android ImageButton单击

Question

I have just a little problem in my layout

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent" android:weightSum="1">

    <ImageButton android:id="@+id/startLogo"
    android:layout_height="230dp"
    android:adjustViewBounds="true"
    android:background="@drawable/whatelsecomics"
    android:layout_width="230dp"
    android:layout_gravity="center_horizontal"/>

</LinearLayout>

in my activity I have

public class WhatelsecomicsActivity extends Activity {

    private ImageButton whatelsecomics;

    @Override
    public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main); // your layout file name

       whatelsecomics = (ImageButton) findViewById(R.id.startLogo); // your image button

    // click event on your button
    whatelsecomics.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Intent wecSeriesList = new Intent(WhatelsecomicsActivity.this, wecSeriesListActivity.class);
            //Start next activity
            WhatelsecomicsActivity.this.startActivity(wecSeriesList);
        }
    });
}

}

in my log

09-23 21:31:05.081: ERROR/AndroidRuntime(3805): FATAL EXCEPTION: main
09-23 21:31:05.081: ERROR/AndroidRuntime(3805): java.lang.RuntimeException: Unable to start activity ComponentInfo{zepod.whatelsecomics/zepod.whatelsecomics.WhatelsecomicsActivity}: java.lang.NullPointerException
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.os.Looper.loop(Looper.java:123)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.ActivityThread.main(ActivityThread.java:3683)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at java.lang.reflect.Method.invokeNative(Native Method)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at java.lang.reflect.Method.invoke(Method.java:507)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at dalvik.system.NativeStart.main(Native Method)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805): Caused by: java.lang.NullPointerException
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at zepod.whatelsecomics.WhatelsecomicsActivity.onCreate(WhatelsecomicsActivity.java:21)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
09-23 21:31:05.081: ERROR/AndroidRuntime(3805):     ... 11 more

Anyone can say me why?

Answer 1

If you're using Eclipse, click Project->Clean... (and rebuild it if you don't have it automatically doing so). The usual cause of problems like this is the R file isn't properly generated so that rebuilds the project to generate it again.

Answer 2

You have NullPointerException on WhatelsecomicsActivity.java:21

What line is that?