DOM030: IgnoreAutoChangeNotification Applied to a Method


Severity	Warning
Reported by	PostSharp.Patterns.Model
Message	`Usage of <Attribute> on "<Method>" is deprecated. <Reason> This warning may become an error in a future version.`

Cause

The IgnoreAutoChangeNotificationAttribute attribute, applied to a property, prevents the NotifyPropertyChangedAttribute aspect from raising the change notifications of this property. For historical reasons, the attribute can also be applied to a method. The aspect then accepts the calls to the method without analyzing them, so the properties whose getters call the method lose the dependencies that the method hides.

PostSharp reports DOM030 on each method that has the attribute. <Attribute> is [IgnoreAutoChangeNotification], and <Reason> is The attribute should not be used on methods.

In the following example, the attribute is applied to ComputeTotal, which the Total property calls.

Full screen

using System;
using System.ComponentModel;
using PostSharp.Patterns.Model;

namespace Errors.DOM030_Error;

[NotifyPropertyChanged]
public class OrderLine
{
    public decimal UnitPrice { get; set; }

    public int Quantity { get; set; }

    public decimal Total => this.ComputeTotal();

    // [IgnoreAutoChangeNotification] is meant for properties, not methods.
    [IgnoreAutoChangeNotification]
    private decimal ComputeTotal() => this.UnitPrice * this.Quantity;
}

public static class Program
{
    public static void Main()
    {
        var line = new OrderLine { UnitPrice = 10m };
        ((INotifyPropertyChanged) line).PropertyChanged +=
            ( _, e ) => Console.WriteLine( $"PropertyChanged: {e.PropertyName}" );

        line.Quantity = 3;
        Console.WriteLine( $"Total: {line.Total}" );
    }
}

Full screen

warning DOM030: DOM030_Error.cs(18,21): Usage of [IgnoreAutoChangeNotification] on "Errors.DOM030_Error.OrderLine.ComputeTotal" is deprecated. The attribute should not be used on methods. This warning may become an error in a future version.

The program runs, but changing Quantity raises no notification for Total:

Full screen

PropertyChanged: Quantity
Total: 30

Resolution

Remove the attribute from the method. Then, depending on what the method does:

When the method belongs to the same class, the aspect analyzes it and finds its dependencies.
When the method depends only on its arguments, mark it with PureAttribute.
Otherwise, add SafeForDependencyAnalysisAttribute to the properties that call the method, and declare their dependencies with On.

In the following example, the attribute is removed, and changing Quantity notifies Total.

Full screen

using System;
using System.ComponentModel;
using PostSharp.Patterns.Model;

namespace Errors.DOM030_Fixed;

[NotifyPropertyChanged]
public class OrderLine
{
    public decimal UnitPrice { get; set; }

    public int Quantity { get; set; }

    public decimal Total => this.ComputeTotal();

    // Without the attribute, the aspect analyzes the method and finds its dependencies.
    private decimal ComputeTotal() => this.UnitPrice * this.Quantity;
}

public static class Program
{
    public static void Main()
    {
        var line = new OrderLine { UnitPrice = 10m };
        ((INotifyPropertyChanged) line).PropertyChanged +=
            ( _, e ) => Console.WriteLine( $"PropertyChanged: {e.PropertyName}" );

        line.Quantity = 3;
        Console.WriteLine( $"Total: {line.Total}" );
    }
}

Full screen

PropertyChanged: Quantity
PropertyChanged: Total
Total: 30

Cause

Resolution

See Also