Capoala.MVVM

Capoala.MVVM is a minimalist framework for MVVM based applications. This framework provides both IPropertyChanged and ICommand implementations, as well as a simple navigation base.

ICommand

CommandRelay

The CommandRelay implements the ICommand interface and comes in two flavors; CommandRelay and CommandRelay<TExecutionParameter> for passing a parameter to the execute method.

Class ViewModel

using Capoala.MVVM;
using System.Diagnostics;

internal class ViewModel
{
    public CommandRelay SaveCommand { get; } 
        = new CommandRelay(() => Debug.WriteLine("Saving..."));

    public CommandRelay<string> AddInputCommand { get; } 
        = new CommandRelay<string>(input => Debug.WriteLine(input));
}

XAML

...

<!-- Bind to SaveCommand -->
<Button Content="Save" 
        Command="{Binding SaveCommand}"/>

...

<!-- Bind to AddInputCommand using a parameter -->
<Button Content="Add" 
        Command="{Binding AddInputCommand}", 
        CommandParameter="{Binding ElementName=InputTextBox, Path=Text}"/>

...

INotifyPropertyChanged

INotifyPropertyChanges

The INotifyPropertyChanges is a custom interface for implementing the INotifyPropertyChanged interface. The INotifyPropertyChanges interface exposes methods for implementing the INotifyPropertyChanged event and is defined - without summaries - as follows:

public interface INotifyPropertyChanges : INotifyPropertyChanged
{
    void Notify([CallerMemberName] string propertyName = null);

    bool SetAndNotify<T>(
        ref T backingField, 
        T value, 
        EqualityComparer<T> equalityComparer = null, 
        [CallerMemberName] string propertyName = null);
}

NotifyPropertyChangesBaseSlim

NotifyPropertyChangesBaseSlim is an abstract class that simply implements the INotifyPropertyChanges interface.

NotifyPropertyChangesBase

NotifyPropertyChangesBase is an abstract class that implements the INotifyPropertyChanges interface and supports the SubscribeToChanges, NotifyOnChange, and CanExecuteDependentOn attributes. These attributes allow a streamlined approach to notifying other properties and re-triggering the NotifyCanExecuteDidChange method on CommandRelay objects.

using Capoala.MVVM;
using System.Windows;

internal class SampleViewModel : NotifyPropertyChangesBase
{
    private bool _isOperationInProgress = false;
    public bool IsOperationInProgress 
    { 
        get => _isOperationInProgress; 
        set => SetAndNotify(ref _isOperationInProgress, value); 
    }

    private string _firstName;
    public string FirstName 
    { 
        get => _firstName; 
        set => SetAndNotify(ref _firstName, value); 
    }

    private string _lastName;
    public string LastName 
    { 
        get => _lastName; 
        set => SetAndNotify(ref _lastName, value); 
    }

    [SubscribeToChanges(nameof(FirstName), nameof(LastName))]
    public string DisplayName => string.IsNullOrEmpty(LastName) && string.IsNullOrEmpty(FirstName)
        ? null
        : string.IsNullOrEmpty(LastName) && !string.IsNullOrEmpty(FirstName)
        ? $"{FirstName}"
        : !string.IsNullOrEmpty(LastName) && string.IsNullOrEmpty(FirstName)
        ? $"{LastName}"
        : $"{LastName}, {FirstName}";

    [CanExecuteDependentOn(nameof(FirstName), nameof(LastName), nameof(IsOperationInProgress))]
    public CommandRelay CreateCommand { get; }

    public SampleViewModel() => CreateCommand = new CommandRelay(() => 
    {
        // Do Something.

    }, () => !IsOperationInProgress && 
             !string.IsNullOrEmpty(FirstName) && 
             !string.IsNullOrEmpty(LastName))
}

NotifyPropertyChangesBaseAutoBackingStore

NotifyPropertyChangesBaseAutoBackingStore is an abstract class that inherits from NotifyPropertyChangesBase, but includes a “backing store” in the form of a Dictionary<string, object>. This allows us to not have to define private fields and is useful for testing and “notifying” models. Using the above sample, below is how the code would look using the NotifyPropertyChangesBaseAutoBackingStore base class.

using Capoala.MVVM;
using System.Windows;

internal class SampleViewModel : NotifyPropertyChangesBaseAutoBackingStore
{
    public bool IsOperationInProgress { get => Get<bool>(); set => Set(value); 
    public string FirstName { get => Get<string>(); set => Set(value); 
    public string LastName { get => Get<string>(); set => Set(value); 

    [SubscribeToChanges(nameof(FirstName), nameof(LastName))]
    public string DisplayName => string.IsNullOrEmpty(LastName) && string.IsNullOrEmpty(FirstName)
        ? null
        : string.IsNullOrEmpty(LastName) && !string.IsNullOrEmpty(FirstName)
        ? $"{FirstName}"
        : !string.IsNullOrEmpty(LastName) && string.IsNullOrEmpty(FirstName)
        ? $"{LastName}"
        : $"{LastName}, {FirstName}";

    [CanExecuteDependentOn(nameof(FirstName), nameof(LastName), nameof(IsOperationInProgress))]
    public CommandRelay CreateCommand { get; }

    public SampleViewModel() => CreateCommand = new CommandRelay(() => 
    {
        // Do Something.

    }, () => !IsOperationInProgress && 
             !string.IsNullOrEmpty(FirstName) && 
             !string.IsNullOrEmpty(LastName))    
}

Navigation

SimpleMvvmNavigator

The SimpleMvvmNavigator<TNavigationItem> class is a simplistic implementation for navigation. This class exposes only an event for subscribing to navigation changes and a method for performing the navigation itself.

internal static class Services
{
    internal static SimpleMvvmNavigator<INotifyPropertyChanges> Navigator { get; } 
        = new SimpleMvvmNavigator<INotifyPropertyChanges>();
}

internal class MainViewModel : NotifyPropertyChangesBaseAutoBackingStore
{
    public INotifyPropertyChanges CurrentViewModel 
    { 
        get => Get<INotifyPropertyChanges>(); 
        set => Set(value); 
    }

    public MainViewModel() => 
        Services.Navigator.NavigationDidHappen += (s, e) => 
            CurrentViewModel = e.NavigationItem;
}

internal class TestViewModel : INotifyPropertyChanges
{
    public CommandRelay<INotifyPropertyChanges> Navigate { get; } 
        = new CommandRelay<INotifyPropertyChanges>(
            (viewModel) => Services.Navigator.NavigateTo(viewModel));
}

MvvmNavigatorBase

MvvmNavigatorBase<TNavigationItem> is an abstract class for implementing a more robust, full featured navigation scheme. This class has default support for going both back and forward as well as additional properties to allow for modification on class inheritance.

MvvmNavigator

MvvmNavigator is a default implementation of MvvmNavigatorBase and allows constructor settings for supporting back and forward navigation, which can yield a small performance benefit.

internal static class Services
{
    internal static MvvmNavigator<INotifyPropertyChanges> Navigator { get; } 
        = new MvvmNavigator<INotifyPropertyChanges>();

    internal static MvvmNavigator<INotifyPropertyChanges> NoForwardNavigator { get; } 
        = new MvvmNavigator<INotifyPropertyChanges>(supportsForwardNavigation: false);

    internal static MvvmNavigator<INotifyPropertyChanges> NoBackNavigator { get; } 
        = new MvvmNavigator<INotifyPropertyChanges>(supportsBackNavigation: false);

    // This is essentially the same as "SimpleMvvmNavigator", but still exposes
    // properties and methods for going back and forward, as we are still
    // inheriting from the base class.     
    internal static MvvmNavigator<INotifyPropertyChanges> NoBackNavigator { get; } 
        = new MvvmNavigator<INotifyPropertyChanges>(
            supportsBackNavigation: false, 
            supportsForwardNavigation: false);
}

Attributes

SubscribeToChanges

SubscribeToChanges is an attribute used to allow a property with this attribute to subscribe to value changes of other properties.

NotifyOnChange

NotifyOnChange is an attribute used to allow a property with this attribute to notify other properties when its value changes.

CanExecuteDependentOn

CanExecuteDependentOn is an attribute used to allow a property - of type CommandRelay or CommandRelay<TExecutionParameter> - to subscribe to value changes of other properties. This attribute differs from SubscribeToChanges, as SubscribeToChanges will raise the PropertyChangedEventHandler event of an INotifyPropertyChanged interface, while this attribute will raise the CanExecuteChanged event of an ICommand interface.

Events and Event Arguments

NavigationChangedEventHandler<TNavigationItem> is a delegate for supporting navigation changes.

The NavigationChangedEventArgs<TNavigationItem> class is used with the NavigationChangedEventHandler<TNavigationItem> event handler for navigation support.