GradientDrawable 支持渐变色的Drawable，与shapeDrawable在画型上是类似的，多了支持渐变色。代码上的GradientDrawable比在xml里的shape下gradient属性强大的多，因为shape下gradient属性只支持三色阶渐变，而GradientDrawable可以有更多的色阶渐变。

画线

        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.LINE);
        //线的宽度 与 线的颜色
        gradientDrawable.setStroke(5, Color.YELLOW);
        textView.setBackground(gradientDrawable);

画虚线

        //要显示虚线一定要关闭硬件加速       
        textView.setLayerType(View.LAYER_TYPE_SOFTWARE,null);
        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.LINE);
        //第一个参数为线的宽度  第二个参数是线的颜色 第三个参数是虚线段的长度 
        //第四个参数是虚线段之间的间距长度
        gradientDrawable.setStroke(1, Color.BLACK, 10, 10);
        textView.setBackground(gradientDrawable);

也可以在布局里关闭指定view的硬件加速

        android:layerType="software"

画圆

        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.OVAL);
        gradientDrawable.setColor(Color.BLUE);
        gradientDrawable.setSize(50,50);
        textView.setBackground(gradientDrawable);

画圆环

        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.OVAL);
        gradientDrawable.setColor(Color.BLUE);
        gradientDrawable.setStroke(10,Color.YELLOW);
        gradientDrawable.setSize(50,50);
        textView.setBackground(gradientDrawable);

圆角矩形

        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.RECTANGLE);
        gradientDrawable.setColor(Color.RED);
        gradientDrawable.setStroke(10,Color.BLUE);
        gradientDrawable.setCornerRadius(10);
        gradientDrawable.setSize(50,50);
        mTextView.setBackground(gradientDrawable);

虚线矩形

        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.LINEAR_GRADIENT);
        gradientDrawable.setStroke(1, Color.GREEN,30, 30);
        textView.setBackground(gradientDrawable);

线性渐变

        int[] colors = {Color.YELLOW, Color.GREEN, Color.BLUE};
        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.RECTANGLE);
        //添加颜色组
        gradientDrawable.setColors(colors);
        //设置线性渐变
        gradientDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);
        gradientDrawable.setSize(50,50);
        textView.setBackground(gradientDrawable);

改变线性渐变方向

        int[] colors = {Color.YELLOW, Color.GREEN, Color.BLUE};
        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.RECTANGLE);
        gradientDrawable.setColors(colors);
        //设置线性渐变
        gradientDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);
        //设置渐变方向
        gradientDrawable.setOrientation(GradientDrawable.Orientation.RIGHT_LEFT);
        gradientDrawable.setSize(50,50);
        textView.setBackground(gradientDrawable);

半径渐变

        int[] colors = {Color.YELLOW, Color.GREEN, Color.BLUE};
        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.RECTANGLE);
        //添加颜色组
        gradientDrawable.setColors(colors); 
        //设置半径渐变
        gradientDrawable.setGradientType(GradientDrawable.RADIAL_GRADIENT);
        //渐变的半径值
        gradientDrawable.setGradientRadius(50);
        gradientDrawable.setSize(50,50);
        textView.setBackground(gradientDrawable);

扫描渐变

        int[] colors = {Color.YELLOW, Color.GREEN, Color.BLUE};
        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.RECTANGLE);
        gradientDrawable.setColors(colors); 
        //设置扫描渐变
        gradientDrawable.setGradientType(GradientDrawable.SWEEP_GRADIENT);
        //渐变中心点
        gradientDrawable.setGradientCenter(0.5f,0.5f);
        gradientDrawable.setSize(50,50);
        textView.setBackground(gradientDrawable);

防抖,可以让渐变的时候颜色阶梯降低,变得更柔和

        gradientDrawable.setDither(true);

透明度

        GradientDrawable gradientDrawable = new GradientDrawable();
        gradientDrawable.setShape(GradientDrawable.RECTANGLE);
        gradientDrawable.setColor(Color.YELLOW); 
        //设置透明度
        gradientDrawable.setAlpha(70);
        textView.setBackground(gradientDrawable);