How to make canvas transparent in Android?

Question

I want to make the drawing surface of my app transparent so that the my app can look like the user can draw on top of my background image, I have the following XML:

Answer 1

package com.logistics.kiddiekuts.Trans;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.widget.RelativeLayout;

public class TransparentPanel extends RelativeLayout {
    private Paint innerPaint, borderPaint;

    public TransparentPanel(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public TransparentPanel(Context context) {
        super(context);
        init();
    }

    private void init() {
        innerPaint = new Paint();
        innerPaint.setARGB(225, 225, 225, 225); // gray
        innerPaint.setAntiAlias(true);

        borderPaint = new Paint();
        borderPaint.setARGB(255, 255, 255, 255);
        borderPaint.setAntiAlias(true);
        borderPaint.setStyle(Style.STROKE);
        borderPaint.setStrokeWidth(2);
    }

    public void setInnerPaint(Paint innerPaint) {
        this.innerPaint = innerPaint;
    }

    public void setBorderPaint(Paint borderPaint) {
        this.borderPaint = borderPaint;
    }

    protected void dispatchDraw(Canvas canvas) {

        RectF drawRect = new RectF();
        drawRect.set(0, 0, getMeasuredWidth(), getMeasuredHeight());

        canvas.drawRoundRect(drawRect, 8, 8, innerPaint);
        // canvas.drawRoundRect(drawRect, 5, 5, borderPaint);

        super.dispatchDraw(canvas);
    }
}

XML::