vb.net - ASP.Net dropdownlist within a detailsview not being set in codebehind

问题描述:

I have the following code in my codebehind Page_Load function that sets the default selected value of a dropdownlist in detailsview based on the name of a record returned from a sql data query.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Me.Page.Title = "Editing record"
'Perform dropdown list population operations
Dim myDDL As DropDownList = DetailsView1.FindControl("reqCategoryDropDown")
If Page.IsPostBack = False Then
Dim ticket_ID As String = getDataKey(DetailsView1)
'Fetch Category ID
Dim sqlText As String = "SELECT TS_REQCATEGORY FROM USR_ITFAC WHERE (TS_ID = " + ticket_ID + ") "
Dim reqDataReader As SqlDataReader = GetDataReader(sqlText)
reqDataReader.Read()
Dim category_ID As String = reqDataReader(0)
'Fetch Category name and set as selected value in dropdown list
sqlText = "SELECT TS_NAME FROM TS_SELECTIONS WHERE (TS_ID = " + category_ID + ") "
reqDataReader = GetDataReader(sqlText)
reqDataReader.Read()
category_Name = reqDataReader(0)
'myDDL.DataBind()
myDDL.SelectedValue = category_Name
End If
End Sub

My problem is that when the page loads for the first time, even though I set the selected value for the dropdownlist it will not display and instead simply displays the default first name in my dropdownlist. I tried Binding my dropdownlist before and after I set the selectedvalue, it is commented out in the sample code above, but that didn't seem to do anything.

UPDATE:

I'm setting the data source in the webform as follows:

Dropdownlist:

<asp:DropDownList DataSourceID="ReqCategoryData" DataTextField="ReqCategory" DataValueField="ReqCategory"
ID="reqCategoryDropDown" runat="server" AppendDataBoundItems="true" AutoPostBack="true">
</asp:DropDownList>

Connects to data source a few lines down:

<asp:SqlDataSource ID="ReqCategoryData" runat="server" ConnectionString="<%$ ConnectionStrings:TTPRODReportsQuery %>"
SelectCommand="SELECT TS_NAME AS ReqCategory FROM dbo.TS_SELECTIONS WHERE (TS_FLDID = 5299 AND TS_STATUS = 0) ORDER BY TS_NAME">
</asp:SqlDataSource>

UPDATE_2:

Ok, so I implemented he SQLDataSource programmatically in the code-behind under the Page_Init function as follows:

Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
DetailsView1.DefaultMode = DetailsViewMode.Edit
''Setup DropDownList SqlDataSource
ddlDataSource.ID = "ReqCategoryData"
Page.Controls.Add(ddlDataSource)
ddlDataSource.ConnectionString = ConfigurationManager.ConnectionStrings("TTPRODReportsQuery").ConnectionString
ddlDataSource.SelectCommand = "SELECT TS_NAME AS ReqCategory FROM dbo.TS_SELECTIONS WHERE (TS_FLDID = 5299 AND TS_STATUS = 0) ORDER BY TS_NAME"
Dim args As New DataSourceSelectArguments
ddlDataSource.Select(args)
ddlDataSource.DataBind()
End Sub

After which I set attempt to set the selected value of the dropdownlist as above. The page is still not setting the selected value.

网友答案:

Perhaps check these items:

ensure you're calling myDDL.DataSource = reqDataReader or some other form of setting the DataSource of your dropdownlist.
ensure the dropdownlist has its DataTextField and DataTextField set properly. This could be in code-behind or in markup.
The 0'th index of reqDataReader -- are you sure that's the intended ordinal for the DataValueField?

Perhaps something like this:

With myDDL
    .DataTextField = "CategoryName"
    .DataValueField = "CategoryID" ' or perhaps CategoryName as your value.
    .DataSource = reqDataReader
    .DataBind()
    .SelectedValue = category_Name ' Name or ID; depends on what was set as DataValueField
End With

DataBinding - Code-Behind vs. Markup DataSources

Consider choosing one style of binding your dropdownlist - in code-behind or with a markup SqlDataSource. Having both generates confusion on which bind wins - the code-behind or the datasource. I think it's the SqlDataSource in this case.

Consider removing the SqlDataSource from out of the markup, and create a method in code-behind whose sole purpose is to create the data binding. This is the only place where the binding should happen. If you ever need to track down a defect or enhance your logic, it's the only one place to visit.

Private Sub BindMyDropDown(Optional ByVal selectedValue as String)
    With myDDL
        .DataTextField = "CategoryName"
        .DataValueField = "CategoryID" ' or perhaps CategoryName as your value.
        .DataSource = LoadTicketReqCategory(TicketID)
        .DataBind()
        .SelectedValue = selectedValue ' Name or ID; depends on what was set as  DataValueField
    End With

End Sub

From your Page_Load(), check for IsPostBack() and call this method when you aren't posting back.

网友答案:

myDDL.ClearSelection item = myDDL.Items.FindByValue(category_Name) item.selected = true

-- You could also try setting the SelectedIndex to 2, for example, to check it that way.

网友答案:

The problem might be that you are assigning the myDDL variable outside of the postback check.

    Dim myDDL As DropDownList = DetailsView1.FindControl("reqCategoryDropDown")
    If Page.IsPostBack = False Then

Should be

    If Page.IsPostBack = False Then
        Dim myDDL As DropDownList = DetailsView1.FindControl("reqCategoryDropDown")

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vb.net - ASP.Net dropdownlist within a detailsview not being set in codebehind