ClientScript.RegisterClientScriptBlock - 无法设置属性'className'的值：对象为空或未定义

Question

我在我的C＃代码（使用webforms）中有IF/ELSE条件，我想使用ClientScript.RegisterClientScriptBlock更改锚标签类

email = Business.Core.Profiles.Email.SetEmailAlertProfile(base.companyId, type); 

// Email obj == null means no alert data for advertiser with this ID. 
if (email == null) 
    { 
     EmailAction = "add"; 
     lblEmailText.Text = "Add to Email Alerts"; 
     //Change Anchor class to show remove image 
     //ClientScript.RegisterClientScriptBlock(typeof(string), "ChangeAnchorClass", "<script>$('.jsPopUp btnAddEList active').addClass('jsPopUp btnRemoveEList active');</script>"); 
    } 
else 
    { 
     EmailAction = "delete"; 
     lblEmailText.Text = "Remove from Emails"; 
     //Change Anchor class to show remove image 
     ClientScript.RegisterClientScriptBlock(typeof(string), "ChangeAnchorClass", "<script>document.getElementById('hrefEmail').className = 'MyClass';</script>"); 

    } 

我ELSE条件使我有以下错误：

Microsoft JScript runtime error: Unable to set value of the property 'className': object is null or undefined 

我已经使用客户端脚本在我的项目在其他地方，但它不是在这里工作。

附加信息：

此代码位于页面加载时调用的方法中。不知道这是否有所作为。

Answer 1

我改变了这一点：

else 
    { 
     EmailAction = "delete"; 
     lblEmailText.Text = "Remove from Emails"; 
     //Change Anchor class to show remove image 
     ClientScript.RegisterClientScriptBlock(typeof(string), "ChangeAnchorClass", "<script>document.getElementById('hrefEmail').className = 'MyClass';</script>"); 

    } 

要这样：

else 
    { 
     EmailAction = "delete"; 
     lblEmailText.Text = "Remove from Emails"; 
     //Change Anchor class to show remove image 
     ClientScript.RegisterStartupScript(typeof(string), "ChangeAnchorClass", "<script>document.getElementById('hrefEmail').className = 'MyClass';</script>"); 

    }