Creating a UserControl with a ViewModel in WinUI 3

Learn how to effectively create a `UserControl` with a `ViewModel` in WinUI 3, including proper structure, data binding, and good practices.
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This video is based on the question stackoverflow.com/q/75934676/ asked by the user 'Panagiotis Vasileiou' ( stackoverflow.com/u/11025934/ ) and on the answer stackoverflow.com/a/75935117/ provided by the user 'Andrew KeepCoding' ( stackoverflow.com/u/2411960/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Creating a UserControl with a ViewModel in WinUI 3: A Step-by-Step Guide

Creating a UserControl in WinUI 3 can seem like a challenging task, especially when integrating it with a ViewModel to maintain the MVVM (Model-View-ViewModel) architecture. This guide will explore a practical example of developing an ImageViewer UserControl that allows for displaying, adding, and deleting photos. Let’s dive into the problem and its solution.

The Problem

The goal is to create a UserControl called ImageViewer that should be capable of:

Displaying photos

Allowing users to navigate through the images (Next/Previous)

Adding and deleting photos

You need to effectively bind the properties of your UserControl to a ViewModel, ensuring that UI updates automatically reflect data changes in the ViewModel. However, there are uncertainties regarding the use of a ViewModel inside a UserControl and how to handle properties properly.

Key Questions to Address

Is it a good idea to have a ViewModel in a UserControl?

Should the collection of models reside in the code-behind or just in the ViewModel?

How to make the Photos collection observable if using a ViewModel is not advised?

Proposed Solution

Having answered the above questions, creating a UserControl with a ViewModel is indeed a good practice in MVVM architecture. Let's break down the solution into steps.

Step 1: Define Your UserControl

The ImageViewer UserControl should contain various properties and commands as follows:

Properties: These include collections like ICollection<Product_PhotoModel> Photos and index details for tracking the current image.

Command Bindings: For actions like adding or removing photos.

Here’s a simplified outline of how your ImageViewer XAML might look:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Implement the Code-Behind

The ImageViewer.xaml.cs file will contain the logic for the UserControl, allowing it to work seamlessly with the ViewModel. It should manage the photos and handle the logic of how the UserControl behaves.

Example Code for ImageViewer.xaml.cs:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Create the ViewModel

Your ImageViewerViewModel should derive from ObservableRecipient and should manage the data independently while binding to the UserControl via dependency properties.

Example Code for ImageViewerViewModel.cs:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Binding the ViewModel to the UserControl

You need to set an instance of the ViewModel in your UserControl's constructor and bind the properties correctly so that the UI reflects the data changes.

Best Practice Insights

Responsibility: Determine what exactly your UserControl should do. You can separate concerns by using the ViewModel to handle data changes, while your UserControl focuses solely on the UI.

Reusability: Design UserControls to be reusable. Ensure their functionality can be exposed through dependency properties and commands.

Conclusion

Creating a UserControl like ImageViewer with a ViewModel in WinUI 3 isn’t just feasible, but also a preferred design practice for clear separation between UI and business logic. By following the steps outlined in this guide, you can set up an effective and reusable UserControl that communicates well with its ViewModel, ensuring a robust and scalable application.

If you have any questions or need further clarifications, feel free to ask in the comments below!