Note that gradientRadius percentages do work in Lollipop. But if you have to support pre-Lollipop I expanded upon @marnaish's answer adding XML attributes. My gradientRadius is defined as a percentage of the parent view's width:
public class RadialGradientView extends View {
private final int endColor;
private final int startColor;
private final float gradientRadiusWidthPercent;
private final float centerY;
private final float centerX;
private Paint paint;
public RadialGradientView(Context context, AttributeSet attrs) {
super(context, attrs);
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.RadialGradientView, 0, 0);
startColor = a.getColor(R.styleable.RadialGradientView_startColor, Color.RED);
endColor = a.getColor(R.styleable.RadialGradientView_endColor, Color.BLACK);
gradientRadiusWidthPercent = a.getFloat(R.styleable.RadialGradientView_gradientRadiusWidthPercent, 1);
centerX = a.getFloat(R.styleable.RadialGradientView_centerX, .5f);
centerY = a.getFloat(R.styleable.RadialGradientView_centerY, .5f);
a.recycle();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int parentWidth = MeasureSpec.getSize(widthMeasureSpec);
int parentHeight = MeasureSpec.getSize(heightMeasureSpec);
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
RadialGradient gradient = new RadialGradient(
parentWidth*centerX,
parentHeight*centerY,
parentWidth*gradientRadiusWidthPercent,
new int[] {startColor, endColor},
null,
android.graphics.Shader.TileMode.CLAMP);
paint.setDither(true);
paint.setShader(gradient);
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawRect(0, 0, getWidth(), getHeight(), paint);
}
}
In attrs.xml:
<declare-styleable name="RadialGradientView">
<attr name="startColor" format="color|reference"/>
<attr name="endColor" format="color|reference"/>
<attr name="gradientRadiusWidthPercent" format="float"/>
<attr name="centerX" format="float"/>
<attr name="centerY" format="float"/>
</declare-styleable>
Unfortunately you can't create an XML drawable from a custom class, so you can't set it as a View's android:background. The workaround is to use a FrameLayout to layer it as the background.
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="100dp">
<com.RadialGradientView
android:layout_width="match_parent"
android:layout_height="match_parent"
app:centerX=".3"
app:centerY=".5"
app:endColor="#0f0"
app:startColor="#f00"
app:gradientRadiusWidthPercent=".5"
/>
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:text="What's up world?"/>
</FrameLayout>
%or%p– Munger