Android 实现圆形的 ImageView 的3种方法

方法1: 裁剪Bitmap,设置ImageView src

主要是取缩放/裁剪Bitmap,然后设置给ImageView src或者background
实际使用中发现系统app 的ICON 比较特殊,比如时钟/日历是动态的,把通过PackageManager 拿到的Drawable 转成BitmapDrawable 后显示出来的图片和在桌面看到的不一样的.具体为什么Drawable 转成BitmapDrawable后有这个异常现象暂时没有去研究.后面找时间去研究.

public static Bitmap cropBitmap(Bitmap bitmap) {//从中间截取一个正方形
	int w = bitmap.getWidth(); // 得到图片的宽，高
	int h = bitmap.getHeight();
	int cropWidth = w >= h ? h : w;// 裁切后所取的正方形区域边长

	return Bitmap.createBitmap(bitmap, (bitmap.getWidth() - cropWidth) / 2,
		(bitmap.getHeight() - cropWidth) / 2, cropWidth, cropWidth);
}

public static Bitmap getCircleBitmap(Bitmap bitmap) {//把图片裁剪成圆形
	if (bitmap == null) {
		return null;
	}
	bitmap = cropBitmap(bitmap);//裁剪成正方形
	try {
		Bitmap circleBitmap = Bitmap.createBitmap(bitmap.getWidth(),
				bitmap.getHeight(), Bitmap.Config.ARGB_8888);
		Canvas canvas = new Canvas(circleBitmap);
		final Paint paint = new Paint();
		final Rect rect = new Rect(0, 0, bitmap.getWidth(),
				bitmap.getHeight());
		final RectF rectF = new RectF(new Rect(0, 0, bitmap.getWidth(),
				bitmap.getHeight()));
		float roundPx = 0.0f;
		roundPx = bitmap.getWidth();
		paint.setAntiAlias(true);
		canvas.drawARGB(0, 0, 0, 0);
		paint.setColor(Color.WHITE);
		canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
		paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
		final Rect src = new Rect(0, 0, bitmap.getWidth(),
				bitmap.getHeight());
		canvas.drawBitmap(bitmap, src, rect, paint);
		return circleBitmap;
	} catch (Exception e) {
		return bitmap;
	}
}

方法2:自定义ImageView,利用Canvas 的clipPath() 

实际效果出来后发现有锯齿,考虑通过Paint的PorterDuff.Mode替代Path实现所需要的效果.
实际测试的时候为了简单,直接在xml 里面固定了view 宽和高度是200dp.

public class ClipPathCircleImage extends ImageView {
	private int width;
	private int height;
	private Path path;
	public ClipPathCircleImage(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
		super(context, attrs, defStyleAttr, defStyleRes);
		path = new Path();
	}
	@Override
	protected void onDraw(Canvas canvas) {
		canvas.save();
		path.reset();
		path.addCircle(width/2, height/2, width/2, Path.Direction.CCW);//CCW:逆时针,这里是一个简单的园,无影响
		canvas.clipPath(path);
		super.onDraw(canvas);
		canvas.restore();
		//使用Path时，如果不与Paint进行共同操作，无法解决抗锯齿问题。
		//这时候只能使用Paint的PorterDuff.Mode替代Path实现所需要的效果
	}
	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
		super.onSizeChanged(w, h, oldw, oldh);
		width = w;
		height = h;
	}
	public ClipPathCircleImage(Context context, AttributeSet attrs, int defStyleAttr) {
		this(context, attrs, defStyleAttr, 0);
	}
	public ClipPathCircleImage(Context context, AttributeSet attrs) {
		this(context, attrs, 0);
	}
	public ClipPathCircleImage(Context context) {
		this(context, null);
	}
}

方法3:自定义ImageView,利用Paint的PorterDuff.Mode替代Path实现所需要的效果

public class CircleImage extends ImageView {
	private int width;
	private int height;
	private Path path;
	private Path srcPath;
	private Paint paint;
	private RectF srcRectF;
	private Xfermode xfermode;
	public CircleImage(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
		super(context, attrs, defStyleAttr, defStyleRes);
		path = new Path();
		srcPath = new Path();
		paint= new Paint();
		xfermode = new PorterDuffXfermode(Mode.DST_OUT);
	}
	@Override
	protected void onDraw(Canvas canvas) {
		canvas.saveLayer(srcRectF, null, Canvas.ALL_SAVE_FLAG);
		super.onDraw(canvas);// ImageView自身的绘制流程，即绘制图片

		path.reset();
		paint.reset();
		path.addCircle(width/2, height/2, width/2, Path.Direction.CW);////CW:顺时针,这里是一个简单的园,无影响
		paint.setStyle(Style.FILL);//Paint 默认就是fill style,不设置也可以
		paint.setAntiAlias(true);//抗锯齿
		paint.setXfermode(xfermode);//设置混合模式 DST_OUT 
		srcPath.addRect(srcRectF, Direction.CCW);
		srcPath.op(path, Path.Op.DIFFERENCE);
		canvas.drawPath(srcPath, paint);
		paint.setXfermode(null);
		canvas.restore();
	}
	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
		super.onSizeChanged(w, h, oldw, oldh);
		width = w;
		height = h;
		srcRectF =  new RectF(0, 0, w, h);
	}
	public CircleImage(Context context, AttributeSet attrs, int defStyleAttr) {
		this(context, attrs, defStyleAttr, 0);
	}
	public CircleImage(Context context, AttributeSet attrs) {
		this(context, attrs, 0);
	}
	public CircleImage(Context context) {
		this(context, null);
	}

具体效果如下:
第一个是未处理的;
第2个是Canvas.clipPatch() 实现的,有锯齿.
第3个是通过Paint的PorterDuff.Mode替代Path实现