# Helpers — index

Cross-cutting utilities. See [`schema.md`](../schema.md) for the memory-map conventions.

| File | Purpose |
|------|---------|
| `ViewModelBase.cs` | `INotifyPropertyChanged` + `SetProperty<T>()` — base for all ViewModels |
| `RelayCommand.cs` | `ICommand` implementation for all button actions |
| `AppLog.cs` | File logger to `%APPDATA%\ytLlive\startup.log`; startup checkpoints + unhandled-exception capture (the crash this map is named for) |
| `FocusPreservingListBox.cs` | `ListBox` subclass that keeps selection/focus coherent when the selected item is deleted; `IsSelectable` predicate skips hidden scenes; drag-reorder guard |
| `OAuthCredentials.cs` | Baked-in Google OAuth client ID/secret (desktop app; loopback callback) |
| `ImageCache.cs` | Image byte caching (assets live in the DB) |
| `InverseBoolToVisibilityConverter.cs` / `NotNullToVisibilityConverter.cs` | XAML value converters for visibility bindings |

Related: [`Themes/Controls.xaml`](../Themes/Controls.xaml) styles the lists this
class backs; [`Models/index.md`](../Models/index.md) and
[`ViewModels/index.md`](../ViewModels/index.md) for the objects it works on.