学习安卓基础之android 拖动和拖动原理

<pre name="code" class="java">iv_dragView.setOnTouchListener(new OnTouchListener){
float startx = 0;
float starty = 0;
public boolean onTouch(View v,MotionEvent event){
switch(event.getAction){
case MotionEvent.ACTION_DOWN:
//1.纪录手指第一次按下的坐标
startx = event.getRowX();
starty = event.getRowY();
break;
case MotionEvent.ACTION_MOVE:
//2.新的坐标
float newX = event.getRawX();
float newY = event.getRawY();
//3.计算偏移量(因为被拖动的是有具体宽和高的控件，而不是点，所以要根据偏移量计算出控件的最终位置)
int dx = (int)newX - startx;
int dy = (int)newY - starty;
//4.根据偏移量更新控件的位置 (layout(l,t,r,b) 标注见下图)
iv_dragView.layout(iv_dragView.getLeft()+dx,iv_dragView.getTop()+dy,iv_dragView.getRight()+dx,iv_dragVIew.getBottom()+dy);
//5.重新纪录坐标
startx = event.getRowX();
starty = event.getRowY();
break;
case MotionEvent.ACTION_UP:
break;
}
}
}