Solving the Issue of DataGrid Replacing Bound Property Values in WPF

Discover how to fix the issue where a WPF `DataGrid` replaces a bound property with old, invalid values when edited. Learn simple solutions to ensure consistent data flow between your view and view model.
---
This video is based on the question https://stackoverflow.com/q/66483568/ asked by the user 'redcurry' ( https://stackoverflow.com/u/1383366/ ) and on the answer https://stackoverflow.com/a/66500396/ provided by the user 'serges_newj' ( https://stackoverflow.com/u/5702335/ ) 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: Why is the DataGrid replacing a bound property with an old, invalid value when edited?

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

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the WPF DataGrid Value Replacement Issue

When building applications with WPF (Windows Presentation Foundation), you may encounter unexpected behavior while working with DataGrids. One common issue arises when a DataGrid replaces a bound property with an old, invalid value when edited. This can be frustrating, especially when you're relying on the data to reflect real-time updates accurately.

This guide dives into the specifics of this problem, explores why it occurs, and provides a clear solution. If you're experiencing this issue, you're not alone, and the good news is there's a way to fix it!

The Scenario

Let's set the stage for our issue. Imagine you have a simple DataGrid bound to an ObservableCollection of view models. One specific column utilizes a DataGridTemplateColumn with a TextBlock for display and a TextBox for editing, where you expect the binding to work seamlessly.

Your view model, let's say PersonViewModel, contains a property called FirstName that holds strings. You can edit this in the DataGrid. However, when you input an invalid value (like an empty string) into the TextBox and then attempt to make a bulk change (for example, setting every FirstName to "Hello" via a button click), an odd behavior occurs. Afterward, the TextBox displays the invalid value again instead of the updated valid value.

Why Is This Happening?

At its core, this issue arises because the TextBox that initiated a validation error does not exist anymore when the HelloCommand is executed. Therefore, the data binding mechanism fails to access the correct value from the view model at the moment the TextBox is created again for editing. In simpler terms, the binding doesn't know about the updated state of FirstName, which results in the reappearance of the old value.

The Solution: Clearing Binding Operations

Fortunately, there's a practical workaround to this issue that allows you to clear any pending binding operations before executing your command. Here's a step-by-step guide to implement this solution:

Step 1: Name Your DataGrid

This helps us reference our DataGrid in the code behind efficiently. Update your XAML like so:

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

Step 2: Add a Click Handler to the Button

Modify the button that triggers the command to include a click event. Your XAML button will look like this:

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

Then, implement the click handler in your code-behind:

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

Alternative for .NET 4.0

As GetSourceUpdatingBindingGroups is not available in .NET 4.0, you can use the following alternative code:

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

While this approach may not seem as elegant, it effectively resolves the issue similar to the previous method.

Conclusion

Navigating the intricacies of data binding in WPF can sometimes lead to unexpected behaviors like the one we've discussed. By understanding the root cause of why the DataGrid replaces bound properties with invalid values, you can implement the solutions provided here to maintain a consistent and accurate data flow in your applications.

With this information at your disposal, you can resolve the frustrating issue of invalid value replacement effectively. Happy coding!

Видео Solving the Issue of DataGrid Replacing Bound Property Values in WPF канала vlogize