为什么 item.getMenuInfo() 为空？

Question

在我的 ListVeiw 项目中，我有 4-8 个 ImageView（其中一些是不可见的，具体取决于某些值）和 4 个 TextView。

当我长按 Listview 的项目时，(AdapterContextMenuInfo) item.getMenuInfo() 返回 null。

在我的适配器中，我定义了以下方法：

public int getCount() {
   return NewList.size();
}

public Object getItem(int position) {
   return position;
}

public long getItemId(int position) {
   return position;
}

public void Remove(int id){
    notifyDataSetChanged();
}


public View getView(int position, View convertView, ViewGroup parent){

   View vi=convertView;
   NewsFeedHolder holder;
   News n= NewList.get(position);
   List<NewsItem> items = n.getNewsItems();
   int ItemsLen = items.size();

   if (convertView == null){

       vi = inflater.inflate(R.layout.newsfeed_item, null);

       holder=new NewsFeedHolder();

       holder.txtTitle        = (TextView)vi.findViewById(R.id.newsfeed_item_name);
       holder.avatar_image    = (ImageView)vi.findViewById(R.id.newsfeed_item_icon);
       holder.txtUpdate       = (TextView)vi.findViewById(R.id.newsfeed_item_update);
       holder.txtLike         = (TextView)vi.findViewById(R.id.newsfeed_item_like); 
       holder.txtDisLike      = (TextView)vi.findViewById(R.id.newsfeed_item_dislike);
       holder.btnLike         = (ImageButton)vi.findViewById(R.id.newsfeed_like_button) ;
       holder.btntxtDisLike   = (ImageButton)vi.findViewById(R.id.newsfeed_dislike_button); 

       holder.imgItemIcon1    = (ImageView)vi.findViewById(R.id.newsfeed_item_icon1);
       holder.imgItemIcon2    = (ImageView)vi.findViewById(R.id.newsfeed_item_icon2);
       holder.imgItemIcon3    = (ImageView)vi.findViewById(R.id.newsfeed_item_icon3);
       holder.btnLike.setOnClickListener(activity.OnLikeClickListener);
       holder.btntxtDisLike.setOnClickListener(activity.OnDisLikeOnClickListener);

        vi.setTag(holder);
    } 
    else {
          holder=(NewsFeedHolder)vi.getTag();
    }

   imageLoader.DisplayImage(n.getUserAvatarUrl(), activity, holder.avatar_image);
   String url1,url2,url3;

    try{

        switch(ItemsLen){


        case 1:
            url1 = n.getNewsItems().get(0).getItemUrl();
            imageLoader.DisplayImage(url1, activity, holder.imgItemIcon1);  
            break;

        case 2:
            url1 = n.getNewsItems().get(1).getItemUrl();
            imageLoader.DisplayImage(url1, activity, holder.imgItemIcon1);  
            url2 = n.getNewsItems().get(1).getItemUrl();
            imageLoader.DisplayImage(url2, activity, holder.imgItemIcon2);
            break;

        case 3:
            url1 = n.getNewsItems().get(2).getItemUrl();
            imageLoader.DisplayImage(url1, activity, holder.imgItemIcon1);  
            url2 = n.getNewsItems().get(2).getItemUrl();
            imageLoader.DisplayImage(url2, activity, holder.imgItemIcon2);
            url3 = n.getNewsItems().get(2).getItemUrl();
            imageLoader.DisplayImage(url3, activity, holder.imgItemIcon3);
            break;

    default:

    }
    }
    catch(Exception e){
        Log.i("adaptex",e.getMessage());
    }


    holder.txtTitle.setText(n.getNewsTitle());
    holder.txtUpdate.setText(n.getUpdate());
    holder.txtLike.setText(Integer.toString(n.getLike()));
    holder.txtDisLike.setText(Integer.toString(n.getDesLike()));

    activity.registerForContextMenu(vi);

    vi.setOnClickListener(activity.OnListItemClickListener);


    return vi;

}

当我尝试获取 item.getMenuInfo() 时，我收到 null。

Answer 1

您需要注册上下文菜单的列表，而不是项目。

// wrong:
activity.registerForContextMenu(vi);

// right:
activity.registerForContextMenu(myList);

Answer 2

它可能与它没有任何关系，但我立即看到的一件明显的事情是：

public Object getItem(int position) {
   return position;
}

public long getItemId(int position) {
   return position;
}

您的 getItem 方法返回对象位置的 int ，而不是实际的 Object其本身如其方法声明中所述。

Answer 3

getMenuInfo() 适用于 ListAdapter，不适用于视图。

但是，您可以使用视图的标签传递附加数据。

在获取视图中：
vi.setTag(位置)
Activity.registerForContextMenu(vi);

在活动中声明
私有 int id；

onCreateContextMenu：
id = (int) v.getTag();

onContextItemSelected：
你可以使用id

Answer 4

不久前我也遇到了类似的问题。深入研究文档后，我发现必须使用 View#setOnCreateContextMenuListener 方法将所选项目的数据传递到视图 View.OnCreateContextMenuListener 内适配器中项目根视图中的 ContextMenu.ContextMenuInfo 对象。但是，没有方法可以执行此操作，并且使用 AdapterView.AdapterContextMenuInfo 构造函数设置对象实际上不会覆盖它的 null 值。因此，我使用自定义对象在 View#setOnCreateContextMenuListener 方法中传递这些值，并在 AppCompatActivity#onContextItemSelected 方法中获取值。这是我的代码...

这是我的项目布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:background="?recyclerItemBackground">

    <TextView android:layout_width="match_parent"
        android:id="@+id/name_tv"
        android:layout_height="wrap_content"
        android:text="anville"
        android:textSize="20sp"/>

    <TextView android:layout_width="match_parent"
        android:id="@+id/number_tv"
        android:layout_height="wrap_content"
        android:text="anville"
        android:textSize="20sp"/>

</LinearLayout>

这是我的适配器，我在 RecyclerView.Adapter#onBindViewHolder 方法中设置了 View#setOnCreateContextMenuListener

package io.github.anville95work.menuexample;

import android.annotation.SuppressLint;
import android.content.Context;
import android.view.ContextMenu;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;

public class Adapter extends RecyclerView.Adapter<ViewHolder> {
    private Context context;
    private ArrayList<People> peopleList;
    private PositionHolder positionHolder;

    public Adapter(Context context, ArrayList<People> peopleList, PositionHolder  positionHolder) {
        this.context = context;
        this.peopleList = peopleList;
        this.positionHolder = positionHolder;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View itemView = inflater.inflate(R.layout.item_layout, parent, false);
        return new ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, @SuppressLint("RecyclerView") int position) {
        holder.getNameTV().setText(peopleList.get(position).getName());
        holder.getPhoneTV().setText(String.valueOf(peopleList.get(position).getNumber()));
        //MUST SET CREATE CONTEXT MENU LISTENER
        holder.getItemView().setOnCreateContextMenuListener(new View.OnCreateContextMenuListener() {
            @Override
            public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
                positionHolder.setPosition(position);
            }
        });
    }

    @Override
    public int getItemCount() {
        return peopleList.size();
    }
}

class ViewHolder extends RecyclerView.ViewHolder {
    public ViewHolder(@NonNull View itemView) {
        super(itemView);
        itemView.setLongClickable(true);
        //YOU MUST SET_LONG_CLICKABLE TO TRUE FOR CONTEXT MENU TO WORK
    }

    private TextView nameTV = itemView.findViewById(R.id.name_tv);
    private TextView phoneTV = itemView.findViewById(R.id.number_tv);

    public TextView getNameTV() {
        return nameTV;
    }

    public TextView getPhoneTV() {
        return phoneTV;
    }

    public View getItemView() {
        return itemView;
    }
}

这是我的 AppCompatActivity，我创建了一个 PositionHolder 的私有对象并将引用传递给创建上下文菜单时进行修改的适配器对象。我在底部添加了 PositionHolder 类。

package io.github.anville95work.menuexample;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.util.Log;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Toast;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private PositionHolder positionHolder = new PositionHolder(0);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView = findViewById(R.id.recycler_view);
        LinearLayoutManager manager = new LinearLayoutManager(this);
        manager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(manager);
        ArrayList<People> peopleArrayList = new ArrayList<People>();

        for(int i = 0; i <= 40; i++) {
            peopleArrayList.add(new People("anville-" + i, 2547 + i));
        }

        Adapter adapter = new Adapter(this, peopleArrayList, positionHolder);
        recyclerView.setAdapter(adapter);

        //CONTEXT MENU
        //YOU MUST SET_LONG_CLICKABLE TO TRUE IN VIEW_HOLDER FOR CONTEXT MENU TO WORK
        registerForContextMenu(recyclerView);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.options_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.option1:
                Toast.makeText(this, "You selected the first option", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.option2:
                Toast.makeText(this, "You selected the second option", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.option3:
                Toast.makeText(this, "You selected the third option", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.option4:
                Toast.makeText(this, "You selected the fourth option", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.option5:
                Toast.makeText(this, "You selected the fifth option", Toast.LENGTH_SHORT).show();
                return true;
            default:
                Toast.makeText(this, "How did this come to be?!!", Toast.LENGTH_SHORT).show();
                return true;
        }
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        //USE THIS METHOD TO MODIFY THE MENU IN RUN_TIME IF NEED BE.
        //to update the menu you must call invalidateOptionsMenu() so as to trigger a callBack for this method
        return true;
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View view, ContextMenu.ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, view, menuInfo);
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.context_menu, menu);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<");
        System.out.println("Position: " + String.valueOf(positionHolder.getPosition()));
        switch(item.getItemId()) {
            case R.id.context_option1:
                Toast.makeText(this, "You want option1 for " + positionHolder.getPosition(), Toast.LENGTH_LONG).show();
                return true;
            case R.id.context_option2:
                Toast.makeText(this, "You want option2 for " + positionHolder.getPosition(), Toast.LENGTH_LONG).show();
                return true;
            case R.id.context_option3:
                Toast.makeText(this, "You want option3 for " + positionHolder.getPosition(), Toast.LENGTH_LONG).show();
                return true;
            case R.id.context_option4:
                Toast.makeText(this, "You want option4 for " + positionHolder.getPosition(), Toast.LENGTH_LONG).show();
                return true;
            case R.id.context_option5:
                Toast.makeText(this, "You want option5 for " + positionHolder.getPosition(), Toast.LENGTH_LONG).show();
                return true;
            default:
                Toast.makeText(this, "I have no idea what you want for " + positionHolder.getPosition(), Toast.LENGTH_LONG).show();
                return super.onContextItemSelected(item);
        }
    }
}

class PositionHolder {
    private int position;

    public PositionHolder(int position) {
        this.position = position;
    }

    public void setPosition(int position) {
        this.position = position;
    }

    public int getPosition() {
        return position;
    }
}

一切顺利。感谢您的阅读，祝您编码愉快。