public class HollowTextView extends AppCompatTextView {
 private Paint mTextPaint, mBackgroundPaint;
 private Bitmap mBackgroundBitmap,mTextBitmap;
 private Canvas mBackgroundCanvas,mTextCanvas;
 private RectF mBackgroundRect;
 private int mBackgroundColor;
 private float mCornerRadius;
 
 public HollowTextView(Context context) {
  this(context,null);
 }
 
 public HollowTextView(Context context, AttributeSet attrs) {
  super(context, attrs);
  initAttrs(attrs,0);
  initPaint();
 }
 
 public HollowTextView(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  initAttrs(attrs,defStyleAttr);
  initPaint();
 }
 
 
 private void initAttrs(AttributeSet attrs,int defStyleAttr){
  if(attrs == null){
   return;
  }
  TypedArray typedArray = getContext().obtainStyledAttributes(attrs, R.styleable.HollowTextView, defStyleAttr, 0);
  mBackgroundColor = typedArray.getColor(R.styleable.HollowTextView_hollowTextView_background_color, Color.TRANSPARENT);
  mCornerRadius = typedArray.getDimension(R.styleable.HollowTextView_hollowTextView_corner_radius,0);
  typedArray.recycle();
 }
 
 /***
  * 初始化畫筆屬性
  */
 private void initPaint() {
  //畫文字的paint
  mTextPaint = new Paint();
  //這是鏤空的關(guān)鍵
  mTextPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
  mTextPaint.setAntiAlias(true);
  mBackgroundPaint = new Paint();
  mBackgroundPaint.setColor(mBackgroundColor);
  mBackgroundPaint.setAntiAlias(true);
 
 }
 
 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  mBackgroundBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_4444);
  mBackgroundCanvas = new Canvas(mBackgroundBitmap);
  mTextBitmap = Bitmap.createBitmap(w,h,Bitmap.Config.ARGB_4444);
  mTextCanvas = new Canvas(mTextBitmap);
  mBackgroundRect = new RectF(0,0,getWidth(),getHeight());
 }
 
 @Override
 protected void onDraw(Canvas canvas) {
  //這里給super傳入的是mTextCanvas，把一些基本屬性都支持進去
  super.onDraw(mTextCanvas);
  drawBackground(mBackgroundCanvas);
  int sc;
  if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP ){
   sc = canvas.saveLayer(0,0,getMeasuredWidth(),getMeasuredHeight(),null);
  }else {
   sc = canvas.saveLayer(0,0,getMeasuredWidth(),getMeasuredHeight(),null,Canvas.ALL_SAVE_FLAG);
  }
  canvas.drawBitmap(mBackgroundBitmap,0,0,null);
  canvas.drawBitmap(mTextBitmap, 0, 0, mTextPaint);
  canvas.restoreToCount(sc);
 }
 
 private void drawBackground(Canvas canvas){
  if(mCornerRadius > 0){
   canvas.drawRoundRect(mBackgroundRect,mCornerRadius,mCornerRadius, mBackgroundPaint);
  }else {
   canvas.drawColor(mBackgroundColor);
  }
 }

<declare-styleable name="HollowTextView">
   <attr name="hollowTextView_background_color" format="color|reference"/>
   <attr name="hollowTextView_corner_radius" format="dimension|reference"/>
 </declare-styleable>

<com.cn.util.HollowTextView
   android:id="@+id/hollowtext"
   android:layout_width="60dp"
   android:layout_height="50dp"
   android:gravity="center"
   android:text="99+"
   android:textSize="30sp"
   android:textStyle="bold"
   app:hollowTextView_background_color="@color/white"
   app:hollowTextView_corner_radius="5dp"
   android:layout_centerInParent="true"/>