Center a button in a Linear layout

Center using a LinearLayout:

<LinearLayout    android:id="@+id/LinearLayout1"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:gravity="center"    android:orientation="vertical" >    <ImageButton        android:id="@+id/btnFindMe"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:background="@drawable/findme" /></LinearLayout>

If you want to center an item in the middle of the screen don't use a LinearLayout as these are meant for displaying a number of items in a row.

Use a RelativeLayout instead.

So replace:

android:layout_gravity="center_vertical|center_horizontal"

for the relevant RelativeLayout option:

android:layout_centerInParent="true"

So your layout file will look like this:

<?xml version="1.0" encoding="utf-8"?><RelativeLayout android:id="@+id/RelativeLayout01"     android:layout_width="fill_parent"     android:layout_height="fill_parent"    xmlns:android="http://schemas.android.com/apk/res/android">    <ImageButton android:id="@+id/btnFindMe"         android:layout_width="wrap_content"         android:layout_height="wrap_content"        android:layout_centerInParent="true"        android:background="@drawable/findme"></ImageButton></RelativeLayout>

Have you tried defining android:gravity="center_vertical|center_horizontal" inside the layout and setting android:layout_weight="1" in the image?