public class GuaGuaView extends View {
    private String mText;
    private Rect mTextRect;
    private Paint mTextPaint;
    private int mTextSize;
    private int mTextColor;

    private Paint mTopPaint;
    private Bitmap topBitmap;
    private Canvas mCanvas;

    //手指的路徑
    private Path mPath;
    //手指上次停留的位置
 

    private float mLastX;
    private float mLastY;

    private volatile boolean mIsComplete = false;
    private OnGuaGuaCompleteListener onGuaGuaCompleteListener;
    private PorterDuffXfermode porterDuffXfermode;

    public void setOnGuaGuaCompleteListener(OnGuaGuaCompleteListener onGuaGuaCompleteListener) {
        this
 
.onGuaGuaCompleteListener = onGuaGuaCompleteListener;
    }

    /**
     * 擡起手指時，若刮開區域大於閾值，給使用者提示
     */
    public interface OnGuaGuaCompleteListener {
        void onComplete();
    }

    public GuaGuaView(Context context) {
        this(context, null);
    }

    public GuaGuaView(Context context, AttributeSet attrs) {
        this
 
(context, attrs, 0);
    }

    public GuaGuaView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();

        TypedArray typedArray = null;
        try {
            typedArray = context.getTheme().obtainStyledAttributes(attrs, R.styleable.GuaGuaView, defStyleAttr, 0);

            int indexCount = typedArray.getIndexCount();
            for (int i = 0; i < indexCount; i++) {
                int attr = typedArray.getIndex(i);
                switch (attr) {
                    case R.styleable.GuaGuaView_text:
                        mText = typedArray.getString(attr);
                        break;
                    case R.styleable.GuaGuaView_textSize:
                        //22sp轉化為畫素值
                        mTextSize = (int) typedArray.getDimension(attr,
                                TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 22, getResources().getDisplayMetrics()));
                        break;
                    case R.styleable.GuaGuaView_textColor:
                        mTextColor = typedArray.getColor(attr, 0x000000);
                        break;
                }
            }
            mTextPaint.setColor(mTextColor);
            mTextPaint.setTextSize(mTextSize);
        } finally {
            if (typedArray != null)
                typedArray.recycle();
        }
    }

    private void init() {
        porterDuffXfermode = new PorterDuffXfermode(PorterDuff.Mode.DST_OUT);
        mText = "謝謝惠顧";
        mTextRect = new Rect();
        mTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mTextSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 22, getResources().getDisplayMetrics());
        mTextPaint.setStyle(Paint.Style.STROKE);

        mTopPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mTopPaint.setColor(Color.parseColor("#c0c0c0"));
        mTopPaint.setStyle(Paint.Style.FILL);
        mTopPaint.setDither(true);
        mTopPaint.setStrokeCap(Paint.Cap.ROUND);
        mTopPaint.setStrokeJoin(Paint.Join.ROUND);
        mTopPaint.setStrokeWidth(30);

        mPath = new Path();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //獲得文字的邊界資訊
        mTextPaint.getTextBounds(mText, 0, mText.length(), mTextRect);
        canvas.drawText(mText, getWidth() / 2 - mTextRect.width() / 2, getHeight() / 2 + mTextRect.height() / 2, mTextPaint);

        if (!mIsComplete) {
            mTopPaint.setStyle(Paint.Style.STROKE);
            //只在源影象和目標影象相交的地方繪製透明
            mTopPaint.setXfermode(porterDuffXfermode);
            mCanvas.drawPath(mPath, mTopPaint);
            //還原混合模式
            mTopPaint.setXfermode(null);

            canvas.drawBitmap(topBitmap, 0, 0, null);
        } else {
            if (onGuaGuaCompleteListener != null) {
                onGuaGuaCompleteListener.onComplete();
            }
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mLastX = event.getX();
                mLastY = event.getY();
                mPath.moveTo(event.getX(), event.getY());
                break;
            case MotionEvent.ACTION_MOVE:
                float dx = Math.abs(event.getX() - mLastX);
                float dy = Math.abs(event.getY() - mLastY);
                //手指移動的距離過小，不擦除
                if (dx > 5 || dy > 5) {
                    mLastX = event.getX();
                    mLastY = event.getY();
                    mPath.lineTo(mLastX, mLastY);
                }
                if (!mIsComplete) {
                    invalidate();
                }
                break;
            case MotionEvent.ACTION_UP:
                if (!mIsComplete) {
                    new Thread(mRunnable).start();
                }
                break;
        }
        return true;
    }

    private Runnable mRunnable = new Runnable() {
        @Override
        public void run() {
            int width = getWidth();
            int height = getHeight();

            int[] pixels = new int[width * height];
            float wipeArea = 0;
            float totalArea = width * height;

            /**
             * getPixels()函式把一張圖片，從指定的偏移位置（offset），指定的位置（x,y）擷取指定的寬高（width,height）
             * 把所得影象的每個畫素顏色轉為int值，存入pixels。
             * stride 引數指定在行之間跳過的畫素的數目。圖片是二維的，存入一個一維陣列中，那麼就需要這個引數來指定多少個畫素換一行。
             * 詳見：http://blog.csdn.net/xx326664162/article/details/52240795
             */
            topBitmap.getPixels(pixels, 0, width, 0, 0, width, height);

            for (int i = 0; i < width; i++) {
                for (int j = 0; j < height; j++) {
                    int index = i + j * width;
                    if (pixels[index] == 0) {
                        wipeArea++;
                    }
                }
            }

            float progress = wipeArea / totalArea;
            Log.d("test", "progress-----" + progress);
            if (progress > 0.6) {
                mIsComplete = true;
                postInvalidate();
            }

        }
    };

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        topBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(topBitmap);
        Bitmap bottomBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.fg_guaguaka);
        //將圖片以合適比例顯示
        //先畫灰色背景，再畫圖片
        mCanvas.drawRoundRect(new RectF(0, 0, w, h), 50, 50, mTopPaint);

        /**
         * bitmap 要繪製的點陣圖物件
         * src 要裁切的位置，若是null則顯示整張圖片
         * dst 裁切後的圖片顯示的區域
         * paint 畫筆
         */
        mCanvas.drawBitmap(bottomBitmap, null, new RectF(0, 0, w, h), null);
    }

    //設定中獎資訊
    public void setText(String mText) {
        this.mText = mText;
    }
}

attr.xml

<declare-styleable name="GuaGuaView">
        <attr name="text" format="string" />
        <attr name="textColor" format="color" />
        <attr name="textSize" format="dimension" />
    </declare-styleable>

使用：

<com.sign.signview.view.GuaGuaView
        android:id="@+id/guagua"
        android:layout_width="300dp"
        android:layout_height="100dp"
        android:layout_centerInParent="true"
        sign:text="我中獎了"
        sign:textColor="#ff0000"
        sign:textSize="22sp" />

guaGuaView.setOnGuaGuaCompleteListener(new GuaGuaView.OnGuaGuaCompleteListener() {
            @Override
            public void onComplete() {
                Toast.makeText(GuaGuaActivity.this, "恭喜你，沒中獎!", Toast.LENGTH_SHORT).show();
            }
        });
        guaGuaView.setText("刮刮卡終於結束了");