无法将类型'string'隐式转换为'System.Web.UI.WebControls.DropDownList' [英] Cannot implicitly convert type 'string' to 'System.Web.UI.WebControls.DropDownList'

问题描述

尝试发送包含文档名称的邮件，然后选择从下拉列表中选择的管理员，例如批准/拒绝/待定，我尝试此代码

TRYING TO SEND mail with document name and then value which admin select from dropdown like approve/reject/pending for this i try this code

Label DocName = ((Label)Repeater2.Items[i].FindControl("DocName"));
DropDownList dropdownvalue =(DropDownList)Repeater2.Items[i].FindControl("lblvalue"));
Label Label2 = ((Label)Repeater2.Items[i].FindControl("Label2"));
string docname = String.Empty;
string dropdownvalues = String.Empty;
string emailId = String.Empty;

if (DocName.Text.ToString() != ""){
    docname = DocName.Text.ToString();
}else{
    docname = "Unavailable";
}

if (dropdownvalue.SelectedItem.ToString() != ""){
    dropdownvalues = dropdownvalue.SelectedItem.ToString();
}else{
    dropdownvalue = "Unavailable";
}

HTML：

HTML:

<td> 
  <asp:Label ID="lblvalue" runat="server" Text='<%# Eval("ApproveID") %>' Visible = "false" /> 
  <asp:DropDownList ID="DropDownList4" runat="server" EnableViewState="true" class="vpb_dropdown" DataTextField="ApproveType" DataValueField="ApproveID" AutoPostBack="true" OnSelectedIndexChanged="DropDownList4_SelectedIndexChanged">
    <asp:ListItem Text="Pending" selected="selected" Value="3">
    </asp:ListItem> 
    <asp:ListItem Text="Approve" Value="1">
    </asp:ListItem>
    <asp:ListItem Text="Reject" Value="2">
    </asp:ListItem> 
  </asp:DropDownList> 
</td>

但此处出现在此代码中

but here occurs in this code

dropdownvalue = "Unavailable";

Error Cannot implicitly convert type 'string' to 'System.Web.UI.WebControls.DropDownList'

推荐答案

您的名为dropdownvalue的名称为DropDownList，不能为其指定字符串。你的意思是

Your inaptly named "dropdownvalue" is of type DropDownList which cannot be assigned a string. Did you mean

dropdownvalue.SelectedItem.Value = "2" // Reject

在你的DropDownList4中（同样，它有一个更好的名字，比如DropDownApprovalStatus）可能的值为1,2和3，对应于Approve，Reject和Pending。我看不到不可用...

In your DropDownList4 (again, can this have a better name, like DropDownApprovalStatus) has possible values of 1, 2 and 3 corresponding to "Approve", "Reject" and "Pending". I cannot see "Unavailable"...

dropdownvalue 是一个DropDownList对象。你不能给它分配一个字符串，这将毫无意义。

你实际上要做的是更改控件上显示的 .Text ，所以尝试类似......

dropdownvalue is a DropDownList object. You can't assign a string to it, that would be meaningless.
What you are actually trying to do is change the .Text displayed on the control, so try something like ...

dropdownvalue.Text = "Unavailable"

。

注意这仅在控件上的项目列表中已有不可用时才有效。如果它不在那里你将不得不添加它。



我认为意味着做的是说

.
Note this will only work if "Unavailable" is already in the list of items on the control. If it isn't there you will have to add it.

What I think you meant to do was say

dropdownvalues = "Unavailable";

dropdownvalue的类型是DropDownList。所以你不能将字符串设置为dropdownlist。

我认为你使用了错误的变量。

试试这个

Type of dropdownvalue is DropDownList. So you can not set string to dropdownlist.
I think you user wrong variable.
Try this

if (dropdownvalue.SelectedItem.ToString() != ""){
    dropdownvalues = dropdownvalue.SelectedItem.ToString();
}else{
    dropdownvalues = "Unavailable";
}

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