Android Shadow Drawing

Shadow.java

package com.example.util.shadow;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Rect;
import android.graphics.drawable.GradientDrawable;
import android.view.View;

import static android.graphics.drawable.GradientDrawable.Orientation.LEFT_RIGHT;
import static android.graphics.drawable.GradientDrawable.Orientation.TOP_BOTTOM;
import static android.graphics.drawable.GradientDrawable.RADIAL_GRADIENT;


public class Shadow {
    private static final int START_COLOR = Color.parseColor("#55000000");
    private static final int END_COLOR = Color.parseColor("#00000000");
    private static final int SHADOW_LENGTH = (int) (5 * Resources.getSystem().getDisplayMetrics().density);

    private static GradientDrawable linearGradient;
    private static GradientDrawable radialGradient;
    private static int[] colors;

    static {
        colors = new int[]{START_COLOR, END_COLOR};
        linearGradient = new GradientDrawable(TOP_BOTTOM, colors);
        radialGradient = new GradientDrawable();
        radialGradient.setGradientType(RADIAL_GRADIENT);
        radialGradient.setColors(colors);
        radialGradient.setGradientRadius(SHADOW_LENGTH);
    }

    public static void onDraw(View view, Canvas canvas) {
        int height = view.getHeight();
        int width = view.getWidth();
        
        linearGradient.setBounds(SHADOW_LENGTH, height, width, height + SHADOW_LENGTH);
        linearGradient.setOrientation(TOP_BOTTOM);
        linearGradient.draw(canvas);

        linearGradient.setBounds(width, SHADOW_LENGTH, width + SHADOW_LENGTH, height);
        linearGradient.setOrientation(LEFT_RIGHT);
        linearGradient.draw(canvas);

        radialGradient.setBounds(0, height, SHADOW_LENGTH, height + SHADOW_LENGTH);
        radialGradient.setGradientCenter(1, 0);
        radialGradient.draw(canvas);

        radialGradient.setBounds(width, height, width + SHADOW_LENGTH, height + SHADOW_LENGTH);
        radialGradient.setGradientCenter(0, 0);
        radialGradient.draw(canvas);

        radialGradient.setBounds(width, 0, width + SHADOW_LENGTH, SHADOW_LENGTH);
        radialGradient.setGradientCenter(0, 1);
        radialGradient.draw(canvas);
    }
}

If you want to use Paint.setShadowLayer(), you must disable hardware acceleration.

I try to change to change it into a custom View and it is not work.
There is not any shadow in it.