Merge pull request #722 from CommunityToolkit/dev/notify-for-changing

Fix generation for OnPropertyChanging for [NotifyPropertyChangedFor]

Author: Sergio0694

src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservablePropertyGenerator.Execute.cs

@@ -109,7 +109,6 @@ public static bool TryGetInfo(
             token.ThrowIfCancellationRequested();
 
             using ImmutableArrayBuilder<string> propertyChangedNames = ImmutableArrayBuilder<string>.Rent();
-            using ImmutableArrayBuilder<string> propertyChangingNames = ImmutableArrayBuilder<string>.Rent();
             using ImmutableArrayBuilder<string> notifiedCommandNames = ImmutableArrayBuilder<string>.Rent();
             using ImmutableArrayBuilder<AttributeInfo> forwardedAttributes = ImmutableArrayBuilder<AttributeInfo>.Rent();
 
@@ -131,12 +130,6 @@ public static bool TryGetInfo(
 
             token.ThrowIfCancellationRequested();
 
-            // Track the property changing event for the property, if the type supports it
-            if (shouldInvokeOnPropertyChanging)
-            {
-                propertyChangingNames.Add(propertyName);
-            }
-
             // The current property is always notified
             propertyChangedNames.Add(propertyName);
 
@@ -296,12 +289,24 @@ public static bool TryGetInfo(
 
             token.ThrowIfCancellationRequested();
 
+            // Prepare the effective property changing/changed names. For the property changing names,
+            // there are two possible cases: if the mode is disabled, then there are no names to report
+            // at all. If the mode is enabled, then the list is just the same as for property changed.
+            ImmutableArray<string> effectivePropertyChangedNames = propertyChangedNames.ToImmutable();
+            ImmutableArray<string> effectivePropertyChangingNames = shouldInvokeOnPropertyChanging switch
+            {
+                true => effectivePropertyChangedNames,
+                false => ImmutableArray<string>.Empty
+            };
+
+            token.ThrowIfCancellationRequested();
+
             propertyInfo = new PropertyInfo(
                 typeNameWithNullabilityAnnotations,
                 fieldName,
                 propertyName,
-                propertyChangingNames.ToImmutable(),
-                propertyChangedNames.ToImmutable(),
+                effectivePropertyChangingNames,
+                effectivePropertyChangedNames,
                 notifiedCommandNames.ToImmutable(),
                 notifyRecipients,
                 notifyDataErrorInfo,

src/CommunityToolkit.Mvvm/ComponentModel/Attributes/NotifyPropertyChangedForAttribute.cs

@@ -46,8 +46,14 @@ namespace CommunityToolkit.Mvvm.ComponentModel;
 ///         get => name;
 ///         set
 ///         {
-///             if (SetProperty(ref name, value))
+///             if (!EqualityComparer<string>.Default.Equals(name, value))
 ///             {
+///                 OnPropertyChanging(nameof(Name));
+///                 OnPropertyChanged(nameof(FullName));
+///                 
+///                 name = value;
+///                 
+///                 OnPropertyChanged(nameof(Name));
 ///                 OnPropertyChanged(nameof(FullName));
 ///             }
 ///         }
@@ -58,8 +64,14 @@ namespace CommunityToolkit.Mvvm.ComponentModel;
 ///         get => surname;
 ///         set
 ///         {
-///             if (SetProperty(ref surname, value))
+///             if (!EqualityComparer<string>.Default.Equals(name, value))
 ///             {
+///                 OnPropertyChanging(nameof(Surname));
+///                 OnPropertyChanged(nameof(FullName));
+///                 
+///                 surname = value;
+///                 
+///                 OnPropertyChanged(nameof(Surname));
 ///                 OnPropertyChanged(nameof(FullName));
 ///             }
 ///         }