安卓中的二维循环视图，示例
原文:https://www . geeksforgeeks . org/二维-recycle view-in-Android-with-example/
在许多情况下，我们必须以这样一种方式显示水平滚动列表，即我们还必须在上面显示标题，以指示列表属于哪个类别。为此，我们必须在我们的应用程序中创建一个二维的 RecyclerView。在本文中，我们将在我们的应用程序中创建一个二维回收视图。
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，其中我们将显示两个回收视图。一个是垂直的，一个是水平的。在我们的垂直回收视图中，我们将显示新闻类别，在这些类别中，我们将以水平可滚动的格式显示属于该类别的不同新闻。下面给出了一个示例 GIF，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。
分步实施
第一步:创建新项目
要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。
步骤 2:在你的 build.gradle 文件中添加下面的依赖项，并在清单文件中添加互联网权限
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从网址图像加载依赖。
// 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’
另外，在清单文件中添加 internet 权限
<uses-permission android:name="android.permission.INTERNET" />
步骤 3:使用 activity_main.xml 文件
导航到应用程序> 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"
tools:context=".MainActivity">
<!--recycler view for displaying categories-->
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/idRVCategories"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
第四步:创建一个模态类来存储我们的新闻
导航到应用> java >你的应用的包名>右键点击>新建> Java 类并命名为新闻模式并添加下面的代码。下面是NewsModal.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)
public class NewsModal {
// string for news title,image and description.
private String newsTitle;
private String newsDesc;
private String newsImg;
// on below line we have created a constructor.
public NewsModal(String newsTitle, String newsDesc, String newsImg) {
this.newsTitle = newsTitle;
this.newsDesc = newsDesc;
this.newsImg = newsImg;
}
public String getNewsImg() {
return newsImg;
}
public void setNewsImg(String newsImg) {
this.newsImg = newsImg;
}
// creating a getter and setter.
public String getNewsTitle() {
return newsTitle;
}
public void setNewsTitle(String newsTitle) {
this.newsTitle = newsTitle;
}
public String getNewsDesc() {
return newsDesc;
}
public void setNewsDesc(String newsDesc) {
this.newsDesc = newsDesc;
}
}
第五步:创建一个模态类来存储我们的新闻类别
同样，创建另一个 Java 类，并将其命名为类别模式，并向其中添加以下代码。以下是CategoriesModal.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 java.util.ArrayList;
public class CategoriesModal {
// creating variable for our category,
// news array list and expanded boolean.
private String newsCategory;
private ArrayList<NewsModal> newsModalArrayList;
// creating a constructor.
public CategoriesModal(String newsCategory, ArrayList<NewsModal> newsModalArrayList) {
this.newsCategory = newsCategory;
this.newsModalArrayList = newsModalArrayList;
}
public String getNewsCategory() {
return newsCategory;
}
public void setNewsCategory(String newsCategory) {
this.newsCategory = newsCategory;
}
public ArrayList<NewsModal> getNewsModalArrayList() {
return newsModalArrayList;
}
public void setNewsModalArrayList(ArrayList<NewsModal> newsModalArrayList) {
this.newsModalArrayList = newsModalArrayList;
}
}
第 6 步:为我们的新闻项目创建布局文件
导航至 app > res >布局>右键点击>新建>布局资源文件并命名为 news_rv_item 并添加以下代码。下面是 news_rv_item.xml 文件的代码。
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="300dp"
android:layout_height="200dp"
android:layout_gravity="center"
android:layout_margin="3dp"
android:backgroundTint="@color/purple_200"
app:cardCornerRadius="4dp">
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="match_parent">
<!--image view for displaying image-->
<ImageView
android:id="@+id/idIVnews"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@id/idTVNewsTitle"
android:src="@drawable/logo1" />
<!--text view for displaying news title-->
<TextView
android:id="@+id/idTVNewsTitle"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@id/idTVNewsDesc"
android:layout_marginStart="4dp"
android:layout_marginTop="8dp"
android:padding="4dp"
android:text="News Title"
android:textAllCaps="false"
android:textColor="@color/white"
android:textStyle="bold" />
<!--text view for displaying news description-->
<TextView
android:id="@+id/idTVNewsDesc"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_marginStart="4dp"
android:layout_marginTop="4dp"
android:layout_marginBottom="8dp"
android:maxLines="3"
android:padding="4dp"
android:text="News Desc"
android:textColor="@color/white"
android:textSize="12sp" />
</RelativeLayout>
</androidx.cardview.widget.CardView>
步骤 7:为新闻类别创建新的布局文件
同样，创建另一个布局资源文件，并将其命名为 news_categories_rv_item ，并向其中添加以下代码。下面是news _ categories _ RV _ item . XML文件的代码。
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="4dp"
app:cardCornerRadius="4dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<!--text view for displaying news category-->
<TextView
android:id="@+id/idTVCategory"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="8dp"
android:text="Category"
android:textSize="15sp" />
<androidx.cardview.widget.CardView
android:id="@+id/idCVCategory"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:elevation="0dp"
app:cardElevation="0dp">
<!--recycler view for displaying news recycler view-->
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/idRVNews"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</androidx.cardview.widget.CardView>
</LinearLayout>
</androidx.cardview.widget.CardView>
步骤 8:创建新的适配器类，用于在新闻回收视图中设置数据
创建另一个新的 Java 类，并将其命名为newsvadapter，并向其中添加以下代码。下面是NewsRVAdapter.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.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 NewsRVAdapter extends RecyclerView.Adapter<NewsRVAdapter.ViewHolder> {
// variables for array list and context.
private ArrayList<NewsModal> newsModalArrayList;
private Context context;
// creating a constructor.
public NewsRVAdapter(ArrayList<NewsModal> newsModalArrayList, Context context) {
this.newsModalArrayList = newsModalArrayList;
this.context = context;
}
@NonNull
@Override
public NewsRVAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
// passing our layout file for displaying our card item
return new NewsRVAdapter.ViewHolder(LayoutInflater.from(context).inflate(R.layout.news_rv_item, parent, false));
}
@Override
public void onBindViewHolder(@NonNull NewsRVAdapter.ViewHolder holder, int position) {
// on below line we are setting data to our ui components.
NewsModal modal = newsModalArrayList.get(position);
holder.newsDescTV.setText(modal.getNewsDesc());
holder.newsTitleTV.setText(modal.getNewsTitle());
Picasso.get().load(modal.getNewsImg()).into(holder.newsIV);
}
@Override
public int getItemCount() {
// returning the size of array list
return newsModalArrayList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
// creating variables for our text view.
private TextView newsTitleTV, newsDescTV;
private ImageView newsIV;
public ViewHolder(@NonNull View itemView) {
super(itemView);
// initializing our text view
newsIV = itemView.findViewById(R.id.idIVnews);
newsTitleTV = itemView.findViewById(R.id.idTVNewsTitle);
newsDescTV = itemView.findViewById(R.id.idTVNewsDesc);
}
}
}
第 9 步:为我们的类别创建适配器类回收视图
同样，创建另一个 Java 类名为 CategoriesRVAdapter 、，并添加下面的代码。下面是CategoriesRVAdapter.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.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.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class CategoriesRVAdapter extends RecyclerView.Adapter<CategoriesRVAdapter.ViewHolder> {
// variables for array list and context.
private ArrayList<CategoriesModal> categoriesModalArrayList;
private Context context;
// creating a constructor
public CategoriesRVAdapter(ArrayList<CategoriesModal> categoriesModalArrayList, Context context) {
this.categoriesModalArrayList = categoriesModalArrayList;
this.context = context;
}
@NonNull
@Override
public CategoriesRVAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
// passing our layout file for displaying our card item
return new CategoriesRVAdapter.ViewHolder(LayoutInflater.from(context).inflate(R.layout.news_categories_rv_item, parent, false));
}
@Override
public void onBindViewHolder(@NonNull CategoriesRVAdapter.ViewHolder holder, int position) {
// setting data to our views on below line.
CategoriesModal modal = categoriesModalArrayList.get(position);
holder.categoryTV.setText(modal.getNewsCategory());
NewsRVAdapter adapter = new NewsRVAdapter(modal.getNewsModalArrayList(), context);
// below line is for setting a layout manager for our recycler view.
// here we are creating horizontal list so we will provide orientation as vertical
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false);
holder.newsRV.setLayoutManager(linearLayoutManager);
holder.newsRV.setAdapter(adapter);
}
@Override
public int getItemCount() {
// returning the size of array list on below line.
return categoriesModalArrayList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
// creating new variables for our views.
private RecyclerView newsRV;
private TextView categoryTV;
public ViewHolder(@NonNull View itemView) {
super(itemView);
// initializing our views.
categoryTV = itemView.findViewById(R.id.idTVCategory);
newsRV = itemView.findViewById(R.id.idRVNews);
}
}
}
步骤 10: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.util.Log;
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.JsonObjectRequest;
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 array list for our categories,
// different news and category recycler view.
private RecyclerView categoriesRV;
private ArrayList<CategoriesModal> categoriesModalArrayList;
private ArrayList<NewsModal> popularNewsArrayList, sportsNews, techNews;
private CategoriesRVAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
categoriesRV = findViewById(R.id.idRVCategories);
LinearLayoutManager manager = new LinearLayoutManager(this);
categoriesRV.setLayoutManager(manager);
categoriesModalArrayList = new ArrayList<>();
sportsNews = new ArrayList<>();
techNews = new ArrayList<>();
popularNewsArrayList = new ArrayList<>();
adapter = new CategoriesRVAdapter(categoriesModalArrayList, this);
categoriesRV.setAdapter(adapter);
getPopularNews(popularNewsArrayList, categoriesModalArrayList);
getSportsNews(categoriesModalArrayList, sportsNews);
getTechnews(categoriesModalArrayList, techNews);
adapter.notifyDataSetChanged();
}
private void getSportsNews(ArrayList<CategoriesModal> categoriesModals, ArrayList<NewsModal> sportsNews) {
Log.e("TAG", "SIZE IS " + categoriesModalArrayList.size());
String url = "https://jsonkeeper.com/b/U1BV";
// 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.
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
Log.e("TAG", "SPORTS RESPONSE IS " + response);
try {
String category = response.getString("newsCategory");
JSONArray newsArray = response.getJSONArray("news");
for (int i = 0; i < newsArray.length(); i++) {
JSONObject newsObj = newsArray.getJSONObject(i);
String newsTitle = newsObj.getString("newsTitle");
String newsDesc = newsObj.getString("newsDesc");
String newsImg = newsObj.getString("newsImg");
sportsNews.add(new NewsModal(newsTitle, newsDesc, newsImg));
}
categoriesModals.add(new CategoriesModal(category, sportsNews));
Log.e("TAG", "MODALS = " + sportsNews.size() + "\n" + categoriesModals.size());
adapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(MainActivity.this, "Fail to get Data", Toast.LENGTH_SHORT).show();
}
});
queue.add(jsonObjectRequest);
}
private void getTechnews(ArrayList<CategoriesModal> categoriesModals, ArrayList<NewsModal> techNews) {
// ArrayList<CategoriesModal> categoriesModals = null;
String url = "https://jsonkeeper.com/b/ZCWD";
// 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.
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
Log.e("TAG", "TECH RESPONSE IS " + response);
try {
String category = response.getString("newsCategory");
JSONArray newsArray = response.getJSONArray("news");
for (int i = 0; i < newsArray.length(); i++) {
JSONObject newsObj = newsArray.getJSONObject(i);
String newsTitle = newsObj.getString("newsTitle");
String newsDesc = newsObj.getString("newsDesc");
String newsImg = newsObj.getString("newsImg");
techNews.add(new NewsModal(newsTitle, newsDesc, newsImg));
}
categoriesModals.add(new CategoriesModal(category, techNews));
adapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(MainActivity.this, "Fail to get Data", Toast.LENGTH_SHORT).show();
}
});
queue.add(jsonObjectRequest);
}
private void getPopularNews(ArrayList<NewsModal> popularNewsArrayList, ArrayList<CategoriesModal> categoriesModals) {
String url = "https://jsonkeeper.com/b/ZCWD";
// 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.
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
Log.e("TAG", "POPULAR NEWS RESPONSE IS " + response);
try {
String category = response.getString("newsCategory");
JSONArray newsArray = response.getJSONArray("news");
for (int i = 0; i < newsArray.length(); i++) {
JSONObject newsObj = newsArray.getJSONObject(i);
String newsTitle = newsObj.getString("newsTitle");
String newsDesc = newsObj.getString("newsDesc");
String newsImg = newsObj.getString("newsImg");
popularNewsArrayList.add(new NewsModal(newsTitle, newsDesc, newsImg));
}
categoriesModals.add(new CategoriesModal(category, popularNewsArrayList));
adapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(MainActivity.this, "Fail to get Data", Toast.LENGTH_SHORT).show();
}
});
queue.add(jsonObjectRequest);
}
}
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/20210428103554/20210428_103451.mp4](https://media.geeksforgeeks.org/wp-content/uploads/20210428103554/20210428_103451.mp4)版权属于：月萌API www.moonapi.com，转载请注明出处
