Android开发教程: 触摸屏模拟实现方向键
Android开发教程: 触摸屏模拟实现方向键
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 {@link #ACTION_DOWN} and {@link #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;
- }
- }
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