Android自定义圆角ImageView

我们经常看到一些app中可以显示圆角图片，比如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，当然如果没有圆角图片资源，我们也可以自己通过程序实现的，下面介绍一个自定义圆角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对应的内存为上面的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，这个会修改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，非常关键
        maskPath.setFillType(Path.FillType.INVERSE_WINDING);
        canvas.drawPath(maskPath, maskPaint);
}
}