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H5 Tutorial
Detailed explanation of html5 image upload supports image preview compression and progress display. Compatible with IE6 and standard browsers.
Detailed explanation of html5 image upload supports image preview compression and progress display. Compatible with IE6 and standard browsers.
以前写过上传组件，见 打造 html5 文件上传组件，实现进度显示及拖拽上传，兼容IE6+及其它标准浏览器，对付一般的上传没有问题，不过如果是上传图片，且需要预览的话，就力有不逮了，趁着闲暇时间，给上传组件添加了单独的图片上传UI，支持图片预览和缩放（通过调整图片的大小以实现图片压缩）。
v1.4版本已支持秒传+分片上传+断点续传（IE10+、其它标准浏览器），具体请参考Github代码。
上传组件特点
轻量级，不依赖任何JS库，核心代码（Q.Uploader.js）仅约700行，min版本加起来不到12KB
纯JS代码，无需Flash，无需更改后台代码即可实现带进度条（IE10+、其它标准浏览器）的上传，其它（eg：IE6+）自动降级为传统方式上传
单独的图片上传UI，支持图片预览（IE6+、其它浏览器）和缩放（IE10+、其它浏览器）
上传核心与UI界面分离，可以很方便的定制上传界面包括上传按钮
上传文件的同时可以指定上传参数，支持上传类型过滤
完善的事件回调，可针对上传的每个过程进行单独处理
方便的UI接口，上传界面可以随心所欲的定制
效果如上图。由于浏览器不同，压缩效果各有不同，一个1.1MB、分辨率为 1920x1200 的图片，分辨率缩放为 1024x640 ,IE11上传后为199KB，Chrome45上传后为277KB，Firefox41上传后为360KB。
使用代码
html代码，导入样式及js上传组件，定义上传按钮及视图：
<link href="../css/uploader-image.css" rel="stylesheet" type="text/css" /><p>
<a id="upload-target" class="x-button">添加图片并上传</a>
</p>
<p id="upload-view">
</p>
<script type="text/javascript" src="../Q.Uploader.image.all.js"></script>js组件调用：
var uploader = new Q.Uploader({
url: "api/upload.ashx",
target: document.getElementById("upload-target"),
view: document.getElementById("upload-view"), //auto: false,
//图片缩放 scale: { //要缩放的图片格式
types: ".jpg", //最大图片大小(width|height)
maxWidth: 1024
}
});//uploader.start();一般无需更改后台代码，但如果使用了图片缩放（压缩），Firefox、Chrome 较早的版本上传后，后台可能会获取不到文件名，需要略微处理一下。以asp.net为例：
HttpRequest request = context.Request;int c = request.Files.Count;
//接收上传的数据并保存到服务器
for (int i = 0; i < c; i++)
{
HttpPostedFile file = request.Files[i];
//为兼容一些较早的浏览器，此处优先使用上传组件传递的文件名
string fileName = request["fileName"];
if (string.IsNullOrEmpty(fileName)) fileName = System.IO.Path.GetFileName(file.FileName);
string path = context.Server.MapPath("~/upload/" + fileName);
file.SaveAs(path);
}关于上传
参见 打造 html5 文件上传组件，实现进度显示及拖拽上传，兼容IE6+及其它标准浏览器
关于预览
IE10+等浏览器使用html5 api，其它浏览器使用滤镜预览。需要注意的是，IE8+由于安全性考虑，会获取不到文件真实地址，需要特殊处理一下。
//生成图片预览地址(html5)function readAsURL(file, callback) {
var URL = window.URL || window.webkitURL;
if (URL) return callback(URL.createObjectURL(file));
if (window.FileReader) {
var fr = new FileReader();
fr.onload = function (e) {
callback(e.target.result);
};
fr.readAsDataURL(file);
} else if (file.readAsDataURL) {
callback(file.readAsDataURL());
}
}//图片预览function previewImage(box, task, callback) {
var input = task.input,
file = task.file || (input.files ? input.files[0] : undefined);
if (file) {
//IE10+、Webkit、Firefox etc
readAsURL(file, function (src) {
if (src) box.innerHTML = '<img src="' + src + '" />';
callback && callback(src);
});
} else if (input) {
var src = input.value;
if (!src || /^\w:\\fakepath/.test(src)) {
input.select();
//解决ie报拒绝访问的问题
parent.document.body.focus();
//获取图片真实地址
if (document.selection) src = document.selection.createRange().text;
} if (src) {
box.innerHTML = '<img src="' + src + '" />';
try {
if (browser_ie > 6)
box.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale',src='" + src + "')";
} catch (e) { }
}
callback && callback(src);
}
}关于缩放（压缩）
原理是先通过canvas调整图片大小，生成base64数据，然后再通过html5 api （Blob） 转换为二进制对象上传。
//将dataURL转为Blob对象，以用于ajax上传
function dataURLtoBlob(base64, mimetype) {
var ds = base64.split(','),
data = atob(ds[1]),
arr = [];
for (var i = 0, len = data.length; i < len; i++) {
arr[i] = data.charCodeAt(i);
} if (Blob) return new Blob([new Uint8Array(arr)], { type: mimetype });
var builder = new BlobBuilder();
builder.append(arr);
return builder.getBlob(mimetype);
}//图片缩放function scaleImage(src, mimetype, ops, callback) {
var image = new Image();
image.src = src;
image.onload = function () {
var width = image.width,
height = image.height,
maxWidth = ops.maxWidth,
maxHeight = ops.maxHeight,
hasWidthScale = maxWidth && width > maxWidth,
hasHeightScale = maxHeight && height > maxHeight,
hasScale = hasWidthScale || hasHeightScale;
//无需压缩
if (!hasScale) return callback && callback(false);
//根据宽度缩放
if (hasWidthScale) {
width = maxWidth;
height = Math.floor(image.height * width / image.width);
} //根据高度缩放
if (hasHeightScale) {
height = maxHeight;
width = Math.floor(image.width * height / image.height);
} var canvas = document.createElement("canvas"),
ctx = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;
ctx.drawImage(image, 0, 0, width, height);
callback && callback(canvas.toDataURL(mimetype), mimetype);
};
}相关文章：
JavaScript进阶(八)JS实现图片预览并导入服务器功能
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