笔记本

When you are in a DataTemplate, the DataContext might not be what you expect. Typically the DataContext in a DataTemplate is set to the item that the DataTemplate represents. If your TextChanged command is on the "main viewmodel" instead of the data item, you need to be more precise in the way that you specify the data binding, for example:

Command="{Binding Source={StaticResource Locator}, Path=Main.TextChanged}"

You can see the issue when you run the code in debug mode (F5) in Studio and observe the Output window. A Data Error will be shown if the DataContext is incorrectly set.