Android -purpose of useLevel in shape tag

Question

What is the purpose of android shape xml tag useLevel attribute ? This is in respect to a layer-list but should not matter. From the docs i found the meanging of the useLevel tag:

Indicates whether the drawable's level affects the way the gradient is drawn.

So if i have the following xml snippet:

    <?xml version="1.0" encoding="utf-8"?> <shape     xmlns:android="http://schemas.android.com/apk/res/android"     android:shape="ring"     android:innerRadius="15dp"     android:thickness="10dp"     android:useLevel="false">      <solid android:color="#ababf2" />      <size         android:height="50dp"         android:width="50dp" /> </shape> 

then with the useLevel=true, the ring is disabled. It must be false for the ring to appear. But what is the purpose of this attribute ? The docs are not clear.

Answer 1

It is for ProgressBars. For example this gist uses a ring shape as a progress drawable.

res/drawable/github_232_circular.xml:

<shape xmlns:android="http://schemas.android.com/apk/res/android"        android:innerRadiusRatio="2.3"        android:shape="ring"        android:thickness="3.8sp"        android:useLevel="true">     <solid android:color="#ff0000" /> </shape> 

In your layout:

<ProgressBar     android:id="@+id/progress"     style="?android:attr/progressBarStyleHorizontal"     android:layout_width="64dp"     android:layout_height="64dp"     android:layout_gravity="top|end"     android:max="100"     android:progress="0"     android:progressDrawable="@drawable/github_232_circular" /> 

Basically, useLevel makes it so the drawable can be drawn partially. For example there is a method ImageView.setImageLevel() that lets you set a "level," e.g. 25% progress, so the ring drawable would be drawn as a quarter-circle. And ProgressBar.setProgress() does the same thing, updating the "level" of the drawable you've set on the ProgressBar.