在支持库的v21中，现在有了一个解决方案:它被称为RoundedBitmapDrawable。

它基本上就像一个普通的Drawable，除了你给它一个角半径的剪辑:

setCornerRadius(float cornerRadius)

所以，从Bitmap src和一个目标ImageView开始，它看起来像这样:

RoundedBitmapDrawable dr = RoundedBitmapDrawableFactory.create(res, src);
dr.setCornerRadius(cornerRadius);
imageView.setImageDrawable(dr);

如果你正在使用格莱德图书馆，这将是有帮助的:

Glide.with(getApplicationContext())
     .load(image_url)
     .asBitmap()
     .centerCrop()
     .into(new BitmapImageViewTarget(imageView) {
        @Override
        protected void setResource(Bitmap resource) {
          RoundedBitmapDrawable circularBitmapDrawable =
                       RoundedBitmapDrawableFactory.create(getApplicationContext().getResources(), resource);
          circularBitmapDrawable.setCornerRadius(dpToPx(10));
          circularBitmapDrawable.setAntiAlias(true);
          imageView.setImageDrawable(circularBitmapDrawable);
        }
     });


public int dpToPx(int dp) {
  DisplayMetrics displayMetrics = getApplicationContext().getResources().getDisplayMetrics();
  return Math.round(dp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT));
}

从材质组件库的1.2.0-alpha03版本开始，有了新的ShapeableImageView。

你可以这样使用:

<com.google.android.material.imageview.ShapeableImageView
    ...
    app:shapeAppearanceOverlay="@style/roundedImageView"
    app:srcCompat="@drawable/ic_image" />

在你的主题。xml:

<style name="roundedImageView" parent="">
    <item name="cornerFamily">rounded</item>
    <item name="cornerSize">8dp</item>
</style>

或通过编程:

float radius = getResources().getDimension(R.dimen.default_corner_radius);
imageView.setShapeAppearanceModel(imageView.getShapeAppearanceModel()
    .toBuilder()
    .setAllCorners(CornerFamily.ROUNDED,radius)
    .build());

使用jetpack compose，您可以使用RoundedCornerShape应用剪辑修饰器:

Image(
    painter = painterResource(R.drawable.xxxx),
    contentDescription = "xxxx",
    contentScale = ContentScale.Crop,            
    modifier = Modifier
        .size(64.dp)
        .clip(RoundedCornerShape(8.dp))             
)

如果你不希望边框影响图像，使用这个类。不幸的是，我没有找到任何方法来绘制画布上的透明区域来到onDraw()。这里创建了一个新的位图它是画在一个真实的画布上的。

如果您想要创建一个消失的边界，该视图非常有用。如果你将borderWidth设置为0，边框将会消失，图像仍然保持圆角，就像边界一样。也就是说，它看起来就像边界完全由图像边缘绘制。

import android.annotation.SuppressLint
import android.content.Context
import android.graphics.Bitmap
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.graphics.PorterDuff
import android.graphics.PorterDuffXfermode
import android.graphics.RectF
import android.util.AttributeSet
import androidx.appcompat.widget.AppCompatImageView


class RoundedImageViewWithBorder @JvmOverloads constructor(
        context: Context,
        attrs: AttributeSet? = null,
        defStyleAttr: Int = 0) : AppCompatImageView(context, attrs, defStyleAttr) {

    var borderColor: Int = 0
        set(value) {
            invalidate()
            field = value
        }
    var borderWidth: Int = 0
        set(value) {
            invalidate()
            field = value
        }
    var cornerRadius: Float = 0f
        set(value) {
            invalidate()
            field = value
        }

    private var bitmapForDraw: Bitmap? = null
    private var canvasForDraw: Canvas? = null
    private val transparentPaint = Paint().apply {
        isAntiAlias = true
        color = Color.TRANSPARENT
        style = Paint.Style.STROKE
        xfermode = PorterDuffXfermode(PorterDuff.Mode.SRC)
    }

    private val borderPaint = Paint().apply {
        isAntiAlias = true
        style = Paint.Style.STROKE
    }

    private val transparentAreaRect = RectF()
    private val borderRect = RectF()

    init {
        val typedArray = context.obtainStyledAttributes(attrs, R.styleable.RoundedImageViewWithBorder)

        try {
            borderWidth = typedArray.getDimensionPixelSize(R.styleable.RoundedImageViewWithBorder_border_width, 0)
            borderColor = typedArray.getColor(R.styleable.RoundedImageViewWithBorder_border_color, 0)
            cornerRadius = typedArray.getDimensionPixelSize(R.styleable.RoundedImageViewWithBorder_corner_radius, 0).toFloat()

        } finally {
            typedArray.recycle()
        }
    }

    @SuppressLint("CanvasSize", "DrawAllocation")
    override fun onDraw(canvas: Canvas) {
        if (canvas.height <=0 || canvas.width <=0) {
            return
        }

        if (canvasForDraw?.height != canvas.height || canvasForDraw?.width != canvas.width) {
            val newBitmap = Bitmap.createBitmap(canvas.width, canvas.height, Bitmap.Config.ARGB_8888)
            bitmapForDraw = newBitmap
            canvasForDraw = Canvas(newBitmap)
        }
        
        bitmapForDraw?.eraseColor(Color.TRANSPARENT)

        // Draw existing content
        super.onDraw(canvasForDraw)

        if (borderWidth > 0) {
            canvasForDraw?.let { drawWithBorder(it) }
        } else {
            canvasForDraw?.let { drawWithoutBorder(it) }
        }

        // Draw everything on real canvas
        bitmapForDraw?.let { canvas.drawBitmap(it, 0f, 0f, null) }
    }

    private fun drawWithBorder(canvas: Canvas) {
        // Draw transparent area
        transparentPaint.strokeWidth = borderWidth.toFloat() * 4
        transparentAreaRect.apply {
            left = -borderWidth.toFloat() * 1.5f
            top = -borderWidth.toFloat() * 1.5f
            right = canvas.width.toFloat() + borderWidth.toFloat() * 1.5f
            bottom = canvas.height.toFloat() + borderWidth.toFloat() * 1.5f
        }
        canvasForDraw?.drawRoundRect(transparentAreaRect, borderWidth.toFloat() * 2 + cornerRadius, borderWidth.toFloat() * 2 + cornerRadius, transparentPaint)

        // Draw border
        borderPaint.color = borderColor
        borderPaint.strokeWidth = borderWidth.toFloat()
        borderRect.apply {
            left = borderWidth.toFloat() / 2
            top = borderWidth.toFloat() / 2
            right = canvas.width.toFloat() - borderWidth.toFloat() / 2
            bottom = canvas.height.toFloat() - borderWidth.toFloat() / 2
        }
        canvas.drawRoundRect(borderRect, cornerRadius - borderWidth.toFloat() / 2, cornerRadius - borderWidth.toFloat() / 2, borderPaint)
    }

    private fun drawWithoutBorder(canvas: Canvas) {
        // Draw transparent area
        transparentPaint.strokeWidth = cornerRadius * 4
        transparentAreaRect.apply {
            left = -cornerRadius * 2
            top = -cornerRadius * 2
            right = canvas.width.toFloat() + cornerRadius * 2
            bottom = canvas.height.toFloat() + cornerRadius * 2
        }
        canvasForDraw?.drawRoundRect(transparentAreaRect, cornerRadius * 3, cornerRadius * 3, transparentPaint)
    }

}

值:

<declare-styleable name="RoundedImageViewWithBorder">
    <attr name="corner_radius" format="dimension|string" />
    <attr name="border_width" format="dimension|reference" />
    <attr name="border_color" format="color|reference" />
</declare-styleable>

你可以使用新的ShapableImageView提供的新版本的Android材料库。

为此，您首先需要在应用程序级别构建中添加以下依赖项。gradle文件

implementation 'com.google.android.material:material:<version>'

另外，确保这个应用程序级别的构建。gradle文件有谷歌的Maven资源库谷歌()如下所示

allprojects {
repositories {
  google()
  jcenter()
}

}

在此之后，您可以引用此资源来实现所需类型或形状的imageview。

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;
        }
    }

}