Android tutorial: custom button background (created programatically)

This post is an extension to the Android custom button layout tutorial.

Creating custom button background is described here. There, in point 3, I show how to build an XML file with selector background.

The selector file has definitions of backgrounds that are shown depending on a button state: if button is pressed, then show pressed background, else show normal background

XML definition is suitable when you know at a compile time which images you will use. When you have to decide at runtime (for example build layout dynamically) – it is not enough. Then you can substitute the XML file with programatically created object: StateListDrawable.

It means that this XML:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <item android:state_pressed="true" android:drawable="@drawable/button_left_pressed"/>
    <item android:state_focused="true" android:drawable="@drawable/button_left_pressed"/>
    <item android:drawable="@drawable/button_left_normal"/>
</selector>

is exactly the same, interchangeable and can be created in Java code this way:

int buttonPressedResId = R.drawable.button_left_pressed;
int buttonNormalResId = R.drawable.button_left_normal;

Resources resources = getApplicationContext().getResources();

StateListDrawable states = new StateListDrawable();
states.addState(new int[] {android.R.attr.state_pressed}, resources.getDrawable(buttonPressedResId));
states.addState(new int[] {android.R.attr.state_focused}, resources.getDrawable(buttonPressedResId));
states.addState(new int[] { }, resources.getDrawable(buttonNormalResId));
((Button) findViewById(R.id.calc_addPerson_button)).setBackgroundDrawable(states);

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