ASP.NET服务器控件PleaseWaitButton[翻译]

",
                                this.ClientID));
    output.Write("

tag of its own
    output.Write(string.Format("");
}
　　这种把button还原成一个字符串缓冲然后处理它的onclick内容的技术是一件很危险的事情（is certainly a hack）. 但它可以让我们在父button类中实施标准的验证代码，然后再实现我们的PleaseWait() Javascript函数调用。如果不这样做，我们只能在验证代码之前就在onclick属性中实施我们的PleaseWait()函数调用，除非我们愿意完全重写父Button类的属性的呈现。这样就算页面上有输入错误也会产生我们并不希望的按钮隐藏和显示"please wait"信息的效果。因此，我们必须在onclick句柄中强行令我们的客户端PleaseWait()函数出现在客户端页面验证之后。
　　onclick属性的修改发生在ModifyJavaScriptOnClick()函数中。这个函数获取按钮呈现的HTML字符串，并检查看是否存在onclick属性。如果是，这个函数会检查是否有使用客户端验证代码。如果是这种情况的话，我们定义的PleaseWait()函数会加在已经存在的onclick代码的最后面，紧跟在客户端检查的boolin变量Page_IsValid后面。这个变量代表是否使用了验证控件。如果Page_IsValid的值是false，"Please wait"信息将不显示。如果为True则显示。
private string ModifyJavaScriptOnClick(string sHtml)
{
    // Thanks to CodeProject member KJELLSJ (Kjell-Sverre Jerijaervi)
    // for code ideas to allow the button to work with client-side validation

    string sReturn = "";
    string sPleaseWaitCode = GeneratePleaseWaitJavascript();

    // is there an existing onclick attribute?
    Regex rOnclick = new Regex("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