Android 圆角ImageView

public class RoundImageView extends AppCompatImageView {


    //圆角
    private int mBorderRadius = 20;

    private Paint mPaint;

    // 3x3 矩阵，主要用于缩小放大
    private Matrix mMatrix;

    //图像着色器
    private BitmapShader mBitmapShader;

    public RoundImageView(Context context) {
        this(context, null);
    }

    public RoundImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RoundImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        mMatrix = new Matrix();
        mPaint = new Paint();
        mPaint.setAntiAlias(true);

    }

    @SuppressLint("DrawAllocation")
    @Override
    protected void onDraw(Canvas canvas) {
        if (getDrawable() == null){
            return;
        }
        Bitmap bitmap = drawableToBitmap(getDrawable());
        mBitmapShader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        float scale = 1.0f;
        if (!(bitmap.getWidth() == getWidth() && bitmap.getHeight() == getHeight()))
        {
            // 算出需要缩放的比例；缩放后的图片需要填充，取大值；
            scale = Math.max(getWidth() * 1.0f / bitmap.getWidth(),
                    getHeight() * 1.0f / bitmap.getHeight());
        }
        // shader的变换矩阵，我们这里主要用于放大或者缩小
        mMatrix.setScale(scale, scale);
        // 设置变换矩阵
        mBitmapShader.setLocalMatrix(mMatrix);
        // 设置shader
        mPaint.setShader(mBitmapShader);
        canvas.drawRoundRect(new RectF(0,0,getWidth(),getHeight()), mBorderRadius, mBorderRadius,
                mPaint);
    }


    private Bitmap drawableToBitmap(Drawable drawable)
    {
        if (drawable instanceof BitmapDrawable)
        {
            BitmapDrawable bd = (BitmapDrawable) drawable;
            return bd.getBitmap();
        }
        // 加载颜色时候获取控件的宽高
        int w = drawable.getIntrinsicWidth() <= 0 ? getWidth() : drawable.getIntrinsicWidth();
        int h = drawable.getIntrinsicHeight() <= 0 ? getHeight() : drawable.getIntrinsicHeight();
        Bitmap bitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, w, h);
        drawable.draw(canvas);
        return bitmap;
    }
}