Androids使用TextvView实现镂空字体效果

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();
  }
 
  /***
   * 初始化画笔属性
   */
  private void initPaint() {
    //画文字的paint
    mTextPaint = new Paint();
    //这是镂空的关键
    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) {
    //这里给super传入的是mTextCanvas，把一些基本属性都支持进去
    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"/>