/// <summary>
/// Gets or creates a <see cref="IDynamicCommand"/> that will be attached to the <paramref name="viewModel"/>.
/// </summary>
/// <param name="viewModel">This <see cref="IViewModel"/>.</param>
/// <param name="name">The command name.</param>
/// <param name="factory">The command factory.</param>
/// <param name="configure">The optional function to configure the command builder.</param>
/// <returns>The attached <see cref="IDynamicCommand"/>. Null is returned if the <see cref="IViewModel"/> is disposed.</returns>
public static IDynamicCommand GetOrCreateCommand(
this IViewModel viewModel,
string name,
Func <string, IDynamicCommandBuilder> factory,
Func <IDynamicCommandBuilder, IDynamicCommandBuilder> configure = null
)
{
if (viewModel.IsDisposed)
{
return(null);
}
if (!viewModel.TryGetDisposable <IDynamicCommand>(name, out var command))
{
var builder = factory(name);
if (configure != null)
{
builder = configure(builder);
}
command = builder.Build();
viewModel.AddDisposable(command.Name, command);
}
return(command);
}
/// <summary>
/// Attaches a child <see cref="IViewModel"/> to a parent <see cref="IViewModel"/>.
/// By being attached, the child will be disposed when the parent is disposed.
/// Both also share the same <see cref="IViewModelView"/>.
/// A child can only be attached once to a single <see cref="IViewModel"/>.
/// </summary>
/// <typeparam name="TChildViewModel">The type of child viewmodel.</typeparam>
/// <param name="viewModel">The parent <see cref="IViewModel"/>.</param>
/// <param name="childViewModel">The child <see cref="IViewModel"/> to attach.</param>
/// <param name="name">The child ViewModel's name. This defaults to <paramref name="childViewModel"/>.Name when not provided.</param>
/// <returns>The attached child <see cref="IViewModel"/>.</returns>
public static TChildViewModel AttachChild <TChildViewModel>(this IViewModel viewModel, TChildViewModel childViewModel, string name = null)
where TChildViewModel : IViewModel
{
if (childViewModel == null)
{
throw new ArgumentNullException(nameof(childViewModel));
}
name = name ?? childViewModel.Name;
if (viewModel.TryGetDisposable(name, out var _))
{
throw new InvalidOperationException($"A child ViewModel with the name '{name}' is already attached to this ViewModel.");
}
viewModel.AddDisposable(name, childViewModel);
childViewModel.View = viewModel.View;
var parentViewChangedDisposable = new ParentViewChangedDisposable(viewModel, childViewModel);
childViewModel.AddDisposable(ParentViewChangedSubscriptionKey, parentViewChangedDisposable);
childViewModel.AddDisposable(RemoveSelfFromParentSubscriptionKey, new ActionDisposable(() => viewModel.RemoveDisposable(name)));
return(childViewModel);
}
/// <summary>
/// Gets or creates a property of the specified <paramref name="name"/>.
/// </summary>
/// <param name="viewModel">The <see cref="IViewModel"/> owning the property.</param>
/// <param name="name">The property's name.</param>
/// <param name="factory">The property factory.</param>
/// <returns>The <see cref="IDynamicProperty"/> matching the specified <paramref name="name"/>. Null is returned if the <see cref="IViewModel"/> is disposed.</returns>
public static IDynamicProperty GetOrCreateDynamicProperty(this IViewModel viewModel, string name, Func <string, IDynamicProperty> factory)
{
if (viewModel.IsDisposed)
{
return(null);
}
if (!viewModel.TryGetDisposable <IDynamicProperty>(name, out var property))
{
property = factory(name);
property.ValueChanged += OnDynamicPropertyChanged;
// We check the same condition twice because it's possible that the factory invocation already added the property.
// This can happen when the property implements IViewModel and was added using AttachChild.
if (!viewModel.TryGetDisposable <IDynamicProperty>(name, out var _))
{
viewModel.AddDisposable(name, property);
}
}
return(property);
void OnDynamicPropertyChanged(IDynamicProperty dynamicProperty)
{
viewModel.RaisePropertyChanged(dynamicProperty.Name);
}
}
/// <summary>
/// Gets or creates a <see cref="IDataLoader"/>.
/// </summary>
/// <param name="viewModel">The <see cref="IViewModel"/>.</param>
/// <param name="key">The key holding the <see cref="IDataLoader"/> in the containing <see cref="IViewModel"/>. This also serves as the default name of the <see cref="IDataLoader"/>.</param>
/// <param name="factory">The <see cref="IDataLoader"/> Factory.</param>
/// <returns>The <see cref="IDataLoader"/>. Null is returned if the <see cref="IViewModel"/> is disposed.</returns>
public static IDataLoader GetOrCreateDataLoader(
this IViewModel viewModel,
string key,
Func <string, IDataLoader> factory
)
{
if (viewModel.IsDisposed)
{
return(null);
}
if (!viewModel.TryGetDisposable <IDataLoader>(key, out var dataLoader))
{
dataLoader = factory(key);
viewModel.AddDisposable(key, dataLoader);
}
return(dataLoader);
}
/// <summary>
/// Registers a custom back button handler for this ViewModel.
/// </summary>
/// <param name="vm">The ViewModel.</param>
/// <param name="handle">The async handler method.</param>
/// <param name="canHandle">The optional canHandle function. When null is provided, the default behavior is applied (canHandle returns true only when the current ViewModel is active in the <see cref="ISectionsNavigator"/>).</param>
/// <param name="handlerName">The optional name of the handler. When null is provided, the ViewModel type name is used.</param>
/// <param name="priority">The optional priority. (See <see cref="IBackButtonManager.AddHandler(IBackButtonHandler, int?)"/> for more info.)</param>
public static void RegisterBackHandler(this IViewModel vm, Func <CancellationToken, Task> handle, Func <bool> canHandle = null, string handlerName = null, int?priority = null)
{
vm = vm ?? throw new ArgumentNullException(nameof(vm));
handlerName = handlerName ?? vm.GetType().Name;
handle = handle ?? throw new ArgumentNullException(nameof(handle));
canHandle = canHandle ?? DefaultCanHandle;
var backButtonManager = vm.GetService <IBackButtonManager>();
var handler = new BackButtonHandler(handlerName, canHandle, handle);
var registration = backButtonManager.RegisterHandler(handler, priority);
vm.AddDisposable("BackButtonHandler_" + handlerName, registration);
bool DefaultCanHandle()
{
var navigator = vm.GetService <ISectionsNavigator>();
// The handler can handle the back only if the associated ViewModel is the one currently active in the navigator.
return(navigator.GetActiveViewModel() == vm);
}
}
public static TDisposable GetOrCreateDisposable <TDisposable>(this IViewModel vm, Func <TDisposable> create, [CallerMemberName] string key = null)
where TDisposable : IDisposable
{
if (vm is null)
{
throw new ArgumentNullException(nameof(vm));
}
if (create is null)
{
throw new ArgumentNullException(nameof(create));
}
if (vm.TryGetDisposable(key, out var existingDisposable))
{
return((TDisposable)existingDisposable);
}
else
{
var disposable = create();
vm.AddDisposable(key, disposable);
return(disposable);
}
}
