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Learn how to ensure your MVVM DataGrid's ComboBox properly updates its DataTable records when selecting items. Follow our easy guide for effective data binding in WPF!
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This video is based on the question https://stackoverflow.com/q/70246979/ asked by the user 'Wolfenstyne' ( https://stackoverflow.com/u/16808525/ ) and on the answer https://stackoverflow.com/a/70247209/ 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 Fix MVVM Datagrid ComboBox Not Updating on Selection

If you are working with an MVVM project that incorporates a DataGrid with ComboBox columns, you may have encountered an issue where selecting an item in the ComboBox does not reflect in the underlying DataTable. This problem can be frustrating and can slow down your development process. Let's break down this issue and present a solution that ensures your ComboBox selections update your DataTable records as intended.

Understanding the Problem

In the case described, a DataGrid is populated using a DataTable as its ItemsSource. The ComboBox columns within the DataGrid are bound to an ObservableCollection representing the items you want to display. Despite being able to select items in the ComboBox, the changes do not appear in the DataTable records. For example, when selecting "Computer" from the ComboBox, the corresponding DataTable cell remains empty.

Context

The key elements involved include:

DataGrid: Displays data in a tabular format.

ComboBox: Allows for the selection of predefined items.

DataTable: Holds the data being displayed and manipulated.

Implementing the Solution

Step 1: Adjust the ComboBox Binding

To ensure the selected item from the ComboBox updates the DataTable correctly, you need to focus on the properties you are binding. Specifically, the SelectedValue property should be directly tied to the specific column of the DataTable that needs to be updated.

Here’s how you should structure your ComboBox binding:

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

Key Changes Explained

SelectedValue: Start binding this property to the specific column in your DataTable that you want to update (in this case, OType). This property should only be bound to one target—either the SelectedValue or SelectedItem, but not both, as they serve different purposes.

UpdateSourceTrigger: Set to PropertyChanged to ensure that updates occur immediately upon selection.

Step 2: Remove Conflicting Bindings

It is crucial not to bind both SelectedValue and SelectedItem. Doing so can create confusion in the data context, causing issues with the intended functionality:

Remove any binding to SelectedItem.

Stick to using either SelectedValue or SelectedItem, but not both.

Step 3: Verify Your DataContext

Ensure that your DataContext is set correctly in your DataGrid and that all your bindings reference this context appropriately. This will help avoid any binding issues that may prevent your data from updating correctly.

Conclusion

By making these adjustments to your ComboBox's binding configuration, you can resolve issues with your DataGrid not displaying updated values in its underlying DataTable. Ensure that your bindings are clear and concise, and always test your changes to verify that updates are reflected accurately. With this setup, your MVVM DataGrid can function as intended, providing a seamless experience for selecting and viewing data.

Feel free to try out the recommended changes in your project, and keep enhancing your MVVM applications with effective data bindings!