powerSwitch | 万能切换插件，选项卡、跑马灯、手风琴、无限切换都不在话下

This is sort of an intellectually lazy solution, but it seems like it would require minimal changes to your existing code:

Use your existing code to create a config file without the "Default" line. Then read that file back into Python as a string. Then erase everything from the file, add the "Default" line to it, and then write back all the other contents of the file that you just read out of it.

The following code will add "Default" to the beginning of a text file (also not great code, just demonstrating what I mean):

The key to your problems is that you set IsSynchronizedWithCurrentItem="True" on your ListBox. What it does is it keeps the ListBox.SelectedItem and ListBox.Items.CurrentItem in sync. Also, ListBox.Items.CurrentItem is synchronized with the ICollectionView.CurrentItem property of the default collection view for the source collection (this view is returned by CollectionViewSource.GetDefaultView(Schemas) in your case). Now when you remove an item from the Schemas collection which also happens to be the CurrentItem of the corresponding collection view, the view by default updates its CurrentItem to the next item (or the previous one if the removed item was the last one, or to null if the removed item was the only item in the collection).

The second part of the problem is that when the ListBox.SelectedItem is changed causing an update to your view-model property, your RaisePropertyChangedEvent(nameof(ActiveSchema)) is processed after the update process is finished, in particular after the control is returned from the ActiveSchema setter. You can observe that the getter is not hit immediately, but only after the setter is done. What's important, the CurrentItem of the Schemas view is also not updated immediately to reflect the newly selected item. On the other hand, when you set IsActive = false on the previously selected item, it causes immediate "removal" of this item from the Schemas collection, which in turn causes an update of the CurrentItem of the collection view, and the chain immediately continues to update the ListBox.SelectedItem. You can observe that at this point the ActiveSchema setter will be hit again. So your ActiveSchema will be changed again (to the item next to the previously selected one) even before you've finished processing the previous change (to the item selected by the user).

There are several ways to address this issue:

#1

Set the IsSynchronizedWithCurrentItem="False" on your ListBox (or leave it untouched). This will make your problem go away with no effort. If however for some reason it is required, use any of the other solutions.

#2

Prevent reentrant attempts to set the ActiveSchema by using a guard flag: