向多级可扩展列表视图的每个子项添加 Toast

Question

我发现这个multilevel expandable listview 对我的项目非常准确，但我还想为每三层（即最后一层视图）子项添加一个不同的 toast。我试过这个：

expandableListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {

             
                Toast.makeText(thirdLevelq1.put(q1[0] this, "The first child" , Toast.LENGTH_LONG).show();
                return false;

            }
        });  

但它给出了错误。我什至尝试对每个 childItem 使用相同的 toast 文本，安装的应用程序在我打开适配器时崩溃了。那么，如何正确添加呢？

Java：

package com.bacon.expandablelistview;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ExpandableListView;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ExpandableListView expandableListView;

    String[] parent = new String[]{"What is View?", "What is  Layout?", "What is Dynamic Views?"};
    String[] q1 = new String[]{"List View", "Grid View"};
    String[] q2 = new String[]{"Linear Layout", "Relative Layout"};
    String[] q3 = new String[]{"Recycle View"};
    String[] des1 = new String[]{"A layout that organizes its children into a single horizontal or vertical row. It creates a scrollbar if the length of the window exceeds the length of the screen."};
    String[] des2 = new String[]{"Enables you to specify the location of child objects relative to each other (child A to the left of child B) or to the parent (aligned to the top of the parent)."};
    String[] des3 = new String[]{"This list contains linear layout information"};
    String[] des4 = new String[]{"This list contains relative layout information,Displays a scrolling grid of columns and rows"};
    String[] des5 = new String[]{"Under the RecyclerView model, several different components work together to display your data. Some of these components can be used in their unmodified form; for example, your app is likely to use the RecyclerView class directly. In other cases, we provide an abstract class, and your app is expected to extend it; for example, every app that uses RecyclerView needs to define its own view holder, which it does by extending the abstract RecyclerView.ViewHolder class."};

    LinkedHashMap<String, String[]> thirdLevelq1 = new LinkedHashMap<>();
    LinkedHashMap<String, String[]> thirdLevelq2 = new LinkedHashMap<>();
    LinkedHashMap<String, String[]> thirdLevelq3 = new LinkedHashMap<>();
    /**
     * Second level array list
     */
    List<String[]> secondLevel = new ArrayList<>();
    /**
     * Inner level data
     */
    List<LinkedHashMap<String, String[]>> data = new ArrayList<>();


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

//The problem starts here

expandableListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {


                Toast.makeText(getApplicationContext(), "The first child", Toast.LENGTH_LONG).show();
                return false;

            }
        });


        setUpAdapter();
    }

    private void setUpAdapter() {
        secondLevel.add(q1);
        secondLevel.add(q2);
        secondLevel.add(q3);
        thirdLevelq1.put(q1[0], des1);
        thirdLevelq1.put(q1[1], des2);
        thirdLevelq2.put(q2[0], des3);
        thirdLevelq2.put(q2[1], des4);
        thirdLevelq3.put(q3[0], des5);

        data.add(thirdLevelq1);
        data.add(thirdLevelq2);
        data.add(thirdLevelq3);
        expandableListView = (ExpandableListView) findViewById(R.id.expandible_listview);
        //passing three level of information to constructor
        ThreeLevelListAdapter threeLevelListAdapterAdapter = new ThreeLevelListAdapter(this, parent, secondLevel, data);
        expandableListView.setAdapter(threeLevelListAdapterAdapter);
        expandableListView.setOnGroupExpandListener(new ExpandableListView.OnGroupExpandListener() {
            int previousGroup = -1;

            @Override
            public void onGroupExpand(int groupPosition) {
                if (groupPosition != previousGroup)
                    expandableListView.collapseGroup(previousGroup);
                previousGroup = groupPosition;
            }
        });


    }
}

提前致谢。

编辑：当我使用 Toast.makeText(getApplicationContext(), "The first child", Toast.LENGTH_LONG).show(); 时，它的崩溃日志显示：

  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ExpandableListView.setOnChildClickListener(android.widget.ExpandableListView$OnChildClickListener)' on a null object reference

Answer 1

@Override
public void onFinalChildClick(int plpos, int slpos, int tlpos) {
    String msg = "";
    switch (tlpos) {
        case 0:
            msg = "Shakespear is a good poet";
            break;
        case 1:
            msg = "Earth isn't flat";
            break;
        default:
            msg = "Unknown";
    }
    Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
}

@Override
public void onFinalItemClick(String plItem, String slItem, String tlItem) {
    String inMsg = plItem + ", " + slItem + ", " + tlItem;
    String outMsg = "";
    if (inMsg.equals("group 1, Child Level 1, A")){
        outMsg = "Shakespear is a good poet";
    } else if (inMsg.equals("group 1, Child Level 1, B")){
        outMsg = "Earth isn't flat";
    } else {
        outMsg = "Unknown";
    }
    Toast.makeText(this, outMsg, Toast.LENGTH_SHORT).show();
}

Answer 2

请在初始化expandableListView 之后设置此侦听器expandableListView.setOnChildClickListener，即在您的情况下setUpAdapter() 之后，因为当您尝试设置侦听器时expandableListView 仍然为空，因为您的初始化是在之后。

这就是NullPointerException 的原因。因为在设置监听器时expandableListView 为空。

干杯