[android-developers] Null pointer exception while using setOnClickListener

[e-satis]

Hi,

My java code look like this :

        // right_arrow button
        ImageButton arrow_button = (ImageButton)findViewById
(R.id.arrow);
        arrow_button.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                 ((View)v.getParent().getParent()).setSelected(true);
            }
        });

And the corresponding XML look like :

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/
android"
    android:id="@+id/row_layout" >

    <LinearLayout android:id="@+id/row_checkbox_container">

        <CheckBox android:id="@+id/row_checkbox" />

    </LinearLayout>

   <LinearLayout android:id="@+id/item_title_container">

        <TextView android:id="@+id/item_title"/>

    </LinearLayout>

    <LinearLayout android:id="@+id/right_arrow_container" >

     <ImageButton android:id="@+id/arrow"
                    android:layout_width="18px"
                    android:layout_height="fill_parent"
                    android:layout_gravity="bottom"
                    android:layout_weight="1"
                    android:src="@drawable/arrow"
                    android:background="#00000000"/>

    </LinearLayout>

</LinearLayout>

I got a null pointer exception right after running the app in the
emulator from eclipse on Ubuntu 8.10 :

E/AndroidRuntime( 1426): java.lang.RuntimeException: Unable to start
activity ComponentInfo{com.getincontext/com.getincontext.InContext}:
java.lang.NullPointerException
E/AndroidRuntime( 1426):        at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:
2141)
E/AndroidRuntime( 1426):        at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:
2157)
E/AndroidRuntime( 1426):        at android.app.ActivityThread.access$1800
(ActivityThread.java:112)
E/AndroidRuntime( 1426):        at android.app.ActivityThread$H.handleMessage
(ActivityThread.java:1581)
E/AndroidRuntime( 1426):        at android.os.Handler.dispatchMessage
(Handler.java:88)
E/AndroidRuntime( 1426):        at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 1426):        at android.app.ActivityThread.main
(ActivityThread.java:3739)
E/AndroidRuntime( 1426):        at java.lang.reflect.Method.invokeNative
(Native Method)
E/AndroidRuntime( 1426):        at java.lang.reflect.Method.invoke
(Method.java:515)
E/AndroidRuntime( 1426):        at com.android.internal.os.ZygoteInit
$MethodAndArgsCaller.run(ZygoteInit.java:739)
E/AndroidRuntime( 1426):        at com.android.internal.os.ZygoteInit.main
(ZygoteInit.java:497)
E/AndroidRuntime( 1426):        at dalvik.system.NativeStart.main(Native
Method)
E/AndroidRuntime( 1426): Caused by: java.lang.NullPointerException
E/AndroidRuntime( 1426):        at com.getincontext.InContext.onCreate
(InContext.java:51)
E/AndroidRuntime( 1426):        at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:
1122)
E/AndroidRuntime( 1426):        at
android.app.ActivityThread.performLaunchActiv

I searched in the other posts something similar, and It seems that it
must be because the ImageButton is set to null.

Unfortunately I can't find anything that would lead to it in the XML
or the Java code. The button is displayed properly and eclipse does
not detect any error. I guess this is runtime.

I tried to cast from ImageButton to button but it doesn't change
anything. So I image the  trouble is from findViewById(), but arrow to
exists, is a regular pgn file and is displayed by the emulator if this
line is commented.

The weirdest is that I got a similar statement just above, and I can't
see any difference.

Any clue ?

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