How do I subscribe to PropertyChanged event in my ViewModel?

问题

I have core functionality encapsulated in ViewModelBase

Now I want to see when PropertyChanged event was raised by ViewModelBase and act on it. For example, when one property was changed on ViewModelBase - I want to change property on my ViewModel

How do I achieve this?

public class MaintainGroupViewModel : BaseViewModel<MEMGroup>
    {


public abstract class BaseViewModel<T> : NotificationObject, INavigationAware
        where T : Entity
    {

回答1:

I am concerned that you're effectively doing a 'manual binding' (bad) for a property in a derived class to a value on the base class (also bad). The whole point of using inheritance is that the derived class can access things in the base class. Use a protected modifier to indicate things should only be accessible to derived classes.

I would suggest this (potentially) more correct method:

Base class:

protected virtual void OnMyValueChanged() { }

Derived class:

protected override void OnMyValueChanged() { /* respond here */ }

Really, subscribing to an event in the base class of the very class you're writing just seems incredibly backwards - what's the point of using inheritance over composition if you're going to compose yourself around yourself? You're literally asking an object to tell itself when something happens. A method call is what you should use for that.

In terms of "when one property was changed on ViewModelBase - I want to change property on my ViewModel", ... they are the same object!

回答2:

Usually I use register to the PropertyChanged event in the class Constructor

public MyViewModel()
{
    this.PropertyChanged += MyViewModel_PropertyChanged;
}

and my PropertyChanged event handler looks like this:

void MyViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    switch (e.PropertyName)
    {
        case "SomeProperty":
            // Do something
            break;
    }
}

回答3:

The direct way to subscribe to property changes is using INotifyPropertyChanged if your BaseViewModel implements it:

PropertyChanged += (obj, args) =>
   { System.Console.WriteLine("Property " + args.PropertyName + " changed"); }

If it doesn't, then it has to be a DependencyObject, and your properties have to be DependencyProperties (which is probably a more complicated way).

This article describes how to subscribe for DependencyProperty changes.

来源：https://stackoverflow.com/questions/7824967/how-do-i-subscribe-to-propertychanged-event-in-my-viewmodel

标签

mvvm

inotifypropertychanged