转载请标明出处：http://blog.csdn.NET/lmj623565791/article/details/24555655
本来想在网上找个圆角的例子看一看，不尽人意啊，基本都是官方的Demo的那张原理图，稍后会贴出。于是自己自定义了个View，实现图片的圆角以及圆形效果。效果图：
第一个是原图，第二个是圆形效果，第三第四设置了不同的圆角大小。
准备改变一个博客的风格，首先给大家讲一下原理，让大家明白了，然后再贴代码，不然可以直接看那么长的代码也比较痛苦，核心代码其实就那么几行：
核心代码分析：
[java] view plain copy print ? /** * 根据原图和变长绘制圆形图片 * * @param source * @param min * @return */ private Bitmap createCircleImage(Bitmap source, int min) { final Paint paint = new Paint(); paint.setAntiAlias(true); Bitmap target = Bitmap.createBitmap(min, min, Config.ARGB_8888); /** * 产生一个同样大小的画布 */ Canvas canvas = new Canvas(target); /** * 首先绘制圆形 */ canvas.drawCircle(min / 2, min / 2, min / 2, paint); /** * 使用SRC_IN */ paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); /** * 绘制图片 */ canvas.drawBitmap(source, 0, 0, paint); return target; } /** * 根据原图和变长绘制圆形图片 * * @param source * @param min * @return */ private Bitmap createCircleImage(Bitmap source, int min) { final Paint paint = new Paint(); paint.setAntiAlias(true); Bitmap target = Bitmap.createBitmap(min, min, Config.ARGB_8888); /** * 产生一个同样大小的画布 */ Canvas canvas = new Canvas(target); /** * 首先绘制圆形 */ canvas.drawCircle(min / 2, min / 2, min / 2, paint); /** * 使用SRC_IN */ paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); /** * 绘制图片 */ canvas.drawBitmap(source, 0, 0, paint); return target; } 其实主要靠：paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));这行代码，为什么呢，我给大家解释下，SRC_IN这种模式，两个绘制的效果叠加后取交集展现后图，怎么说呢，咱们第一个绘制的是个圆形，第二个绘制的是个Bitmap，于是交集为圆形，展现的是BItmap，就实现了圆形图片效果。圆角，其实就是先绘制圆角矩形，是不是很简单，以后别人再说实现圆角，你就把这一行代码给他就行了。从Android的示例中，给大家证明一下：
下面有一张PorterDuff.Mode的16中效果图，咱们的只是其一：
源码咱们只关心谁先谁后绘制的：
[java] view plain copy print ? canvas.translate(x, y); canvas.drawBitmap(mDstB, 0, 0, paint); paint.setXfermode(sModes[i]); canvas.drawBitmap(mSrcB, 0, 0, paint); paint.setXfermode(null); canvas.restoreToCount(sc); canvas.translate(x, y); canvas.drawBitmap(mDstB, 0, 0, paint); paint.setXfermode(sModes[i]); canvas.drawBitmap(mSrcB, 0, 0, paint); paint.setXfermode(null); canvas.restoreToCount(sc);可以看出先绘制的Dst,再绘制的Src，最后的展示是SrcIn那个图：显示的区域是二者交集，展示的是Src(后者)。和咱们前面结论一致。效果16种，大家可以自由组合展示不同的效果。好了，原理和核心代码解释完成。下面开始写自定义View。
1、自定义属性：
[html] view plain copy print ? <?xml version=“1.0” encoding=“utf-8”?> <resources> <attr name=“borderRadius” format=“dimension” /> <attr name=“type”> <enum name=“circle” value=“0” /> <enum name=“round” value=“1” /> </attr> <attr name=“src” format=“reference”></attr> <declare-styleable name=“CustomImageView”> <attr name=“borderRadius” /> <attr name=“type” /> <attr name=“src” /> </declare-styleable> </resources> <?xml version="1.0" encoding="utf-8"?> <resources> <attr name="borderRadius" format="dimension" /> <attr name="type"> <enum name="circle" value="0" /> <enum name="round" value="1" /> </attr> <attr name="src" format="reference"></attr> <declare-styleable name="CustomImageView"> <attr name="borderRadius" /> <attr name="type" /> <attr name="src" /> </declare-styleable> </resources> 2、构造中获取自定义的属性： [java] view plain copy print ? /** * TYPE_CIRCLE / TYPE_ROUND */ private int type; private static final int TYPE_CIRCLE = 0; private static final int TYPE_ROUND = 1; /** * 图片 */ private Bitmap mSrc; /** * 圆角的大小 */ private int mRadius; /** * 控件的宽度 */ private int mWidth; /** * 控件的高度 */ private int mHeight; public CustomImageView(Context context, AttributeSet attrs) { this(context, attrs, 0); } public CustomImageView(Context context) { this(context, null); } /** * 初始化一些自定义的参数 * * @param context * @param attrs * @param defStyle */ public CustomImageView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.CustomImageView, defStyle, 0); int n = a.getIndexCount(); for (int i = 0; i < n; i++) { int attr = a.getIndex(i); switch (attr) { case R.styleable.CustomImageView_src: mSrc = BitmapFactory.decodeResource(getResources(), a.getResourceId(attr, 0)); break; case R.styleable.CustomImageView_type: type = a.getInt(attr, 0);// 默认为Circle break; case R.styleable.CustomImageView_borderRadius: mRadius= a.getDimensionPixelSize(attr, (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 10f, getResources().getDisplayMetrics()));// 默认为10DP break; } } a.recycle(); } /** * TYPE_CIRCLE / TYPE_ROUND */ private int type; private static final int TYPE_CIRCLE = 0; private static final int TYPE_ROUND = 1; /** * 图片 */ private Bitmap mSrc; /** * 圆角的大小 */ private int mRadius; /** * 控件的宽度 */ private int mWidth; /** * 控件的高度 */ private int mHeight; public CustomImageView(Context context, AttributeSet attrs) { this(context, attrs, 0); } public CustomImageView(Context context) { this(context, null); } /** * 初始化一些自定义的参数 * * @param context * @param attrs * @param defStyle */ public CustomImageView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.CustomImageView, defStyle, 0); int n = a.getIndexCount(); for (int i = 0; i < n; i++) { int attr = a.getIndex(i); switch (attr) { case R.styleable.CustomImageView_src: mSrc = BitmapFactory.decodeResource(getResources(), a.getResourceId(attr, 0)); break; case R.styleable.CustomImageView_type: type = a.getInt(attr, 0);// 默认为Circle break; case R.styleable.CustomImageView_borderRadius: mRadius= a.getDimensionPixelSize(attr, (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 10f, getResources().getDisplayMetrics()));// 默认为10DP break; } } a.recycle(); }3、onMeasure中获取控件宽高：
[java] view plain copy print ? /** * 计算控件的高度和宽度 */ @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { // super.onMeasure(widthMeasureSpec, heightMeasureSpec); /** * 设置宽度 */ int specMode = MeasureSpec.getMode(widthMeasureSpec); int specSize = MeasureSpec.getSize(widthMeasureSpec); if (specMode == MeasureSpec.EXACTLY)// match_parent , accurate { mWidth = specSize; } else { // 由图片决定的宽 int desireByImg = getPaddingLeft() + getPaddingRight() + mSrc.getWidth(); if (specMode == MeasureSpec.AT_MOST)// wrap_content { mWidth = Math.min(desireByImg, specSize); } else mWidth = desireByImg; } /*** * 设置高度 */ specMode = MeasureSpec.getMode(heightMeasureSpec); specSize = MeasureSpec.getSize(heightMeasureSpec); if (specMode == MeasureSpec.EXACTLY)// match_parent , accurate { mHeight = specSize; } else { int desire = getPaddingTop() + getPaddingBottom() + mSrc.getHeight(); if (specMode == MeasureSpec.AT_MOST)// wrap_content { mHeight = Math.min(desire, specSize); } else mHeight = desire; } setMeasuredDimension(mWidth, mHeight); } /** * 计算控件的高度和宽度 */ @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { // super.onMeasure(widthMeasureSpec, heightMeasureSpec); /** * 设置宽度 */ int specMode = MeasureSpec.getMode(widthMeasureSpec); int specSize = MeasureSpec.getSize(widthMeasureSpec); if (specMode == MeasureSpec.EXACTLY)// match_parent , accurate { mWidth = specSize; } else { // 由图片决定的宽 int desireByImg = getPaddingLeft() + getPaddingRight() + mSrc.getWidth(); if (specMode == MeasureSpec.AT_MOST)// wrap_content { mWidth = Math.min(desireByImg, specSize); } else mWidth = desireByImg; } /*** * 设置高度 */ specMode = MeasureSpec.getMode(heightMeasureSpec); specSize = MeasureSpec.getSize(heightMeasureSpec); if (specMode == MeasureSpec.EXACTLY)// match_parent , accurate { mHeight = specSize; } else { int desire = getPaddingTop() + getPaddingBottom() + mSrc.getHeight(); if (specMode == MeasureSpec.AT_MOST)// wrap_content { mHeight = Math.min(desire, specSize); } else mHeight = desire; } setMeasuredDimension(mWidth, mHeight); }4、根据Type绘制：
[java] view plain copy print ? /** * 绘制 */ @Override protected void onDraw(Canvas canvas) { switch (type) { // 如果是TYPE_CIRCLE绘制圆形 case TYPE_CIRCLE: int min = Math.min(mWidth, mHeight); /** * 长度如果不一致，按小的值进行压缩 */ mSrc = Bitmap.createScaledBitmap(mSrc, min, min, false); canvas.drawBitmap(createCircleImage(mSrc, min), 0, 0, null); break; case TYPE_ROUND: canvas.drawBitmap(createRoundConerImage(mSrc), 0, 0, null); break; } } /** * 根据原图和变长绘制圆形图片 * * @param source * @param min * @return */ private Bitmap createCircleImage(Bitmap source, int min) { final Paint paint = new Paint(); paint.setAntiAlias(true); Bitmap target = Bitmap.createBitmap(min, min, Config.ARGB_8888); /** * 产生一个同样大小的画布 */ Canvas canvas = new Canvas(target); /** * 首先绘制圆形 */ canvas.drawCircle(min / 2, min / 2, min / 2, paint); /** * 使用SRC_IN，参考上面的说明 */ paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); /** * 绘制图片 */ canvas.drawBitmap(source, 0, 0, paint); return target; } /** * 根据原图添加圆角 * * @param source * @return */ private Bitmap createRoundConerImage(Bitmap source) { final Paint paint = new Paint(); paint.setAntiAlias(true); Bitmap target = Bitmap.createBitmap(mWidth, mHeight, Config.ARGB_8888); Canvas canvas = new Canvas(target); RectF rect = new RectF(0, 0, source.getWidth(), source.getHeight()); canvas.drawRoundRect(rect, mRadius, mRadius, paint); paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); canvas.drawBitmap(source, 0, 0, paint); return target; } /** * 绘制 */ @Override protected void onDraw(Canvas canvas) { switch (type) { // 如果是TYPE_CIRCLE绘制圆形 case TYPE_CIRCLE: int min = Math.min(mWidth, mHeight); /** * 长度如果不一致，按小的值进行压缩 */ mSrc = Bitmap.createScaledBitmap(mSrc, min, min, false); canvas.drawBitmap(createCircleImage(mSrc, min), 0, 0, null); break; case TYPE_ROUND: canvas.drawBitmap(createRoundConerImage(mSrc), 0, 0, null); break; } } /** * 根据原图和变长绘制圆形图片 * * @param source * @param min * @return */ private Bitmap createCircleImage(Bitmap source, int min) { final Paint paint = new Paint(); paint.setAntiAlias(true); Bitmap target = Bitmap.createBitmap(min, min, Config.ARGB_8888); /** * 产生一个同样大小的画布 */ Canvas canvas = new Canvas(target); /** * 首先绘制圆形 */ canvas.drawCircle(min / 2, min / 2, min / 2, paint); /** * 使用SRC_IN，参考上面的说明 */ paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); /** * 绘制图片 */ canvas.drawBitmap(source, 0, 0, paint); return target; } /** * 根据原图添加圆角 * * @param source * @return */ private Bitmap createRoundConerImage(Bitmap source) { final Paint paint = new Paint(); paint.setAntiAlias(true); Bitmap target = Bitmap.createBitmap(mWidth, mHeight, Config.ARGB_8888); Canvas canvas = new Canvas(target); RectF rect = new RectF(0, 0, source.getWidth(), source.getHeight()); canvas.drawRoundRect(rect, mRadius, mRadius, paint); paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); canvas.drawBitmap(source, 0, 0, paint); return target; } 好了，我就不解析代码了，自定义View这是第五篇了，，，，写得好恶心，，，，各位赞一个或者留个言，算是对我的支持~
=========================================简单修复了一下，在ScrollView以及AdapterView中的headview的显示异常的bug============
修复后代码下载：
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