Android开发中图片控件ImageView默认的样子是矩形，方方正正的。在我们实际的项目中，有时候这些方正的图片显得有些呆板，我们就需要其它样式的图片，比较圆形图片（The rounded picture）， 常见的就是app中用户头像等。要得到圆形图片有很多方式，比如draw一个circle，也可以用切好的圆形图片做背景或者写一个xml实现圆角功能等 等。不过在项目中，如果我们有多个地方要把图片展示出圆形的，而且图片是从网络上取的，这种情况还一个个处理就麻烦了，我们可以定义个圆形图片组件 RoundImageView，然后在要用的地方把RoundImageView 当成ImageView一样使用就行了。我在最近做的项目中也用到了圆形图片，所以做个笔记，方便下次使用！

首先看我们定义的RoundImageView:

public class RoundImageView extends ImageView {
private int mBorderThickness = 0;
private Context mContext;
private int defaultColor = 0xFFFFFFFF;
// 如果只有其中一个有值，则只画一个圆形边框
private int mBorderOutsideColor = 0;
private int mBorderInsideColor = 0;
// 控件默认长、宽
private int defaultWidth = 0;
private int defaultHeight = 0;

public RoundImageView(Context context) {
super(context);
mContext = context;
}


public RoundImageView(Context context, AttributeSet attrs) {
super(context, attrs);
mContext = context;
setCustomAttributes(attrs);
}


public RoundImageView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mContext = context;
setCustomAttributes(attrs);
}


private void setCustomAttributes(AttributeSet attrs) {//这里要用到自定义属性
TypedArray a = mContext.obtainStyledAttributes(attrs,
R.styleable.RoundImageView);
mBorderThickness = a.getDimensionPixelSize(
R.styleable.RoundImageView_border_thickness, 0);
mBorderOutsideColor = a
.getColor(R.styleable.RoundImageView_border_outside_color,
defaultColor);
mBorderInsideColor = a.getColor(
R.styleable.RoundImageView_border_inside_color, defaultColor);
}


@Override
protected void onDraw(Canvas canvas) {
Drawable drawable = getDrawable();
if (drawable == null) {
return;
}


if (getWidth() == 0 || getHeight() == 0) {
return;
}

if (drawable.getClass() == NinePatchDrawable.class)
return;
Bitmap b = ((BitmapDrawable) drawable).getBitmap();
Bitmap bitmap = b.copy(Bitmap.Config.ARGB_8888, true);
if (defaultWidth == 0) {
defaultWidth = getWidth();
}
if (defaultHeight == 0) {
defaultHeight = getHeight();
}

int radius = 0;
if (mBorderInsideColor != defaultColor
&& mBorderOutsideColor != defaultColor) {// 定义画两个边框，分别为外圆边框和内圆边框
radius = (defaultWidth < defaultHeight ? defaultWidth
: defaultHeight) / 2 - 2 * mBorderThickness;
// 画内圆
drawCircleBorder(canvas, radius + mBorderThickness / 2,
mBorderInsideColor);
// 画外圆
drawCircleBorder(canvas, radius + mBorderThickness
+ mBorderThickness / 2, mBorderOutsideColor);
} else if (mBorderInsideColor != defaultColor
&& mBorderOutsideColor == defaultColor) {// 定义画一个边框
radius = (defaultWidth < defaultHeight ? defaultWidth
: defaultHeight) / 2 - mBorderThickness;
drawCircleBorder(canvas, radius + mBorderThickness / 2,
mBorderInsideColor);
} else if (mBorderInsideColor == defaultColor
&& mBorderOutsideColor != defaultColor) {// 定义画一个边框
radius = (defaultWidth < defaultHeight ? defaultWidth
: defaultHeight) / 2 - mBorderThickness;
drawCircleBorder(canvas, radius + mBorderThickness / 2,
mBorderOutsideColor);
} else {// 没有边框
radius = (defaultWidth < defaultHeight ? defaultWidth
: defaultHeight) / 2;
}
Bitmap roundBitmap = getCroppedRoundBitmap(bitmap, radius);
bitmap = null;
canvas.drawBitmap(roundBitmap, defaultWidth / 2 - radius, defaultHeight
/ 2 - radius, null);
}


/**
* 获取裁剪后的圆形图片
*/
public Bitmap getCroppedRoundBitmap(Bitmap bmp, int radius) {
Bitmap scaledSrcBmp;
int diameter = radius * 2;


// 为了防止宽高不相等，造成圆形图片变形，因此截取长方形中处于中间位置最大的正方形图片
int bmpWidth = bmp.getWidth();
int bmpHeight = bmp.getHeight();
int squareWidth = 0, squareHeight = 0;
int x = 0, y = 0;
Bitmap squareBitmap;
if (bmpHeight > bmpWidth) {// 高大于宽
squareWidth = squareHeight = bmpWidth;
x = 0;
y = (bmpHeight - bmpWidth) / 2;
// 截取正方形图片
squareBitmap = Bitmap.createBitmap(bmp, x, y, squareWidth,
squareHeight);
} else if (bmpHeight < bmpWidth) {// 宽大于高
squareWidth = squareHeight = bmpHeight;
x = (bmpWidth - bmpHeight) / 2;
y = 0;
squareBitmap = Bitmap.createBitmap(bmp, x, y, squareWidth,
squareHeight);
} else {
squareBitmap = bmp;
}


if (squareBitmap.getWidth() != diameter
|| squareBitmap.getHeight() != diameter) {
scaledSrcBmp = Bitmap.createScaledBitmap(squareBitmap, diameter,
diameter, true);


} else {
scaledSrcBmp = squareBitmap;
}
Bitmap output = Bitmap.createBitmap(scaledSrcBmp.getWidth(),
scaledSrcBmp.getHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(output);


Paint paint = new Paint();
Rect rect = new Rect(0, 0, scaledSrcBmp.getWidth(),
scaledSrcBmp.getHeight());


paint.setAntiAlias(true);
paint.setFilterBitmap(true);
paint.setDither(true);
canvas.drawARGB(0, 0, 0, 0);
canvas.drawCircle(scaledSrcBmp.getWidth() / 2,
scaledSrcBmp.getHeight() / 2, scaledSrcBmp.getWidth() / 2,
paint);
paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
canvas.drawBitmap(scaledSrcBmp, rect, rect, paint);
// bitmap回收(recycle导致在布局文件XML看不到效果)
// bmp.recycle();
// squareBitmap.recycle();
// scaledSrcBmp.recycle();
squareBitmap = null;
scaledSrcBmp = null;
return output;
}


/**
* 边缘画圆
*/
private void drawCircleBorder(Canvas canvas, int radius, int color) {
Paint paint = new Paint();
/* 去锯齿 */
paint.setAntiAlias(true);
paint.setFilterBitmap(true);
paint.setDither(true);
paint.setColor(color);
/* 设置paint的　style　为STROKE：空心 */
paint.setStyle(Paint.Style.STROKE);
/* 设置paint的外框宽度 */
paint.setStrokeWidth(mBorderThickness);
canvas.drawCircle(defaultWidth / 2, defaultHeight / 2, radius, paint);
}
}

在res/values建一个attrs.xml文件，加入自定义属性字段

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="RoundImageView">
        <attr name="border_thickness" format="dimension" />
        <attr name="border_outside_color" format="color" />
        <attr name="border_inside_color" format="color" />
    </declare-styleable>

</resources>

最后就直接把这个RoundImageView看作ImageView在你需要用的地方用就可以了。