改写Android的Snake例子，使之运行于我的三星手机上。判断规则如下：如果x方向移动距离大于y方向，则认为是水平移动，反之则是上下移动。如果水平移动，x移动正距离x-x0>0 则认为向右移动，负距离x-x0<0 则认为向左移动；上下移动的判断同理。
代码如下，需要注意的是MotionEvent的ACTION_DOWN, ACTION_UP 是这么理解的:
ACTION_DOWN - A pressed gesture has started, the motion contains the initial starting location.
ACTION_UP - A pressed gesture has finished, the motion contains the final release location as well as any intermediate points since the last down or move event.
ACTION_MOVE - A change has happened during a press gesture (between [email protected] #ACTION_DOWN} and [email protected] #ACTION_UP}). The motion contains the most recent point, as well as any intermediate points since the last down or move event. -
简而言之，ACTION_DOWN, ACTION_UP 类似于Javascript里面键盘事件OnKeyDown, OnKeyUp 或鼠标事件OnMouseDown, OnMouseUp, 而不是说手指往上划拉或往下划拉了一下。
/** * Re write onKeyDown() for SAMSUNG */ public boolean onTouchEvent(MotionEvent event) { // Set the game status to running if (event.getAction() == MotionEvent.ACTION_DOWN) { if (mMode == READY | mMode == LOSE) { initNewGame(); setMode(RUNNING); update(); return true; } if (mMode == PAUSE) { setMode(RUNNING); update(); return true; } } float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: mX = x; mY = y; update(); return true; case MotionEvent.ACTION_UP: float dx = x - mX; float dy = y - mY; if (Math.abs(dx) >= TOUCH_TOLERANCE || Math.abs(dy) >= TOUCH_TOLERANCE) { if (Math.abs(dx) >= Math.abs(dy)) { // move from left -> right // or right -> left if (dx > 0.0f) { turnTo(EAST); } else { turnTo(WEST); } } else { // move from top -> bottom or bottom -> top if (dy > 0.0f) { turnTo(SOUTH); } else { turnTo(NORTH); } } update(); return true; } } return super.onTouchEvent(event); } private void turnTo(int direction) { if (direction == WEST & mDirection != EAST) { mNextDirection = WEST; } if (direction == EAST & mDirection != WEST) { mNextDirection = EAST; } if (direction == SOUTH & mDirection != NORTH) { mNextDirection = SOUTH; } if (direction == NORTH & mDirection != SOUTH) { mNextDirection = NORTH; } }