Is there a way to set drawable's Alpha using XML?

Question

Easy like itself . I wanna make an alpha button , which would have a selected drawable this way:

Answer 1

It's been a while since the OP, but personally found a solution that worked a lot better for me than the suggested answers. Creating a BitmapDrawable makes is easily possible to set the alpha:

<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/your_drawble"
    android:alpha="77">
</bitmap>

Alpha can be any value between 0 and 255. Note that it is sort of the inverse of the HEX color value alpha, as for example 70% alpha would be B3 in HEX and 77 in the BitmapDrawable.

Answer 2

My goal was to make a button have it's selected and pressed states at a different alpha - but using the same (png) resource and affecting as few files as possible.

My solution is similar to altering the alpha in a BitmapDrawable - but it does it from the selector so only one file is affected.

Use the tint function of Bitmap, remember that the tint will color the existing pixels so use a white color. Eg, #80FFFFFF - to keep color as original but reduce alpha by 50% This could also be used to change color of the icon when pressed.

This is my drawable XML file:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_selected="true">
        <bitmap
            android:src="@drawable/ic_camera"
            android:tint="#80FFFFFF">
        </bitmap>
    </item>
    <item android:state_pressed="true">
        <bitmap
            android:src="@drawable/ic_camera"
            android:tint="#80FFFFFF">
        </bitmap>
    </item>
    <item>
        <bitmap
            android:src="@drawable/ic_camera">
        </bitmap>
    </item>
</selector>

Answer 3

I'm using the following for a custom radio button which should be diagonally strikethrough when it is disabled.

Example Image of 5 radio buttons where 4 of them are enabled

  <item android:state_enabled="false">
    <layer-list>
      <item>
        <shape android:shape="rectangle">
          <size
              android:height="35dp"
              android:width="35dp"/>
          <stroke
              android:color="@color/someGrey"
              android:width="1dp"/>
          <corners android:radius="1dp"/>
        </shape>
      </item>
      <item>
        <rotate
            android:fromDegrees="135"
            android:pivotX="50%"
            android:pivotY="50%"
            android:toDegrees="135">
          <shape android:shape="line">
            <stroke
                android:color="@color/someGrey"
                android:width="1dp"/>
          </shape>
        </rotate>
      </item>
    </layer-list>
  </item>

Answer 4

i think you could create your own drawable which could take this argument as a parameter. i've never done such a thing though.

check out this link :

How to set alpha value for drawable in a StateListDrawable?

if that's not possible, you can always do it in code...

here are 2 links i've found about it, in case you wish to use bitmaps instead:

• https://plus.google.com/+RomanNurik/posts/FZQcNW8G75K
• https://gist.github.com/romannurik/5779875

Answer 5

For those who have the same problem as OP, AppCompat now allows you to set 'alpha' parameter, as he wished in his target code:

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

    <!-- Play/Pause -->
    <item android:alpha="125" android:state_selected="false" android:drawable="@drawable/item" />
    <item android:alpha="255" android:state_selected="true" android:drawable="@drawable/item" />

</selector>

More info here.

Answer 6

I agree with Kasium sugest, so for some Android versions the especification to Alpha is in percent.

<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/your_drawble"
    android:alpha="0.5">
</bitmap>