<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="someViewstategibberish"/></div><脚本语言='javascript'>var lbl = document.getElementById('lblDisplayDate');//因为 lbl 为空，所以在下一行抛出错误.lbl.style.color = '绿色';
因此，总而言之，如果您打算渲染函数定义，则应该调用后一种方法.然后，您可以使用前一种方法(或添加客户端属性)呈现 对该函数的调用.
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例如，下面的函数会起作用:
protected void btnPostBack2_Click(object sender, EventArgs e){System.Text.StringBuilder sb = new System.Text.StringBuilder();sb.Append("<脚本语言='javascript'>function ChangeColor() {");sb.Append("var lbl = document.getElementById('lblDisplayDate');");sb.Append("lbl.style.color='green';");sb.Append("}");//渲染函数定义.if (!ClientScript.IsClientScriptBlockRegistered("JSScriptBlock")){ClientScript.RegisterClientScriptBlock(this.GetType(), "JSScriptBlock", sb.ToString());}//渲染函数调用.string funcCall = "<脚本语言='javascript'>ChangeColor();</script>";if (!ClientScript.IsStartupScriptRegistered("JSScript")){ClientScript.RegisterStartupScript(this.GetType(), "JSScript", funcCall);}}
Is the only difference between the RegisterStartupScript and the RegisterClientScriptBlock is that RegisterStartupScript puts the javascript before the closing </form> tag of the page and RegisterClientScriptBlock puts it right after the starting <form> tag of the page?
Also, when would you choose one over the other? I wrote up a quick sample page where I had an issue and I am not sure the exact reason of why it is happening.
Hereistheaspxmarkup:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Label ID="lblDisplayDate" runat="server"
Text="Label" /><br />
<asp:Button ID="btnPostback" runat="server"
Text="Register Startup Script"
onclick="btnPostback_Click" /><br />
<asp:Button ID="btnPostBack2" runat="server"
Text="Register"
onclick="btnPostBack2_Click" />
</div>
</form>
</body>
</html>
HereistheCodeBehind:
protected void Page_Load(object sender, EventArgs e)
{
lblDisplayDate.Text = DateTime.Now.ToString("T");
}
protected void btnPostback_Click(object sender, EventArgs e)
{
System.Text.StringBuilder sb = new System.Text.StringBuilder();
sb.Append(@"<script language='javascript'>");
sb.Append(@"var lbl = document.getElementById('lblDisplayDate');");
sb.Append(@"lbl.style.color='red';");
sb.Append(@"</script>");
if(!ClientScript.IsStartupScriptRegistered("JSScript"))
{
ClientScript.RegisterStartupScript(this.GetType(),"JSScript",
sb.ToString());
}
}
protected void btnPostBack2_Click(object sender, EventArgs e)
{
System.Text.StringBuilder sb = new System.Text.StringBuilder();
sb.Append(@"<script language='javascript'>");
sb.Append(@"var lbl = document.getElementById('lblDisplayDate');");
sb.Append(@"lbl.style.color='red';");
sb.Append(@"</script>");
if (!ClientScript.IsClientScriptBlockRegistered("JSScriptBlock"))
{
ClientScript.RegisterClientScriptBlock(this.GetType(), "JSScriptBlock",
sb.ToString());
}
}
The problem is when I click the btnPostBack button, it does a postback and changes the label to red, but when I click the btnPostBack2, it does a postback, but the label color does not change to red. Why is this? Is it because the label is not initialized?
I also read that if you are using an UpdatePanel, you need to use ScriptManager.RegisterStartupScript, but if I have a MasterPage, would I use ScriptManagerProxy?
解决方案
Here's an old discussion thread where I listed the main differences and the conditions in which you should use each of these methods. I think you may find it useful to go through the discussion.
To explain the differences as relevant to your posted example:
a. When you use RegisterStartupScript, it will render your script after all the elements in the page (right before the form's end tag). This enables the script to call or reference page elements without the possibility of it not finding them in the Page's DOM.
Here is the rendered source of the page when you invoke the RegisterStartupScript method:
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1"><title></title></head>
<body>
<form name="form1" method="post" action="StartupScript.aspx" id="form1">
<div>
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="someViewstategibberish" />
</div>
<div> <span id="lblDisplayDate">Label</span>
<br />
<input type="submit" name="btnPostback" value="Register Startup Script" id="btnPostback" />
<br />
<input type="submit" name="btnPostBack2" value="Register" id="btnPostBack2" />
</div>
<div>
<input type="hidden" name="__EVENTVALIDATION" id="__EVENTVALIDATION" value="someViewstategibberish" />
</div>
<!-- Note this part -->
<script language='javascript'>
var lbl = document.getElementById('lblDisplayDate');
lbl.style.color = 'red';
</script>
</form>
<!-- Note this part -->
</body>
</html>
b. When you use RegisterClientScriptBlock, the script is rendered right after the Viewstate tag, but before any of the page elements. Since this is a direct script (not a function that can be called, it will immediately be executed by the browser. But the browser does not find the label in the Page's DOM at this stage and hence you should receive an "Object not found" error.
Here is the rendered source of the page when you invoke the RegisterClientScriptBlock method:
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1"><title></title></head>
<body>
<form name="form1" method="post" action="StartupScript.aspx" id="form1">
<div>
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="someViewstategibberish" />
</div>
<script language='javascript'>
var lbl = document.getElementById('lblDisplayDate');
// Error is thrown in the next line because lbl is null.
lbl.style.color = 'green';
Therefore, to summarize, you should call the latter method if you intend to render a function definition. You can then render the call to that function using the former method (or add a client side attribute).
Edit after comments:
For instance, the following function would work:
protected void btnPostBack2_Click(object sender, EventArgs e)
{
System.Text.StringBuilder sb = new System.Text.StringBuilder();
sb.Append("<script language='javascript'>function ChangeColor() {");
sb.Append("var lbl = document.getElementById('lblDisplayDate');");
sb.Append("lbl.style.color='green';");
sb.Append("}</script>");
//Render the function definition.
if (!ClientScript.IsClientScriptBlockRegistered("JSScriptBlock"))
{
ClientScript.RegisterClientScriptBlock(this.GetType(), "JSScriptBlock", sb.ToString());
}
//Render the function invocation.
string funcCall = "<script language='javascript'>ChangeColor();</script>";
if (!ClientScript.IsStartupScriptRegistered("JSScript"))
{
ClientScript.RegisterStartupScript(this.GetType(), "JSScript", funcCall);
}
}
这篇关于RegisterStartupScript 和 RegisterClientScriptBlock 之间的区别?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！
