ASP.NET AJAX Advance Tips & Tricks (9) DropDownList在Firefox下的奇怪现象和解决方案——谁的BUG？
前言：
今天在ASP.NET Forum里面遇到了一个及其怪异的问题，一个看似非常简单的demo在IE及其它浏览器中正常运行，然而在Firefox中却导致了奇怪的问题，使页面中的DropDownList死掉，经过研究，终于找到了一个解决方案，但此问题是谁的Bug仍不得而知。
问题重现：
一个ScriptManager
一个DropDownList
一个UpdatePanel，内有一个Button
在按钮点击事件中使用ScriptManager.RegisterStartupScript来输出一个window.alert
OK，够简单吧？！代码如下：
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e) { }
protected void Button1_Click(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this.Button2, Button2.GetType(), "CodeAlert", "alert('kao!');", true);
Button2.Text = "Updated " + DateTime.Now.ToString();
}
</script>
<html>
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
</div>
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem>Text1</asp:ListItem>
<asp:ListItem>Text2</asp:ListItem>
<asp:ListItem>Text3</asp:ListItem>
<asp:ListItem>Text4</asp:ListItem>
<asp:ListItem>Text5</asp:ListItem>
</asp:DropDownList>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button ID="Button2" runat="server" Text="Button" OnClick="Button1_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</form>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e) { }
protected void Button1_Click(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this.Button2, Button2.GetType(), "CodeAlert", "alert('kao!');", true);
Button2.Text = "Updated " + DateTime.Now.ToString();
}
</script>
<html>
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
</div>
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem>Text1</asp:ListItem>
<asp:ListItem>Text2</asp:ListItem>
<asp:ListItem>Text3</asp:ListItem>
<asp:ListItem>Text4</asp:ListItem>
<asp:ListItem>Text5</asp:ListItem>
</asp:DropDownList>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button ID="Button2" runat="server" Text="Button" OnClick="Button1_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</form>
</body>
</html>
好！接下来，在IE浏览器中，结果就不用说了，非常正常。 让我们来看看在Firefox中的神奇现象：
大家可以看到，在按钮点击之后，我点击DropDownList，却发现不能选择想要的Item了！再点——下拉列表框根本就不出来了！
这时候，如果在页面上 右键——查看网页源码，关掉源码窗口，再回来试试——一切又恢复了正常。。。
Trouble Shooting
将RegisterStartupScript换成RegisterClientScriptBlock，问题依然如故。
调用其它JavaScript方法（非window.alert）则不会出现此问题。
解决方案
既然调用其它JavaScript方法（非window.alert）则不会出现此问题，那么我们试着用window.SetTimeout来间接执行alert：
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e) { }
protected void Button1_Click(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this.Button2, Button2.GetType(), "CodeAlert", "window.setTimeout(\"alert('Your code is expired at " + DateTime.Now.ToString() + "')\",0);", true);
Button2.Text = "Updated " + DateTime.Now.ToString();
}
</script>
<html>
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
</div>
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem>Text1</asp:ListItem>
<asp:ListItem>Text2</asp:ListItem>
<asp:ListItem>Text3</asp:ListItem>
<asp:ListItem>Text4</asp:ListItem>
<asp:ListItem>Text5</asp:ListItem>
</asp:DropDownList>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button ID="Button2" runat="server" Text="Button" OnClick="Button1_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</form>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e) { }
protected void Button1_Click(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this.Button2, Button2.GetType(), "CodeAlert", "window.setTimeout(\"alert('Your code is expired at " + DateTime.Now.ToString() + "')\",0);", true);
Button2.Text = "Updated " + DateTime.Now.ToString();
}
</script>
<html>
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
</div>
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem>Text1</asp:ListItem>
<asp:ListItem>Text2</asp:ListItem>
<asp:ListItem>Text3</asp:ListItem>
<asp:ListItem>Text4</asp:ListItem>
<asp:ListItem>Text5</asp:ListItem>
</asp:DropDownList>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button ID="Button2" runat="server" Text="Button" OnClick="Button1_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</form>
</body>
</html>
测试，在Firefox下终于正常了。
疑惑
至于为什么会有这样的现象，是Firefox的bug还是ASP.NET AJAX的bug，仍不得而知...
