使用翻新库在Android中进行JSON解析

JSON也称为(JavaScript Object Notation)，它是一种用于交换来自服务器的数据的格式。以JSON格式存储的数据是轻量级的，并且易于处理。借助JSON，我们可以以JsonArray，JsonObject和JsonStringer的形式访问数据。在本文中，我们将专门研究如何使用Android中的Retrofit库实现JsonObject。

Note: To parse JSON object in android using Voley library please refer to JSON Parsing in Android using Volley Library

JSON Object: Json Object can be easily identified with “{” braces opening and “}” braces closing. We can fetch data from JSON objects with their key value. From that key, we can access the value of that key.  

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，其中将显示一个简单的CardView，其中将显示Geeks for Geeks上可用的单个课程。下面提供了一个示例视频，以使您对本文中的工作有个大概的了解。注意，我们将使用Java语言实现该项目。

下面是JSON对象，我们将在该JSON对象中显示Android应用程序中的数据。

{

 “courseName”:”Fork CPP”,

 “courseimg”:”https://media.geeksforgeeks.org/img-practice/banner/fork-cpp-thumbnail.png”,

 “courseMode”:”Online Batch”,

 “courseTracks”:”6 Tracks”

}

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：在您的build.gradle文件中添加以下依赖项

以下是Volley的依赖关系，我们将使用它们来从API获取数据。要添加此依赖关系，请导航至应用程序> Gradle脚本> build.gradle(app)，然后在“依赖关系”部分添加以下依赖关系。我们已将Picasso依赖项用于从URL加载图像。

// below dependancy for using retrofit.

implementation ‘com.squareup.retrofit2:retrofit:2.9.0’

implementation ‘com.squareup.retrofit2:converter-gson:2.5.0’

// below dependancy for using picasso image loading library

implementation ‘com.squareup.picasso:picasso:2.71828’

添加此依赖项后，同步您的项目，现在移至AndroidManifest.xml部分。

步骤3：在AndroidManifest.xml文件中向Internet添加权限

导航至应用程序> AndroidManifest.xml，然后将以下代码添加到其中。

步骤4：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。

第5步：创建用于存储数据的模式类

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RecyclerData，然后将以下代码添加到其中。在代码内部添加了注释，以更详细地了解代码。

Java

public class RecyclerData {
    // string variables for our data
    // make sure that the variable name 
    // must be similar to that of key value 
    // which we are getting from our json file.
    private String courseName;
    private String courseimg;
    private String courseMode;
    private String courseTracks;
  
    public String getCourseName() {
        return courseName;
    }
  
    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }
  
    public String getCourseimg() {
        return courseimg;
    }
  
    public void setCourseimg(String courseimg) {
        this.courseimg = courseimg;
    }
  
    public String getCourseMode() {
        return courseMode;
    }
  
    public void setCourseMode(String courseMode) {
        this.courseMode = courseMode;
    }
  
    public String getCourseTracks() {
        return courseTracks;
    }
  
    public void setCourseTracks(String courseTracks) {
        this.courseTracks = courseTracks;
    }
  
    public RecyclerData(String courseName, String courseimg, String courseMode, String courseTracks) {
        this.courseName = courseName;
        this.courseimg = courseimg;
        this.courseMode = courseMode;
        this.courseTracks = courseTracks;
    }
}

第6步：为我们的API调用创建一个接口类

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，将其选择为Interface并将文件命名为RetrofitAPI并向其添加以下代码。在代码内部添加了注释，以更详细地了解代码。

Java

import retrofit2.Call;
import retrofit2.http.GET;
  
public interface RetrofitAPI {
  
    // as we are making get request 
    // so we are displaying GET as annotation.
    // and inside we are passing 
    // last parameter for our url.
    @GET("63OH")
      
    // as we are calling data from array
    // so we are calling it with json object
    // and naming that method as getCourse();
    Call getCourse();
}

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.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
  
import androidx.appcompat.app.AppCompatActivity;
import androidx.cardview.widget.CardView;
  
import com.squareup.picasso.Picasso;
  
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
  
public class MainActivity extends AppCompatActivity {
    // creating variables for our textview,
    // imageview,cardview and progressbar.
    private TextView courseNameTV, courseTracksTV, courseBatchTV;
    private ImageView courseIV;
    private ProgressBar loadingPB;
    private CardView courseCV;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
          
        // initializing our variables.
        loadingPB = findViewById(R.id.idLoadingPB);
        courseCV = findViewById(R.id.idCVCourse);
        courseNameTV = findViewById(R.id.idTVCourseName);
        courseTracksTV = findViewById(R.id.idTVTracks);
        courseBatchTV = findViewById(R.id.idTVBatch);
        courseIV = findViewById(R.id.idIVCourse);
        getCourse();
    }
  
    private void getCourse() {
  
        // on below line we are creating a retrofit
        // builder and passing our base url
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://jsonkeeper.com/b/")
                // on below line we are calling add Converter
                // factory as GSON converter factory.
                .addConverterFactory(GsonConverterFactory.create())
                // at last we are building our retrofit builder.
                .build();
        // below line is to create an instance for our retrofit api class.
        RetrofitAPI retrofitAPI = retrofit.create(RetrofitAPI.class);
        Call call = retrofitAPI.getCourse();
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                if (response.isSuccessful()) {
                    // inside the on response method.
                    // we are hiding our progress bar.
                    loadingPB.setVisibility(View.GONE);
                    // in below line we are making our card
                    // view visible after we get all the data.
                    courseCV.setVisibility(View.VISIBLE);
                    RecyclerData modal = response.body();
                    // after extracting all the data we are
                    // setting that data to all our views.
                    courseNameTV.setText(modal.getCourseName());
                    courseTracksTV.setText(modal.getCourseTracks());
                    courseBatchTV.setText(modal.getCourseMode());
                    // we are using picasso to load the image from url.
                    Picasso.get().load(modal.getCourseimg()).into(courseIV);
                }
            }
  
            @Override
            public void onFailure(Call call, Throwable t) {
                // displaying an error message in toast
                Toast.makeText(MainActivity.this, "Fail to get the data..", 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：

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