MSDN文档中的一个不那么和谐的示例
最近写网站用到FileUpload控件,好长时间不用手生了,所以特地又仔细地看了一遍MSDN文档。在看到其FileBytes属性时,看到其中的示例代码,颇感郁闷。
// 后面有给dudu的附言,如果有幸dudu莅临,请阅
感觉其中有不少问题,虽然很细微,但出现在MSDN中,总感却不那么和谐。
下面是完整的示例。
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问题1
注释中的1.1、1.2、1.3
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在这里,DisplayFileContents方法接受一个HttpPostedFile类型的参数file,表示从FileUpload控件上传的文件。的确,在1.3处将FileUpload1.PostedFile属性传了进来。
先往复杂了说,从方法的名字和参数可以猜想,作者的目的是降低显示文件内容的操作和FileUpload控件的耦合度。比如,如果页面上有多个FileUpload控件时,就可以重用该方法;或者如果不使用FileUpload控件了,而是用了自己编写的上传控件,只要能提供HttpPostedFile类型的对象,也可以使用该方法。但1.1和1.2两个地方颠覆了这个初衷,这个方法还是紧紧地与FileUpload1控件紧紧地关联在了一起。如果添加了另外一个FileUpload控件,或者原控件改名了,这个方法必须同时修改。
再往简单了说,整个方法体都没有用到过这个file参数,又何必添加呢?
问题2
注释中的2
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这是一个比较严重的内存泄露问题。首先,之前的一行byte[] input = new byte[fileLen];在堆上分配了与文件大小相同的字节数组(注意数组都是引用类型),然后input = FileUpload1.FileBytes;直接修改了input变量所引用的对象,而原来new byte[fileLen]得到的数组成了孤立对象,遗留在堆中等待被回收。
试想如果这个代码出现在产品中,如果允许用户数MB甚至更大的文件,如果同时(或很短一段时间内)有数百甚至更多的人上传文件……
改进方法:1 直接使用FileUpload1.FileBytes属性,或者直接作这样的赋值:byte[] input = FileUpload1.FileBytes,然后使用input变量;2 如果有必要用一个数组的话,写一个循环将FileUpload1.FileBytes的内容复制到input中。
问题3
注释中的3
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这也是一个比较严重的问题,但我就不用多说了,几乎提到了字符串操作的每篇技术文章或每本书都提到,慎用字符串的相加(连接)操作,尤其是在循环内部。
问题4
注释中的4
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这是一个小问题,主要在于用户体验。每上传一次就要创建一个文本框显示文件内容,并且文本框是在服务器端添加的,刷新页面也无法消除。这样的话,如果用户查看了几个文件的内容后,要想清空页面,只有关闭浏览器重新打开,这样的用户体验是非常不好的。实际上,硬编码一个文本框,每次修改其Text属性即可。
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实际上,对于示例代码来说,问题1和4无伤大雅,毕竟受众所关心的是如何通过FileBytes得到文件中的字节。但问题2和3些许有些“误人子弟”(如果有人直接像这样读取文件字节,那就得浪费fileLen个字节的内存,如果有n个人用这个功能,那就得浪费n*fileLen个字节,你付得起责任吗?——小学老师如是教育)。而如果是在产品中,这4个问题恐怕都会产生不良后果。
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P.S.
to dudu:
园子的回复下面有一个“刷新评论列表”,实在是个好东西。
但有个问题,就是如果一篇文章一条回复也没有的话,这个链接是不会出现的。
可如果我在浏览一个 尚没有回复的文章 时,希望刷一下看看有没有人在我浏览的时候发表了回复,那就只有刷新页面了。
所以,能否改进一下,让这个链接任何时候都能出现?
小问题,呵呵~