Question

i want, that the first imagebutton fill the top place and the second imagebutton fill the bottom place. Did I forget something?

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<ImageButton
    android:id="@+id/imageButton1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentTop="true"
    android:background="@color/white"
    android:src="@android:drawable/btn_star"
    android:layout_gravity="top" />

<ImageButton
    android:id="@+id/imageButton2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:background="@color/white"
    android:src="@android:drawable/btn_star"
    android:layout_gravity="bottom" />

</LinearLayout>

Answer 1

The problem is that you need to use a RelativeLayout Try:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<ImageButton
    android:id="@+id/imageButton1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentTop="true"
    android:background="#ffffff"
    android:src="@android:drawable/btn_star"
    android:layout_gravity="top" />

<ImageButton
    android:id="@+id/imageButton2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:background="#ffffff"
    android:src="@android:drawable/btn_star"
    android:layout_gravity="bottom" />

</RelativeLayout>

Hope that helps. Tell me if that is what you want to accomplish, or if you want both buttons to fill halve the height of the screen equally.

If is then second option then try this:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ImageButton
    android:id="@+id/imageButton1"
    android:layout_weight="1"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:background="#ffffff"
    android:src="@drawable/icon"
 />

<ImageButton
    android:id="@+id/imageButton2"
    android:layout_weight="1"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:background="#ffffff"
    android:src="@drawable/icon"
 />

</LinearLayout>

Which would look like this: