如何将ArrayList保存到Android中的SharedPreferences？

Android中的SharedPreferences是本地存储，用于在电话存储中存储字符串，整数和变量，以便我们可以管理应用程序的状态。我们已经看到将简单变量存储在具有键和值对的共享首选项中。在本文中，我们将看到如何在我们的Android应用程序中将ArrayList存储到共享首选项。

我们将在本文中构建什么?

我们将构建一个简单的应用程序，在其中将在简单的RecyclerView中显示课程名称及其描述，并将所有这些数据存储在共享的首选项中。因此，当我们关闭应用程序并重新打开应用程序时，所有数据将保存在共享的首选项中，并保持回收者视图的状态。下面提供了一个示例视频，以使您对我们在本文中将要做的事情有个大概的了解。注意，我们将使用Java语言实现该项目。

分步实施

步骤1：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。

步骤2：在build.gradle中为gson添加依赖项

导航到应用程序> Gradle脚本> build.gradle(app)并在依赖项部分添加以下依赖项。

implementation ‘com.google.code.gson:gson:2.8.5’

添加此依赖项后，同步您的项目。

第3步：创建用于存储数据的模式类

导航到应用程序> Java >您的应用程序的程序包名称>右键单击它>新建> Java类，并将您的类命名为CourseModal，然后将以下代码添加到其中。

Java

public class CourseModal {
  
    // variables for our course 
    // name and description.
    private String courseName;
    private String courseDescription;
  
    // creating constructor for our variables.
    public CourseModal(String courseName, String courseDescription) {
        this.courseName = courseName;
        this.courseDescription = courseDescription;
    }
  
    // 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;
    }
}

步骤4：为我们的RecyclerView项目创建一个布局文件

导航到应用程序> res>布局>右键单击它>新建>布局资源文件，并将您的布局命名为course_rv_item ，并将以下代码添加到其中。

第5步：创建一个适配器类以将数据设置为我们RecyclerView的项目

导航到应用程序> Java >应用程序的程序包名称>右键单击它>新建> Java类，并将其命名为CourseAdapter，然后将以下代码添加到其中。

Java

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
  
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
  
import java.util.ArrayList;
  
public class CourseAdapter extends RecyclerView.Adapter {
      
    // creating a variable for array list and context.
    private ArrayList courseModalArrayList;
    private Context context;
  
    // creating a constructor for our variables.
    public CourseAdapter(ArrayList courseModalArrayList, Context context) {
        this.courseModalArrayList = courseModalArrayList;
        this.context = context;
    }
  
    @NonNull
    @Override
    public CourseAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        // below line is to inflate our layout.
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.course_rv_item, parent, false);
        return new ViewHolder(view);
    }
  
    @Override
    public void onBindViewHolder(@NonNull CourseAdapter.ViewHolder holder, int position) {
        // setting data to our views of recycler view.
        CourseModal modal = courseModalArrayList.get(position);
        holder.courseNameTV.setText(modal.getCourseName());
        holder.courseDescTV.setText(modal.getCourseDescription());
    }
  
    @Override
    public int getItemCount() {
        // returning the size of array list.
        return courseModalArrayList.size();
    }
  
    public class ViewHolder extends RecyclerView.ViewHolder {
          
        // creating variables for our views.
        private TextView courseNameTV, courseDescTV;
  
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
              
            // initializing our views with their ids.
            courseNameTV = itemView.findViewById(R.id.idTVCourseName);
            courseDescTV = itemView.findViewById(R.id.idTVCourseDescription);
        }
    }
}

步骤6：使用activity_main.xml文件

导航到应用程序> res>布局> activity_main.xml，然后将以下代码添加到该文件中。以下是activity_main.xml文件的代码。

步骤7：使用MainActivity。 Java文件

转到MainActivity。 Java文件并参考以下代码。下面是MainActivity的代码。 Java文件。在代码内部添加了注释，以更详细地了解代码。

Java

import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
  
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
  
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
  
import java.lang.reflect.Type;
import java.util.ArrayList;
  
public class MainActivity extends AppCompatActivity {
  
    // creating variables for our ui components.
    private EditText courseNameEdt, courseDescEdt;
    private Button addBtn, saveBtn;
    private RecyclerView courseRV;
      
    // variable for our adapter class and array list
    private CourseAdapter adapter;
    private ArrayList courseModalArrayList;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
          
        // initializing our variables.
        courseNameEdt = findViewById(R.id.idEdtCourseName);
        courseDescEdt = findViewById(R.id.idEdtCourseDescription);
        addBtn = findViewById(R.id.idBtnAdd);
        saveBtn = findViewById(R.id.idBtnSave);
        courseRV = findViewById(R.id.idRVCourses);
          
        // calling method to load data
        // from shared prefs.
        loadData();
          
        // calling method to build
        // recycler view.
        buildRecyclerView();
          
        // on click listener for adding data to array list.
        addBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // below line is use to add data to array list.
                courseModalArrayList.add(new CourseModal(courseNameEdt.getText().toString(), courseDescEdt.getText().toString()));
                // notifying adapter when new data added.
                adapter.notifyItemInserted(courseModalArrayList.size());
            }
        });
        // on click listener for saving data in shared preferences.
        saveBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // calling method to save data in shared prefs.
                saveData();
            }
        });
    }
  
    private void buildRecyclerView() {
        // initializing our adapter class.
        adapter = new CourseAdapter(courseModalArrayList, MainActivity.this);
          
        // adding layout manager to our recycler view.
        LinearLayoutManager manager = new LinearLayoutManager(this);
        courseRV.setHasFixedSize(true);
          
        // setting layout manager to our recycler view.
        courseRV.setLayoutManager(manager);
          
        // setting adapter to our recycler view.
        courseRV.setAdapter(adapter);
    }
  
    private void loadData() {
        // method to load arraylist from shared prefs
        // initializing our shared prefs with name as 
        // shared preferences.
        SharedPreferences sharedPreferences = getSharedPreferences("shared preferences", MODE_PRIVATE);
         
        // creating a variable for gson.
        Gson gson = new Gson();
          
        // below line is to get to string present from our 
        // shared prefs if not present setting it as null.
        String json = sharedPreferences.getString("courses", null);
          
        // below line is to get the type of our array list.
        Type type = new TypeToken>() {}.getType();
          
        // in below line we are getting data from gson 
        // and saving it to our array list
        courseModalArrayList = gson.fromJson(json, type);
          
        // checking below if the array list is empty or not
        if (courseModalArrayList == null) {
            // if the array list is empty
            // creating a new array list.
            courseModalArrayList = new ArrayList<>();
        }
    }
  
    private void saveData() {
        // method for saving the data in array list.
        // creating a variable for storing data in
        // shared preferences.
        SharedPreferences sharedPreferences = getSharedPreferences("shared preferences", MODE_PRIVATE);
          
        // creating a variable for editor to 
        // store data in shared preferences.
        SharedPreferences.Editor editor = sharedPreferences.edit();
          
        // creating a new variable for gson.
        Gson gson = new Gson();
         
        // getting data from gson and storing it in a string.
        String json = gson.toJson(courseModalArrayList);
          
        // below line is to save data in shared 
        // prefs in the form of string.
        editor.putString("courses", json);
         
        // below line is to apply changes 
        // and save data in shared prefs.
        editor.apply();
          
        // after saving data we are displaying a toast message.
        Toast.makeText(this, "Saved Array List to Shared preferences. ", Toast.LENGTH_SHORT).show();
    }
}

现在运行您的应用程序，并查看该应用程序的输出。

输出：

想要一个节奏更快，更具竞争性的环境来学习Android的基础知识吗?

单击此处，前往由我们的专家精心策划的指南，以使您立即做好行业准备！