Adding Toast to Every ChildItem of a Multi Level Expandable LisView

Question

I found this multilevel expandable listview which is very accurate with my project, but I also want to add a different toast to every third level (which is the last layer of view) child items. I tried this:

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;

            }
        });  

But it gives error. I even tried to use same toast text to every childItem, app installed but crashed when I opened the adapter. So, how to add them properly?

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;
            }
        });


    }
}

Thanks in advance.

Edit: When I use Toast.makeText(getApplicationContext(), "The first child", Toast.LENGTH_LONG).show(); its crash logs says:

  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

Please set this listener expandableListView.setOnChildClickListener after the expandableListView is initialized, that is after setUpAdapter() in your case as expandableListView is still null when you are trying to set the listener because your initialization of this is afterwards.

That is the reason for NullPointerException. because expandableListView is null while setting the listener.

Cheers

Answer 2

@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();
}