How to Call Parent View Model Functions from Child View Models in WPF?

How to Execute Functions in the Parent View Model from Child View Models

Your application consists of a TreeView, two contentPresenters, and separate view models for each UI element, including the main window. To update the display, you seek to invoke a method in the MainWindowViewModel from the TreeViewViewModel.

Like similar cases, a viable solution involves utilizing delegate objects. Check the previous forum response titled "Passing parameters between viewmodels" for an in-depth explanation and practical implementation. Just replace the delegates in that example with the desired methods, and they will function similarly.

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Update

To directly call methods instead of passing parameters, consider the modified delegate handler below:

public void ParameterViewModel_OnParameterChange(string parameter)
{
    // Call your method here
}

This delegate serves as a pathway to the parent view model, enabling event-like functionality ("ReadyForYouToCallMethodNow"). Alternatively, you could define the delegate without any input parameter:

public delegate void ReadyForUpdate();

public ReadyForUpdate OnReadyForUpdate { get; set; }

In the parent view model, after attaching the handler as illustrated in the previous example, you can invoke the method:

public void ChildViewModel_OnReadyForUpdate()
{
    // Call your method here
    UpdateDisplay();
}

If multiple child view models are involved, you can define the delegate in a separate class accessible by all models.

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Update 2

Upon further analysis, a simpler approach may suffice. You can directly bind child view elements to properties in the parent view model. For instance, the following code snippet in your TreeViewView binds the Button.Command property to an ICommand property in MainWindowViewModel:

<Button Content="Click Me" Command="{Binding DataContext.ParentCommand, 
RelativeSource={RelativeSource AncestorType={x:Type MainWindow}}}" />

This assumes that the parent view model instance is set as the DataContext of the MainWindow.

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