我们常常看到一些app中能够显示圆角图片。比方qq的联系人图标等等，实现圆角图片一种办法是直接使用圆角图片资源，当然假设没有圆角图片资源。我们也能够自己通过程序实现的，以下介绍一个自己定义圆角ImageView的方法：

package com.yulongfei.imageview;

import android.content.Context;

import android.content.res.TypedArray;

import android.graphics.Bitmap;

import android.graphics.Bitmap.Config;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Path;

import android.graphics.PorterDuff;

import android.graphics.PorterDuffXfermode;

import android.graphics.RectF;

import android.util.AttributeSet;

import android.widget.ImageView;

public class RoundAngleImageView extends ImageView {

	private int roundWidth = 13;

	private int roundHeight = 13;

	public RoundAngleImageView(Context context) {

		super(context);

		init(context, null);

	}

	public RoundAngleImageView(Context context, AttributeSet attrs, int defStyle) {

		super(context, attrs, defStyle);

		init(context, attrs);

	}

	public RoundAngleImageView(Context context, AttributeSet attrs) {

		super(context, attrs);

		init(context, attrs);

	}

	private void init(Context context, AttributeSet attrs) {

		if (attrs != null) {

			TypedArray a = context.obtainStyledAttributes(attrs,

					R.styleable.RoundAngleImageView);

			roundWidth = a.getDimensionPixelSize(

					R.styleable.RoundAngleImageView_roundWidth, roundWidth);

			roundHeight = a.getDimensionPixelSize(

					R.styleable.RoundAngleImageView_roundHeight, roundHeight);

			a.recycle();

		} else {

			float density = context.getResources().getDisplayMetrics().density;

			roundWidth = (int)(roundWidth * density);

			roundHeight = (int)(roundHeight * density);

		}

	}

	/** 重写draw() */

	@Override

	public void draw(Canvas canvas) {

		//实例化一个和ImageView一样大小的bitmap

		Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(),

				Config.ARGB_8888);

		//实例化一个canvas，这个canvas相应的内存为上面的bitmap

		Canvas canvas2 = new Canvas(bitmap);

		if (bitmap.isRecycled()) {

			bitmap = Bitmap.createBitmap(getWidth(), getHeight(),

					Config.ARGB_8888);

			canvas2 = new Canvas(bitmap);

		}

		//将imageView自己绘制到canvas2上，这个导致bitmap里面存放了imageView

		super.draw(canvas2);

		//利用canvas画一个圆角矩形，这个会改动bitmap的数据

		drawRoundAngle(canvas2);

		//将裁剪好的bitmap绘制到系统当前canvas上，这样裁剪好的imageview就能显示到屏幕上

		Paint paint = new Paint();

		paint.setXfermode(null);

		canvas.drawBitmap(bitmap, 0, 0, paint);

		bitmap.recycle();

	}

	public void setRoundWidth(int roundWidth, int roundHeight) {

		this.roundWidth = roundWidth;

		this.roundHeight = roundHeight;

	}

	private void drawRoundAngle(Canvas canvas)

	{

		Paint maskPaint = new Paint();

        maskPaint.setAntiAlias(true);

		maskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

        Path maskPath = new Path();

        maskPath.addRoundRect(new RectF(0.0F, 0.0F, getWidth(), getHeight()), roundWidth, roundHeight, Path.Direction.CW);

        //这是设置了填充模式。很关键

        maskPath.setFillType(Path.FillType.INVERSE_WINDING);

        canvas.drawPath(maskPath, maskPaint);

	}

}