Android控件拖动实例详解

android控件拖动

android控件的拖动，主要是通过设置控件的setontouchlistener()方法，重写它的ontouch()方法。然后通过motionevent的不同事件，进行判断，主要是在motionevent.action_move中不断重绘控件在画布中的位置，而实现拖动的效果。

public class dragviewactivity extends appcompatactivity { 
  private button btn_drag; 
 
  @override 
  protected void oncreate(bundle savedinstancestate) { 
    super.oncreate(savedinstancestate); 
    setcontentview(r.layout.activity_drag_view); 
 
 
    // 获取屏幕的宽高 
    displaymetrics dm = getresources().getdisplaymetrics(); 
    final int screenwith = dm.widthpixels; 
    final int screenheight = dm.heightpixels; 
 
    btn_drag = (button) findviewbyid(r.id.btn_drag); 
    btn_drag.setontouchlistener(new view.ontouchlistener() { 
        int lastx; 
        int lasty; 
        boolean isdraging = false; 
 
      @override 
      public boolean ontouch(view v, motionevent event) { 
        int ee = event.getaction(); 
        switch (ee){ 
          case motionevent.action_down: 
            isdraging = true; 
            lastx = (int) event.getrawx(); 
            lasty = (int) event.getrawy(); 
            break; 
          case motionevent.action_move: 
            if (isdraging){ 
              // x轴方向的位移差 
              int dx = (int) event.getrawx() - lastx; 
              // y轴方向的位移差 
              int dy = (int) event.getrawy() - lasty; 
 
              int l = v.getleft() + dx; 
              int t = v.gettop() + dy; 
              int r = v.getright() + dx; 
              int b = v.getbottom() + dy; 
 
              // 判断超出屏幕 
              if (l < 0){ 
                l = 0; 
                r = l + v.getwidth(); 
              } 
              if (t < 0){ 
                t = 0; 
                b = t + v.getheight(); 
              } 
              if (r > screenwith){ 
                r = screenwith; 
                l = r - v.getwidth(); 
              } 
              if (b > screenheight){ 
                b = screenheight; 
                t = b - v.getheight(); 
              } 
 
              // 重绘view 
              v.layout(l, t, r, b); 
              v.postinvalidate(); 
 
              lastx = (int) event.getrawx(); 
              lasty = (int) event.getrawy(); 
            } 
            break; 
 
          case motionevent.action_up: 
            isdraging = false; 
            break; 
          default: 
            break; 
        } 
        return false; 
      } 
    }); 
  } 

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