浅析JavaScript动画模拟拖拽原理
模拟拖拽的原理:
x1等于div.offsetLeft
y1等于div.offsetTop
x2等于ev.clientX(ev表示event事件)
y2等于ev.clientY
当我们在方块上按下鼠标的时候,x2-x1即可确定。移动鼠标之后,我们用鼠标当前的位置即x4、y4减去x2-x1、y2-y1就可以得到方块现在的位置。
代码:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <style> #box{ width: 100px; height: 100px; background: red; position: absolute; } </style> </head> <body> <div id="box"></div> <script type="text/javascript"> var oBox = document.getElementById('box'); oBox.onmousedown = function(ev){ // 鼠标按下 var ev = ev || event; // 获取鼠标离div得距离 var mouseBoxleft = ev.clientX - this.offsetLeft; var mouseBoxTop = ev.clientY - this.offsetTop; oBox.onmousemove = function(ev){ // 鼠标按下左键并移动 var ev = ev || event; // 设置div移动时,它的位置 oBox.style.left = ev.clientX - mouseBoxleft + 'px'; oBox.style.top = ev.clientY - mouseBoxleft + 'px'; } oBox.onmouseup = function(){ // 鼠标左键抬起 oBox.onmousemove = oBox.onmouseup = null; } } </script> </body> </html>
优化代码:
【1】鼠标移动快的时候,鼠标会移出方块,这时方块就不会再跟随鼠标动了。
解决办法:就是将onmousemove和onmouseup加到document对象上
代码:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <style> #box{ width: 100px; height: 100px; background: red; position: absolute; } </style> </head> <body> <div id="box"></div> <script> var oBox = document.getElementById('box'); oBox.onmousedown = function(ev){ // 鼠标按下 var ev = ev || event; // 获取鼠标离div得距离 var mouseBoxleft = ev.clientX - this.offsetLeft; var mouseBoxTop = ev.clientY - this.offsetTop; document.onmousemove = function(ev){ // 鼠标按下左键并移动 var ev = ev || event; // 设置div移动时,它的位置 oBox.style.left = ev.clientX - mouseBoxleft + 'px'; oBox.style.top = ev.clientY - mouseBoxleft + 'px'; } document.onmouseup = function(){ // 鼠标左键抬起 document.onmousemove = document.onmouseup = null; } } </script> </body> </html>
【2】当要拖动的方块中有文字时会触发浏览器的默认行为
解决办法:1、使用return false添加到onmousedown事件中阻止浏览器的默认行为(IE除外)
2、使用全局捕获(IE)
1、使用return false添加到onmousedown事件中阻止浏览器的默认行为(IE除外)
代码:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <style> #box{ width: 100px; height: 100px; background: red; position: absolute; top: 0; left: 0; } </style> </head> <body> <div id="box">模拟拖拽</div> <script> var oBox = document.getElementById('box'); oBox.onmousedown = function(ev){ // 鼠标按下 var ev = ev || event; // 获取鼠标离div得距离 var mouseBoxleft = ev.clientX - this.offsetLeft; var mouseBoxTop = ev.clientY - this.offsetTop; document.onmousemove = function(ev){ // 鼠标按下左键并移动 var ev = ev || event; // 设置div移动时,它的位置 oBox.style.left = ev.clientX - mouseBoxleft + 'px'; oBox.style.top = ev.clientY - mouseBoxleft + 'px'; } document.onmouseup = function(){ // 鼠标左键抬起 document.onmousemove = document.onmouseup = null; } // 阻止默认行为 return false; } </script> </body> </html>
2、使用全局捕获(IE)
全局捕获:当我们给一个元素这只全局捕获后,改元素会监听后续发生的所有事件,当有事件发生的时候就会触发改元素的事件
代码:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> </head> <body> <input type="button" id="button1" value="弹出1" /> <input type="button" id="button2" value="弹出2" /> <script type="text/javascript"> window.onload = function(){ var Btn1 = document.getElementById('button1'); var Btn2 = document.getElementById('button2'); Btn1.setCapture(); Btn1.onclick = function(){ alert(1); } Btn2.onclick = function(){ alert(2); } } </script> </body> </html>
给Btn1设置了全局捕获之后,即使我们点击了Btn2还是会触发Btn1的点击事件
在模拟拖拽中,给要拖拽的方块onmousedown添加全局捕获然后再onmouseup中取消全局捕获
代码:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <style> #box{ width: 100px; height: 100px; background: red; position: absolute; } </style> </head> <body> <div id="box">模拟拖拽</div> <script> var oBox = document.getElementById('box'); oBox.onmousedown = function(ev){ // 鼠标按下 var ev = ev || event; // 获取鼠标离div得距离 var mouseBoxleft = ev.clientX - this.offsetLeft; var mouseBoxTop = ev.clientY - this.offsetTop; // IE浏览器,全局捕获 if(oBox.setCapture){ oBox.setCapture(); } document.onmousemove = function(ev){ // 鼠标按下左键并移动 var ev = ev || event; // 设置div移动时,它的位置 oBox.style.left = ev.clientX - mouseBoxleft + 'px'; oBox.style.top = ev.clientY - mouseBoxleft + 'px'; } document.onmouseup = function(){ // 鼠标左键抬起 document.onmousemove = document.onmouseup = null; //IE下,释放全局捕获 releaseCapture(); if ( oBox.releaseCapture ) { oBox.releaseCapture(); } } // 阻止默认行为 return false; } </script> </body> </html>
【3】封装模拟拖拽函数
代码:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <style> #box{ width: 100px; height: 100px; background: red; position: absolute; } </style> </head> <body> <div id="box">模拟拖拽</div> <script> var oBox = document.getElementById('box'); drag(oBox); function drag(obj){ obj.onmousedown = function(ev){ // 鼠标按下 var ev = ev || event; // 获取鼠标离div得距离 var mouseBoxleft = ev.clientX - this.offsetLeft; var mouseBoxTop = ev.clientY - this.offsetTop; // IE浏览器,全局捕获 if(obj.setCapture){ obj.setCapture(); } document.onmousemove = function(ev){ // 鼠标按下左键并移动 var ev = ev || event; // 设置div移动时,它的位置 obj.style.left = ev.clientX - mouseBoxleft + 'px'; obj.style.top = ev.clientY - mouseBoxleft + 'px'; } document.onmouseup = function(){ // 鼠标左键抬起 document.onmousemove = document.onmouseup = null; //IE下,释放全局捕获 releaseCapture(); if ( obj.releaseCapture ) { obj.releaseCapture(); } } // 阻止默认行为 return false; } } </script> </body> </html>
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