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Home Backend Development C++ How Can Child View Models Call Functions in a Parent ViewModel?

How Can Child View Models Call Functions in a Parent ViewModel?

Dec 26, 2024 pm 06:36 PM

How Can Child View Models Call Functions in a Parent ViewModel?

Calling Functions in the Main ViewModel from Child View Models

In scenarios involving multiple view models with a hierarchical relationship, it may be necessary to invoke functions in the main view model from within child view models. This article addresses precisely this requirement, providing a solution that leverages delegate objects.

Consider the scenario described. A main window view model governs the content displayed in child views. The task is to manually update the display by calling a function in the main window view model from a child view model.

Using Delegate Objects

The delegate method approach employed in the solution and the reference article allows for communication in any parent-child scenario. Access is possible from child view models to parent view models, from Window code behinds to child Window code behinds, and even among data relationships.

Implementation

  1. Define a delegate in the parent view model:

    public delegate void ReadyForUpdate();
public ReadyForUpdate OnReadyForUpdate { get; set; }

  2. Within the child view model, attach a handler to the delegate:

    public void ReadyForUpdateHandler()
{
    // Call the desired method in the parent view model
}

  3. In the parent view model, call the method when appropriate:

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

Alternative Approach

In some cases, a simpler approach may suffice. Direct Binding from child views to the parent view model allows for direct access to ICommand properties in the parent view model:

<!-- In a child view -->
<Button Content="Click Me" Command="{Binding DataContext.ParentCommand, RelativeSource={RelativeSource AncestorType={x:Type MainWindow}}}" />

This method assumes the parent view model instance is set as the DataContext of the main window.

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