Error: "This operation is valid only on elements that have this template applied"

Question

I have a C# WPF application that contains a user control:

<UserControl
        x:Name="payrollEntryControl"
        x:Class="MyNamespace.PayrollEntryControl"
        [...]
        >
    [...]
</UserControl>

Within the user control, I have a Telerik RadDataForm:

<telerik:RadDataForm
        x:Name="payrollAddForm"
        CurrentItem="[...]"
        EditTemplate="{StaticResource myEditTemplate}"
        />

The template contains a Telerik RadGridView and a Button:

<telerik:RadGridView Grid.Row="0" Grid.Column="0"
        x:Name="workGridView"
        [...]
        ItemsSource="{Binding [...]}"
        >
    <telerik:RadGridView.Columns>
        [...]
    </telerik:RadGridView.Columns>
</telerik:RadGridView>
<Button Grid.Row="1" Grid.Column="0"
        Command="{Binding addWorkCommand, ElementName=payrollEntryControl}"
        >
    Add
</Button>

I want the command to do is call BeginInsert() on workGridView. But I can't seem to get access to workGridView.

My command, so far:

private DelegateCommand addWorkCommand_ = null;
public DelegateCommand addWorkCommand
{
    get
    {
        if (this.addWorkCommand_ == null)
        {
            this.addWorkCommand_ = new DelegateCommand(
                o => addWork(o)
            );
        }

        return this.addWorkCommand_;
    }
}

private void addWork(object o)
{
    var addForm = this.payrollAddForm;
    var editTemplate = addForm.EditTemplate;
    var workGrid = editTemplate.FindName("workGridView", addForm);
}

My problem? When I make the call to editTemplate.FindName(), I get an exception:

This operation is valid only on elements that have this template applied.

I don't understand. I'm getting the template from the form. How can it not be applied?

This question seems to be very specific to the Telerik libraries. You'll likely need help specifically from someone familiar with that vendor's products. Beyond that, without a good [mcve] it may be difficult for anyone to directly diagnose the issue. Please explain what you've already tried with respect to debugging and researching the error message (including the relevance of the items returned [here](https://stackoverflow.com/search?q=%5Bc%23%5D+%22This+operation+is+valid+only+on+elements+that+have+this+template+applied.%22)). — Peter Duniho, Jul 29 '16 at 23:27

score 1 · Accepted Answer · edited May 23 '17 at 11:51

Peter Duniho's comment pointed me to this answer, which addressed my problem.

This method will help you:

public T FindElementByName<T>(FrameworkElement element, string sChildName) where T : FrameworkElement
{
    T childElement = null;
    var nChildCount = VisualTreeHelper.GetChildrenCount(element);
    for (int i = 0; i < nChildCount; i++)
    {
        FrameworkElement child = VisualTreeHelper.GetChild(element, i) as FrameworkElement;

        if (child == null)
            continue;

        if (child is T && child.Name.Equals(sChildName))
        {
            childElement = (T)child;
            break;
        }

        childElement = FindElementByName<T>(child, sChildName);

        if (childElement != null)
            break;
    }

    return childElement;
}

And, how I use it, just add button, and on button Click:

private void Button_OnClick(object sender, RoutedEventArgs e)
{
    var element = FindElementByName<ComboBox>(ccBloodGroup, "cbBloodGroup");
}
 [1]: https://stackoverflow.com/a/19907800/243563

An alternative is to pass the workGridView as a CommandParameter:

<Button Grid.Row="1" Grid.Column="0"
    CommandParameter="{Binding ElementName=workGridView}"
    Command="{Binding addWorkCommand}" >
 ....

private void addWork(object o)
{
    RadGridView grid = o as RadGridView;
    grid.BeginInsert();
}

Error: "This operation is valid only on elements that have this template applied"

1 Answers1