getText().toString();
                String pwd = passwordEdt.getText().toString();
                String cnfPwd = confirmPwdEdt.getText().toString();
  
                // checking if the password and confirm password is equal or not. 
                if (!pwd.equals(cnfPwd)) {
                    Toast.makeText(RegisterActivity.this, "Please check both having same password..", Toast.LENGTH_SHORT).show();
                } else if (TextUtils.isEmpty(userName) && TextUtils.isEmpty(pwd) && TextUtils.isEmpty(cnfPwd)) {
  
                    // checking if the text fields are empty or not. 
                    Toast.makeText(RegisterActivity.this, "Please enter your credentials..", Toast.LENGTH_SHORT).show();
                } else {
  
                    // on below line we are creating a new user by passing email and password.
                    mAuth.createUserWithEmailAndPassword(userName, pwd).addOnCompleteListener(new OnCompleteListener() {
                        @Override
                        public void onComplete(@NonNull Task task) {
                            // on below line we are checking if the task is success or not. 
                            if (task.isSuccessful()) {
  
                                // in on success method we are hiding our progress bar and opening a login activity. 
                                loadingPB.setVisibility(View.GONE);
                                Toast.makeText(RegisterActivity.this, "User Registered..", Toast.LENGTH_SHORT).show();
                                Intent i = new Intent(RegisterActivity.this, LoginActivity.class);
                                startActivity(i);
                                finish();
                            } else {
  
                                // in else condition we are displaying a failure toast message. 
                                loadingPB.setVisibility(View.GONE);
                                Toast.makeText(RegisterActivity.this, "Fail to register user..", Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
                }
            }
        });
    }
}

步骤 10：使用 activity_login.xml 文件

导航到app > res > activity_login.xml并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

第 11 步：使用 LoginActivity。 Java文件

导航到应用程序 > Java > 您应用程序的包名称 > LoginActivity。 Java文件并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
  
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputEditText;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
  
public class LoginActivity extends AppCompatActivity {
  
    // creating variable for edit text, textview, 
    // button, progress bar and firebase auth.
    private TextInputEditText userNameEdt, passwordEdt;
    private Button loginBtn;
    private TextView newUserTV;
    private FirebaseAuth mAuth;
    private ProgressBar loadingPB;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        // initializing all our variables. 
        userNameEdt = findViewById(R.id.idEdtUserName);
        passwordEdt = findViewById(R.id.idEdtPassword);
        loginBtn = findViewById(R.id.idBtnLogin);
        newUserTV = findViewById(R.id.idTVNewUser);
        mAuth = FirebaseAuth.getInstance();
        loadingPB = findViewById(R.id.idPBLoading);
        // adding click listener for our new user tv.
        newUserTV.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // on below line opening a login activity. 
                Intent i = new Intent(LoginActivity.this, RegisterActivity.class);
                startActivity(i);
            }
        });
  
        // adding on click listener for our login button. 
        loginBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // hiding our progress bar. 
                loadingPB.setVisibility(View.VISIBLE);
                // getting data from our edit text on below line. 
                String email = userNameEdt.getText().toString();
                String password = passwordEdt.getText().toString();
                // on below line validating the text input. 
                if (TextUtils.isEmpty(email) && TextUtils.isEmpty(password)) {
                    Toast.makeText(LoginActivity.this, "Please enter your credentials..", Toast.LENGTH_SHORT).show();
                    return;
                }
                // on below line we are calling a sign in method and passing email and password to it. 
                mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(new OnCompleteListener() {
                    @Override
                    public void onComplete(@NonNull Task task) {
                        // on below line we are checking if the task is succes or not. 
                        if (task.isSuccessful()) {
                            // on below line we are hiding our progress bar. 
                            loadingPB.setVisibility(View.GONE);
                            Toast.makeText(LoginActivity.this, "Login Successful..", Toast.LENGTH_SHORT).show();
                            // on below line we are opening our mainactivity. 
                            Intent i = new Intent(LoginActivity.this, MainActivity.class);
                            startActivity(i);
                            finish();
                        } else {
                            // hiding our progress bar and displaying a toast message.
                            loadingPB.setVisibility(View.GONE);
                            Toast.makeText(LoginActivity.this, "Please enter valid user credentials..", Toast.LENGTH_SHORT).show();
                        }
                    }
                });
            }
        });
    }
  
    @Override
    protected void onStart() {
        super.onStart();
        // in on start method checking if
        // the user is already sign in. 
        FirebaseUser user = mAuth.getCurrentUser();
        if (user != null) {
            // if the user is not null then we are
              // opening a main activity on below line. 
            Intent i = new Intent(LoginActivity.this, MainActivity.class);
            startActivity(i);
            this.finish();
        }
    }
}

第 12 步：为要在 RecyclerView 中显示的数据创建一个 Modal 类

导航到应用程序 > Java > 您应用程序的包名称 > 右键单击它 > 新建 > Java类并将其命名为CourseRVModal并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.os.Parcel;
import android.os.Parcelable;
  
public class CourseRVModal implements Parcelable {
    // creating variables for our different fields. 
    private String courseName;
    private String courseDescription;
    private String coursePrice;
    private String bestSuitedFor;
    private String courseImg;
    private String courseLink;
    private String courseId;
  
  
    public String getCourseId() {
        return courseId;
    }
  
    public void setCourseId(String courseId) {
        this.courseId = courseId;
    }
  
  
    // creating an empty constructor. 
    public CourseRVModal() {
  
    }
  
    protected CourseRVModal(Parcel in) {
        courseName = in.readString();
        courseId = in.readString();
        courseDescription = in.readString();
        coursePrice = in.readString();
        bestSuitedFor = in.readString();
        courseImg = in.readString();
        courseLink = in.readString();
    }
  
    public static final Creator CREATOR = new Creator() {
        @Override
        public CourseRVModal createFromParcel(Parcel in) {
            return new CourseRVModal(in);
        }
  
        @Override
        public CourseRVModal[] newArray(int size) {
            return new CourseRVModal[size];
        }
    };
  
    // creating getter and setter methods. 
    public String getCourseName() {
        return courseName;
    }
  
    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }
  
    public String getCourseDescription() {
        return courseDescription;
    }
  
    public void setCourseDescription(String courseDescription) {
        this.courseDescription = courseDescription;
    }
  
    public String getCoursePrice() {
        return coursePrice;
    }
  
    public void setCoursePrice(String coursePrice) {
        this.coursePrice = coursePrice;
    }
  
    public String getBestSuitedFor() {
        return bestSuitedFor;
    }
  
    public void setBestSuitedFor(String bestSuitedFor) {
        this.bestSuitedFor = bestSuitedFor;
    }
  
    public String getCourseImg() {
        return courseImg;
    }
  
    public void setCourseImg(String courseImg) {
        this.courseImg = courseImg;
    }
  
    public String getCourseLink() {
        return courseLink;
    }
  
    public void setCourseLink(String courseLink) {
        this.courseLink = courseLink;
    }
  
  
    public CourseRVModal(String courseId, String courseName, String courseDescription, String coursePrice, String bestSuitedFor, String courseImg, String courseLink) {
        this.courseName = courseName;
        this.courseId = courseId;
        this.courseDescription = courseDescription;
        this.coursePrice = coursePrice;
        this.bestSuitedFor = bestSuitedFor;
        this.courseImg = courseImg;
        this.courseLink = courseLink;
    }
  
    @Override
    public int describeContents() {
        return 0;
    }
  
    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(courseName);
        dest.writeString(courseId);
        dest.writeString(courseDescription);
        dest.writeString(coursePrice);
        dest.writeString(bestSuitedFor);
        dest.writeString(courseImg);
        dest.writeString(courseLink);
    }
}

数据库中的 CREATE 操作

第 13 步：使用 activity_add_course.xml 文件

导航到app > res > layout > activity_add_course.xml并将以下代码添加到其中。代码中添加了注释以了解更多细节。

第 14 步：使用 AddCourseActivity。 Java文件

导航到应用程序 > Java > 您应用程序的包名称 > AddCourseActivity。 Java文件并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
  
import com.google.android.material.textfield.TextInputEditText;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
  
public class AddCourseActivity extends AppCompatActivity {
  
    // creating variables for our button, edit text,
    // firebase database, database refrence, progress bar.
    private Button addCourseBtn;
    private TextInputEditText courseNameEdt, courseDescEdt, coursePriceEdt, bestSuitedEdt, courseImgEdt, courseLinkEdt;
    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    private ProgressBar loadingPB;
    private String courseID;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_course);
        // initializing all our variables. 
        addCourseBtn = findViewById(R.id.idBtnAddCourse);
        courseNameEdt = findViewById(R.id.idEdtCourseName);
        courseDescEdt = findViewById(R.id.idEdtCourseDescription);
        coursePriceEdt = findViewById(R.id.idEdtCoursePrice);
        bestSuitedEdt = findViewById(R.id.idEdtSuitedFor);
        courseImgEdt = findViewById(R.id.idEdtCourseImageLink);
        courseLinkEdt = findViewById(R.id.idEdtCourseLink);
        loadingPB = findViewById(R.id.idPBLoading);
        firebaseDatabase = FirebaseDatabase.getInstance();
        // on below line creating our database reference. 
        databaseReference = firebaseDatabase.getReference("Courses");
        // adding click listener for our add course button. 
        addCourseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                loadingPB.setVisibility(View.VISIBLE);
                // getting data from our edit text. 
                String courseName = courseNameEdt.getText().toString();
                String courseDesc = courseDescEdt.getText().toString();
                String coursePrice = coursePriceEdt.getText().toString();
                String bestSuited = bestSuitedEdt.getText().toString();
                String courseImg = courseImgEdt.getText().toString();
                String courseLink = courseLinkEdt.getText().toString();
                courseID = courseName;
                // on below line we are passing all data to our modal class. 
                CourseRVModal courseRVModal = new CourseRVModal(courseID, courseName, courseDesc, coursePrice, bestSuited, courseImg, courseLink);
                // on below line we are calling a add value event 
                // to pass data to firebase database. 
                databaseReference.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {
                        // on below line we are setting data in our firebase database. 
                        databaseReference.child(courseID).setValue(courseRVModal);
                        // displaying a toast message. 
                        Toast.makeText(AddCourseActivity.this, "Course Added..", Toast.LENGTH_SHORT).show();
                        // starting a main activity. 
                        startActivity(new Intent(AddCourseActivity.this, MainActivity.class));
                    }
  
                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {
                        // displaying a failure message on below line. 
                        Toast.makeText(AddCourseActivity.this, "Fail to add Course..", Toast.LENGTH_SHORT).show();
                    }
                });
            }
        });
    }
}

从数据库读取操作

第 15 步：在我们的 Recycler 视图中为每门课程创建一个项目。

导航到app > res > 右键单击它 > 新建布局资源文件并将其命名为course_rv_item并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

第 16 步：使用 activity_main.xml 文件

导航到app > res > layout > activity_main.xml并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

第十七步：创建一个Adapter类，用于为RecyclerView的每一项设置数据

导航到应用程序 > Java > 您应用程序的包名称 > 右键单击它 > 新建 > Java类并将其命名为CourseRVAdapter并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.ImageView;
import android.widget.TextView;
  
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
  
import com.squareup.picasso.Picasso;
  
import java.util.ArrayList;
  
public class CourseRVAdapter extends RecyclerView.Adapter {
    // creating variables for our list, context, interface and position. 
    private ArrayList courseRVModalArrayList;
    private Context context;
    private CourseClickInterface courseClickInterface;
    int lastPos = -1;
  
    // creating a constructor. 
    public CourseRVAdapter(ArrayList courseRVModalArrayList, Context context, CourseClickInterface courseClickInterface) {
        this.courseRVModalArrayList = courseRVModalArrayList;
        this.context = context;
        this.courseClickInterface = courseClickInterface;
    }
  
    @NonNull
    @Override
    public CourseRVAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        // inflating our layout file on below line. 
        View view = LayoutInflater.from(context).inflate(R.layout.course_rv_item, parent, false);
        return new ViewHolder(view);
    }
  
    @Override
    public void onBindViewHolder(@NonNull CourseRVAdapter.ViewHolder holder, int position) {
        // setting data to our recycler view item on below line. 
        CourseRVModal courseRVModal = courseRVModalArrayList.get(position);
        holder.courseTV.setText(courseRVModal.getCourseName());
        holder.coursePriceTV.setText("Rs. " + courseRVModal.getCoursePrice());
        Picasso.get().load(courseRVModal.getCourseImg()).into(holder.courseIV);
        // adding animation to recycler view item on below line. 
        setAnimation(holder.itemView, position);
        holder.courseIV.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                courseClickInterface.onCourseClick(position);
            }
        });
    }
  
    private void setAnimation(View itemView, int position) {
        if (position > lastPos) {
            // on below line we are setting animation. 
            Animation animation = AnimationUtils.loadAnimation(context, android.R.anim.slide_in_left);
            itemView.setAnimation(animation);
            lastPos = position;
        }
    }
  
    @Override
    public int getItemCount() {
        return courseRVModalArrayList.size();
    }
  
    public static class ViewHolder extends RecyclerView.ViewHolder {
        // creating variable for our image view and text view on below line. 
        private ImageView courseIV;
        private TextView courseTV, coursePriceTV;
  
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            // initializing all our variables on below line. 
            courseIV = itemView.findViewById(R.id.idIVCourse);
            courseTV = itemView.findViewById(R.id.idTVCOurseName);
            coursePriceTV = itemView.findViewById(R.id.idTVCousePrice);
        }
    }
  
    // creating a interface for on click 
    public interface CourseClickInterface {
        void onCourseClick(int position);
    }
}

步骤 18：创建用于显示菜单选项的菜单文件

导航到应用程序 > res > 右键单击它 > 新建 > 目录并将其命名为菜单。现在导航到菜单目录，右键单击它 > 新建 > 菜单资源文件并将其命名为menu_main.xml并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

步骤 19：创建用于显示底部工作表的布局文件

导航到应用程序 > res > 布局 > 右键单击它 > 新建 > 布局资源文件并将其命名为bottom_sheet_layout并向其添加以下代码。代码中添加了注释，以便更详细地了解。

第 20 步：使用 MainActivity。 Java文件

导航到应用程序 > Java > 您应用程序的包名称 > MainActivity。 Java文件并将以下代码添加到其中。代码中添加注释，详细了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
  
import com.google.android.material.bottomsheet.BottomSheetDialog;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.squareup.picasso.Picasso;
  
import java.util.ArrayList;
  
public class MainActivity extends AppCompatActivity implements CourseRVAdapter.CourseClickInterface {
  
    // creating variables for fab, firebase database, 
    // progress bar, list, adapter,firebase auth,
    // recycler view and relative layout.
    private FloatingActionButton addCourseFAB;
    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    private RecyclerView courseRV;
    private FirebaseAuth mAuth;
    private ProgressBar loadingPB;
    private ArrayList courseRVModalArrayList;
    private CourseRVAdapter courseRVAdapter;
    private RelativeLayout homeRL;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // initializing all our variables.
        courseRV = findViewById(R.id.idRVCourses);
        homeRL = findViewById(R.id.idRLBSheet);
        loadingPB = findViewById(R.id.idPBLoading);
        addCourseFAB = findViewById(R.id.idFABAddCourse);
        firebaseDatabase = FirebaseDatabase.getInstance();
        mAuth = FirebaseAuth.getInstance();
        courseRVModalArrayList = new ArrayList<>();
        // on below line we are getting database reference.
        databaseReference = firebaseDatabase.getReference("Courses");
        // on below line adding a click listener for our floating action button.
        addCourseFAB.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // opening a new activity for adding a course.
                Intent i = new Intent(MainActivity.this, AddCourseActivity.class);
                startActivity(i);
            }
        });
        // on below line initializing our adapter class.
        courseRVAdapter = new CourseRVAdapter(courseRVModalArrayList, this, this::onCourseClick);
        // setting layout malinger to recycler view on below line.
        courseRV.setLayoutManager(new LinearLayoutManager(this));
        // setting adapter to recycler view on below line.
        courseRV.setAdapter(courseRVAdapter);
        // on below line calling a method to fetch courses from database.
        getCourses();
    }
  
    private void getCourses() {
        // on below line clearing our list.
        courseRVModalArrayList.clear();
        // on below line we are calling add child event listener method to read the data.
        databaseReference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                // on below line we are hiding our progress bar.
                loadingPB.setVisibility(View.GONE);
                // adding snapshot to our array list on below line.
                courseRVModalArrayList.add(snapshot.getValue(CourseRVModal.class));
                // notifying our adapter that data has changed.
                courseRVAdapter.notifyDataSetChanged();
            }
  
            @Override
            public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                // this method is called when new child is added
                // we are notifying our adapter and making progress bar
                // visibility as gone.
                loadingPB.setVisibility(View.GONE);
                courseRVAdapter.notifyDataSetChanged();
            }
  
            @Override
            public void onChildRemoved(@NonNull DataSnapshot snapshot) {
                // notifying our adapter when child is removed.
                courseRVAdapter.notifyDataSetChanged();
                loadingPB.setVisibility(View.GONE);
  
            }
  
            @Override
            public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                // notifying our adapter when child is moved.
                courseRVAdapter.notifyDataSetChanged();
                loadingPB.setVisibility(View.GONE);
            }
  
            @Override
            public void onCancelled(@NonNull DatabaseError error) {
  
            }
        });
    }
  
    @Override
    public void onCourseClick(int position) {
        // calling a method to display a bottom sheet on below line.
        displayBottomSheet(courseRVModalArrayList.get(position));
    }
  
    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        // adding a click listener for option selected on below line.
        int id = item.getItemId();
        switch (id) {
            case R.id.idLogOut:
                // displaying a toast message on user logged out inside on click.
                Toast.makeText(getApplicationContext(), "User Logged Out", Toast.LENGTH_LONG).show();
                // on below line we are signing out our user.
                mAuth.signOut();
                // on below line we are opening our login activity.
                Intent i = new Intent(MainActivity.this, LoginActivity.class);
                startActivity(i);
                this.finish();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
  
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // on below line we are inflating our menu
        // file for displaying our menu options.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }
  
    private void displayBottomSheet(CourseRVModal modal) {
        // on below line we are creating our bottom sheet dialog.
        final BottomSheetDialog bottomSheetTeachersDialog = new BottomSheetDialog(this, R.style.BottomSheetDialogTheme);
        // on below line we are inflating our layout file for our bottom sheet.
        View layout = LayoutInflater.from(this).inflate(R.layout.bottom_sheet_layout, homeRL);
        // setting content view for bottom sheet on below line.
        bottomSheetTeachersDialog.setContentView(layout);
        // on below line we are setting a cancelable
        bottomSheetTeachersDialog.setCancelable(false);
        bottomSheetTeachersDialog.setCanceledOnTouchOutside(true);
        // calling a method to display our bottom sheet.
        bottomSheetTeachersDialog.show();
        // on below line we are creating variables for
        // our text view and image view inside bottom sheet
        // and initialing them with their ids.
        TextView courseNameTV = layout.findViewById(R.id.idTVCourseName);
        TextView courseDescTV = layout.findViewById(R.id.idTVCourseDesc);
        TextView suitedForTV = layout.findViewById(R.id.idTVSuitedFor);
        TextView priceTV = layout.findViewById(R.id.idTVCoursePrice);
        ImageView courseIV = layout.findViewById(R.id.idIVCourse);
        // on below line we are setting data to different views on below line.
        courseNameTV.setText(modal.getCourseName());
        courseDescTV.setText(modal.getCourseDescription());
        suitedForTV.setText("Suited for " + modal.getBestSuitedFor());
        priceTV.setText("Rs." + modal.getCoursePrice());
        Picasso.get().load(modal.getCourseImg()).into(courseIV);
        Button viewBtn = layout.findViewById(R.id.idBtnVIewDetails);
        Button editBtn = layout.findViewById(R.id.idBtnEditCourse);
  
        // adding on click listener for our edit button.
        editBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // on below line we are opening our EditCourseActivity on below line.
                Intent i = new Intent(MainActivity.this, EditCourseActivity.class);
                // on below line we are passing our course modal
                i.putExtra("course", modal);
                startActivity(i);
            }
        });
        // adding click listener for our view button on below line.
        viewBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // on below line we are navigating to browser
                  // for displaying course details from its url
                Intent i = new Intent(Intent.ACTION_VIEW);
                i.setData(Uri.parse(modal.getCourseLink()));
                startActivity(i);
            }
        });
    }
}

数据库中的编辑和删除操作

步骤 21：使用 activity_edit_course.xml 文件

导航到app > res > layout > activity_edit_course.xml并将以下代码添加到其中。代码中添加注释，详细了解。

第 22 步：使用 EditCourseActivity。 Java文件

导航到应用程序 > Java > 您应用程序的包名称 > EditCourseActivity。 Java文件并将以下代码添加到其中。代码中添加了注释，以便更详细地了解。

Java

package com.gtappdevelopers.firebasecrudapp;
  
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
  
import com.google.android.material.textfield.TextInputEditText;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
  
import java.util.HashMap;
import java.util.Map;
  
public class EditCourseActivity extends AppCompatActivity {
  
    // creating variables for our edit text, firebase database,
    // database reference, course rv modal,progress bar. 
    private TextInputEditText courseNameEdt, courseDescEdt, coursePriceEdt, bestSuitedEdt, courseImgEdt, courseLinkEdt;
    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    CourseRVModal courseRVModal;
    private ProgressBar loadingPB;
    // creating a string for our course id. 
    private String courseID;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_edit_course);
        // initializing all our variables on below line. 
        Button addCourseBtn = findViewById(R.id.idBtnAddCourse);
        courseNameEdt = findViewById(R.id.idEdtCourseName);
        courseDescEdt = findViewById(R.id.idEdtCourseDescription);
        coursePriceEdt = findViewById(R.id.idEdtCoursePrice);
        bestSuitedEdt = findViewById(R.id.idEdtSuitedFor);
        courseImgEdt = findViewById(R.id.idEdtCourseImageLink);
        courseLinkEdt = findViewById(R.id.idEdtCourseLink);
        loadingPB = findViewById(R.id.idPBLoading);
        firebaseDatabase = FirebaseDatabase.getInstance();
        // on below line we are getting our modal class on which we have passed.
        courseRVModal = getIntent().getParcelableExtra("course");
        Button deleteCourseBtn = findViewById(R.id.idBtnDeleteCourse);
  
        if (courseRVModal != null) {
            // on below line we are setting data to our edit text from our modal class. 
            courseNameEdt.setText(courseRVModal.getCourseName());
            coursePriceEdt.setText(courseRVModal.getCoursePrice());
            bestSuitedEdt.setText(courseRVModal.getBestSuitedFor());
            courseImgEdt.setText(courseRVModal.getCourseImg());
            courseLinkEdt.setText(courseRVModal.getCourseLink());
            courseDescEdt.setText(courseRVModal.getCourseDescription());
            courseID = courseRVModal.getCourseId();
        }
  
        // on below line we are initialing our database reference and we are adding a child as our course id. 
        databaseReference = firebaseDatabase.getReference("Courses").child(courseID);
        // on below line we are adding click listener for our add course button. 
        addCourseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // on below line we are making our progress bar as visible. 
                loadingPB.setVisibility(View.VISIBLE);
                // on below line we are getting data from our edit text. 
                String courseName = courseNameEdt.getText().toString();
                String courseDesc = courseDescEdt.getText().toString();
                String coursePrice = coursePriceEdt.getText().toString();
                String bestSuited = bestSuitedEdt.getText().toString();
                String courseImg = courseImgEdt.getText().toString();
                String courseLink = courseLinkEdt.getText().toString();
                // on below line we are creating a map for 
                // passing a data using key and value pair. 
                Map map = new HashMap<>();
                map.put("courseName", courseName);
                map.put("courseDescription", courseDesc);
                map.put("coursePrice", coursePrice);
                map.put("bestSuitedFor", bestSuited);
                map.put("courseImg", courseImg);
                map.put("courseLink", courseLink);
                map.put("courseId", courseID);
  
                // on below line we are calling a database reference on
                // add value event listener and on data change method
                databaseReference.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {
                        // making progress bar visibility as gone. 
                        loadingPB.setVisibility(View.GONE);
                        // adding a map to our database. 
                        databaseReference.updateChildren(map);
                        // on below line we are displaying a toast message. 
                        Toast.makeText(EditCourseActivity.this, "Course Updated..", Toast.LENGTH_SHORT).show();
                        // opening a new activity after updating our coarse. 
                        startActivity(new Intent(EditCourseActivity.this, MainActivity.class));
                    }
  
                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {
                        // displaying a failure message on toast. 
                        Toast.makeText(EditCourseActivity.this, "Fail to update course..", Toast.LENGTH_SHORT).show();
                    }
                });
            }
        });
  
        // adding a click listener for our delete course button.
        deleteCourseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // calling a method to delete a course. 
                deleteCourse();
            }
        });
  
    }
  
    private void deleteCourse() {
        // on below line calling a method to delete the course.
        databaseReference.removeValue();
        // displaying a toast message on below line. 
        Toast.makeText(this, "Course Deleted..", Toast.LENGTH_SHORT).show();
        // opening a main activity on below line.
        startActivity(new Intent(EditCourseActivity.this, MainActivity.class));
    }
}

Note: All the drawable used inside the application are present in the app > res > drawable. You can check out the project on the below GitHub link.  

现在运行您的应用程序并查看应用程序的输出。

输出：