的getElementById没有找到控制由ASP.net产生 [英] getElementById not finding control generated by ASP.net

问题描述

我只是想存储在JavaScript，但由于某种原因，这是不以的document.getElementById（'控制'）的工作变量的标签; 。我知道我的JavaScript是链接到我的html文件很好，因为一切工作的。

I am simply trying to store a label in a variable in javascript but for some reason this isn't working with document.getElementById('control');. I know my javascript is linking to my html file fine because everything else works.

下面是我的javascript code：

Here is my javascript code:

function performEvapCooledCircuit(txt)
{
    var error = document.getElementById('lblError');


    if (txt.value == null || isNaN(txt.value))
    {
       error.style.visibility = "visible";
    }
}

下面是HTML code为我的标签：

Here is the html code for my label:

<asp:Label ID="lblError" class="NormLabel" runat="server" 
   style="color:red; visibility:hidden;" Text="Invalid Input."></asp:Label>

我收到，说对象预期??

I am getting an error that says object expected??

推荐答案

在的ID ASP.NET会产生不会是lblError所以你需要通过它的客户端ID

The ID that ASP.NET will generate will not be "lblError" so you'll need to reference it by its ClientID

document.getElementById('<%=lblError.ClientID %>');

---

如果您的JavaScript文件是外部的，我通常已经不得不写一个类型的初始化的JavaScript方法，以确保我的ID分别设置属性。

---

If your javascript file is external I've usually had to write a type of "Init" javascript method to make sure my ID's were set up property

在您的ASPX页面：

<script type="text/javascript">
    var lblError = null;
    function InitializeVariables()
    {
        if (lblError == null) // make sure you only do this once
        {
            lblError = document.getElementById("<%=lblError.ClientID %>");
        }
    }
</script>
<asp:Label 
    ID="lblError"
    class="NormLabel"
    runat="server" 
    style="color:red; visibility:hidden;"
    Text="Invalid Input."></asp:Label>

然后在您的JavaScript文件中，你必须调用 InitializeVariables（），以确保你有指向正确的asp.net控制变量

Then in your javascript file you'll have to call InitializeVariables() to make sure you've got the variables pointing to the proper asp.net controls

function performEvapCooledCircuit(txt)
{
    InitializeVariables();

    if (txt.value == null || isNaN(txt.value))
    {
        lblError.style.visibility = "visible";
    }
}

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