WPF Tree Binding Problem using Methods

Question

I have bound a WPF TreeView to an ObservableCollection. When a Connection node gets expanded in the UI, I want Connection.GetDatabases() to be called, which returns an collection of Databases.

I'm using HierarchicalDataTemplate:

<HierarchicalDataTemplate DataType="{x:Type dbcore:Connection}" ItemsSource="<WHAT GOES HERE?>">
            <StackPanel Orientation="Horizontal">
                <Image Source="{StaticResource DataServerIcon}" Margin="5,2" />
                <TextBlock Text="{Binding Converter={StaticResource connToStringConverter}}" />
            </StackPanel>
</HierarchicalDataTemplate>

But because I want to use a method instead of a property, I'm not sure what to use in the ItemsSource property.

Why not use a property that simply calls whatever service/method you want to return the data? — Aaron McIver, Dec 15 '10 at 16:27
Duplicate of http://stackoverflow.com/questions/502250/bind-to-a-method-in-wpf — Bryan Watts, Dec 15 '10 at 16:30
@Bryan - Thanks. I did search before hand but didn't find that. Looks promising. — Ronnie Overby, Dec 15 '10 at 16:35

markmnl · Accepted Answer · 2010-12-15T16:39:50.310

Since you want to get the values when the item is expanded you cannot do it in XAML at design time. You can do it when you your item is expanded in code behind:

<TreeView TreeViewItem.Expanded="OnExpanded" ... >


private void OnExpanded(object sender, RoutedEventArgs e)
{
      TreeViewItem tvi = e.OriginalSource as TreeViewItem;
      if (tvi != null)
      {
        tvi.Focus(); // to ensure the expanded item is selected
        tvi.ItemsSource = ((Connection)myTreeView.SelectedItem).GetDatabases();
      }
}

score 0 · Answer 2 · answered Dec 15 '10 at 16:28

0

You can make an IValueConverter which takes your object and calls the method.

However, it would be much simpler, and probably a little bit faster, to add a proeprty to the original object that calls the method.
You may want to add [Obsolete("Please call MyMethod() instead.", true)] to prevent the property form being used in code. (This will not interfere with data-binding)

answered Dec 15 '10 at 16:28

SLaks

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Binding to properties that call potentially long running methods should be avoided. – markmnl Dec 15 '10 at 16:46

score -1 · Answer 3 · answered Dec 15 '10 at 16:29

-1

Why not simply use a property which will return the data via whatever method/service you want? You can't natively bind to a method; so either access your method within the properties getter or make use of an IValueConverter and parameter which could contain the method to call.

public ObservableColection<Database> Databases
{
     get
     {
        return GetDatabases();
     }
}

answered Dec 15 '10 at 16:29

Aaron McIver

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I CAN'T ADD A PROPERTY TO A CLASS THAT I DIDN'T CREATE! – Ronnie Overby Dec 15 '10 at 16:32
2

@Ronnie Wrap the data in your own class; ala a ViewModel...the fact that you have a class you didn't create this far up the onion is a red flag in and of itself. – Aaron McIver Dec 15 '10 at 16:33

WPF Tree Binding Problem using Methods

3 Answers3