Capoala.MVVM 2017.1.2.5

Capoala.MVVM

Capoala.MVVM is a featherlight MVVM framework designed for simple-to-moderate MVVM design pattern applications. This framework includes basic implementations for handling property notifications, command bindings, and navigation.

INotifyPropertyChanged

NotifyingObjectBaseSlim

The NotifyingObjectBaseSlim class is a slim, standard INotifyPropertyChanged implementation. A streamlined method named SetAndNotify() will set the referenced property's value and raise the PropertyChanged event in one swell swoop.

public class ViewModel : Capoala.MVVM.NotifyingObjectBaseSlim
{
    string _name = null;
    public string Name { get => _name; set => SetAndNotify(ref _name, value); }
}

In cases where extra work or additional notifications are required, you can use standard getter setter syntax and utilize the Notify() method to raise the PropertyChanged event on the property being set.

public class ViewModel : Capoala.MVVM.NotifyingObjectBaseSlim
{
    string _firstName = null;
    public string FirstName
    {
        get => _firstName;
        set
        {
            _firstName = value;
            Notify();
            Notify(nameof(FullName));
        }
    }

    string _lastName = null;
    public string LastName
    {
        get => _lastName;
        set
        {
            if (SetAndNotify(ref _lastName, value))
                Notify(nameof(FullName));
        }
    }

    public string FullName => $"{FirstName} {LastName}";
}

NotifyingObjectBase

The NotifyingObjectBase class is a more feature-rich implementation of the INotifyPropertyChanged interface. This class removes the requirement of a backing field and moves it into a backing store in the form of a Dictionary<string, object>.

This class also provides an attribute approach to streamlining property notification dependencies. In the below example, the property FullName subscribes to the FirstName and LastName event changes. When either FirstName or LastName is changed, FullName is also notified.

public class ViewModel : Capoala.MVVM.NotifyingObjectBase
{
    public string FirstName { get => Get<string>(); set => Set(value); }
    public string LastName { get => Get<string>(); set => Set(value); }

    [NotifiedOnChange(nameof(FirstName), nameof(LastName))]
    public string FullName => $"{FirstName} {LastName}";
}

ICommand

RelayCommand

The RelayCommand implements the ICommand interface and comes in two flavors; RelayCommand and RelayCommand<T> for passing command paramters.

using Capoala.MVVM;
using DW = System.Diagnostics.Debug;

public class ViewModel
{
    public RelayCommand SaveCommand { get; } 
        = new RelayCommand(() => DW.WriteLine("Saving..."));

    public RelayCommand<string> GetRecordCommand { get; } 
        = new RelayCommand<string>(entryName => DW.WriteLine(entryName));
}

...
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition Width="Auto"/>
    </Grid.ColumnDefinitions>
    <TextBox x:Name="RecordID"/>
    <Button Grid.Column="1" 
            Margin="10 0 0 0" 
            Command="{Binding GetRecordCommand}" 
            CommandParameter="{Binding ElementName=RecordID, Path=Text}">Retreive</Button>
</Grid>
<Grid Grid.Row="1" Margin="0 20 0 0">
    
</Grid>
<Grid Grid.Row="2" Margin="0 20 0 0">
    <Button HorizontalAlignment="Right" 
            Command="{Binding SaveCommand}">Save</Button>
</Grid>
...

Navigation

A simplistic navigation implementation is also available which should satisfy most requirements. The navigation system includes an INavigationService<TNavigationItem> interface, and a NavigationServiceBase<TNavigationItem> base class.

using Capoala.MVVM;

public static class NavigationHelper
{
    public static INavigationService<object> Navigator { get; } 
        = new DefaultNavigationService();
}

public class ViewModel { }

public class MainViewModel : NotifyingObjectBase
{
    public object CurrentViewModel { get => Get<object>(); set => Set(value); }

    public MainViewModel()
    {
        NavigationHelper.Navigator.NavigationDidHappen += (s, e) =>
        {
            CurrentViewModel = NavigationHelper.Navigator.Current;
        };

        NavigationHelper.Navigator.Navigate(new ViewModel());
    }
}