1.Suppose you have a declaration of attributes for your widget (in attrs.xml):
<declare-styleable name="CustomImageButton">
<attr name="customAttr" format="string"/>
</declare-styleable>
2.Declare an attribute you will use for a style reference (in attrs.xml):
<declare-styleable name="CustomTheme">
<attr name="customImageButtonStyle" format="reference"/>
</declare-styleable>
3.Declare a set of default attribute values for the widget (in styles.xml):
<style name="Widget.ImageButton.Custom" parent="android:style/Widget.ImageButton">
<item name="customAttr">some value</item>
</style>
4.Declare a custom theme (in themes.xml):
<style name="Theme.Custom" parent="@android:style/Theme">
<item name="customImageButtonStyle">@style/Widget.ImageButton.Custom</item>
</style>
5.Use this attribute as the third argument in your widget's constructor (in CustomImageButton.java):
public class CustomImageButton extends ImageButton {
private String customAttr;
public CustomImageButton( Context context ) {
this( context, null );
}
public CustomImageButton( Context context, AttributeSet attrs ) {
this( context, attrs, R.attr.customImageButtonStyle );
}
public CustomImageButton( Context context, AttributeSet attrs,
int defStyle ) {
super( context, attrs, defStyle );
final TypedArray array = context.obtainStyledAttributes( attrs,
R.styleable.CustomImageButton, defStyle,
R.style.Widget_ImageButton_Custom ); // see below
this.customAttr =
array.getString( R.styleable.CustomImageButton_customAttr, "" );
array.recycle();
}
}
6.Now you have to apply Theme.Custom to all activities that use CustomImageButton (in AndroidManifest.xml):
<activity android:name=".MyActivity" android:theme="@style/Theme.Custom"/>