name: gum-tool-dialogs
description: Gum dialog/popup systems. Triggers: DialogService, DialogWindow, DeleteOptionsWindow, dialog scrolling/layout, adding new dialog types, ShowMessage/ShowYesNoMessage, mocking IDialogService in unit tests.
Gum Dialog Systems Reference
Two Separate Systems
Gum has two independent dialog systems. Knowing which one is involved is critical before making changes.
1. DialogService System (MVVM, most dialogs)
Used by: message popups, yes/no confirmations, text input, choice selection, plugin management, import dialogs.
Flow: DialogService creates a DialogWindow, sets its DataContext to a view model. The Dialog control inside uses a DialogTemplateSelector to resolve the view model type to a UserControl view. After the view loads, Dialog.OnContentChanged binds attached properties from the view up to the Dialog control via deferred dispatch (DispatcherPriority.Loaded).
Key attached properties on views (set in XAML on the UserControl):
Dialog.DialogTitle — window titleDialog.Actions — custom button area (replaces default OK/Cancel)Dialog.AuxiliaryActions — extra buttons on the left side (e.g. Browse)Dialog.ScrollContent — true (default) enables outer ScrollViewer; false disables it so the view can manage its own scrolling (used by ImportFromGumxView)
View resolution: DialogViewResolver maps view model types to views by naming convention (FooViewModel -> FooView) or by [Dialog(typeof(VM))] attribute. Scans assemblies lazily and caches results. It always scans the VM's own assembly first, then - if unresolved - falls back to IDialogViewAssemblyProvider (default: every assembly currently loaded in the process) to find a VM whose View lives elsewhere (e.g. a DialogViewModel relocated into the headless Gum.Presentation assembly, paired with a View that stays in the Gum tool assembly or a dynamically-loaded plugin). The fallback only works via [Dialog(typeof(VM))] - naming-convention matching pairs a VM+View found within the same scanned assembly, so it can never bridge a cross-assembly pairing. Attribute the View before moving its VM out of the tool assembly.
Window sizing: DialogWindow starts with SizeToContent="WidthAndHeight". After content loads, Dialog.OnContentChanged switches to SizeToContent.Manual and clears the view's fixed Width/Height (sets to NaN), allowing the window to be resizable. DialogService.CreateDialogWindow sets MaxHeight to the owner window's ActualHeight.
2. DeleteOptionsWindow (standalone, code-behind)
Used by: delete confirmation only (DeleteLogic.ShowDeleteDialog).
Why it exists separately: The delete dialog needs runtime UI composition — plugins inject checkboxes and options into a StackPanel (e.g., "Delete associated files?", "Remove child instances?"). This cannot be done through the MVVM template system.
Never give an injected control an explicit Width. WPF centers an element that has a fixed size inside space it would otherwise stretch into, so a fixed-width checkbox renders indented relative to its neighbours, and a label longer than that width is clipped rather than wrapped. Being standalone, this window gets none of Dialog.OnContentChanged's fixed-size clearing described above. Set HorizontalAlignment.Left instead.
A checkbox label only wraps with an explicit MaxWidth on its own TextBlock. The themed CheckBox template (Themes/Frb.Styles.Defaults.xaml) measures its ContentPresenter in an Auto column, which supplies no width to wrap against, so TextWrapping alone is a no-op that widens the window instead. This applies to every checkbox in the tool, not just this dialog.
Flow: DeleteLogic (headless, Tools/Gum.Presentation/Managers/DeleteLogic.cs) calls the WPF-shell IDeleteDialogService, whose implementation DeleteDialogService creates the DeleteOptionsWindow, sets Message/Title, calls the concrete PluginManager.ShowDeleteDialog() (which lets plugins add controls to MainStackPanel), then calls ShowDialog(). DeleteDialogService depends on the concrete PluginManager, not IPluginManager — that interface dropped ShowDeleteDialog/DeleteConfirmed entirely when it moved into headless Gum.Presentation (#3754); those two WPF-typed calls live only on the concrete class now.
Not managed by DialogService — no view model, no template selection, no attached property binding. Changes to DialogWindow.xaml or Dialog.cs have zero effect on this window.
Key Files
| File | System | Purpose |
|---|
Gum/Services/Dialogs/DialogService.cs | MVVM | Creates and shows DialogWindow instances |
Gum/Services/Dialogs/DialogWindow.xaml | MVVM | Window chrome, layout template with ScrollViewer + button footer |
Gum/Services/Dialogs/Dialog.cs | MVVM | ContentControl with attached properties and template selector |
Gum/Services/Dialogs/DialogViewResolver.cs | MVVM | Maps view model types to view types; falls back to scanning its own (tool) assembly for a relocated VM's [Dialog]-attributed View |
Gum/Services/Dialogs/DialogViewModel.cs | MVVM | Base class with affirm/negative commands and RequestClose event |
Gum/Gui/Windows/DeleteOptionsWindow.xaml | Standalone | Delete confirmation window layout |
Gum/Gui/Windows/DeleteOptionsWindow.xaml.cs | Standalone | Code-behind with plugin-accessible StackPanel |
Gum/Services/Dialogs/DeleteDialogService.cs | Standalone | Creates and shows DeleteOptionsWindow; calls the concrete PluginManager |
Tools/Gum.Presentation/Managers/DeleteLogic.cs | Standalone | Orchestrates the delete flow via IDeleteDialogService |
Common Pitfalls
Wrong system: The most common mistake is modifying DialogWindow.xaml or Dialog.cs expecting it to affect the delete dialog. Always verify which system shows the dialog you're fixing.
File copy prompt: The "copy or reference?" dialog shown when a SourceFile/Font path outside the project folder is assigned lives in SetVariableLogic.AskIfShouldCopy (Gum/Plugins/InternalPlugins/VariableGrid/SetVariableLogic.cs), triggered via ReactIfChangedMemberIsSourceFile — not in the drag-drop layer.
ScrollViewer behavior: The Dialog template wraps content in a ScrollViewer. With Auto scrolling, child controls get infinite available height during WPF measure — so internal scroll viewers (like a TreeView) won't scroll. Set Dialog.ScrollContent="False" on views that need bounded height for internal scrolling.
Deferred binding: Dialog.OnContentChanged binds attached properties at DispatcherPriority.Loaded, not immediately. Code that reads these values before the dispatch fires will see defaults.
Testing Dialog Interactions (mocking IDialogService)
IDialogService exposes one message primitive: ShowMessage(message, title?, MessageDialogStyle?), returning a MessageDialogResult enum (Affirmative / Negative / Canceled; Negative == 0 is the unmocked Moq default → a Mock<IDialogService> returns "No" unless you set it up). The friendly helpers — ShowYesNoMessage, ShowChoices, etc. — are extension methods in IDialogServiceExtensions (Gum.Presentation), so a Moq mock can only Setup/Verify the underlying ShowMessage. A Yes/No prompt arrives as ShowMessage(msg, title, MessageDialogStyle.YesNo).
Gotcha: MessageDialogStyle is a class, and .Ok / .YesNo / .OkCancel each new up a fresh instance with no equality override — you cannot match a specific style by reference or equality. Distinguish a styled prompt (Yes/No, OK/Cancel) from a plain informational popup by style != null vs style == null — a bare ShowMessage(msg) passes null — or by inspecting AffirmativeText.
