Скачать или смотреть How to Add a New Element to a ComboBox in a DataGrid Using MVVM in WPF

Discover effective strategies to add new items to a ComboBox in a WPF DataGrid using the MVVM pattern. Learn how to solve common problems with event handling and data binding.
---
This video is based on the question https://stackoverflow.com/q/65369688/ asked by the user 'Istvan Heckl' ( https://stackoverflow.com/u/5852947/ ) and on the answer https://stackoverflow.com/a/65394414/ provided by the user 'Istvan Heckl' ( https://stackoverflow.com/u/5852947/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Adding new element to a ComboBox which is in a DataGrid in WPF using MVVM

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Adding New Elements to a ComboBox in a DataGrid Using MVVM in WPF

In modern application development with WPF (Windows Presentation Foundation), it's common to use the MVVM (Model-View-ViewModel) pattern. A challenge many developers face is how to effectively manage ComboBox elements within a DataGrid, especially when allowing users to add new items dynamically. In this guide, we'll explore a specific problem concerning ComboBoxes in DataGrids and provide a clear solution that avoids common pitfalls.

The Problem: Enhancing ComboBox Functionality

Let's consider a scenario where you have a DataGrid displaying transactions, with one column featuring a ComboBox for selecting interest or dividend types. While everything functions as expected for selection, the new requirement is to allow users to enter and add new values directly into the ComboBox.

Here are the two main issues developers often encounter:

Problem 1: Event Triggering Issues

Unexpected Triggers: The command associated with the ComboBox (InterestOrDividendSelectionChangedCommand) gets fired not only when the selection changes but also when the DataGrid is scrolled, causing visible rows to trigger the event incorrectly.

Failure to Trigger on New Input: When a user inputs a new value not present in the ComboBox's list, the event does not trigger, leaving the new value unprocessed.

Problem 2: Binding Issues

Outdated Values: The Text property of the ComboBox, which needs to represent the newly added value, binds too early in the sequence. Often, it retrieves the old value instead of the new value, inconveniently hindering the user’s option to input data correctly.

The Solution: Adjusting Binding Strategies

To effectively resolve these issues, an adjustment in how we manage bindings and event triggers within WPF is necessary. Here's a simplified step-by-step approach.

Step 1: Replace Event Triggers

Good practice suggests that rather than relying on EventTrigger, we should capture input changes directly through properties. This can be done by modifying the binding for NewInterestOrDividend.

Step 2: Utilize LostFocus Triggering

To ensure that we capture the new input accurately, we can set the UpdateSourceTrigger of the ComboBox's Text property to LostFocus. This way, when the user navigates away from the ComboBox, we can confirm that the new input is retrieved correctly.

Sample Implementation

Here's how your updated XAML could look:

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

Key Changes:

UpdateSourceTrigger=PropertyChanged for SelectedItem: This immediately updates the corresponding property whenever its value changes.

UpdateSourceTrigger=LostFocus for Text: This ensures that when the user moves away from the ComboBox, we record any new input provided by them.

Conclusion

By effectively managing the way we handle user inputs in ComboBoxes within a DataGrid using MVVM, we can create a more sophisticated, user-friendly interface. This not only resolves issues related to events triggering unexpectedly but also ensures data integrity by capturing the values as intended.

By following the highlighted strategies, developers can significantly enhance the functionality of their WPF applications, leading to a better user experience.

For anyone encountering similar complications in their projects, I hope this guide serves as a clear roadmap to implementing a reliable solution!