我的ImageView圆角小部件的实现，(下||上)大小图像到所需的尺寸。它利用了CaspNZ的代码形式。

public class ImageViewRounded extends ImageView {

    public ImageViewRounded(Context context) {
        super(context);
    }

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

    public ImageViewRounded(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        BitmapDrawable drawable = (BitmapDrawable) getDrawable();

        if (drawable == null) {
            return;
        }

        if (getWidth() == 0 || getHeight() == 0) {
            return; 
        }

        Bitmap fullSizeBitmap = drawable.getBitmap();

        int scaledWidth = getMeasuredWidth();
        int scaledHeight = getMeasuredHeight();

        Bitmap mScaledBitmap;
        if (scaledWidth == fullSizeBitmap.getWidth() && scaledHeight == fullSizeBitmap.getHeight()) {
            mScaledBitmap = fullSizeBitmap;
        } else {
            mScaledBitmap = Bitmap.createScaledBitmap(fullSizeBitmap, scaledWidth, scaledHeight, true /* filter */);
        }

        Bitmap roundBitmap = ImageUtilities.getRoundedCornerBitmap(getContext(), mScaledBitmap, 5, scaledWidth, scaledHeight,
                false, false, false, false);
        canvas.drawBitmap(roundBitmap, 0, 0, null);

    }

}

我已经通过自定义ImageView完成:

public class RoundRectCornerImageView extends ImageView {

    private float radius = 18.0f;
    private Path path;
    private RectF rect;

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

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

    public RoundRectCornerImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        path = new Path();

    }

    @Override
    protected void onDraw(Canvas canvas) {
        rect = new RectF(0, 0, this.getWidth(), this.getHeight());
        path.addRoundRect(rect, radius, radius, Path.Direction.CW);
        canvas.clipPath(path);
        super.onDraw(canvas);
    }
}

使用方法:

<com.mypackage.RoundRectCornerImageView
     android:id="@+id/imageView"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@drawable/image"
     android:scaleType="fitXY" />

输出:

希望这对你有所帮助。

非常感谢第一个回答。下面是修改后的版本，将矩形图像转换为正方形(和圆形)，填充颜色作为参数传递。

public static Bitmap getRoundedBitmap(Bitmap bitmap, int pixels, int color) {

    Bitmap inpBitmap = bitmap;
    int width = 0;
    int height = 0;
    width = inpBitmap.getWidth();
    height = inpBitmap.getHeight();

    if (width <= height) {
        height = width;
    } else {
        width = height;
    }

    Bitmap output = Bitmap.createBitmap(width, height, Config.ARGB_8888);
    Canvas canvas = new Canvas(output);

    final Paint paint = new Paint();
    final Rect rect = new Rect(0, 0, width, height);
    final RectF rectF = new RectF(rect);
    final float roundPx = pixels;

    paint.setAntiAlias(true);
    canvas.drawARGB(0, 0, 0, 0);
    paint.setColor(color);
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);

    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
    canvas.drawBitmap(inpBitmap, rect, rect, paint);

    return output;
}

我发现这两种方法在提出可行的解决方案时都非常有用。这是我的合成版本，它与像素无关，允许你有一些正方形的角，其余的角具有相同的半径(这是通常的用例)。 感谢以上两种解决方案:

public static Bitmap getRoundedCornerBitmap(Context context, Bitmap input, int pixels , int w , int h , boolean squareTL, boolean squareTR, boolean squareBL, boolean squareBR  ) {

    Bitmap output = Bitmap.createBitmap(w, h, Config.ARGB_8888);
    Canvas canvas = new Canvas(output);
    final float densityMultiplier = context.getResources().getDisplayMetrics().density;

    final int color = 0xff424242;
    final Paint paint = new Paint();
    final Rect rect = new Rect(0, 0, w, h);
    final RectF rectF = new RectF(rect);

    //make sure that our rounded corner is scaled appropriately
    final float roundPx = pixels*densityMultiplier;

    paint.setAntiAlias(true);
    canvas.drawARGB(0, 0, 0, 0);
    paint.setColor(color);
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);


    //draw rectangles over the corners we want to be square
    if (squareTL ){
        canvas.drawRect(0, h/2, w/2, h, paint);
    }
    if (squareTR ){
        canvas.drawRect(w/2, h/2, w, h, paint);
    }
    if (squareBL ){
        canvas.drawRect(0, 0, w/2, h/2, paint);
    }
    if (squareBR ){
        canvas.drawRect(w/2, 0, w, h/2, paint);
    }


    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(input, 0,0, paint);

    return output;
}

我重写了ImageView，把这个放进去，这样我就可以用xml定义它了。 您可能想在这里添加一些super调用所做的逻辑，但我已经对其进行了注释，因为它对我的情况没有帮助。

    @Override
protected void onDraw(Canvas canvas) {
    //super.onDraw(canvas);
        Drawable drawable = getDrawable();

        Bitmap b =  ((BitmapDrawable)drawable).getBitmap() ;
        Bitmap bitmap = b.copy(Bitmap.Config.ARGB_8888, true);

        int w = getWidth(), h = getHeight();


        Bitmap roundBitmap =  CropImageView.getRoundedCornerBitmap( getContext(), bitmap,10 , w, h , true, false,true, false);
        canvas.drawBitmap(roundBitmap, 0,0 , null);
}

希望这能有所帮助!

以下是我的解决方案:

<com.myproject.ui.RadiusCornerImageView
        android:id="@+id/imageViewPhoto"
        android:layout_width="160dp"
        android:layout_height="160dp"
        app:corner_radius_dp="5"
        app:corner_radius_position="top"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

在java代码中:

public class RadiusCornerImageView extends android.support.v7.widget.AppCompatImageView {
    private int cornerRadiusDP = 0; // dp
    private int corner_radius_position;

    public RadiusCornerImageView(Context context) {
        super(context);
    }

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

    public RadiusCornerImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        TypedArray typeArray = context.getTheme().obtainStyledAttributes(attrs, R.styleable.RadiusCornerImageView, 0, 0);
        try {
            cornerRadiusDP = typeArray.getInt(R.styleable.RadiusCornerImageView_corner_radius_dp, 0);
            corner_radius_position = typeArray.getInteger(R.styleable.RadiusCornerImageView_corner_radius_position, 0);
        } finally {
            typeArray.recycle();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        float radiusPx = AndroidUtil.dpToPx(getContext(), cornerRadiusDP);
        Path clipPath = new Path();
        RectF rect = null;
        if (corner_radius_position == 0) { // all
            // round corners on all 4 angles
            rect = new RectF(0, 0, this.getWidth(), this.getHeight());
        } else if (corner_radius_position == 1) {
            // round corners only on top left and top right
            rect = new RectF(0, 0, this.getWidth(), this.getHeight() + radiusPx);

    } else {
        throw new IllegalArgumentException("Unknown corner_radius_position = " + corner_radius_position);
    }
    clipPath.addRoundRect(rect, radiusPx, radiusPx, Path.Direction.CW);
    canvas.clipPath(clipPath);
    super.onDraw(canvas);
 }
}

答案中提供的方法没有一个对我有用。我发现如果你的android版本是5.0或以上，以下方法是有效的:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {

    ViewOutlineProvider provider = new ViewOutlineProvider() {
        @Override
        public void getOutline(View view, Outline outline) {
            int curveRadius = 24;
            outline.setRoundRect(0, 0, view.getWidth(), (view.getHeight()+curveRadius), curveRadius);
        }
    };
    imageview.setOutlineProvider(provider);
    imageview.setClipToOutline(true);
}

不需要定义xml形状，上面的代码只为顶部创建角，这是普通方法无法实现的。如果你需要4个圆角，移除:

"+ curveRadius"  

从setRoundRect中底部的参数。您可以通过指定适合您需要的轮廓来进一步将该形状扩展到任何其他形状。请查看以下链接:

Android开发者文档。

注意，与Android中的任何度量一样，你必须从DP“转换”大小。在上面的例子中，假设你想让半径为24

                            int curveRadius = 24;

例如，您可能稍后在可绘制对象中添加半径设置为“24”的边界，并希望它与之匹配。因此,

    float desiredRadius = 24;
    float radiusConverted = TypedValue.applyDimension(
            TypedValue.COMPLEX_UNIT_DIP,
            desiredRadius,
            itemView.getContext().getResources().getDisplayMetrics());

然后

                            int curveRadius = radiusConverted;