自定义Drawable

## 重写draw ##

@Override
    public void draw(Canvas canvas) {
        int height = canvas.getHeight();
        int width = canvas.getWidth();
        //设置渐变色
        LinearGradient linearGradient = new LinearGradient(width / 2, 0, width / 2,      canvas.getHeight(), mBgColor, 0xffffffff, Shader.TileMode.MIRROR);

        mBgPaint.setShader(linearGradient);

        canvas.drawRect(new RectF(0, 0, canvas.getWidth(), canvas.getHeight()), mBgPaint);

        int radius = DisplayUtil.dip2px(mContext, 38);
        paint.setColor(0x4dffffff);
        canvas.drawCircle(0, height / 5 * 2 - 28, radius, paint);

        radius = DisplayUtil.dip2px(mContext, 20);
        paint.setColor(0x1affffff);
        canvas.drawCircle(width / 3, 0, radius, paint);

        radius = DisplayUtil.dip2px(mContext, 18);
        paint.setColor(0x4dffffff);
        canvas.drawCircle(width / 5 * 3, height / 4, radius, paint);

        radius = DisplayUtil.dip2px(mContext, 68);
        paint.setColor(0x33ffffff);
        canvas.drawCircle(width , 0, radius, paint);

    }