如何使用Volley Library从Android的JSON数组中提取数据？

在上一篇有关使用Volley Library在Android中进行JSON解析的文章中，我们了解了如何从android应用程序中的JSON Object获取数据并在我们的应用程序中显示该JSON Object。在本文中，我们将研究如何从JSON数组提取数据并将其显示在我们的应用程序中。

JSON Array: JSON Array is a set or called a collection of data that holds multiple JSON Objects with similar sort of data. JSON Array can be easily identified with “[” braces opening and “]” braces closing. A JSON array is having multiple JSON objects which are having similar data. And each JSON object is having data stored in the form of key and value pair. 

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，在其中显示CardView列表，并在其中显示一些适用于Geeks for Geeks的课程。下面给出了一个示例GIF，以了解我们将在本文中做些什么。注意，我们将使用Java语言实现该项目。

下面是我们的JSON数组，我们将通过该数组在Android App中显示数据。

[

  {

     “courseName”:”Fork CPP”,

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

     “courseMode”:”Online Batch”,

     “courseTracks”:”6 Tracks”

  },

  {

     “courseName”:”Linux & Shell Scripting Foundation”,

     “courseimg”:”https://media.geeksforgeeks.org/img-practice/banner/linux-shell-scripting-thumbnail.png”,

     “courseMode”:”Online Batch”,

     “courseTracks”:”8 Tracks”

  },

  {

     “courseName”:”11 Weeks Workshop on Data Structures and Algorithms”,

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

     “courseMode”:”Online Batch”,

     “courseTracks”:”47 Tracks”

  },

  {

     “courseName”:”Data Structures and Algorithms”,

     “courseimg”:”https://media.geeksforgeeks.org/img-practice/banner/dsa-self-paced-thumbnail.png”,

     “courseMode”:”Online Batch”,

     “courseTracks”:”24 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 line is used for volley library

implementation ‘com.android.volley:volley:1.1.1’

// below line is used for 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Modal类

为了存储我们的数据，我们必须创建一个新的Java类。要创建新的Java类，请导航至应用程序> 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CourseModal ，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

public class CourseModal {
  
    // variables for our course 
    // name and description.
    private String courseName;
    private String courseimg;
    private String courseMode;
    private String courseTracks;
  
    // creating constructor for our variables.
    public CourseModal(String courseName, String courseimg, String courseMode, String courseTracks) {
        this.courseName = courseName;
        this.courseimg = courseimg;
        this.courseMode = courseMode;
        this.courseTracks = courseTracks;
    }
  
    // creating getter and setter methods.
    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;
    }
}

第6步：为我们的RecyclerView的每个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，并将文件名命名为course_rv_item ，并将以下代码添加到其中。在代码中添加了注释，以便更详细地了解。

步骤7：创建用于将数据设置到我们的RecyclerView项的Adapter类

要创建新的适配器类，请导航至应用程序> Java >应用程序的包名称>右键单击它>新建> Java类，并将其命名为CourseAdapter并向其中添加以下代码。

Java

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
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 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.courseTracksTV.setText(modal.getCourseTracks());
        holder.courseModeTV.setText(modal.getCourseMode());
        Picasso.get().load(modal.getCourseimg()).into(holder.courseIV);
    }
  
    @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, courseModeTV, courseTracksTV;
        private ImageView courseIV;
  
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            
            // initializing our views with their ids.
            courseNameTV = itemView.findViewById(R.id.idTVCourseName);
            courseModeTV = itemView.findViewById(R.id.idTVBatch);
            courseTracksTV = itemView.findViewById(R.id.idTVTracks);
            courseIV = itemView.findViewById(R.id.idIVCourse);
        }
    }
}

步骤8：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.ProgressBar;
import android.widget.Toast;
  
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
  
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.Volley;
  
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
  
import java.util.ArrayList;
  
public class MainActivity extends AppCompatActivity {
  
    // creating variables for 
    // our ui components.
    private RecyclerView courseRV;
      
    // variable for our adapter 
    // class and array list
    private CourseAdapter adapter;
    private ArrayList courseModalArrayList;
     
    // below line is the variable for url from
    // where we will be querying our data.
    String url = "https://jsonkeeper.com/b/WO6S";
    private ProgressBar progressBar;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
          
        // initializing our variables.
        courseRV = findViewById(R.id.idRVCourses);
        progressBar = findViewById(R.id.idPB);
          
        // below line we are creating a new array list
        courseModalArrayList = new ArrayList<>();
        getData();
          
        // calling method to 
        // build recycler view.
        buildRecyclerView();
    }
  
    private void getData() {
        // creating a new variable for our request queue
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        // in this case the data we are getting is in the form
        // of array so we are making a json array request.
        // below is the line where we are making an json array 
        // request and then extracting data from each json object.
        JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.GET, url, null, new Response.Listener() {
            @Override
            public void onResponse(JSONArray response) {
                progressBar.setVisibility(View.GONE);
                courseRV.setVisibility(View.VISIBLE);
                for (int i = 0; i < response.length(); i++) {
                    // creating a new json object and 
                    // getting each object from our json array.
                    try {
                        // we are getting each json object.
                        JSONObject responseObj = response.getJSONObject(i);
                          
                        // now we get our response from API in json object format.
                        // in below line we are extracting a string with
                        // its key value from our json object.
                        // similarly we are extracting all the strings from our json object.
                        String courseName = responseObj.getString("courseName");
                        String courseTracks = responseObj.getString("courseTracks");
                        String courseMode = responseObj.getString("courseMode");
                        String courseImageURL = responseObj.getString("courseimg");
                        courseModalArrayList.add(new CourseModal(courseName, courseImageURL, courseMode, courseTracks));
                        buildRecyclerView();
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(MainActivity.this, "Fail to get the data..", Toast.LENGTH_SHORT).show();
            }
        });
        queue.add(jsonArrayRequest);
    }
  
    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);
    }
}

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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