Android开发教程：触摸屏模拟达成方向键

发布时间：2021-12-16 13:32:43 所属栏目：教程来源：互联网

导读：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-x00 则认为向右移动，负距离x-x00 则认为向左移动；上下移动的判断同理。代码如下，需要

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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Android开发教程： 触摸屏模拟达成方向键

Android开发教程：触摸屏模拟达成方向键