android gallery

Question

I'm studying android-development myself. When I use Gallery, there is a problem. Here is the code:

Gallery cf=new Gallery(this);
cf.setSpacing(20);
cf.setAdapter(imageAdapter);
cf.setAnimationDuration(1500);
setContentView(cf);

But when I try that, it's wrong.

Gallery cf=(Gallery)this.findViewById(R.id.Gallery);
cf.setSpacing(20);
cf.setAdapter(imageAdapter);
cf.setAnimationDuration(1500);
setContentView(R.layout.display);

<Gallery
android:id="@+id/Gallery" 
android:layout_width="fill_parent" 
android:layout_height="wrap_content" 
android:layout_centerInParent="true"
android:spacing="-60px"/
 >

What should I do?

EDIT: Logcat:

02-25 15:22:45.009: E/AndroidRuntime(500): FATAL EXCEPTION: main 
02-25 15:22:45.009: E/AndroidRuntime(500): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.vic.android.BluetoothContacts/com.vic.android.BluetoothContact‌​s.PhotoDisplay}: java.lang.NullPointerException 
02-25 15:22:45.009: E/AndroidRuntime(500): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
02-25 15:22:45.009: E/AndroidRuntime(500): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)

Answer 1

You are setContentView after findById - i think that's the problem Try

 setContentView(R.layout.display);
 Gallery cf=(Gallery)this.findViewById(R.id.Gallery);
 cf.setSpacing(20);
 cf.setAdapter(imageAdapter);
 cf.setAnimationDuration(1500);