如何使用改装库从安卓中的 JSON 数组中提取数据?
在上一篇关于使用改装库在安卓中解析 JSON 的文章中,我们已经看到了如何在我们的安卓应用程序中从 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,我们将看看如何从 JSON 数组中提取数据并在我们的应用程序中显示。
注: To e 使用凌空库从安卓 JSON 数组中提取数据请参考 如何使用凌空库从安卓 JSON 数组中提取数据?
JSON 数组 : JSON 数组是一个集合或称为数据集合,它保存多个具有相似数据类型的 JSON 对象。JSON 数组可以很容易地用“[”大括号开头和“]”大括号结尾来标识。一个 JSON 数组包含多个具有相似数据的 JSON 对象。每个 JSON 对象都以键和值对的形式存储数据。
本文我们要构建什么?
我们将构建一个简单的应用程序,其中我们将显示一个列表卡片视图,其中我们将显示一些在极客上为极客提供的课程。下面给出了一个示例视频,以了解我们将在本文中做什么。请注意,我们将使用 Java 语言来实现这个项目。
[https://media.geeksforgeeks.org/wp-content/uploads/20210217154438/Screenrecorder-2021-01-24-13-21-47-357.mp4](https://media.geeksforgeeks.org/wp-content/uploads/20210217154438/Screenrecorder-2021-01-24-13-21-47-357.mp4)下面是我们的 JSON 数组,我们将在我们的安卓应用程序中显示数据。
[
{
"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
第一步:创建新项目
在安卓工作室创建新项目请参考 【如何在安卓工作室创建/启动新项目】 。注意选择 Java 作为编程语言。
第二步:在你的 build.gradle 文件中添加下面的依赖项
下面是凌空的依赖,我们将使用它从应用编程接口获取数据。要添加此依赖项,请导航至应用程序>渐变脚本> build.gradle(应用程序),并在依赖项部分添加以下依赖项。我们已经使用了毕加索依赖从网址加载图像。
//下方依赖关系为使用改装。
实现‘com . squareup . retro fit 2:改装:2 . 9 . 0’
实现‘com . squareup . retro fit 2:converter-gson:2 . 5 . 0’
//下面的依赖关系为使用毕加索图像加载库
实现‘com . squareup . Picasso:Picasso:2.71828’
添加这个依赖项后,同步你的项目,现在进入 AndroidManifest.xml 部分。
第三步:在 AndroidManifest.xml 文件中添加互联网权限
导航到应用程序> AndroidManifest.xml ,并添加以下代码。
可扩展标记语言
<!--permissions for INTERNET-->
<uses-permission android:name="android.permission.INTERNET"/>
第 4 步:使用 activity_main.xml 文件
导航到 app > res >布局> activity_main.xml 并将下面的代码添加到该文件中。下面是activity _ main . XML文件的代码。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center"
android:gravity="center"
android:orientation="vertical"
tools:context=".MainActivity">
<!--progress bar for loading indicator-->
<ProgressBar
android:id="@+id/idPBLoading"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true" />
<!--creating a recycler view for displaying
our list of courses-->
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/idRVCourse"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
第五步:创建一个模态类来存储我们的数据
导航到应用程序> java >你的应用程序的包名>右键点击它>新建> Java 类并将其命名为 RecyclerData 并添加下面的代码。在代码中添加注释,以更详细地理解代码。
Java 语言(一种计算机语言,尤用于创建网站)
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:为我们的回收视图的每个项目创建一个布局文件
导航至 app > res >布局>右键点击>新建>布局资源文件,文件名为 card_layout ,并添加以下代码。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="8dp"
android:elevation="8dp"
app:cardCornerRadius="8dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<!--image view to display our course image-->
<ImageView
android:id="@+id/idIVCourse"
android:layout_width="match_parent"
android:layout_height="300dp"
android:layout_margin="5dp" />
<!--text view for our course name-->
<TextView
android:id="@+id/idTVCourseName"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:padding="5dp"
android:text="Course Name "
android:textColor="@color/black"
android:textSize="18sp"
android:textStyle="bold" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:orientation="horizontal"
android:weightSum="2">
<!--text view for our batch name-->
<TextView
android:id="@+id/idTVBatch"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:padding="5dp"
android:text="Batch"
android:textColor="@color/black" />
<!--text view to display course tracks-->
<TextView
android:id="@+id/idTVTracks"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:padding="5dp"
android:text="Tracks"
android:textColor="@color/black" />
</LinearLayout>
</LinearLayout>
</androidx.cardview.widget.CardView>
第 7 步:创建一个适配器类,用于将数据设置到我们的回收视图项目
要创建一个新的适配器类,导航到应用程序> java >你的应用程序的包名>右键单击它>新建> Java 类并将其命名为recycleriviewadapter并添加下面的代码。
Java 语言(一种计算机语言,尤用于创建网站)
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 RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.RecyclerViewHolder> {
// creating a variable for our array list and context.
private ArrayList<RecyclerData> courseDataArrayList;
private Context mcontext;
// creating a constructor class.
public RecyclerViewAdapter(ArrayList<RecyclerData> recyclerDataArrayList, Context mcontext) {
this.courseDataArrayList = recyclerDataArrayList;
this.mcontext = mcontext;
}
@NonNull
@Override
public RecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
// Inflate Layout
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_layout, parent, false);
return new RecyclerViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerViewHolder holder, int position) {
// Set the data to textview from our modal class.
RecyclerData modal = courseDataArrayList.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() {
// this method returns the size of recyclerview
return courseDataArrayList.size();
}
// View Holder Class to handle Recycler View.
public class RecyclerViewHolder extends RecyclerView.ViewHolder {
// creating variables for our views.
private TextView courseNameTV, courseModeTV, courseTracksTV;
private ImageView courseIV;
public RecyclerViewHolder(@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);
}
}
}
第 8 步:创建一个接口类来编写我们的 API 调用
导航到 app > java >你的 app 的包名>右键点击它>新建> Java 类 选择它为 界面 并将文件命名为retracifitapi并给它添加下面的代码。 在代码内部增加注释,更详细地理解代码。
Java 语言(一种计算机语言,尤用于创建网站)
import java.util.ArrayList;
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("WO6S")
// as we are calling data from array so we are calling
// it with array list and naming that method as getAllCourses();
Call<ArrayList<RecyclerData>> getAllCourses();
}
第九步:使用MainActivity.java 文件
转到MainActivity.java文件,参考以下代码。以下是MainActivity.java文件的代码。代码中添加了注释,以更详细地理解代码。
Java 语言(一种计算机语言,尤用于创建网站)
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 java.util.ArrayList;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
public class MainActivity extends AppCompatActivity {
// creating a variable for recycler view,
// array list and adapter class.
private RecyclerView courseRV;
private ArrayList<RecyclerData> recyclerDataArrayList;
private RecyclerViewAdapter recyclerViewAdapter;
private ProgressBar progressBar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initializing our variables.
courseRV = findViewById(R.id.idRVCourse);
progressBar = findViewById(R.id.idPBLoading);
// creating new array list.
recyclerDataArrayList = new ArrayList<>();
// calling a method to
// get all the courses.
getAllCourses();
}
private void getAllCourses() {
// 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);
// on below line we are calling a method to get all the courses from API.
Call<ArrayList<RecyclerData>> call = retrofitAPI.getAllCourses();
// on below line we are calling method to enqueue and calling
// all the data from array list.
call.enqueue(new Callback<ArrayList<RecyclerData>>() {
@Override
public void onResponse(Call<ArrayList<RecyclerData>> call, Response<ArrayList<RecyclerData>> response) {
// inside on response method we are checking
// if the response is success or not.
if (response.isSuccessful()) {
// on successful we are hiding our progressbar.
progressBar.setVisibility(View.GONE);
// below line is to add our data from api to our array list.
recyclerDataArrayList = response.body();
// below line we are running a loop to add data to our adapter class.
for (int i = 0; i < recyclerDataArrayList.size(); i++) {
recyclerViewAdapter = new RecyclerViewAdapter(recyclerDataArrayList, MainActivity.this);
// below line is to set layout manager for our recycler view.
LinearLayoutManager manager = new LinearLayoutManager(MainActivity.this);
// setting layout manager for our recycler view.
courseRV.setLayoutManager(manager);
// below line is to set adapter to our recycler view.
courseRV.setAdapter(recyclerViewAdapter);
}
}
}
@Override
public void onFailure(Call<ArrayList<RecyclerData>> call, Throwable t) {
// in the method of on failure we are displaying a
// toast message for fail to get data.
Toast.makeText(MainActivity.this, "Fail to get data", Toast.LENGTH_SHORT).show();
}
});
}
}
现在运行您的应用程序,并查看应用程序的输出。
输出:
[https://media.geeksforgeeks.org/wp-content/uploads/20210217154438/Screenrecorder-2021-01-24-13-21-47-357.mp4](https://media.geeksforgeeks.org/wp-content/uploads/20210217154438/Screenrecorder-2021-01-24-13-21-47-357.mp4)版权属于:月萌API www.moonapi.com,转载请注明出处