android – 如何在点之间画一条线,拉这些点？

这是如何完成的.假设你有点,使这些全局：

PointF topLeft = new PointF(10,10);
PointF topRight = new PointF(90,10);
PointF bottomLeft = new PointF(10,90);
PointF bottomRight = new PointF(90,90);

你需要做的是在每个点周围做一个RectF. RectF越大,触摸面积就越大.

float sizeOfRect = 5f;
RectF topLeftTouchArea = new RectF(topLeft.x - sizeOfRect,topLeft.y - sizeOfRect,topLeft.x + sizeOfRect,topLeft.y + sizeOfRect);
//Do this for the other points too

定义一些全局变量来跟踪用户在onTouch中的操作.一个int是被触摸的角落,另外四个是角落的标识符.

private final int nONE = -1,TOUCH_TOP_LEFT = 0,TOUCH_TOP_RIGHT = 1,TOUCH_BOT_LEFT = 2,TOUCH_BOT_RIGHT = 3;
int currentTouch = NONE;

现在,在您的onTouch事件中,您可以检查用户感兴趣的点,如下所示：

@Override
public Boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
    //The user just put @R_944_8917@ finger down.
    //We check to see which corner the user is touching
    //And set our global,currentTouch,to the appropriate constant.
    case MotionEvent.ACTION_DOWN:
        if (topLeftTouchArea.contains(event.getX(),event.getY()) {
            currentTouch = TOUCH_TOP_LEFT;
        } else if (topRightTouchArea.contains(event.getX(),event.getY()) {
            currentTouch = TOUCH_TOP_RIGHT;
        } else if (botLeftTouchArea.contains(event.getX(),event.getY()) {
            currentTouch = TOUCH_BOT_LEFT;
        } else if (botrightTouchArea.contains(event.getX(),event.getY()) {
            currentTouch = TOUCH_BOT_RIGHT;
        } else {
            return false; //Return false if user touches none of the corners
        }
        return true; //Return true if the user touches one of the corners
    //Now we kNow which corner the user is touching.
    //When the user moves @R_944_8917@ finger,we update the point to the user position and invalidate.
    case MotionEvent.ACTION_MOVE:
        switch (currentTouch) {
        case TOUCH_TOP_LEFT:
             topLeft.x = event.getX();
             topLeft.y = event.getY();
             //The bottom left x position has to move with the top left corner
             bottomLeft.x = topLeft.x;
             //The top right y position has to move with the top left corner
             topRight.y = topLeft.y;
             invalidate();
             return true;
        case TOUCH_TOP_RIGHT:
             topRight.x = event.getX();
             topRight.y = event.getY();
             //The top left y position has to move with the top right corner
             topLeft.y = topRight.y;
             //The bottom right x position has to move with the top right corner
             bottomRight.x = topRight.x;
             invalidate();
             return true;
        case TOUCH_BOT_LEFT:
             bottomLeft.x = event.getX();
             bottomLeft.y = event.getY();
             bottomRight.y = bottomLeft.y;
             topLeft.x = bottomLeft.x;
             invalidate();
             return true;
        case TOUCH_BOT_RIGHT:
             bottomRight.x = event.getX();
             bottomRight.y = event.getY();
             topRight.x = bottomRight.x;
             bottomLeft.y = bottomRight.y;
             invalidate();
             return true;
        }
        //We returned true for all of the above cases,because we used the event
        return false; //If currentTouch is none of the above cases,return false

    //Here the user lifts up @R_944_8917@ finger.
    //We update the points one last time,and set currentTouch to NONE.
    case MotionEvent.ACTION_UP:
        switch (currentTouch) {
        case TOUCH_TOP_LEFT:
             topLeft.x = event.getX();
             topLeft.y = event.getY();
             //The bottom left x position has to move with the top left corner
             bottomLeft.x = topLeft.x;
             //The top right y position has to move with the top left corner
             topRight.y = topLeft.y;
             invalidate();
             currentTouch = NONE;
             return true;
        case TOUCH_TOP_RIGHT:
             topRight.x = event.getX();
             topRight.y = event.getY();
             //The top left y position has to move with the top right corner
             topLeft.y = topRight.y;
             //The bottom right x position has to move with the top right corner
             bottomRight.x = topRight.x;
             invalidate();
             currentTouch = NONE;
             return true;
        case TOUCH_BOT_LEFT:
             bottomLeft.x = event.getX();
             bottomLeft.y = event.getY();
             bottomRight.y = bottomLeft.y;
             topLeft.x = bottomLeft.x;
             invalidate();
             currentTouch = NONE;
             return true;
        case TOUCH_BOT_RIGHT:
             bottomRight.x = event.getX();
             bottomRight.y = event.getY();
             topRight.x = bottomRight.x;
             bottomLeft.y = bottomRight.y;
             invalidate();
             currentTouch = NONE;
             return true;
        }
        return false;
    }
}

这是做一个围绕你的点的矩形.想像一下在图片周围的绘图框.这些是由Rect对象创建的“触摸板”.矩形的大小由sizeOfRect设置.在onTouchEvent中,它检查每个矩形对象以查看用户的触摸是否在矩形内,从而指示用户尝试触摸该点.