ASP.NET服务器控件PleaseWaitButton[翻译](3)

, this.ClientID, this.ClientID, sMessage);
sCode = sCode.Replace("\"", """);

return sCode;
}
　　如果指定了一个PleaseWaitImage，就必须包含额外的一段Javascript代码来通知客户端预载该图像。这段脚本的注册应该出现在重写的OnPreRender方法中。注册的键是图像的名称；如果多个按钮都使用同一图像，预载脚本只需要实施一次。这里使用了一个正则表达式来创建Javascript图像变量，以保证特殊字字符（比如文件路径中的斜线）转化成下划线。

protected override void OnPreRender(EventArgs e)
{
base.OnPreRender (e);

// If we're using an image, register some javascript
// for client-side image preloading
if (_pleaseWaitImage != String.Empty
&& _pleaseWaitType != PleaseWaitTypeEnum.TextOnly)
RegisterJavascriptPreloadImage(_pleaseWaitImage);
}

private void RegisterJavascriptPreloadImage(string sImage)
{
Regex rex = new Regex("[^a-zA-Z0-9]");
string sImgName = "img_" rex.Replace(sImage, "_");

StringBuilder sb = new StringBuilder();
sb.Append("<script language='JavaScript'>");
sb.Append("if (document.images) { ");
sb.AppendFormat("{0} = new Image();", sImgName);
sb.AppendFormat("{0}.src = \"{1}\";", sImgName, sImage);
sb.Append(" } ");
sb.Append("</script>");

this.Page.RegisterClientScriptBlock(sImgName "_PreloadScript",
sb.ToString());
}

Client-side functions

　　嵌入的文本文件javascript.txt包含了隐藏按钮的<div>和显示"please wait"信息或图像的客户端代码。这些代码在重写的OnInit()方法中调用的私有方法RegisterJavascriptFromResource()加载。这个方法调用泛型方法GetEmbeddedTextFile() ，在这个泛型方法中把文件做为源加载而把内容返回成字符串。

protected override void OnInit(EventArgs e)
{
base.OnInit(e);

// the client-side javascript code is kept
// in an embedded resource; load the script
// and register it with the page.
RegisterJavascriptFromResource();
}

private void RegisterJavascriptFromResource()
{
// load the embedded text file "javascript.txt"
// and register its contents as client-side script
string sScript = GetEmbeddedTextFile("javascript.txt");
this.Page.RegisterClientScriptBlock("PleaseWaitButtonScript", sScript);
}

private string GetEmbeddedTextFile(string sTextFile)
{
// generic function for retrieving the contents
// of an embedded text file resource as a string

// we'll get the executing assembly, and derive
// the namespace using the first type in the assembly
Assembly a = Assembly.GetExecutingAssembly();
String sNamespace = a.GetTypes()[0].Namespace;

// with the assembly and namespace, we'll get the
// embedded resource as a stream
Stream s = a.GetManifestResourceStream(
string.Format("{0}.{1}", sNamespace, sTextFile)
);

// read the contents of the stream into a string
StreamReader sr = new StreamReader(s);
String sContents = sr.ReadToEnd();

sr.Close();
s.Close();

return sContents;
}
　　javascript.txt嵌入资源包含了按钮在Javascript的onclick句柄中执行的客户端方法PleaseWait()。这段代码也调用了一个客户端方法HideDiv()以隐藏按钮的容器<div>，然后通过设置innerHTML属性把信息或图像组装进之前空的<div>标记中。辅助函数GetDiv()则是通过检查document.getElementById, document.all, 和 document.layers用id返回一个<div>对象，保证了不同浏览器的兼容性。下面是javascript.txt的全部代码：
<script language="JavaScript">
function GetDiv(sDiv)
{
var div;
if (document.getElementById)
div = document.getElementById(sDiv);
else if (document.all)
div = eval("window." sDiv);
else if (document.layers)
div = document.layers[sDiv];
else
div = null;

return div;
}

function HideDiv(sDiv)
{
d = GetDiv(sDiv);
if (d)
{
if (document.layers) d.visibility = "hide";
else d.style.visibility = "hidden";
}
}

function PleaseWait(sDivButton, sDivMessage, sInnerHtml)
{
HideDiv(sDivButton);
var d = GetDiv(sDivMessage);
if (d) d.innerHTML = sInnerHtml;
}
</script>

原文链接：http://www.codeproject.com/aspnet/PleaseWaitButton.asp
Download Source Project - 7 Kb
Download Demo Project - 30 Kb

http://www.cnblogs.com/jeffamy/archive/2006/08/20/481952.html

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