How It Works
PleaseWaitButton控件在
protected override void Render(HtmlTextWriter output)
{
// Output the button's html (with attributes)
// to a dummy HtmlTextWriter
StringWriter sw = new StringWriter();
HtmlTextWriter wr = new HtmlTextWriter(sw);
base.Render(wr);
string sButtonHtml = sw.ToString();
wr.Close();
sw.Close();
// now modify the code to include an "onclick" handler
// with our PleaseWait() function called appropriately
// after any client-side validation.
sButtonHtml = ModifyJavaScriptonClick(sButtonHtml);
// before rendering the button, output an empty
// render the button in an encapsulating
string sReturn = "";
string sPleaseWaitCode = GeneratePleaseWaitJavascript();
// is there an existing onclick attribute?
Regex ronclick = new Regex("onclick=\"(?<onclick>[^\"]*)");
Match monclick = ronclick.Match(sHtml);
if (monclick.Success)
{
// there is an existing onclick attribute;
// add our code to the end of it; if client-side
// validation has been rendered, make sure
// we check to see if the page is valid;
string sExisting = monclick.Groups["onclick"].Value;
string sReplace = sExisting
+ (sExisting.Trim().EndsWith(";") ? "" : "; ");
if (IsValidatorIncludeScript() && this.CausesValidation)
{
// include code to check if the page is valid
string sCode = "if (Page_IsValid) " + sPleaseWaitCode
+ " return Page_IsValid;";
// add our code to the end of the existing onclick code;
sReplace = sReplace + sCode;
}
else
{
// don't worry about the page being valid;
sReplace = sReplace + sPleaseWaitCode;
}
// now substitute our onclick code
sReplace = "onclick=\"" + sReplace;
sReturn = ronclick.Replace(sHtml, sReplace);
}
else
{
// there isn't an existing onclick attribute;
// add ours
int i = sHtml.Trim().Length - 2;
string sInsert = " onclick=\"" + sPleaseWaitCode + "\" ";
sReturn = sHtml.Insert(i, sInsert);
}
return sReturn;
}
这个IsValidatorIncludeScript() 利用上面的检查来查看是否有使用页面注册的asp.net验证控件的标准Javascript代码块。下面则用一个简单的方法测试了是否有验证代码和像Page_IsValid的变量存在。
private bool IsValidatorIncludeScript()
{
// return TRUE if this page has registered javascript
// for client-side validation; this code may not be registered
// if ASP.NET detects what it thinks (correctly or incorrectly)
// is a down-level browser.
return this.Page.IsStartupScriptRegistered("ValidatorIncludeScript");
} 下面这个GeneratePleaseWaitJavascript()构建了包含在onclick属性中的PleaseWait() Javascript函数。我们可以通过检查控件的属性来决定想要的布局。
private string GeneratePleaseWaitJavascript()
{
// create a JavaScript "PleaseWait()" function call
// suitable for use in an onclick event handler
string sMessage = "";
string sText = _pleaseWaitText;
string sImage = (_pleaseWaitImage != String.Empty
? string.Format(
""
, _pleaseWaitImage, _pleaseWaitText )
: String.Empty);
// establish the layout based on PleaseWaitType
switch (_pleaseWaitType)
{
case PleaseWaitTypeEnum.TextThenImage:
sMessage = sText + sImage;
break;
case PleaseWaitTypeEnum.ImageThenText:
sMessage = sImage + sText;
break;
case PleaseWaitTypeEnum.TextOnly:
sMessage = sText;
break;
case PleaseWaitTypeEnum.ImageOnly:
sMessage = sImage;
break;
}
// return the final code chunk
string sCode = string.Format(
"PleaseWait('pleaseWaitButtonDiv_{0}',
'pleaseWaitButtonDiv2_{1}', '{2}');"
, 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("");
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
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
原文链接:http://www.codeproject.com/aspnet/PleaseWaitButton.asp