不能隱式轉換類型'字符串'爲'System.Web.UI.WebControls.DropDownList'

Question

試着發送帶有文檔名稱的郵件，然後確定哪些管理員從下拉列表中選擇，如批准/拒絕/待定 爲此，我嘗試此代碼

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：

<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> 

但在這裏，發生在這個代碼

dropdownvalue = "Unavailable"; 

錯誤 無法隱式轉換類型「字符串」到「System.Web.UI.WebControls.DropDownList」

Answer 1

你的錯誤是，在你的HTML lblvalue是一個標籤，你想投一個Dropdowm：

//HTML 
    <asp:Label ID="lblvalue" runat="server" Text='<%# Eval("ApproveID") %>' Visible = "false" /> 

//CodeBehind 
    DropDownList dropdownvalue = 
        ((DropDownList)Repeater2.Items[i].FindControl("lblvalue")); 

我認爲你正在尋找一個標籤來獲取值：

Label dropdownvalue = 
        ((Label)Repeater2.Items[i].FindControl("lblvalue")); 

但無論你想獲取和設置在下拉列表中的值：

DropDownList dropdownvalue = 
         ((DropDownList)Repeater2.Items[i].FindControl("DropDownList4")); 

我希望你看到錯誤。