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Accepted
Edwin V
Asked: 2020-02-04 12:06:29 +0800 CST 2020-02-04 12:06:29 +0800 CST

What is the correct way to initialize a property in MVVM

  • 772

I have a question, is it correct to initialize a property fullin ViewModelthe following way?

public class MainViewModel : ViewModelBase
{
    private ObservableCollection<Driver> _drivers = new ObservableCollection<Driver>();
    public ObservableCollection<Driver> Drivers
    {
        get { return _drivers; }
        set { _drivers = value;
            RaisePropertyChanged();
        }
    }

}

Is it correct? Is it a bad practice? Or should it be done in another way? My question arises because I was trying to fill that collection with a method that initialized the field but the changes were not reflected in the XAMLone that is bound to the property Drivers, only instantiating the field _driversin this way made it work. Thanks.

c#

2 Answers

  1. Best Answer

    I don't see it wrong, but I would recommend initializing in the constructor of theViewModel

    public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        _drivers = new ObservableCollection<Driver>();
    }

    private ObservableCollection<Driver> _drivers = null;
    public ObservableCollection<Driver> Drivers
    {
        get { return _drivers; }
        set 
        { 
            _drivers = value;
            RaisePropertyChanged();
        }
    }

}
    • 3

  2. Be careful , it seems that you are implementing INotifyPropertyChanged, if you bind to a property before instantiating it, and you instantiate it like this:

    _drivers = new ObservableCollection<Driver>();

    You are not going to call the Setter of the property and therefore the XAML (GUI) is not going to react to the change.

    That is, you have:

    <DataGrid ItemsSource={Binding Drivers}> ... </DataGrid>

    And you are creating an instance of the private _drivers field, without going through the Drivers observable property, the XAML (GUI) will not notice the change

    Create the instance using the observable property to "tell" the GUI that there is a new instance:

    Drivers = new ObservableCollection<Driver>();

    Regardless of this and answering your original question, I recommend instantiating your properties and variables in the constructor, or even in a separate method eg "Initialize()" and call this method from the constructor, so you have more control over where you are creating your instances , but this depends on the preferences of each person

    You can even have your properties in a static class and have them globally accessible to the entire application (similar to the "singleton" pattern)

    • 1