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?

A commonly-used method that works with linear layout is to set a property on the image button

android:layout_gravity="center"

You can choose whether to left-align, center-align, or right-align each object in the linear layout. Note that the above line is precisely the same as

android:layout_gravity="center_vertical|center_horizontal"

Add this

android:gravity="center"

In LinearLayout.