[Solved] Problem with Templated column on Postback

[Adrian]

Hi There,

I have a Grid control with a column which is used to render an icon based on a bound value.

The DocumentIconTemplate class looks like this

 

 

Public Class DocumentIconTemplate
    Implements ITemplate

    Private m_Name As String

    Public Sub New(ByVal name As String)
        m_Name = name
    End Sub


    Public Sub InstantiateIn(ByVal container As System.Web.UI.Control) Implements System.Web.UI.ITemplate.InstantiateIn

        Dim dataCell As GridTableCell = container
        Dim dataItem As GridDataItem = CType(container.NamingContainer, GridDataItem)

        Dim img As New Image()
        img.ID = m_Name
        AddHandler img.DataBinding, AddressOf BindImage

        container.Controls.Add(img)

    End Sub

    Public Sub BindImage(ByVal sender As Object, ByVal e As EventArgs)
        Dim img As Image = CType(sender, Image)
        Dim container As GridDataItem = CType(img.NamingContainer, GridDataItem)
        img.ID = m_Name
        img.ImageUrl = "Scr.Bmp"
    End Sub


End Class

and the custom column looks like this

            Dim column As GridTemplateColumn

            column = New GridTemplateColumn()
            column.HeaderText = "Type"
            column.DataField = "Type"
            column.UniqueName = "Type"
            column.ItemTemplate = New DocumentIconTemplate("Type")
            gridControl.MasterTableView.Columns.Add(column)

All is well and this renders fine until I create a hierarchical grid or use some operation that requires a postback. When I expand the row (to show the second level of the hierarchy) my custom image disappears although all "text" based fields remain.When you expand the row the grid posts back to the server and when it comes back Grid columns that have Text set on them still have their values. I'm not sure if it the viewstate or the control heirarchy that is the problem here. On postback the grid doesn't call the InstantiateIn again so I presume it's trying to re-render itself just using viewstate.

It does keep the image if you use the <ItemTemplate> and create the image declaratively however outside of this simple test app the columns need to be created dynamically.

Any help/thoughts appreciated.

Adrian

[Veli]

Hello Adrian,

As you guessed, RadGrid restore its control data from the ViewState on successive postbacks when the gridi is not rebound. However, note that your DocumentIconTemplate class is not saving anything in the ViewState. So it cannot restore any data. Additionally, I see that you are setting your image properties in the DataBinding event of the Image control. This event, however, is not fired on successive postbacks if your grid is not rebound.

Additionally, if you are dynamically creating the columns of a statically declared RadGrid, note that you need to add the columns to the MasterTableView.Columns collection first, before setting their values:

Dim column As GridTemplateColumn

column = New GridTemplateColumn()
gridControl.MasterTableView.Columns.Add(column)
column.HeaderText = "Type"
column.DataField = "Type"
column.UniqueName = "Type"
column.ItemTemplate = New DocumentIconTemplate("Type")

Best wishes,
Veli
the Telerik team

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