js實現可拖動Div

       隨着時代的變化，越來越感覺到js的重要性，js不僅可以做web頁面(如Ext框架)，還可以做一些web的特效，這些特效不僅兼容PC，而且兼容手機端，畢竟是基於瀏覽器的，和平台沒關系。現在微軟的windows8 系統的App都可以用js開發了，大家有時間可以去嘗試一下。

       現在切入正題，說一下js 實現可拖動Div.實現這個功能我們先說一下思路：

     1.捕捉鼠標div的mousedown事件

     2.捕捉 document的   mousemove事件

      3.取消事件

  

然后我們看一下代碼：

	function Drag(id) {
            var $ = function (flag) {
                return document.getElementById(flag);
            }
            $(id).onmousedown = function (e) {
                var d = document;
                var  that=this;
                var page = {
                    event: function (evt) {
                        var ev = evt || window.event;
                        return ev;
                    },
                    pageX: function (evt) {
                        var e = this.event(evt);
                        return e.pageX || (e.clientX + document.body.scrollLeft - document.body.clientLeft);
                    },
                    pageY: function (evt) {
                        var e = this.event(evt);
                        return e.pageY || (e.clientY + document.body.scrollTop - document.body.clientTop);

                    },
                    layerX: function (evt) {
                        var e = this.event(evt);
                        return e.layerX || e.offsetX;
                    },
                    layerY: function (evt) {
                        var e = this.event(evt);
                        return e.layerY || e.offsetY;
                    }
                }             
                var x = page.layerX(e);
                var y = page.layerY(e);        
                if (that.setCapture) {
                    that.setCapture();
                }
                else if (window.captureEvents) {
                    window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);
                }
                d.onmousemove = function (e) {                    
                    var tx = page.pageX(e) - x;
                    var ty = page.pageY(e) - y;
                    that.style.left = tx + "px";
                    that.style.top = ty + "px";
                }
                d.onmouseup = function () {
                    if (that.releaseCapture) {
                        that.releaseCapture();
                    }
                    else if (window.releaseEvents) {
                        window.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP);
                    }
                    d.onmousemove = null;
                    d.onmouseup = null;
                }
            }
        }
		

 

代碼分析：

1.  

   獲取div對象

   var $ = function (flag) {
                   return document.getElementById(flag);
               }    

2. 捕捉document的mousedown事件：

   里面有這么一段代碼：

        var page = {
                       event: function (evt) {
                           var ev = evt || window.event;
                           return ev;
                       },
                       pageX: function (evt) {
                           var e = this.event(evt);
                           return e.pageX || (e.clientX + document.body.scrollLeft - document.body.clientLeft);
                       },
                       pageY: function (evt) {
                           var e = this.event(evt);
                           return e.pageY || (e.clientY + document.body.scrollTop - document.body.clientTop);
   
                       },
                       layerX: function (evt) {
                           var e = this.event(evt);
                           return e.layerX || e.offsetX;
                       },
                       layerY: function (evt) {
                           var e = this.event(evt);
                           return e.layerY || e.offsetY;
                       }
                   }

   其中event獲取鼠標事件，pageX，pageY獲取鼠標的坐標，layerX，layerY獲取鼠標距離div邊框的距離。

   還有一段代碼：

                if (dv.setCapture) {
                       dv.setCapture();
                   }
                   else if (window.captureEvents) {
                       window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);
                   }

   這個就是捕捉div的MouseMove和MouseUp事件，不懂得tx可以到網上查查。
3.  document的MouseMove和mouseUp事件： 

d.onmousemove = function (e) {                    
                    var tx = page.pageX(e) - x;
                    var ty = page.pageY(e) - y;
                    dv.style.left = tx + "px";
                    dv.style.top = ty + "px";
                }   
                d.onmouseup = function () {
                    if (dv.releaseCapture) {
                        dv.releaseCapture();
                    }
                    else if (window.releaseEvents) {
                        window.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP);
                    }
                    d.onmousemove = null;
                    d.onmouseup = null;
                }

其中的tx,ty就是最重要的代碼了，是設置div坐標的

有的人可能會問為什么要-x,-y?

x,y其實就是獲取鼠標距離div邊框的距離，如果不減掉的話

鼠標箭頭的坐標和div的x,y坐標一樣了，這樣拖動之后，鼠標的位置會偏到左上角，效果就是，拖動之后會彈動一下。

                if (dv.releaseCapture) {
                        dv.releaseCapture();
                    }
                    else if (window.releaseEvents) {
                        window.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP);
                    }
                    d.onmousemove = null;
                    d.onmouseup = null;

上面這段代碼就是在鼠標松開之后取消document的onmousemove，onmouseup事件。

 

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