How can i RaisePropertyChanged on property change?

Question

Here I added a model to my viewmodel...

public dal.UserAccount User  {
  get
  {
    return _user;
  }
  set
  {
    _user = value;
    RaisePropertyChanged(String.Empty); 
   }
}

I handle property change event...

public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
  if (this.PropertyChanged != null)
    this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}

This is the binding i use.

<TextBox Text="{Binding User.firstname, Mode=TwoWay, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}" />

Problem is propertychange event is not trigger on updating view ? Can anybody tell me what i am doing wrong...

Answer 1

You can invoke a property changed event from another class. Not particularly useful if you have all the sources. For closed source it might be. Though I wouldn't consider it experimental and not production ready.

See this console copy paste example:

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;

namespace ConsoleApp1
{
    public class Program
    {
        static void Main(string[] args)
        {
            var a = new A();
            a.PropertyChanged += A_PropertyChanged;
            var excpl = new Excpl();
            excpl.Victim = a;
            excpl.Ghost.Do();
        }

        private static void A_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            Console.WriteLine("Event triggered");
        }
    }

    [StructLayout(LayoutKind.Explicit)]
    public struct Excpl
    {
        [FieldOffset(0)]
        public A Victim;
        [FieldOffset(0)]
        public C Ghost;
    }

    public class A : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
    }

    public class C : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public void Do()
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(""));
        }
    }
}

Answer 2

PropertyChanged is used to notify the UI that something has been changed in the Model. Since you're changing an inner property of the User object - the User property itself is not changed and therefore the PropertyChanged event isn't raised.

Second - your Model should implement the INotifyPropertyChanged interface. - In other words make sure UserAccount implements INotifyPropertyChanged, otherwise changing the firstname will not affect the view either.

Another thing:

The parameter RaisePropertyChanged should receive is the Name of the property that has changed. So in your case:

Change:
RaisePropertyChanged(String.Empty);

To
RaisePropertyChanged("User");

From MSDN:

The PropertyChanged event can indicate all properties on the object have changed by using either null or String.Empty as the property name in the PropertyChangedEventArgs.

(No need to refresh all the Properties in this case)

You can read more on the concept of PropertyChanged here