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RadControls version
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RadComboBox for ASP.NET AJAX
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| .NET version |
2.0+
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| Visual Studio version |
VS 2005/2008/2010
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| programming language |
C#/VB.NET
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| browser support |
all browsers supported by RadControls
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PROJECT DESCRIPTION
This sample project demonstrates how to preselect an item in RadComboBox with Load-On-Demand enabled and nested within the EditItemTemplate of RadGrid (or other parent databound control).
THE ISSUE
RadComboBox with Load-On-Demand enabled is often nested in EditItemTemplate of RadGrid or another data-bound control.
However preselecting a RadComboBoxItem at EditItemTemplate of the parent control in such scenario is a tricky task. Sometimes developers try to set the SelectedValue property of the RadComboBox via declarative databinding and receive this error: “
Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.”
Please note that when the RadComboBox with Load-On-Demand feature initially loads -
it is empty and it has no items. Load-On-Demand fires and populates the control with data when user types in the input area or clicks on the drop-down toggle image (if there are no items in the RadComboBox).
That is why when the parent control enters “Edit” mode – there are no items at the RadComboBox and trying to preselect an item raises an error.
THE SOLUTION
We can overcome this issue by handling the
RadGrid.OnItemDatabound event and creating an initial RadComboBoxItem to be displayed at the control input.
[C#]
[VB.NET]
When we delete the text initially displayed at RadComboBox input - Load-On-Demand will fire and will populate the control dropdown with items.
In order to perform Add, Edit and Delete operation handle
RadGrid.OnInsertCommand,
RadGrid.OnUpdateCommand and RadGrid.
OnDeleteCommand events and obtain the RadComboBox selected value:
[C#]
protected void RadGrid1_UpdateCommand(object source, Telerik.Web.UI.GridCommandEventArgs e)
{
GridEditableItem editedItem = e.Item as GridEditableItem;
RadComboBox comboBox = (RadComboBox)editedItem.FindControl("RadComboBox1");
SqlDataSource1.UpdateParameters.Add(
new Parameter("CategoryID", DbType.Int32, comboBox.SelectedValue));
SqlDataSource1.UpdateParameters.Add(
new Parameter("UnitPrice", DbType.Double,
(e.Item.FindControl("UnitPriceTextBox") as TextBox).Text));
SqlDataSource1.UpdateParameters.Add(
new Parameter("ProductName", DbType.String,
(e.Item.FindControl("ProductNameBox") as TextBox).Text));
SqlDataSource1.UpdateParameters.Add(
new Parameter("ProductID", DbType.Int32,
(e.Item.FindControl("ProductIDBox") as TextBox).Text));
SqlDataSource1.Update();
}
protected void RadGrid1_InsertCommand(object sender, GridCommandEventArgs e)
{
GridEditableItem editedItem = e.Item as GridEditableItem;
RadComboBox comboBox = (RadComboBox)editedItem.FindControl("RadComboBox1");
SqlDataSource1.InsertParameters.Add(
new Parameter("CategoryID", DbType.Int32, comboBox.SelectedValue));
...
...
...
SqlDataSource1.Insert();
}
protected void RadGrid1_DeleteCommand(object source, GridCommandEventArgs e)
{
GridDataItem item = (GridDataItem)e.Item;
string ProductID = item.OwnerTableView.DataKeyValues[item.ItemIndex]["ProductID"].ToString();
SqlDataSource1.DeleteParameters.Add(
new Parameter("ProductID", DbType.Int32, ProductID));
SqlDataSource1.Delete();
}
[VB.NET]
Protected Sub RadGrid1_UpdateCommand(ByVal source As Object, ByVal e As Telerik.Web.UI.GridCommandEventArgs)
Dim editedItem As GridEditableItem = TryCast(e.Item, GridEditableItem)
Dim comboBox As RadComboBox = DirectCast(editedItem.FindControl("RadComboBox1"), RadComboBox)
SqlDataSource1.UpdateParameters.Add(New Parameter("CategoryID", DbType.Int32, comboBox.SelectedValue))
SqlDataSource1.UpdateParameters.Add(New Parameter("UnitPrice", DbType.[Double], TryCast(e.Item.FindControl("UnitPriceTextBox"), TextBox).Text))
SqlDataSource1.UpdateParameters.Add(New Parameter("ProductName", DbType.[String], TryCast(e.Item.FindControl("ProductNameBox"), TextBox).Text))
SqlDataSource1.UpdateParameters.Add(New Parameter("ProductID", DbType.Int32, TryCast(e.Item.FindControl("ProductIDBox"), TextBox).Text))
SqlDataSource1.Update()
End Sub
Protected Sub RadGrid1_InsertCommand(ByVal sender As Object, ByVal e As GridCommandEventArgs)
Dim editedItem As GridEditableItem = TryCast(e.Item, GridEditableItem)
Dim comboBox As RadComboBox = DirectCast(editedItem.FindControl("RadComboBox1"), RadComboBox)
SqlDataSource1.InsertParameters.Add(New Parameter("CategoryID", DbType.Int32, comboBox.SelectedValue))
...
...
...
SqlDataSource1.Insert()
End Sub
Protected Sub RadGrid1_DeleteCommand(ByVal source As Object, ByVal e As GridCommandEventArgs)
Dim item As GridDataItem = DirectCast(e.Item, GridDataItem)
Dim ProductID As String = item.OwnerTableView.DataKeyValues(item.ItemIndex)("ProductID").ToString()
SqlDataSource1.DeleteParameters.Add(New Parameter("ProductID", DbType.Int32, ProductID))
SqlDataSource1.Delete()
End Sub
The same approach can be used to nest Load-On-Demand RadComboBox in EditItemTemplate of FormView or GridView – please find more details at the sample project attached. Passing the update parameters is implemented using ControlParameters (at the FormView example) and SessionParameter(GridView example).