回顾下JS里的resize属性。
比如我用canvas绘制了一个chart,当canvas的size发生变化的时候,需要重新绘制里面的内容,这个时候就需要监听resize事件做处理。
window上虽然可以添加resize事件监听,但这并不能满足我们的需求,因为很多时候,div的size发生了变化,但是window的size并没有改变。
不过我们可以间接利用window的resize事件监听来实现对于某个div的resize事件监听,请看下面具体实现。
对于div的resize事件的监听,实现方式有很多,比如周期性检查,通过scroll事件等等,本文主要介绍通过object元素来实现监听。
测试代码:
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Resize</title> <style> html, body { margin: 0; padding: 0; width: 100%; height: 100%; } #resizeDiv { width: 60%; height: 60%; border: 1px solid red; margin: 20px; } button { margin: 20px 20px 0; } </style> </head> <body> <button onclick="addListener()">addListener</button> <button onclick="removeListener()">removeListener</button> <button onclick="resize()">resize</button> <div id="resizeDiv"></div> <script> var EleResize = { _handleResize: function (e) { var ele = e.target || e.srcElement; var trigger = ele.__resizeTrigger__; if (trigger) { var handlers = trigger.__z_resizeListeners; if (handlers) { var size = handlers.length; for (var i = 0; i < size; i++) { var h = handlers[i]; var handler = h.handler; var context = h.context; handler.apply(context, [e]); } } } }, _removeHandler: function (ele, handler, context) { var handlers = ele.__z_resizeListeners; if (handlers) { var size = handlers.length; for (var i = 0; i < size; i++) { var h = handlers[i]; if (h.handler === handler && h.context === context) { handlers.splice(i, 1); return; } } } }, _createResizeTrigger: function (ele) { var obj = document.createElement('object'); obj.setAttribute('style', 'display: block; position: absolute; top: 0; left: 0; height: 100%; width: 100%; overflow: hidden;opacity: 0; pointer-events: none; z-index: -1;'); obj.onload = EleResize._handleObjectLoad; obj.type = 'text/html'; ele.appendChild(obj); obj.data = 'about:blank'; return obj; }, _handleObjectLoad: function (evt) { this.contentDocument.defaultView.__resizeTrigger__ = this.__resizeElement__; this.contentDocument.defaultView.addEventListener('resize', EleResize._handleResize); } }; if (document.attachEvent) {//ie9-10 EleResize.on = function (ele, handler, context) { var handlers = ele.__z_resizeListeners; if (!handlers) { handlers = []; ele.__z_resizeListeners = handlers; ele.__resizeTrigger__ = ele; ele.attachEvent('onresize', EleResize._handleResize); } handlers.push({ handler: handler, context: context }); }; EleResize.off = function (ele, handler, context) { var handlers = ele.__z_resizeListeners; if (handlers) { EleResize._removeHandler(ele, handler, context); if (handlers.length === 0) { ele.detachEvent('onresize', EleResize._handleResize); delete ele.__z_resizeListeners; } } } } else { EleResize.on = function (ele, handler, context) { var handlers = ele.__z_resizeListeners; if (!handlers) { handlers = []; ele.__z_resizeListeners = handlers; if (getComputedStyle(ele, null).position === 'static') { ele.style.position = 'relative'; } var obj = EleResize._createResizeTrigger(ele); ele.__resizeTrigger__ = obj; obj.__resizeElement__ = ele; } handlers.push({ handler: handler, context: context }); }; EleResize.off = function (ele, handler, context) { var handlers = ele.__z_resizeListeners; if (handlers) { EleResize._removeHandler(ele, handler, context); if (handlers.length === 0) { var trigger = ele.__resizeTrigger__; if (trigger) { trigger.contentDocument.defaultView.removeEventListener('resize', EleResize._handleResize); ele.removeChild(trigger); delete ele.__resizeTrigger__; } delete ele.__z_resizeListeners; } } } } </script> <script> var resizeDiv = document.getElementById('resizeDiv'); function resize() { resizeDiv.style.width = "200px"; } var listener = function () { console.log("resize"); }; function addListener() { EleResize.on(resizeDiv, listener); } function removeListener() { EleResize.off(resizeDiv, listener) } </script> </body> </html>
这里的具体实现分两类,
ie9-10
默认支持div的resize事件,可以直接通过div.attachEvent('onresize', handler);的方式实现
其它浏览器
通过在div中添加一个内置object元素实现监听。
设置object元素的style使其填充满div,这样当div的size发生变化时,object的size也会发生变化。
然后监听object元素的contentDocument.defaultView(window对象)的resize事件。
注:本文提供的是如何监听resize事件,其实在resize时,可能会连续快速的触发(比如拖动浏览器),为了提高效率,可以考虑使用批处理的模式。
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