Android自定义控件之圆形/圆角的实现代码

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：

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：

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 

 
 
 


View layout 

 
 
  
  
  
 
 
 
 
 

  
 
 
 
 
 
 

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。