为什么不在draw()中进行剪辑?

以下是我的解决方案:

用剪切扩展RelativeLayout 将ImageView(或其他视图)放入布局中:

代码:

public class RoundRelativeLayout extends RelativeLayout {

    private final float radius;

    public RoundRelativeLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        TypedArray attrArray = context.obtainStyledAttributes(attrs,
                R.styleable.RoundRelativeLayout);
        radius = attrArray.getDimension(
                R.styleable.RoundRelativeLayout_radius, 0);
    }

    private boolean isPathValid;
    private final Path path = new Path();

    private Path getRoundRectPath() {
        if (isPathValid) {
            return path;
        }

        path.reset();

        int width = getWidth();
        int height = getHeight();
        RectF bounds = new RectF(0, 0, width, height);

        path.addRoundRect(bounds, radius, radius, Direction.CCW);
        isPathValid = true;
        return path;
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        canvas.clipPath(getRoundRectPath());
        super.dispatchDraw(canvas);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.clipPath(getRoundRectPath());
        super.draw(canvas);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        int oldWidth = getMeasuredWidth();
        int oldHeight = getMeasuredHeight();
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int newWidth = getMeasuredWidth();
        int newHeight = getMeasuredHeight();
        if (newWidth != oldWidth || newHeight != oldHeight) {
            isPathValid = false;
        }
    }

}

虽然前两个答案是可行的，但我希望再多描述一点。 比如说，ImageView所在的地方有一个活动或片段。您希望绘制图像并按比例缩放。然后你应该在onCreate或onCreateView中写入如下代码:

LinearLayout rootLayout = (LinearLayout) findViewById(R.id.rootLayout);
ImageView image = (ImageView) findViewById(R.id.image);
// Wait till an activity is visible and image can be measured.
rootLayout.post(new Runnable() {
    @Override
    public void run() {
        // Setting ImageView height with aspect ratio.
        Drawable drawable = ContextCompat.getDrawable(getActivity(), R.drawable.your_image);
        int height = getImageViewHeight(drawable, image);

        // Rounding image corners.
        float radius = getResources().getDimension(R.dimen.your_radius_in_dp);
        Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
        Bitmap result = getRoundedBitmap(bitmap, image.getWidth(), height, radius);
        image.setImageBitmap(result);
    }
});

其中设置新的图像高度为:

public static int getImageViewHeight(Drawable drawable, ImageView imageView) {
    imageView.setImageDrawable(drawable);
    int width = drawable.getIntrinsicWidth();
    int height = 0;
    if (width > 0) {
        height = (drawable.getIntrinsicHeight() * imageView.getWidth()) / width;
        imageView.getLayoutParams().height = height;
        imageView.requestLayout();
    }
    return height;
}

然后，您应该编写一个方法来缩放图像并使其圆角。这里的width和height是位图的新维度(更小或更大)。在下面的例子中，我只圆角上的两个角。

private Bitmap getRoundedBitmap(Bitmap bitmap, int width, int height, float radius) {
    // Create scaled bitmap.
    Bitmap scaledBitmap = Bitmap.createScaledBitmap(bitmap, width, height, false);
    BitmapShader shader = new BitmapShader(scaledBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);

    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setShader(shader);

    Bitmap result = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(result);
    // First make all corners round.
    canvas.drawRoundRect(new RectF(0, 0, width, height), radius, radius, paint);
    // Then draw bottom rectangle.
    canvas.drawRect(0, height - radius, radius, height, paint);
    canvas.drawRect(width - radius, height - radius, width, height, paint);
    return result;
}

相当多的答案!

我遵循了一些人也建议的这个例子:http://www.techrepublic.com/article/pro-tip-round-corners-on-an-android-imageview-with-this-hack/

然而，我需要的是一个透明图像后面的彩色圆圈。对于任何有兴趣做同样事情的人…

1)设置FrameLayout的宽度和高度-在我的情况下，图像的大小(50dp)。 2)将带有src = "@drawable/…"的ImageView放在带有图像的ImageView之上。给它一个id，在我的例子中，我叫它iconShape 3) Drawable mask.xml应该是纯色的#ffffffff 4)如果你想在你的代码中动态地改变圆圈的颜色，可以这样做

ImageView iv2 = (ImageView) v.findViewById(R.id.iconShape);
Drawable shape = getResources().getDrawable(R.drawable.mask);
shape.setColorFilter(Color.BLUE, Mode.MULTIPLY);
iv2.setImageDrawable(shape);

芬兰湾的科特林版:

@GlideExtension
object GamersGeekGlideExtension {

    @NonNull
    @JvmStatic
    @GlideOption
    fun roundedCorners(options: BaseRequestOptions<*>, context: Context, cornerRadius: Int): BaseRequestOptions<*> {
        val px =
            (cornerRadius * (context.resources.displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT)).roundToInt()
        return options.transforms(RoundedCorners(px))
    }
}

注意:Glide扩展现在需要BaseRequestOptions而不是RequestOptions。此外，它与@Sir Codesalot答案在kotlin中转换的函数相同。

您应该扩展ImageView并绘制自己的圆角矩形。

如果你想在图像周围添加一个框架，你也可以在布局中将圆形框架叠加在图像视图的顶部。

例如，通过使用FrameLayout将帧叠加到原始图像上。FrameLayout的第一个元素将是你想要显示的图像。然后添加另一个ImageView与框架。第二个ImageView将显示在原始ImageView的顶部，因此Android将在原始ImageView上方绘制它的内容。

对我来说，下面的解决方案似乎是最优雅的:

ImageView roundedImageView = new ImageView (getContext());
roundedImageView.setClipToOutline(true);
Bitmap bitmap = AppUtil.decodeSampledBitmapFromResource(new File(valueListItemsView.getImagePath()), width, height);
roundedImageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
roundedImageView.setImageBitmap(bitmap);
roundedImageView.setBackgroundResource(R.drawable.rounded_corner);

而可绘制的rounded_corner.xml的代码是:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <solid android:color="@color/colorAccent" />
    <corners android:radius="24dp" />
</shape>