Android Button with Text with different images for Enabled and Pressed

问题

I am trying to create a stateful Button having Text and an Image on the top via the following code:

<Button
android:id="@+id/btnMultiplayer"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:drawableTop="@drawable/multiplayer"
android:paddingLeft="20dp"
android:paddingRight="20dp"
android:text="Multiplayer"/>

to get this:

However, I couldn't find the way to change the drawable on the top when the image is pressed.

I tried to set android:drawableTop to @drawable/multiplayer_stateful where @drawable/multiplayer_stateful is :

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

<item android:drawableTop="@drawable/multiplayer" android:state_enabled="true" android:state_window_focused="false"/>
<item android:drawableTop="@drawable/multiplayer_pressed" android:state_pressed="true"/>

</selector>

but this doesn't work. (Note that @drawable/multiplayer and @drawable/multiplayer_pressed are png files)

Any suggestions?

回答1:

You have to use android:dither = "true"

Try this.

<?xml version="1.0" encoding="utf-8"?>
<selector 
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:dither="true" >

<item android:drawableTop="@drawable/multiplayer" android:state_enabled="true" android:state_window_focused="false"/>
<item android:drawableTop="@drawable/multiplayer_pressed" android:state_pressed="true"/>

</selector>

From Android Docs:

Enables or disables dithering of the bitmap if the bitmap does not have the same pixel configuration as the screen (for instance: a ARGB 8888 bitmap with an RGB 565 screen).

Must be a boolean value, either "true" or "false".

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

Dithering affects how colors that are higher precision than the device are down-sampled. No dithering is generally faster, but higher precision colors are just truncated down (e.g. 8888 -> 565). Dithering tries to distribute the error inherent in this process, to reduce the visual artifacts.

I hope it helps!

回答2:

enable dither attribute in your selector.

android:dither

Boolean. Enables or disables dithering of the bitmap if the bitmap does not have the same pixel configuration as the screen (for instance: a ARGB 8888 bitmap with an RGB 565 screen). For more detail refer this link:http://developer.android.com/guide/topics/resources/drawable-resource.html

来源：https://stackoverflow.com/questions/32264654/android-button-with-text-with-different-images-for-enabled-and-pressed