Android 實現圓形的 ImageView 的3種方法

方法1: 裁剪Bitmap,設置ImageView src

主要是取縮放/裁剪Bitmap,然後設置給ImageView src或者background
實際使用中發現系統app 的ICON 比較特殊,比如時鐘/日曆是動態的,把通過PackageManager 拿到的Drawable 轉成BitmapDrawable 後顯示出來的圖片和在桌面看到的不一樣的.具體爲什麼Drawable 轉成BitmapDrawable後有這個異常現象暫時沒有去研究.後面找時間去研究.

public static Bitmap cropBitmap(Bitmap bitmap) {//從中間截取一個正方形
	int w = bitmap.getWidth(); // 得到圖片的寬，高
	int h = bitmap.getHeight();
	int cropWidth = w >= h ? h : w;// 裁切後所取的正方形區域邊長

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

public static Bitmap getCircleBitmap(Bitmap bitmap) {//把圖片裁剪成圓形
	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:自定義ImageView,利用Canvas 的clipPath() 

實際效果出來後發現有鋸齒,考慮通過Paint的PorterDuff.Mode替代Path實現所需要的效果.
實際測試的時候爲了簡單,直接在xml 裏面固定了view 寬和高度是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:逆時針,這裏是一個簡單的園,無影響
		canvas.clipPath(path);
		super.onDraw(canvas);
		canvas.restore();
		//使用Path時，如果不與Paint進行共同操作，無法解決抗鋸齒問題。
		//這時候只能使用Paint的PorterDuff.Mode替代Path實現所需要的效果
	}
	@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:自定義ImageView,利用Paint的PorterDuff.Mode替代Path實現所需要的效果

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自身的繪製流程，即繪製圖片

		path.reset();
		paint.reset();
		path.addCircle(width/2, height/2, width/2, Path.Direction.CW);////CW:順時針,這裏是一個簡單的園,無影響
		paint.setStyle(Style.FILL);//Paint 默認就是fill style,不設置也可以
		paint.setAntiAlias(true);//抗鋸齒
		paint.setXfermode(xfermode);//設置混合模式 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);
	}

具體效果如下:
第一個是未處理的;
第2個是Canvas.clipPatch() 實現的,有鋸齒.
第3個是通過Paint的PorterDuff.Mode替代Path實現