Raise an event whenever a property s value changed

Question

There is a property  it s named ImageFullPath1  public string ImageFullPath1  get  set      I m going fire an event whenever its value changed  I am aware of changing INotifyPropertyChanged  but I want to do it with events

User · Answer

If you change your property to use a backing field  instead of an automatic property   you can do the following   public event EventHandler ImageFullPath1Changed  private string  imageFullPath1   string Empty   public string ImageFullPath1      get         return imageFullPath1         set         if   imageFullPath1    value                imageFullPath1   value         EventHandler handler   ImageFullPathChanged        if  handler    null          handler this  e

User · Answer

The INotifyPropertyChanged interface is implemented with events   The interface has just one member  PropertyChanged  which is an event that consumers can subscribe to   The version that Richard posted is not safe   Here is how to safely implement this interface   public class MyClass   INotifyPropertyChanged       private string imageFullPath       protected void OnPropertyChanged PropertyChangedEventArgs e                PropertyChangedEventHandler handler   PropertyChanged          if  handler    null              handler this  e              protected void OnPropertyChanged string propertyName                OnPropertyChanged new PropertyChangedEventArgs propertyName               public string ImageFullPath               get   return imageFullPath            set                       if  value    imageFullPath                                imageFullPath   value                  OnPropertyChanged  ImageFullPath                                       public event PropertyChangedEventHandler PropertyChanged      Note that this does the following things    Abstracts the property-change notification methods so you can easily apply this to other properties  Makes a copy of the PropertyChanged delegate before attempting to invoke it  failing to do this will create a race condition   Correctly implements the INotifyPropertyChanged interface    If you want to additionally create a notification for a specific property being changed  you can add the following code   protected void OnImageFullPathChanged EventArgs e        EventHandler handler   ImageFullPathChanged      if  handler    null          handler this  e      public event EventHandler ImageFullPathChanged    Then add the line OnImageFullPathChanged EventArgs Empty  after the line OnPropertyChanged  ImageFullPath     Since we have  Net 4 5 there exists the CallerMemberAttribute  which allows to get rid of the hard-coded string for the property name in the source code       protected void OnPropertyChanged           System Runtime CompilerServices CallerMemberName  string propertyName                     OnPropertyChanged new PropertyChangedEventArgs propertyName               public string ImageFullPath               get   return imageFullPath            set                       if  value    imageFullPath                                imageFullPath   value                  OnPropertyChanged

User · Answer

Raising an event when a property changes is precisely what INotifyPropertyChanged does  There s one required member to implement INotifyPropertyChanged and that is the PropertyChanged event  Anything you implemented yourself would probably be identical to that implementation  so there s no advantage to not using it

User · Answer

public event EventHandler ImageFullPath1Changed   public string ImageFullPath1       get                  insert getter logic           set                  insert setter logic                    EDIT -- this example is not thread safe -- do not use in production code         if  ImageFullPath1Changed    null  amp  amp  value     backingField              ImageFullPath1Changed this  new EventArgs   whatever                                       That said  I completely agree with Ryan   This scenario is precisely why INotifyPropertyChanged exists

User · Answer

I use largely the same patterns as Aaronaught  but if you have a lot of properties it could be nice to use a little generic method magic to make your code a little more DRY  public class TheClass   INotifyPropertyChanged       private int  property1      private string  property2      private double  property3       protected virtual void OnPropertyChanged PropertyChangedEventArgs e            PropertyChangedEventHandler handler   PropertyChanged          if handler    null                handler this  e                        protected void SetPropertyField lt T gt  string propertyName  ref T field  T newValue            if  EqualityComparer lt T gt  Default Equals field  newValue                 field   newValue              OnPropertyChanged new PropertyChangedEventArgs propertyName                         public int Property1           get   return  property1            set   SetPropertyField  Property1   ref  property1  value               public string Property2           get   return  property2            set   SetPropertyField  Property2   ref  property2  value               public double Property3           get   return  property3            set   SetPropertyField  Property3   ref  property3  value                 region INotifyPropertyChanged Members      public event PropertyChangedEventHandler PropertyChanged        endregion     Usually I also make the OnPropertyChanged method virtual to allow sub-classes to override it to catch property changes

[c#] Raise an event whenever a property's value changed?

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