Programatically use a DataBound <%# ... %> variable?

Urgh. Right. This is basically what I want to do:

VB Code:

<%# If Not Container.DataItem("strImagePath") = vbNullString Then %>
    <img src="<%# Container.DataItem("strImagePath") %>" />
<% Else %>
    &nbsp;
<% End If %>

No combinatio of that seems to work :(

You can do this using CSS, but not sure when binding to datagrid :(

Woka

Blergh? :confused:

Basically right, if I have a Repeater or thingie like that, I want to be able to display some fields and maybe not others depending on their content.

So one cell in the table im using is to display an image, but not every record has an image. I don't want to include a path to some blank gif file, I'd prefer to leave that field empty in the DB.
So if I have this code:

VB Code:

<img src="<%# Container.DataItem("strImagePath") %>">

That works perfectly... provided there is actually some data in that column. But if its blank, I get a red x symbol for the image tag. So if there's data in that column, display the image, otherwise just a non breaking space.....

What you need to do is use:

VB Code:

Private Sub Repeater1_ItemCreated(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.RepeaterItemEventArgs) Handles Repeater1.ItemCreated
 
End Sub

Using e what you would do is make the image invisible if the databound value is nullstring.

Make sense?

Not good enough at .NET to give you an example, but that is definately the way to go.

Does that help?

Woka

OK, I am good enough to give you an example...I think :)

VB Code:

Private Sub Repeater1_ItemCreated(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.RepeaterItemEventArgs) Handles Repeater1.ItemCreated
    Dim MyImage As System.Web.ui.webcontrols.Image
    Select Case e.Item.ItemType
        Case ListItemType.Item, ListItemType.AlternatingItem
            MyImage = CType(e.Item.FindControl("imgPic"), System.Web.ui.webcontrols.Image)
            If MyImage.ImageUrl.Length = 0 Then
                MyImage.Visible = False
            End If
    End Select
End Sub

Is that what you want?

Woka

Along the lines of what woka said (sorry woka you missed one thing - the datarecord)

VB Code:

'ItemCreated is called each time the datalist is rendered.
    'ItemDataBound is called only when the data is bound
    'use ItemDatabound if you enable viewstate for the page
    'otherwise on each render ItemCreated duplicates unnecessary steps
    Private Sub DataList1_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) _ 
Handles DataList1.ItemDataBound
        If e.Item.ItemType = ListItemType.AlternatingItem OrElse e.Item.ItemType = ListItemType.Item Then
            'use dbdatarecord if binding to datareader, datarowview for datatable
            Dim dbr As System.Data.Common.DbDataRecord = DirectCast(e.Item.DataItem, Data.Common.DbDataRecord)
            'if column 1 (you could use dbr("imageurl") to access) is empty string
            If DirectCast(dbr(1), String) = String.Empty Then
                'cast the control, you can use findcontrol like woka did
                'or just bind the control dependant on its location
                '(starts at 1 and continues with odd numbers, so the 2nd control
                'would be accessed by e.item.controls(3)
                DirectCast(e.Item.Controls(1), System.Web.UI.WebControls.Image).Visible = False
 
            End If
        End If
    End Sub

in your aspx you would simply have
<asp:repeater>
<ItemTemplate>
<asp:image runat="server" ></asp:image>
</ItemTemplate>
</asp:repeater>

This actually is how I develop apps, which allows for
cleaner front side code and seperates appearance from logic.

I retract my statement and revert back to my 1st statement..."Not good enough at .NET to give you an example" :D

Although...I now know ;)

Woka

Ahhhh thank-you guys. Never thought about that :thumb: :D

Call yourself a .NET developer...HA!


:D Hehe

Woof

Hmmm.

VB Code:

Private Sub rptSales_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) Handles rptSales.ItemDataBound
        If e.Item.ItemType = ListItemType.AlternatingItem OrElse e.Item.ItemType = ListItemType.Item Then                        
[b]            If DirectCast(e.Item.DataItem("strImagePath"), String) = String.Empty Then[/b]
                Response.Write("nothing")
            Else
                Dim x As New System.Web.UI.WebControls.Image
                x.ImageUrl = e.Item.DataItem("strImagePath")
                x.Visible = True
            End If
        End If
    End Sub
End Class

produces

Code:

---

Line 110:        If e.Item.ItemType = ListItemType.AlternatingItem OrElse e.Item.ItemType = ListItemType.Item Then           
Line 111:            'Dim dbr As System.Data.Common.DbDataRecord = DirectCast(e.Item.DataItem, Data.Common.DbDataRecord)                       
Line 112:            If DirectCast(e.Item.DataItem("strImagePath"), String) = String.Empty Then
Line 113:                Response.Write("nothing")
Line 114:            Else

---

I assume you are getting an error?

The only issue I see is if your that data item is null. So you would check for dbnull first, depending if your pulling from a proc or what not.

VB Code:

If not dbr("strImagePath") is Dbnull.Value Then

Duh sorry never posted the error :rolleyes:




Server Error in '/Gaffs.ie' Application.
--------------------------------------------------------------------------------

Specified cast is not valid.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidCastException: Specified cast is not valid.

Source Error:

Line 109: Private Sub rptSales_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) Handles rptSales.ItemDataBound
Line 110: If e.Item.ItemType = ListItemType.AlternatingItem OrElse e.Item.ItemType = ListItemType.Item Then
Line 111: If DirectCast(e.Item.DataItem("strImagePath"), String) = String.Empty Then
Line 112: Response.Write("nothing")
Line 113: Else


Source File: C:\Inetpub\wwwroot\Gaffs.ie\uctl\SalesRepeater.ascx.vb Line: 111

Stack Trace:

[InvalidCastException: Specified cast is not valid.]
Gaffs.ie.SalesRepeater.rptSales_ItemDataBound(Object sender, DataListItemEventArgs e) in C:\Inetpub\wwwroot\Gaffs.ie\uctl\SalesRepeater.ascx.vb:111
System.Web.UI.WebControls.DataList.OnItemDataBound(DataListItemEventArgs e) +109
System.Web.UI.WebControls.DataList.CreateItem(Int32 itemIndex, ListItemType itemType, Boolean dataBind, Object dataItem) +139
System.Web.UI.WebControls.DataList.CreateControlHierarchy(Boolean useDataSource) +689
System.Web.UI.WebControls.BaseDataList.OnDataBinding(EventArgs e) +49
System.Web.UI.WebControls.BaseDataList.DataBind() +23
Gaffs.ie.SalesRepeater.Page_Load(Object sender, EventArgs e) in C:\Inetpub\wwwroot\Gaffs.ie\uctl\SalesRepeater.ascx.vb:75
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Control.LoadRecursive() +98
System.Web.UI.Page.ProcessRequestMain() +750




--------------------------------------------------------------------------------
Version Information: Microsoft .NET Framework Version:1.1.4322.2032; ASP.NET Version:1.1.4322.2032

Well, I never tried accessing the data directly from e.data.dataitem.

That is property returns an object more than likely, and so I always cast it to either a dbDataRecord or DataRowView first.

VB Code:

Dim dbr as System.Data.Common.DbDataRecord = DirectCast(e.Item.DataItem, System.Data.Common.DbDataRecord)
 
If Not dbr("strImpagePath") is DbNull.Value Then
If dbr("strImagePath") = String.Empty Then
...
End If
End If

Argh this is driving me mad :(

Put a breakpoint there... see what the object contains...

The object's a null reference. I haven't sat down to tackle this problem for more than 5 minutes at a time over the past week. I'll give it a proper looking at tomorrow morning :thumb: :)

If this is Sql Server then you may be allowing nulls in that field. If so use the t-sql function isnull when selecting data. e.g. select isnull(strImpagePath, ''), etc.
This will ensure that if it's null it will return an empty string instead. Also it's probably not a good idea to have an asp.net image control on every line unless you set enableviewstate=false. Otherwise even the invisible controls will be stored in the viewstate. Another option I recommend is to use a public function in your code behind to accept the strImpagePath value and return either an image or nothing:-

public function GetImage(imagepath as string) as string
if imagepath.length=0 then
return ""
else
return "<img src=""" & imagepath & """>"
end if
end function

Then in your html use the following:-

<%# GetImage(Container.DataItem("strImagePath")) %>

Musician,

You bring up a good point on not using an asp image control, a simple html img tag with a runat=server attribute will suffice.

But I disagree with your statement of using late-binding (aka implicit conversion) means of Container.DataItem to accept a image path by means of a openly public statement through the code behind. Several reasons:

1) Performance hit - while not drastic, if you had 100+ images, the binding statement as provided by using the <% %> binding tags will stifle performance on the server. There's a large degree of implicit type casting occuring here.

2) Having an openly accessible function in the assembly when it does not need to be is opening a channel for misuse, malicious or not. At worst, it should be declared Protected.

3) Incorporating <% %> tags does not foster cleanly seperating content from the code-logic. This throwsback to old style ASP coding. I think you'll agree that if you had 5 or 6 controls in one databound item in a data template control, the front side aspx looks messy as sin. Many tutorials for teaching asp.net use this method only for simplicity sake.

4) Functionality ... what if there was a textbox that needed to have a red background color when its text property was empty, and default to a '<no value>' text setting? Using code-behind binding allows for cleaner manipulation of the control:

VB Code:

If dbr("textboxText") Is Dbnull.Value Then myTextBox.BackColor=Color.Red
myTextBox.BackColor="<no value>"
End If

Plenderj simply has to test for a DbNull.Value before attempting to assign the data. Or, if he incorporates the proc change you mentioned, then test for String.Empty.

Quite right. Allow me to refer to it as an example for simplicity's sake.

Finally working. Thanks guys :D

Code:

---

<td vAlign="top" align="middle" width="170">
        <a style="color: #0000dd" href="#">
                <%# GetImage(Container.DataItem(20)) %>
        </a>
</td>

---

VB Code:

Public Function GetImage(ByVal objImage As Object) As String
        Dim strRetVal As String, strImage As String
        If Not objImage Is Nothing Then
            Try
                strImage = CType(objImage, String)
                If Not strImage = vbNullString Then
                    strRetVal = "<img src=" & Chr(34)
                    strRetVal &= strImage & Chr(34)
                    strRetVal &= " />"
                End If
            Catch ex As Exception
                strImage = vbNullString : strRetVal = vbNullString
                GoTo eof
            End Try
        Else
            strRetVal = "nothing"
        End If
eof:
        Return strRetVal
    End Function

yipeeeeeeeeeeeeee :D

I'm gald you got it working but I would recommend you take nemaroller's points into consideration. It might be worth trying to do it in the code behind itemdatabound event instead of taking the performance hit of the method above.

Well I've since implemented it as a user control, and am not using viewstate, so seems to be running quite swimmingly :)

Glad to see you got it working.

I don't suppose you know the code to make a datagrid, or datarepeater, look like my screen shot.

Woka

Yeah I'm getting surprisingly good at this kind of thing now. I have some beautiful looking repeaters now. Took me a while to cop it.
Going to dinner in my mother's tonight and perhaps cinema, but I can send you over some code for it later k?

Basically what I do is create a template in dreamweaver or frontpage, then replace the real data with some placeholders, convert the placeholders into proper asp tags, and copy and paste that into the design view of the page :)