DOM025: Property Depends on a Variable Assigned in a Try Statement


Severity	Error
Reported by	PostSharp.Patterns.Model
Message	`NotifyPropertyChangedAttribute: automatic analysis of property <Property> failed. Method <Method> depends on a variable that is assigned inside a try statement. This is not currently supported. To ignore this message, add the [SafeForDependencyAnalysis] attribute to the property <Property>, and call Depends.On to specify its dependencies explicitly.`

Cause

The NotifyPropertyChangedAttribute aspect analyzes the getter of each property, and the methods of the same class that it calls, to find what the property depends on. When the code reads a local variable, the analysis follows the assignments of this variable. It does not support an assignment that is inside a try statement, in the try block or in one of its catch or finally blocks.

PostSharp reports DOM025 on <Property> when <Method>, the getter or a method that it calls, reads a local variable that is assigned inside a try statement.

In the following example, the AverageLine property calls ComputeAverageLine, which assigns result in a try statement to handle a division by zero.

Full screen

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

namespace Errors.DOM025_Error;

[NotifyPropertyChanged]
public class Invoice
{
    public int Total { get; set; }

    public int LineCount { get; set; }

    // The getter calls a method that assigns a variable in a try block.
    public int AverageLine => this.ComputeAverageLine();

    private int ComputeAverageLine()
    {
        int result;

        try
        {
            result = this.Total / this.LineCount;
        }
        catch ( DivideByZeroException )
        {
            result = 0;
        }

        return result;
    }
}

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

        invoice.Total = 120;
        invoice.LineCount = 3;
        Console.WriteLine( $"AverageLine: {invoice.AverageLine}" );
    }
}

Full screen

error DOM025: DOM025_Error.cs(15,16): NotifyPropertyChangedAttribute: automatic analysis of property Errors.DOM025_Error.Invoice.AverageLine failed. Method Errors.DOM025_Error.Invoice.ComputeAverageLine depends on a variable that is assigned inside a try statement. This is not currently supported. To ignore this message, add the [SafeForDependencyAnalysis] attribute to the property Errors.DOM025_Error.Invoice.AverageLine, and call Depends.On to specify its dependencies explicitly.

Resolution

Remove the try statement from the getter and from the methods that it calls, for example by testing that a divisor is not zero instead of catching the exception.
Otherwise, add SafeForDependencyAnalysisAttribute to the property, and call On in its getter with the properties that it depends on. The attribute makes you responsible for the dependencies that the analysis does not find.

In the following example, AverageLine declares its dependencies on Total and LineCount, so the aspect notifies it when either changes.

Full screen

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

namespace Errors.DOM025_Fixed;

[NotifyPropertyChanged]
public class Invoice
{
    public int Total { get; set; }

    public int LineCount { get; set; }

    // The property declares its dependencies itself.
    [SafeForDependencyAnalysis]
    public int AverageLine
    {
        get
        {
            Depends.On( this.Total, this.LineCount );

            return this.ComputeAverageLine();
        }
    }

    private int ComputeAverageLine()
    {
        int result;

        try
        {
            result = this.Total / this.LineCount;
        }
        catch ( DivideByZeroException )
        {
            result = 0;
        }

        return result;
    }
}

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

        invoice.Total = 120;
        invoice.LineCount = 3;
        Console.WriteLine( $"AverageLine: {invoice.AverageLine}" );
    }
}

Full screen

PropertyChanged: Total
PropertyChanged: AverageLine
PropertyChanged: LineCount
PropertyChanged: AverageLine
AverageLine: 40

Cause

Resolution

See Also