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Learn how to transfer the `SelectedItem` from a WPF popup's ViewModel to the MainWindow for seamless data management in your application.
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This video is based on the question https://stackoverflow.com/q/62408885/ asked by the user 'Telefisch' ( https://stackoverflow.com/u/10155541/ ) and on the answer https://stackoverflow.com/a/62410378/ provided by the user 'mm8' ( https://stackoverflow.com/u/7252182/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Retrieve SelectedItem from a Bound ViewModel in a WPF Popup

WPF (Windows Presentation Foundation) allows developers to create rich desktop applications with a complex user interface. A common pattern is to use the MVVM (Model-View-ViewModel) design, which encourages separation of concerns, making your code more maintainable and testable. One scenario often encountered is transferring data from a modal popup back to the main application window, especially when working with bound ViewModels.
This guide explains how to effectively transfer the SelectedItem from a popup ViewModel back to the MainWindow, ensuring your application's data flow is seamless and efficient.

Understanding the Scenario

In your application, you've created a popup window that displays a list of items. This popup is bound to a ViewModel (GeneratorSelectionViewModel), which contains properties and commands related to the selected item.
Here is a brief overview of what your setup looks like:

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The SelectedItem property stores the selected item from a list in the popup. However, when you try to access SelectedItem from the main window after displaying the popup, you run into trouble, as SelectionPopup.SelectedItems isn't available directly.

The Solution

To transfer the SelectedItem from the GeneratorSelectionPopup back to the MainWindow, follow these steps:

1. Open the Popup

You typically display the popup using the ShowDialog() method, which pauses execution until the popup is closed. Here's how you already open the popup:

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2. Retrieve the DataContext

After closing the popup, you can access its DataContext, which will give you access to the ViewModel. You need to cast it back to the appropriate type. Use the following code to pull the SelectedItem:

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3. Use the Retrieved Data

Once you have the selectedItem, you can use it as needed within your MainWindow. For example, you might want to update UI elements or trigger other commands based on this selected data.

Complete Example

Combining the above points, your code in the main window should look like this:

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Conclusion

Transferring data from a popup window's ViewModel back to the MainWindow in WPF is straightforward once you understand the concept of DataContext. By properly casting the DataContext of the popup and accessing the bound properties, you can efficiently manage your application's state and ensure a smooth user experience.
Implementing such patterns adheres to best practices in WPF development, keeping your application organized and maintainable.

Feel free to explore more scenarios and enhance your applications with these techniques. Happy Coding!