一、问题在哪里？
问题来源于app开发中一个很常见的场景——用户头像要展示成圆的：
二、怎么搞？
机智的我，第一想法就是，切一张中间圆形透明、四周与底色相同、尺寸与头像相同的蒙板图片，盖在头像上不就完事了嘛，哈哈哈！
在背景纯色的前提下，这的确能简单解决问题，但是如果背景没有这么简单呢？
在这种不规则背景下，有两个问题：
1)、背景图常常是适应手机宽度缩放，而头像的尺寸又是固定宽高DP的，所以固定的蒙板图片是没法保证在不同机型上都和背景图案吻合的。
2)、在这种非纯色背景下，哪天想调整一下头像位置就得重新换图片蒙板，实在是太难维护了……
所以呢，既然头像图片肯定是方的，那就就让ImageView圆起来吧。
三、开始干活
基本思路是，自定义一个ImageView，通过重写onDraw方法画出一个圆形的图片来：
public class ImageViewPlus extends ImageView{ private Paint mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG); private Bitmap mRawBitmap; private BitmapShader mShader; private Matrix mMatrix = new Matrix(); public ImageViewPlus(Context context, AttributeSet attrs) { super(context, attrs); } @Override protected void onDraw(Canvas canvas) { Bitmap rawBitmap = getBitmap(getDrawable()); if (rawBitmap != null){ int viewWidth = getWidth(); int viewHeight = getHeight(); int viewMinSize = Math.min(viewWidth, viewHeight); float dstWidth = viewMinSize; float dstHeight = viewMinSize; if (mShader == null || !rawBitmap.equals(mRawBitmap)){ mRawBitmap = rawBitmap; mShader = new BitmapShader(mRawBitmap, TileMode.CLAMP, TileMode.CLAMP); } if (mShader != null){ mMatrix.setScale(dstWidth / rawBitmap.getWidth(), dstHeight / rawBitmap.getHeight()); mShader.setLocalMatrix(mMatrix); } mPaintBitmap.setShader(mShader); float radius = viewMinSize / 2.0f; canvas.drawCircle(radius, radius, radius, mPaintBitmap); } else { super.onDraw(canvas); } } private Bitmap getBitmap(Drawable drawable){ if (drawable instanceof BitmapDrawable){ return ((BitmapDrawable)drawable).getBitmap(); } else if (drawable instanceof ColorDrawable){ Rect rect = drawable.getBounds(); int width = rect.right - rect.left; int height = rect.bottom - rect.top; int color = ((ColorDrawable)drawable).getColor(); Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888); Canvas canvas = new Canvas(bitmap); canvas.drawARGB(Color.alpha(color), Color.red(color), Color.green(color), Color.blue(color)); return bitmap; } else { return null; } } }
分析一下代码：
canvas.drawCircle 决定了画出来的形状是圆形，而圆形的内容则是通过 mPaintBitmap.setShader 搞定的。
其中，BitmapShader需要设置Bitmap填充ImageView的方式(CLAMP：拉伸边缘, MIRROR：镜像, REPEAT：整图重复)。
这里其实设成什么不重要，因为我们实际需要的是将Bitmap按比例缩放成跟ImageView一样大，而不是预置的三种效果。
所以，别忘了 mMatrix.setScale 和 mShader.setLocalMatrix 一起用，将图片缩放一下。
四、更多玩法 —— 支持边框
看下面的效果图，如果想给圆形的头像上加一个边框，该怎么搞呢？
public class ImageViewPlus extends ImageView{ private Paint mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG); private Paint mPaintBorder = new Paint(Paint.ANTI_ALIAS_FLAG); private Bitmap mRawBitmap; private BitmapShader mShader; private Matrix mMatrix = new Matrix(); private float mBorderWidth = dip2px(15); private int mBorderColor = 0xFF0080FF; public ImageViewPlus(Context context, AttributeSet attrs) { super(context, attrs); } @Override protected void onDraw(Canvas canvas) { Bitmap rawBitmap = getBitmap(getDrawable()); if (rawBitmap != null){ int viewWidth = getWidth(); int viewHeight = getHeight(); int viewMinSize = Math.min(viewWidth, viewHeight); float dstWidth = viewMinSize; float dstHeight = viewMinSize; if (mShader == null || !rawBitmap.equals(mRawBitmap)){ mRawBitmap = rawBitmap; mShader = new BitmapShader(mRawBitmap, TileMode.CLAMP, TileMode.CLAMP); } if (mShader != null){ mMatrix.setScale((dstWidth - mBorderWidth * 2) / rawBitmap.getWidth(), (dstHeight - mBorderWidth * 2) / rawBitmap.getHeight()); mShader.setLocalMatrix(mMatrix); } mPaintBitmap.setShader(mShader); mPaintBorder.setStyle(Paint.Style.STROKE); mPaintBorder.setStrokeWidth(mBorderWidth); mPaintBorder.setColor(mBorderColor); float radius = viewMinSize / 2.0f; canvas.drawCircle(radius, radius, radius - mBorderWidth / 2.0f, mPaintBorder); canvas.translate(mBorderWidth, mBorderWidth); canvas.drawCircle(radius - mBorderWidth, radius - mBorderWidth, radius - mBorderWidth, mPaintBitmap); } else { super.onDraw(canvas); } } private Bitmap getBitmap(Drawable drawable){ if (drawable instanceof BitmapDrawable){ return ((BitmapDrawable)drawable).getBitmap(); } else if (drawable instanceof ColorDrawable){ Rect rect = drawable.getBounds(); int width = rect.right - rect.left; int height = rect.bottom - rect.top; int color = ((ColorDrawable)drawable).getColor(); Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888); Canvas canvas = new Canvas(bitmap); canvas.drawARGB(Color.alpha(color), Color.red(color), Color.green(color), Color.blue(color)); return bitmap; } else { return null; } } private int dip2px(int dipVal) { float scale = getResources().getDisplayMetrics().density; return (int)(dipVal * scale + 0.5f); } }
看代码中，加边框实际上就是用实心纯色的 Paint 画了一个圆边，在此基础上画上原来的头像即可。
需要的注意的地方有三个：
1)、圆框的半径不是 radius ，而应该是 radius - mBorderWidth / 2.0f 。想象着拿着笔去画线，线其实是画在右图中白色圈的位置，只不过它很粗。
2)、在ImageView大小不变的基础上，头像的实际大小要比没有边框的时候小了，所以 mMatrix.setScale 的时候要把边框的宽度去掉。
3)、画头像Bitmap的时候不能直接 canvas.drawCircle(radius, radius, radius - mBorderWidth, mPaintBitmap) ，这样你会发现头像的右侧和下方边缘被拉伸了（右图）
为什么呢？因为 Paint 默认是以左上角为基准开始绘制的，此时头像的实际区域是右图中的红框，而超过红框的部分（圆形的右侧和下方），自然被 TileMode.CLAMP效果沿边缘拉伸了。
所以，需要通过挪动坐标系的位置和调整圆心，才能把头像画在正确的区域（右图绿框）中。
五、更多玩法 —— 支持xml配置
既然有了边框，那如果想配置边框的宽度和颜色该如何是好呢？
基本上两个思路：
1)给ImageViewPlus加上set接口，设置完成之后通过 invalidate(); 重绘一下即可；
2)在xml里就支持配置一些自定义属性，这样用起来会方便很多。
这里重点说一下支持xml配置自定义属性。
自定义控件要支持xml配置自定义属性的话，首先需要在 \res\values 里去定义属性：
<?xml version="1.0" encoding="utf-8"?> <resources> <attr name="borderColor" format="color" /> <attr name="borderWidth" format="dimension" /> <declare-styleable name="ImageViewPlus"> <attr name="borderColor" /> <attr name="borderWidth" /> </declare-styleable> </resources>
View attrs_imageviewplus.xml
然后在ImageViewPlus的构造函数中去读取这些自定义属性：
private static final int DEFAULT_BORDER_COLOR = Color.TRANSPARENT; private static final int DEFAULT_BORDER_WIDTH = 0; public ImageViewPlus(Context context, AttributeSet attrs) { super(context, attrs); //取xml文件中设定的参数 TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.ImageViewPlus); mBorderColor = ta.getColor(R.styleable.ImageViewPlus_borderColor, DEFAULT_BORDER_COLOR); mBorderWidth = ta.getDimensionPixelSize(R.styleable.ImageViewPlus_borderWidth, dip2px(DEFAULT_BORDER_WIDTH)); ta.recycle(); }
在xml布局中使用自定义属性：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" xmlns:snser="http://schemas.android.com/apk/res/cc.snser.imageviewplus" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/wallpaper" android:orientation="vertical" tools:context="${relativePackage}.${activityClass}" > <cc.snser.imageviewplus.ImageViewPlus android:id="@+id/imgplus" android:layout_width="200dp" android:layout_height="300dp" android:layout_marginBottom="50dp" android:layout_centerHorizontal="true" android:layout_alignParentBottom="true" android:src="@drawable/img_square" snser:borderColor="#FF0080FF" snser:borderWidth="15dp" /> </RelativeLayout>
六、更多玩法 —— 圆角ImageView
搞定了圆形ImageView以及对应的边框，那如何实现下面这种圆角的ImageView呢？
其实原理上一样，把 canvas.drawCircle 对应改成 canvas.drawRoundRect 就OK了，直接贴代码吧：
public class ImageViewPlus extends ImageView{ /** * android.widget.ImageView */ public static final int TYPE_NONE = 0; /** * 圆形 */ public static final int TYPE_CIRCLE = 1; /** * 圆角矩形 */ public static final int TYPE_ROUNDED_RECT = 2; private static final int DEFAULT_TYPE = TYPE_NONE; private static final int DEFAULT_BORDER_COLOR = Color.TRANSPARENT; private static final int DEFAULT_BORDER_WIDTH = 0; private static final int DEFAULT_RECT_ROUND_RADIUS = 0; private int mType; private int mBorderColor; private int mBorderWidth; private int mRectRoundRadius; private Paint mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG); private Paint mPaintBorder = new Paint(Paint.ANTI_ALIAS_FLAG); private RectF mRectBorder = new RectF(); private RectF mRectBitmap = new RectF(); private Bitmap mRawBitmap; private BitmapShader mShader; private Matrix mMatrix = new Matrix(); public ImageViewPlus(Context context, AttributeSet attrs) { super(context, attrs); //取xml文件中设定的参数 TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.ImageViewPlus); mType = ta.getInt(R.styleable.ImageViewPlus_type, DEFAULT_TYPE); mBorderColor = ta.getColor(R.styleable.ImageViewPlus_borderColor, DEFAULT_BORDER_COLOR); mBorderWidth = ta.getDimensionPixelSize(R.styleable.ImageViewPlus_borderWidth, dip2px(DEFAULT_BORDER_WIDTH)); mRectRoundRadius = ta.getDimensionPixelSize(R.styleable.ImageViewPlus_rectRoundRadius, dip2px(DEFAULT_RECT_ROUND_RADIUS)); ta.recycle(); } @Override protected void onDraw(Canvas canvas) { Bitmap rawBitmap = getBitmap(getDrawable()); if (rawBitmap != null && mType != TYPE_NONE){ int viewWidth = getWidth(); int viewHeight = getHeight(); int viewMinSize = Math.min(viewWidth, viewHeight); float dstWidth = mType == TYPE_CIRCLE ? viewMinSize : viewWidth; float dstHeight = mType == TYPE_CIRCLE ? viewMinSize : viewHeight; float halfBorderWidth = mBorderWidth / 2.0f; float doubleBorderWidth = mBorderWidth * 2; if (mShader == null || !rawBitmap.equals(mRawBitmap)){ mRawBitmap = rawBitmap; mShader = new BitmapShader(mRawBitmap, TileMode.CLAMP, TileMode.CLAMP); } if (mShader != null){ mMatrix.setScale((dstWidth - doubleBorderWidth) / rawBitmap.getWidth(), (dstHeight - doubleBorderWidth) / rawBitmap.getHeight()); mShader.setLocalMatrix(mMatrix); } mPaintBitmap.setShader(mShader); mPaintBorder.setStyle(Paint.Style.STROKE); mPaintBorder.setStrokeWidth(mBorderWidth); mPaintBorder.setColor(mBorderWidth > 0 ? mBorderColor : Color.TRANSPARENT); if (mType == TYPE_CIRCLE){ float radius = viewMinSize / 2.0f; canvas.drawCircle(radius, radius, radius - halfBorderWidth, mPaintBorder); canvas.translate(mBorderWidth, mBorderWidth); canvas.drawCircle(radius - mBorderWidth, radius - mBorderWidth, radius - mBorderWidth, mPaintBitmap); } else if (mType == TYPE_ROUNDED_RECT){ mRectBorder.set(halfBorderWidth, halfBorderWidth, dstWidth - halfBorderWidth, dstHeight - halfBorderWidth); mRectBitmap.set(0.0f, 0.0f, dstWidth - doubleBorderWidth, dstHeight - doubleBorderWidth); float borderRadius = mRectRoundRadius - halfBorderWidth > 0.0f ? mRectRoundRadius - halfBorderWidth : 0.0f; float bitmapRadius = mRectRoundRadius - mBorderWidth > 0.0f ? mRectRoundRadius - mBorderWidth : 0.0f; canvas.drawRoundRect(mRectBorder, borderRadius, borderRadius, mPaintBorder); canvas.translate(mBorderWidth, mBorderWidth); canvas.drawRoundRect(mRectBitmap, bitmapRadius, bitmapRadius, mPaintBitmap); } } else { super.onDraw(canvas); } } private int dip2px(int dipVal) { float scale = getResources().getDisplayMetrics().density; return (int)(dipVal * scale + 0.5f); } private Bitmap getBitmap(Drawable drawable){ if (drawable instanceof BitmapDrawable){ return ((BitmapDrawable)drawable).getBitmap(); } else if (drawable instanceof ColorDrawable){ Rect rect = drawable.getBounds(); int width = rect.right - rect.left; int height = rect.bottom - rect.top; int color = ((ColorDrawable)drawable).getColor(); Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888); Canvas canvas = new Canvas(bitmap); canvas.drawARGB(Color.alpha(color), Color.red(color), Color.green(color), Color.blue(color)); return bitmap; } else { return null; } } }
View ImageViewPlus.java
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" xmlns:snser="http://schemas.android.com/apk/res/cc.snser.imageviewplus" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/wallpaper" android:orientation="vertical" tools:context="${relativePackage}.${activityClass}" > <cc.snser.imageviewplus.ImageViewPlus android:id="@+id/imgplus" android:layout_width="200dp" android:layout_height="300dp" android:layout_marginBottom="50dp" android:layout_centerHorizontal="true" android:layout_alignParentBottom="true" android:src="@drawable/img_rectangle" snser:type="rounded_rect" snser:borderColor="#FF0080FF" snser:borderWidth="10dp" snser:rectRoundRadius="30dp" /> </RelativeLayout> View layout <?xml version="1.0" encoding="utf-8"?> <resources> <attr name="type"> <enum name="none" value="0" /> <enum name="circle" value="1" /> <enum name="rounded_rect" value="2" /> </attr> <attr name="borderColor" format="color" /> <attr name="borderWidth" format="dimension" /> <attr name="rectRoundRadius" format="dimension" /> <declare-styleable name="ImageViewPlus"> <attr name="type" /> <attr name="borderColor" /> <attr name="borderWidth" /> <attr name="rectRoundRadius" /> </declare-styleable> </resources> View attrs_imageviewplus.xml
以上就是本文的全部内容，希望对大家学习Android软件编程有所帮助。