I’ve run into this exact kind of binding loop issue with WPF ComboBoxes before—let’s walk through the most likely causes and fixes to get you un-stuck.

Common Causes & Fixes for the Binding Loop #

1. Two-Way Binding + Command Feedback Loop

Your SelectedValue is two-way bound to SelectedModule, and you’ve got a PropertyChangeBehavior.Command that triggers ModuleCommand when the selection changes. If that command (or the SelectedModule setter) updates the Modules collection, which then triggers another selection change via binding, you’ve got a loop.

• Debug step: Temporarily comment out the commands:PropertyChangeBehavior.Command binding. If the loop stops, this is your culprit.
• Fix: Add a simple flag in your ViewModel to block command execution during collection updates:

  private bool _isUpdatingModules;
  
  private void UpdateModules()
  {
      _isUpdatingModules = true;
      // Clear and repopulate your Modules collection here
      Modules.Clear();
      foreach (var newModule in NewModuleData)
      {
          Modules.Add(newModule);
      }
      // Manually set SelectedModule if needed
      SelectedModule = Modules.FirstOrDefault()?.Key;
      _isUpdatingModules = false;
  }
  
  // In your ModuleCommand's CanExecute logic
  public bool CanExecuteModuleCommand()
  {
      return !_isUpdatingModules;
  }
  

2. IsSynchronizedWithCurrentItem Causing Unwanted Syncs

Setting IsSynchronizedWithCurrentItem="True" ties your ComboBox to the CollectionView of Modules. When you clear and refill the collection, the CollectionView’s current item resets (to null or the first item), which triggers a SelectedValue change, which triggers your command, which updates the collection… and the cycle repeats.

• Debug step: Set IsSynchronizedWithCurrentItem="False" and test if the loop goes away.
• Fix: Manage the selected item manually instead of relying on sync:
  • Before clearing the collection, save the current SelectedModule value.
  • After refilling, set SelectedModule back to the saved value (or a default) only if it exists in the new collection.
  • Keep IsSynchronizedWithCurrentItem off unless you explicitly need it for other parts of your UI.

3. Collection Clear/Refill Triggering Selection Changes

When you call Modules.Clear(), the SelectedValue automatically becomes null, which fires the SelectedModule setter and your ModuleCommand. If that command tries to repopulate the collection immediately, the new collection might trigger another selection change, restarting the loop.

• Fix: Minimize binding triggers during collection updates. For an ObservableCollection, use a batch add helper to reduce notifications:

  // Helper extension for ObservableCollection
  public static void AddRange<T>(this ObservableCollection<T> collection, IEnumerable<T> items)
  {
      foreach (var item in items)
      {
          collection.Add(item);
      }
  }
  
  // Update collection with fewer binding triggers
  Modules.Clear();
  Modules.AddRange(NewModuleData);
  

  This reduces the number of times binding updates fire, making it easier to control when selection changes trigger your command.

内容的提问来源于stack exchange，提问作者Wojciech Szabowicz