微信公众号有很多都做刮刮乐的活动，本文就实现了刮刮乐的效果，具体代码如下：

首先要做一个类似橡皮擦的东西吧，然后才能把纸上的笔迹擦除

/** * FileName: SplashActivity.java * * @desc 橡皮擦功能，类似刮刮乐效果 * @author HTP * @Date 20140311 * @version 1.00 */ public class Text_Rubbler extends TextView { private float TOUCH_TOLERANCE; // 填充距离，使线条更自然，柔和,值越小，越柔和。 // private final int bgColor; // 位图 private Bitmap mBitmap; // 画布 private Canvas mCanvas; // 画笔 private Paint mPaint; private Path mPath; private float mX, mY; private boolean isDraw = false; public Text_Rubbler(Context context) { /** * @param context 上下文 */ super(context); } public Text_Rubbler(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); // bgColor = // attrs.getAttributeIntValue("http://schemas.android.com/apk/res/android", // "textColor", 0xFFFFFF); // System.out.println("Color:"+bgColor); } public Text_Rubbler(Context context, AttributeSet attrs) { super(context, attrs); // bgColor = // attrs.getAttributeIntValue("http://schemas.android.com/apk/res/android", // "textColor", 0xFFFFFF); // System.out.println(bgColor); // System.out.println(attrs.getAttributeValue("http://schemas.android.com/apk/res/android", // "layout_width")); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); if (isDraw) { mCanvas.drawPath(mPath, mPaint); // mCanvas.drawPoint(mX, mY, mPaint); canvas.drawBitmap(mBitmap, 0, 0, null); } } /** * 开启檫除功能 * * @param bgColor * 覆盖的背景颜色 * @param paintStrokeWidth * 触点（橡皮）宽度 * @param touchTolerance * 填充距离,值越小，越柔和。 */ public void beginRubbler(final int bgColor, final int paintStrokeWidth, float touchTolerance) { TOUCH_TOLERANCE = touchTolerance; // 设置画笔 mPaint = new Paint(); // mPaint.setAlpha(0); // 画笔划过的痕迹就变成透明色了 mPaint.setColor(Color.BLACK); // 此处不能为透明色 mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT)); // 或者 // mPaint.setAlpha(0); // mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN)); mPaint.setAntiAlias(true); mPaint.setDither(true); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); // 前圆角 mPaint.setStrokeCap(Paint.Cap.ROUND); // 后圆角 mPaint.setStrokeWidth(paintStrokeWidth); // 笔宽 // 痕迹 mPath = new Path(); ; // 覆盖 // if (getLayoutParams().width == LayoutParams.FILL_PARENT) { // // } mBitmap = Bitmap.createBitmap(getLayoutParams().width, getLayoutParams().height, Config.ARGB_8888); mCanvas = new Canvas(mBitmap); mCanvas.drawColor(bgColor); isDraw = true; } @Override public boolean onTouchEvent(MotionEvent event) { if (!isDraw) { return true; } switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // 触点按下 // touchDown(event.getRawX(),event.getRawY()); touchDown(event.getX(), event.getY()); invalidate(); break; case MotionEvent.ACTION_MOVE: // 触点移动 touchMove(event.getX(), event.getY()); invalidate(); break; case MotionEvent.ACTION_UP: // 触点弹起 touchUp(event.getX(), event.getY()); invalidate(); break; default: break; } return true; } private void touchDown(float x, float y) { mPath.reset(); mPath.moveTo(x, y); mX = x; mY = y; } private void touchMove(float x, float y) { float dx = Math.abs(x - mX); float dy = Math.abs(y - mY); if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2); mX = x; mY = y; } } private void touchUp(float x, float y) { mPath.lineTo(x, y); mCanvas.drawPath(mPath, mPaint); mPath.reset(); } }

接下来就是使用橡皮檫擦除了

/** * FileName: RubblerAct.java * @Desc 该类通过调用Text_Rubbler这个类将在Activity上显示一片刮一刮的区域，可以出发触摸事件 * @author HTP * @Date 20140312 * @version 1.00 */ public class RubblerAct extends Activity { // 刮开后文字显示 private TextView tv_rubbler; // 得到刮一刮的内容 private Sentence mSentence; // 下一张 private TextView tv_next; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // setContentView(new Rubble(this,"谢谢惠顾",new Rect(100, 200, // 300,250),2,1f,14)); // ///////////////////////////////////////// setContentView(R.layout.rubbler); // 设置的颜色必须要有透明度。 ((Text_Rubbler) findViewById(R.id.rubbler)).beginRubbler(0xFFFFFFFF, 20, 1f);// 设置橡皮擦的宽度等 mSentence = new Sentence(); // 随机初始化文字 tv_rubbler = (TextView) findViewById(R.id.rubbler); String str = mSentence.getSentence(); tv_rubbler.setText(str); tv_next = (TextView) findViewById(R.id.tv_next); // 点击下一步 tv_next.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub String str = mSentence.getSentence(); tv_rubbler.setText(str); ((Text_Rubbler) findViewById(R.id.rubbler))// 初始化状态 .beginRubbler(0xFFFFFFFF, 20, 1f); } }); } class Rubble extends View { private final int PAINT_STROKE_WIDTH; private final float TOUCH_TOLERANCE; // 填充距离，使线条更自然，柔和,值越小，越柔和。 private final int TEXT_SIZE; private Bitmap mBitmap; // 画布 private Canvas mCanvas; // 画笔 private Paint mPaint; private Path mPath; private float mX, mY; private final int X, Y, W, H; private final Rect touchRect; public Rubble(Context context, String bgText, Rect rect, int paintStrokeWidth, float touchTolerance, int textSize) { super(context); setFocusable(true); touchRect = rect; W = rect.right - rect.left; H = rect.bottom - rect.top; X = rect.left; Y = rect.top; TEXT_SIZE = textSize; PAINT_STROKE_WIDTH = paintStrokeWidth; TOUCH_TOLERANCE = touchTolerance; setBackground(touchRect, bgText); initDrowTools(); } private void setBackground(Rect rect, String bgText) { DisplayMetrics dm = new DisplayMetrics(); dm = this.getResources().getDisplayMetrics(); Bitmap bitmap = Bitmap.createBitmap(dm.widthPixels, dm.heightPixels, Config.ARGB_8888); Canvas canvas = new Canvas(bitmap); Paint paint = new Paint(); paint.setColor(0x88000000); // paint.setStyle(Style.STROKE); // paint.setTextAlign(Align.CENTER); paint.setTextSize(TEXT_SIZE); // paint.setTextScaleX(1.5f); canvas.drawColor(Color.WHITE); // 画字的坐标不好控制 int x = rect.left + (rect.right - rect.left - bgText.length() * TEXT_SIZE) / 2; int y = rect.top + (rect.bottom - rect.top - TEXT_SIZE) / 2; // int y = 218+25; canvas.drawText(bgText, x, y, paint); Drawable drawable = new BitmapDrawable(bitmap); setBackgroundDrawable(drawable); } private void initDrowTools() { // 设置画笔 mPaint = new Paint(); // mPaint.setAlpha(0); // 画笔划过的痕迹就变成透明色了 mPaint.setColor(Color.BLACK); // 此处不能为透明色 mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT)); // 或者 // mPaint.setAlpha(0); // mPaint.setXfermode(new // PorterDuffXfermode(PorterDuff.Mode.DST_IN)); mPaint.setAntiAlias(true); mPaint.setDither(true); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); // 前圆角 mPaint.setStrokeCap(Paint.Cap.ROUND); // 后圆角 mPaint.setStrokeWidth(PAINT_STROKE_WIDTH); // 笔宽 // 痕迹 mPath = new Path(); ; // 覆盖 mBitmap = Bitmap.createBitmap(W, H, Config.ARGB_8888); mCanvas = new Canvas(mBitmap); mCanvas.drawColor(0x88000000); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); mCanvas.drawPath(mPath, mPaint); // mCanvas.drawPoint(mX, mY, mPaint); canvas.drawBitmap(mBitmap, X, Y, null); } @Override public boolean onTouchEvent(MotionEvent event) { System.out.print("X--" + event.getX()); System.out.println("Y--" + event.getY()); if (!touchRect.contains((int) event.getX(), (int) event.getY())) { return false; } switch (event.getAction()) { // 触点按下 case MotionEvent.ACTION_DOWN: { touchDown(event.getRawX(), event.getRawY()); touchDown(event.getX() - touchRect.left, event.getY() - touchRect.top); invalidate(); break; } case MotionEvent.ACTION_MOVE: // 触点移动 touchMove(event.getX() - touchRect.left, event.getY() - touchRect.top); invalidate(); break; case MotionEvent.ACTION_UP: // 触点弹起 touchUp(event.getX() - touchRect.left, event.getY() - touchRect.top); invalidate(); break; default: break; } return true; } private void touchDown(float x, float y) { mPath.reset(); mPath.moveTo(x, y); mX = x; mY = y; } private void touchMove(float x, float y) { float dx = Math.abs(x - mX); float dy = Math.abs(y - mY); if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2); mX = x; mY = y; } } private void touchUp(float x, float y) { mPath.lineTo(x, y); mCanvas.drawPath(mPath, mPaint); mPath.reset(); } } /** * 键盘事件，当按下back键的时候询问是否再按一次退出程序 */ // 退出时间 private long exitTime = 0; @Override public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN) { if ((System.currentTimeMillis() - exitTime) > 2000) { Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show(); exitTime = System.currentTimeMillis(); } else { finish(); System.exit(0); } return true; } return super.onKeyDown(keyCode, event); } }

实现效果如下：

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