check if checkbox is checked return null pointer

Question

I have this code for an expandable list, I want to have a checkbox in the childgroups of the list view, and check if one of the checkboxes is checked. The problem is that when I check if the checkbox is checked I get a NULL Pointer Exception.

Can you please tell me whats wrong?

here's my code - I've edited the code to inflate a view of the child_row.xml that holds that checkbox but I still get that null pointer, what am I doing wrong?!?!

   package send.Shift;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import android.app.ExpandableListActivity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.Window;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.CompoundButton.OnCheckedChangeListener;
import android.widget.ExpandableListView;
import android.widget.SimpleExpandableListAdapter;
import android.widget.TextView;

public class Shifts extends ExpandableListActivity implements
        OnCheckedChangeListener {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.list);

        SimpleExpandableListAdapter expListAdapter = new SimpleExpandableListAdapter(
                this, createGroupList(), R.layout.group_row,
                new String[] { "Group Item" }, new int[] { R.id.row_name },
                createChildList(), R.layout.child_row,
                new String[] { "Sub Item" }, new int[] { R.id.grp_child });
        getExpandableListView().setGroupIndicator(
                getResources().getDrawable(R.drawable.expander_group));

        ExpandableListView EX = (ExpandableListView) findViewById(android.R.id.list);
        EX.setAdapter(expListAdapter);

        final CheckBox childBox = (CheckBox) findViewById(R.id.childBOX);

        final TextView choosenGroup = (TextView) findViewById(R.id.choosen);



        LayoutInflater inflater = LayoutInflater.from(Shifts.this);
        View view2 = inflater.inflate(R.layout.child_row, null);


        childBox.setOnCheckedChangeListener(new OnCheckedChangeListener() {

            @Override
            public void onCheckedChanged(CompoundButton buttonView,
                    boolean isChecked) {
                // TODO Auto-generated method stub
                if(childBox.isChecked() == true){
                choosenGroup.setText("Shift Set");
                }
            }
        });

    }

Here is some of the Logcat log:

12-23 07:38:00.644: W/dalvikvm(880): threadid=1: thread exiting with uncaught exception (group=0x40015560)
12-23 07:38:00.654: E/AndroidRuntime(880): FATAL EXCEPTION: main
12-23 07:38:00.654: E/AndroidRuntime(880): java.lang.RuntimeException: Unable to start activity ComponentInfo{send.Shift/send.Shift.Shifts}: java.lang.NullPointerException
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.os.Handler.dispatchMessage(Handler.java:99)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.os.Looper.loop(Looper.java:123)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.ActivityThread.main(ActivityThread.java:3683)
12-23 07:38:00.654: E/AndroidRuntime(880):  at java.lang.reflect.Method.invokeNative(Native Method)
12-23 07:38:00.654: E/AndroidRuntime(880):  at java.lang.reflect.Method.invoke(Method.java:507)
12-23 07:38:00.654: E/AndroidRuntime(880):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
12-23 07:38:00.654: E/AndroidRuntime(880):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
12-23 07:38:00.654: E/AndroidRuntime(880):  at dalvik.system.NativeStart.main(Native Method)
12-23 07:38:00.654: E/AndroidRuntime(880): Caused by: java.lang.NullPointerException
12-23 07:38:00.654: E/AndroidRuntime(880):  at send.Shift.Shifts.onCreate(Shifts.java:41)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
12-23 07:38:00.654: E/AndroidRuntime(880):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
12-23 07:38:00.654: E/AndroidRuntime(880):  ... 11 more

Answer 1

If you get a nullpointer on a certain line, something on that line is null . If it is the if(childBox.isChecked() line, probably childBox is null . Hard to say without the stack, but most probable cause is the line where you retrieve that checkbox.

 final CheckBox childBox = (CheckBox) findViewById(R.id.childBOX);

Might be returning null , and this could be for several reasons. It could be your id is childBox instead of childBOX . Or that it is not in R.layout.list .

The best thing you can do is start debugging. What line is the error. Find the object that is null . Find out why it is null and if that is expected or not.

Answer 2

Instead of checking the childBox.isChecked() you can use the isChecked value. So your code would look like this:

@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
    if(isChecked == true){
      choosenGroup.setText("Shift Set");
    }
}

Answer 3

Check your layout list.xml I think this layout may is missing android:id="@+id/childBOX" for Check Box or android:id="@+id/choosen" for TextView

Check the folowin sample

<CheckBox android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/childBOX"/>
    <TextView android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/choosen"/>