How to show the text on a ImageButton?

It is technically possible to put a caption on an ImageButton if you really want to do it. Just put a TextView over the ImageButton using FrameLayout. Just remember to not make the Textview clickable.

Example:

<FrameLayout>
    <ImageButton
        android:id="@+id/button_x"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="@null"
        android:scaleType="fitXY"
        android:src="@drawable/button_graphic" >
    </ImageButton>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:clickable="false"
        android:text="TEST TEST" >
    </TextView>
</FrameLayout>

As you can't use android:text I recommend you to use a normal button and use one of the compound drawables. For instance:

<Button 
    android:id="@+id/buttonok" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"
    android:drawableLeft="@drawable/buttonok"
    android:text="OK"/>

You can put the drawable wherever you want by using: drawableTop, drawableBottom, drawableLeft or drawableRight.

UPDATE

For a button this too works pretty fine. Putting android:background is fine!

<Button
    android:id="@+id/fragment_left_menu_login"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/button_bg"
    android:text="@string/login_string" />

I just had this issue and is working perfectly.