By

Contents
  1. 1. Part 1: LevelListDrawable
  2. 2. Notes
  3. 3. What does it help?

In this post series, I will share some cases I used Android drawable in more efficient ways. They can help your code looks cleaner, separating Java vs. XML, or even reduce the complexity of your View hierachy.

Types of Drawable I will be writing about in this series are: LevelList / Bitmap / StateList / Layer / Clip Drawable

  • Part 1: LevelListDrawable
  • Part 2: BitmapDrawable
  • Part 3: StateListDrawable
  • Part 4: LayerDrawable

Part 1: LevelListDrawable

Developers Docs

Imagine I am developing a multiple choice question game. After user end a series of questions, I will show an result dialog in which there’s one medal image. The medal image has 3 states: bronze / silver / gold but show only one at a time corresponding to how many correct answer that user made. The logic is below:

Show Bronze medal - complete 1 correct answer

Show Silver medal - complete 5 questions correctly

Show Gold medal - complete all 10 questions correctly

Step 1: I will create a LevelListDrawable in XML and name it in: res/drawable/levels_result_medal.xml

1
2
3
4
5
 
<level-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item android:drawable="@drawable/medal_bronze" android:maxLevel="4"/>
<item android:drawable="@drawable/medal_silver" android:maxLevel="9"/>
<item android:drawable="@drawable/medal_gold" android:maxLevel="10"/>
level-list>

Step 2: Set it as image source of the medal ImageView in your layout:

1
2
3
4
 
<ImageView
android:id="..." android:layout_width="..." android:layout_height="..."
android:src="@drawable/levels_result_medal"
/>

Step 3: My Java code for the switching logic will look like this:

1
2
 
medalImageView.setImageLevel(nUserCorrectAnswered);
// nUserCorrectAnswered is a variable having value range of [0..10].

Notes

  • LevelListDrawable has also minLevel attribute for more customization
  • LevelListDrawable does not allow negative for max/min (will make runtime crash if so)
  • You can invoke level change in Drawable instance by:

[code language=”java”]
medalImageView.getDrawable().setLevel(nUserCorrectAnswered);
[/code]

  • setImageLevel() / setLevel() allow negative parameter.
  • setLevel() is also used with ClipDrawable
  • For unlucky zero, if you want to set an image for it as well (show a unavailable state image of medal when user have no correct answer), just add one more item in level-list with maxLevel=”0”

What does it help?

  • With this type of Drawable, you might save some lines of code for switching logic (if / switch case …) or even more if you are implementing a graphics having more states than the medal (battery states, progress bar, …).
  • This also helps separate Java code and XML code so your class may look cleaner.
Contents
  1. 1. Part 1: LevelListDrawable
  2. 2. Notes
  3. 3. What does it help?