Mastering the DebuggerDisplay Attribute in C#

Underrated powerful attribute while debugging

Debugging is an essential part of software development, and having the right tools and techniques can make the process significantly smoother. One such tool in C# is the DebuggerDisplay attribute. This attribute allows developers to customize how objects appear in the debugger, providing clearer insights into the application's state during runtime.

In this blog post, we'll delve deep into the DebuggerDisplay attribute, exploring its usage, benefits, and best practices. We'll also provide code examples to illustrate how you can leverage this attribute to enhance your debugging experience.

What is the DebuggerDisplay Attribute?

The DebuggerDisplay attribute is part of the System.Diagnostics namespace and is used to control how a class or field is displayed in the debugger variable windows. Instead of the default display (usually the class name), you can specify a custom string that provides more meaningful information about the object's state.

[DebuggerDisplay("Display string")]
public class MyClass
{
    // Class implementation
}

The string inside the DebuggerDisplay attribute can include expressions enclosed in curly braces {}. These expressions are evaluated at runtime and can reference fields, properties, or methods of the class.

Why Use DebuggerDisplay?

When debugging complex applications, you often deal with objects that contain numerous fields and properties. By default, the debugger may not provide an immediate understanding of an object's state. The DebuggerDisplay attribute helps by:

• Improving Readability: Display essential information directly in the debugger, reducing the need to drill down into object hierarchies.

• Saving Time: Quickly identify issues by seeing relevant data upfront.

• Customizing Display: Tailor the debug display to show what's most important for your debugging context.

Basic Usage

Applying DebuggerDisplay to a Class

Here's a simple example of how to use the DebuggerDisplay attribute on a class:

using System.Diagnostics;

[DebuggerDisplay("Name = {Name}, Age = {Age}")]
public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

// Usage
var person = new Person { Name = "Alice", Age = 28 };

In the Debugger, the person object will display:

Name = Alice, Age = 28

How It Works

• Expressions in Curly Braces: {Name} and {Age} are placeholders that the debugger replaces with the actual values of those properties at runtime.

• Static Text: You can include any static text outside the braces, such as "Name =" and ", Age =".

Advanced Scenarios

Displaying Private Members

The DebuggerDisplay attribute can access private fields and properties, which can be incredibly useful when you need to see internal state not exposed publicly.

[DebuggerDisplay("ID = {_id}, Status = {_status}")]
public class Order
{
    private Guid _id;
    private string _status;

    public Order()
    {
        _id = Guid.NewGuid();
        _status = "Pending";
    }
}

// Usage
var order = new Order();

In the Debugger, the order object will display:

ID = 123e4567-e89b-12d3-a456-426614174000, Status = Pending

Evaluating Methods

You can call methods within the DebuggerDisplay attribute, even if they are private.

[DebuggerDisplay("FullName = {GetFullName()}")]
public class Employee
{
    private string _firstName;
    private string _lastName;

    public Employee(string firstName, string lastName)
    {
        _firstName = firstName;
        _lastName = lastName;
    }

    private string GetFullName()
    {
        return $"{_firstName} {_lastName}";
    }
}

// Usage
var employee = new Employee("John", "Doe");

In the Debugger, the employee object will display:

FullName = John Doe

Conditional Display

You can use conditional expressions within the display string:

[DebuggerDisplay("{IsActive ? \"Active\" : \"Inactive\"}, User = {Username}")]
public class UserAccount
{
    public string Username { get; set; }
    public bool IsActive { get; set; }
}

// Usage
var user = new UserAccount { Username = "jane.doe", IsActive = true };

In the Debugger, the user object will display:

Active, User = jane.doe

Arrays and Collections

When working with collections, you might want to display the count or specific elements.

[DebuggerDisplay("Count = {Items.Count}")]
public class ShoppingCart
{
    public List<string> Items { get; set; } = new List<string>();
}

// Usage
var cart = new ShoppingCart();
cart.Items.Add("Laptop");
cart.Items.Add("Mouse");

In the Debugger, the cart object will display:

Count = 2

Best Practices

Keep It Simple

• Avoid Complex Expressions: The evaluation of the display string should be quick. Complex expressions can slow down debugging.

• Focus on Key Information: Display the most critical information that helps you understand the object's state.

Handle Null Values

Ensure that your display string accounts for possible null values to prevent exceptions during debugging.

[DebuggerDisplay("Name = {Name ?? \"Unknown\"}")]
public class Customer
{
    public string Name { get; set; }
}

Use nameof Operator

To avoid errors due to renaming, use the nameof operator within the display string:

[DebuggerDisplay($"Name = {{{nameof(Name)}}}")]
public class Product
{
    public string Name { get; set; }
}

Avoid Side Effects

Do not call methods or properties that alter the state of the object. The debugger may evaluate the display string multiple times, leading to unintended side effects.

Common Pitfalls

Exceptions in Display String

If the expressions in the DebuggerDisplay attribute throw exceptions, the debugger will display an error message.

Incorrect Usage:

[DebuggerDisplay("Value = {GetValue()}")]
public class Sample
{
    public int Value { get; set; }

    public int GetValue()
    {
        throw new Exception("Error");
    }
}

Debugger Output:

'Sample' threw an exception: 'System.Exception: Error'

Solution: Ensure that methods used in the display string are exception-safe.

Performance Overhead

While the overhead is generally minimal, complex expressions can slow down debugging sessions. Keep the expressions simple and efficient.

Debug vs. Release Builds

The DebuggerDisplay attribute is only active in debug builds. Be aware that any code within the expressions will not be executed in release builds.

Conclusion

The DebuggerDisplay attribute is a powerful tool for enhancing your debugging experience in C#. By customizing how objects appear in the debugger, you can quickly glean important information about your application's state, saving time and reducing errors.

Key Takeaways:

• Use DebuggerDisplay to display meaningful information about objects.

• Keep display strings simple and efficient.

• Be cautious of exceptions and side effects in expressions.

• Utilize access to private members for comprehensive debugging.

By incorporating the DebuggerDisplay attribute into your classes, you make your code more maintainable and easier to debug, benefiting not just yourself but anyone else who works with your codebase.