WPF

public override void OnApplyTemplate()
{
    base.OnApplyTemplate();

    if ((object)Template != null)
    {
        CheckBox chkBox = Template.FindName("chkBox", this) as CheckBox;

        // do stuff with checkbox
    }
}

public class BusySlider : Slider
{
    public bool SliderBusy
    {
        get;
        private set;
    }

    protected override void OnMouseLeftButtonDown(System.Windows.Input.MouseButtonEventArgs e)
    {
        this.SliderBusy = true;

        base.OnMouseLeftButtonDown(e);
    }

    protected override void OnMouseLeftButtonUp(System.Windows.Input.MouseButtonEventArgs e)
    {
        base.OnMouseLeftButtonUp(e);

        this.SliderBusy = false;
    }
}

Dispatcher.BeginInvoke(new Action(delegate()
                { 
                    ...
  
                    //Slider position
                    if (!slidePosition.SliderBusy)
                    {
                        slidePosition.Maximum = (double)state.CurrentTrack.Length;
                        slidePosition.Value = (double)state.CurrentTrack.Position;
                    }
                }));

// Update ItemsSource first time
tvTree.ItemsSource = root.Branches; // Works

// Update ItemsSource second time
tvTree.ItemsSource = root.Branches; // Works

<Window x:Class="Tree.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:node="clr-namespace:Tree.TreeNodes"
        Title="MainWindow" Height="350" Width="525">
    
    <Grid>
        <TreeView Name="tvTree" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="5,5,0,0" Width="400" Height="500">
            <TreeView.ItemTemplate>
                <HierarchicalDataTemplate ItemsSource="{Binding Branches}"  DataType="{x:Type node:Node}">
                    <Grid>
                        <TextBlock Text="{Binding Header}" />
                    </Grid>
                </HierarchicalDataTemplate>
            </TreeView.ItemTemplate>
        </TreeView>
    </Grid>
</Window>