如何在 Android 中删除多个 RecyclerView 项目？

RecyclerView 是 ListView 的高级版本，具有改进的性能。当您有很长的项目列表要显示时，您可以使用 RecyclerView。它具有重用其视图的能力。在 RecyclerView 中，当视图离开屏幕或对用户不可见时，它不会破坏它，它将重用这些视图。此功能有助于降低功耗并为应用程序提供更高的响应能力。在本文中，我们将看到如何从 android studio 的回收器视图中删除多个项目。在进一步移动之前，让我们了解 RecyclerView。

先决条件：

在实现本文教授的概念之前，您应该具备在 android studio 中实现回收器视图的知识。如果您不知道如何实现回收器视图，请阅读以下文章：Android 中的 RecyclerView 示例

我们将在本文中构建什么？

这是我们将在本文中实现的示例视频。请注意，我们将使用Java语言来实现这个应用程序。

分步实施

第 1 步：创建一个新项目

• 打开一个新项目。
• 我们将使用Java语言开发 Empty Activity。保持所有其他选项不变。
• 您可以在方便时更改项目的名称。
• 将有两个名为 activity_main.xml 和 MainActivity 的默认文件。Java

如果您不知道如何在 Android Studio 中创建新项目，可以参考如何在 Android Studio 中创建/启动新项目？

第 2 步：添加所需的依赖项

打开 Gradle 脚本 > build.gradle(module)。转到应用>右键单击>打开模块设置>依赖项>添加依赖项>库依赖项。

在搜索栏中输入材料，然后单击搜索。选择下图中显示的依赖项-

在搜索栏中输入“lifecycle-extensions”，然后单击搜索。选择下图中显示的依赖项-

第 3 步：在 drawable 中添加新的矢量资源

导航到可绘制 > 右键单击 > 新建 > 矢量资产，然后从剪贴画中选择以下资产。

1.检查圈：

2. 全选：

第 4 步：使用 xml 文件

导航到app > res > layout > activity_main.xml并将以下代码添加到该文件。下面是activity_main.xml文件的代码。

按照路径 app > res > 布局 > 右键单击 > 新建 > 布局资源文件并创建一个名为item_main.xml 的新文件。在 item_main.xml 文件中使用以下代码 -

按照路径 app > res > 右键单击 > 新建 > android 资源文件 > 资源类型 > 菜单并创建一个名为 menu.xml 的新文件。在 menu.xml 文件中使用以下代码 -

第 5 步：使用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。代码中添加了注释以更详细地理解代码。

Java

package com.example.multiple_item_delete;
  
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
  
import android.os.Bundle;
import android.widget.TextView;
  
import java.util.ArrayList;
import java.util.Arrays;
  
public class MainActivity extends AppCompatActivity {
  
    // initialize variables
    RecyclerView recyclerView;
    TextView tvEmpty;
    ArrayList arrayList=new ArrayList<>();
    MainAdapter adapter;
  
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
  
        // assign variable
        recyclerView=findViewById(R.id.recycler_view);
        tvEmpty=findViewById(R.id.tv_empty);
  
        // add values in arraylist
        arrayList.addAll(Arrays.asList("One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven"
        ,"Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen","Twenty"));
  
        // set layout manager
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
          
          // Initialize adapter
        adapter=new MainAdapter(this,arrayList,tvEmpty);
          
          // set adapter
        recyclerView.setAdapter(adapter);
    }
}

按照路径 app > Java > com.example.multiple_item_delete > 右键单击 > new > Java类并创建一个名为 MainAdapter 的新文件。Java在 MainAdapter 中使用以下代码。 Java文件——

Java

package com.example.multiple_item_delete;
  
import android.app.Activity;
import android.graphics.Color;
import android.text.Layout;
import android.view.ActionMode;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentActivity;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import androidx.recyclerview.widget.RecyclerView;
  
import java.util.ArrayList;
  
public class MainAdapter extends RecyclerView.Adapter {
  
    // initialize variables
    Activity activity;
    ArrayList arrayList;
    TextView tvEmpty;
    MainViewModel mainViewModel;
    boolean isEnable=false;
    boolean isSelectAll=false;
    ArrayList selectList=new ArrayList<>();
  
    // create constructor
    public MainAdapter(Activity activity,ArrayList arrayList,TextView tvEmpty)
    {
        this.activity=activity;
        this.arrayList=arrayList;
        this.tvEmpty=tvEmpty;
    }
  
    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
           // initialize variables
        View view= LayoutInflater.from(parent.getContext()).
                inflate(R.layout.item_main,parent,false);
          
          // initialize view Model
        mainViewModel= ViewModelProviders.of((FragmentActivity) activity)
                .get(MainViewModel.class);
  
        // return view
        return new ViewHolder(view);
    }
  
    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
          
          // set text on text view
        holder.textView.setText(arrayList.get(position));
  
        holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                // check condition
                if (!isEnable)
                {
                    // when action mode is not enable
                    // initialize action mode
                    ActionMode.Callback callback=new ActionMode.Callback() {
                        @Override
                        public boolean onCreateActionMode(ActionMode mode, Menu menu) {
                            // initialize menu inflater
                            MenuInflater menuInflater= mode.getMenuInflater();
                            // inflate menu
                            menuInflater.inflate(R.menu.menu,menu);
                            // return true
                            return true;
                        }
  
                        @Override
                        public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
                            // when action mode is prepare
                            // set isEnable true
                            isEnable=true;
                            // create method
                            ClickItem(holder);
                            // set observer on getText method
                            mainViewModel.getText().observe((LifecycleOwner) activity
                                    , new Observer() {
                                        @Override
                                        public void onChanged(String s) {
                                            // when text change
                                            // set text on action mode title
                                            mode.setTitle(String.format("%s Selected",s));
                                        }
                                    });
                            // return true
                            return true;
                        }
  
                        @Override
                        public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
                            // when click on action mode item
                            // get item  id
                            int id=item.getItemId();
                            // use switch condition
                            switch(id)
                            {
                                case R.id.menu_delete:
                                    // when click on delete
                                    // use for loop
                                    for(String s:selectList)
                                    {
                                        // remove selected item list
                                        arrayList.remove(s);
                                    }
                                    // check condition
                                    if(arrayList.size()==0)
                                    {
                                        // when array list is empty
                                        // visible text view
                                        tvEmpty.setVisibility(View.VISIBLE);
                                    }
                                    // finish action mode
                                    mode.finish();
                                    break;
  
                                case R.id.menu_select_all:
                                    // when click on select all
                                    // check condition
                                    if(selectList.size()==arrayList.size())
                                    {
                                        // when all item selected
                                        // set isselectall false
                                        isSelectAll=false;
                                        // create select array list
                                        selectList.clear();
                                    }
                                    else
                                    {
                                        // when  all item unselected
                                        // set isSelectALL true
                                        isSelectAll=true;
                                        // clear select array list
                                        selectList.clear();
                                        // add value in select array list
                                        selectList.addAll(arrayList);
                                    }
                                    // set text on view model
                                    mainViewModel.setText(String .valueOf(selectList.size()));
                                    // notify adapter
                                    notifyDataSetChanged();
                                    break;
                            }
                            // return true
                            return true;
                        }
  
                        @Override
                        public void onDestroyActionMode(ActionMode mode) {
                            // when action mode is destroy
                            // set isEnable false
                            isEnable=false;
                            // set isSelectAll false
                            isSelectAll=false;
                            // clear select array list
                            selectList.clear();
                            // notify adapter
                            notifyDataSetChanged();
                        }
                    };
                    // start action mode
                    ((AppCompatActivity) v.getContext()).startActionMode(callback);
                }
                else
                {
                    // when action mode is already enable
                    // call method
                    ClickItem(holder);
                }
                // return true
                return true;
            }
        });
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // check condition
                if(isEnable)
                {
                    // when action mode is enable
                    // call method
                    ClickItem(holder);
                }
                else
                {
                    // when action mode is not enable
                    // display toast
                    Toast.makeText(activity,"You Clicked"+arrayList.get(holder.getAdapterPosition()),
                            Toast.LENGTH_SHORT).show();
                }
            }
        });
        // check condition
        if(isSelectAll)
        {
            // when value selected
            // visible all check boc image
            holder.checkbox.setVisibility(View.VISIBLE);
            //set background color
            holder.itemView.setBackgroundColor(Color.LTGRAY);
        }
        else
        {
            // when all value unselected
            // hide all check box image
            holder.checkbox.setVisibility(View.GONE);
            // set background color
            holder.itemView.setBackgroundColor(Color.TRANSPARENT);
        }
    }
  
    private void ClickItem(ViewHolder holder) {
  
        // get selected item value
        String s=arrayList.get(holder.getAdapterPosition());
        // check condition
        if(holder.checkbox.getVisibility()==View.GONE)
        {
            // when item not selected
            // visible check box image
            holder.checkbox.setVisibility(View.VISIBLE);
            // set background color
            holder.itemView.setBackgroundColor(Color.LTGRAY);
            // add value in select array list
            selectList.add(s);
        }
        else
        {
            // when item selected
            // hide check box image
            holder.checkbox.setVisibility(View.GONE);
            // set background color
            holder.itemView.setBackgroundColor(Color.TRANSPARENT);
            // remove value from select arrayList
            selectList.remove(s);
  
        }
        // set text on view model
        mainViewModel.setText(String.valueOf(selectList.size()));
    }
  
    @Override
    public int getItemCount() {
        return arrayList.size();
    }
  
    public class ViewHolder extends RecyclerView.ViewHolder {
        // initialize variables
        TextView textView;
        ImageView checkbox;
  
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
  
            // assign variables
            textView=itemView.findViewById(R.id.text_view);
            checkbox=itemView.findViewById(R.id.check_box);
  
        }
    }
}

按照路径 app > Java > com.example.multiple_item_delete > 右键单击 > new > Java class 并创建一个名为 MainViewModel 的新文件。Java在MainViewModel 中使用以下代码。 Java文件——

Java

package com.example.multiple_item_delete;
  
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;
  
public class MainViewModel extends ViewModel {
  
    // initialize variables
    MutableLiveData mutableLiveData=new MutableLiveData<>();
  
    // create set text method
    public void setText(String s)
    {
        // set value
        mutableLiveData.setValue(s);
    }
  
    // create get text method
    public MutableLiveData getText()
    {
        return mutableLiveData;
    }
}

输出：

这是我们应用程序的最终输出。