Inspecting methods and properties in C Sharp (C#)

Introduction

Sometimes, you want to see what actions (methods) and details (properties) an object has. This helps you understand or use it better.

When you get an object and want to know what you can do with it.

When debugging to check what properties an object holds.

When learning a new class or library and want to explore its features.

When writing code that works with different objects dynamically.

When you want to list all methods or properties for documentation or display.

Syntax

C Sharp (C#)

Type type = typeof(ClassName);
// or
Type type = objectInstance.GetType();

// To get methods
MethodInfo[] methods = type.GetMethods();

// To get properties
PropertyInfo[] properties = type.GetProperties();

typeof(ClassName) gets the type info from a class name.

GetType() gets the type info from an object instance.

Examples

This lists all method names of the string class.

C Sharp (C#)

Type type = typeof(string);
MethodInfo[] methods = type.GetMethods();
foreach (var method in methods)
{
    Console.WriteLine(method.Name);
}

This lists all property names of the int object.

C Sharp (C#)

var number = 123;
Type type = number.GetType();
PropertyInfo[] properties = type.GetProperties();
foreach (var prop in properties)
{
    Console.WriteLine(prop.Name);
}

Sample Program

This program creates a Person object and prints its public properties and methods. It shows how to inspect an object's details.

C Sharp (C#)

using System;
using System.Reflection;

class Person
{
    public string Name { get; set; }
    public int Age { get; set; }

    public void SayHello()
    {
        Console.WriteLine($"Hello, my name is {Name}.");
    }

    private void SecretMethod() { }
}

class Program
{
    static void Main()
    {
        Person p = new Person { Name = "Alice", Age = 30 };
        Type type = p.GetType();

        Console.WriteLine("Properties:");
        foreach (var prop in type.GetProperties())
        {
            Console.WriteLine(prop.Name);
        }

        Console.WriteLine("Methods:");
        foreach (var method in type.GetMethods(BindingFlags.Public | BindingFlags.Instance))
        {
            Console.WriteLine(method.Name);
        }
    }
}

Important Notes

By default, GetMethods() returns public methods including inherited ones.

Use BindingFlags to control which methods or properties you want (public, private, static, instance).

Properties have getter and setter methods behind the scenes, which also appear in methods list.

Summary

Use typeof() or GetType() to get type info.

Use GetMethods() and GetProperties() to list methods and properties.

Inspecting helps understand and use objects better.

Practice

1. Which C# method is used to get the type information of an object instance?

easy

A. typeof()

B. GetMethods()

C. GetProperties()

D. GetType()

Solution

1. Step 1: Understand the difference between GetType() and typeof()

   GetType() is called on an object instance to get its runtime type, while typeof() is used with a type name at compile time.

2. Step 2: Identify the method that works on an object instance

   Since the question asks for the method used on an object instance, GetType() is the correct choice.

3. Final Answer:

   GetType() -> Option D

4. Quick Check:

   Object instance method for type info = GetType() [OK]

Hint: Use GetType() on objects, typeof() on type names [OK]

Common Mistakes:

• Confusing typeof() with GetType()
• Using GetMethods() to get type info
• Thinking GetProperties() returns type

2. Which of the following is the correct syntax to get all methods of the String type in C#?

easy

A. typeof(String).GetMethods()

B. typeof(String).GetProperties()

C. String.GetMethods()

D. GetType(String).GetMethods()

Solution

1. Step 1: Recall how to get methods from a type

   Use typeof(TypeName).GetMethods() to get all methods of a type.

2. Step 2: Check each option's syntax

   typeof(String).GetMethods() uses typeof(String).GetMethods(), which is correct. typeof(String).GetProperties() calls GetProperties(), not methods. String.GetMethods() tries to call GetMethods() on the type name directly, which is invalid. GetType(String).GetMethods() uses GetType(String), which is incorrect syntax.

3. Final Answer:

   typeof(String).GetMethods() -> Option A

4. Quick Check:

   Get methods from type = typeof(Type).GetMethods() [OK]

Hint: Use typeof(Type).GetMethods() to list methods [OK]

Common Mistakes:

• Calling GetMethods() on type name directly
• Mixing GetProperties() with GetMethods()
• Using GetType() with a type name instead of instance

3. What will the following C# code output?

var props = typeof(DateTime).GetProperties();
Console.WriteLine(props.Length);

medium

A. 0

B. More than 0

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Understand what GetProperties() returns

   GetProperties() returns an array of all public properties of the type.

2. Step 2: Check if DateTime has properties

   DateTime has many properties like Now, Today, Year, Month, etc., so the array length will be more than zero.

3. Final Answer:

   More than 0 -> Option B

4. Quick Check:

   DateTime properties count > 0 [OK]

Hint: Types like DateTime have many properties, so length > 0 [OK]

Common Mistakes:

• Assuming no properties means length 0
• Expecting compilation or runtime errors
• Confusing methods with properties

4. Identify the error in this C# code snippet:

var typeInfo = "hello".GetType();
var methods = typeInfo.GetMethod();

medium

A. GetType() is invalid on string

B. Missing parentheses on GetType

C. GetMethod() should be GetMethods()

D. Cannot call GetMethod() on typeInfo

Solution

1. Step 1: Check usage of GetType()

   "hello".GetType() is valid and returns the type of the string instance.

2. Step 2: Check method name on typeInfo

   There is no method called GetMethod() without parameters; to get all methods, use GetMethods().

3. Final Answer:

   GetMethod() should be GetMethods() -> Option C

4. Quick Check:

   Use GetMethods() to get all methods [OK]

Hint: Use GetMethods() (plural) to list all methods [OK]

Common Mistakes:

• Using GetMethod() without parameters
• Thinking GetType() is invalid on string
• Missing parentheses on method calls

5. You want to list all public properties of a custom class Person and print their names. Which code snippet correctly does this?

hard

A. var props = typeof(Person).GetProperties(); foreach(var p in props) Console.WriteLine(p.Name);

B. var props = new Person().GetProperties(); foreach(var p in props) Console.WriteLine(p.Name);

C. var props = typeof(Person).GetMethods(); foreach(var p in props) Console.WriteLine(p.Name);

D. var props = Person.GetProperties(); foreach(var p in props) Console.WriteLine(p.Name);

Solution

1. Step 1: Identify how to get properties of a type

   Use typeof(Person).GetProperties() to get all public properties of the Person class.

2. Step 2: Check the foreach loop to print property names

   Iterate over the properties and print each p.Name to display property names.

3. Step 3: Verify other options

   var props = new Person().GetProperties(); foreach(var p in props) Console.WriteLine(p.Name); tries to call GetProperties() on an instance, which is invalid. var props = typeof(Person).GetMethods(); foreach(var p in props) Console.WriteLine(p.Name); gets methods, not properties. var props = Person.GetProperties(); foreach(var p in props) Console.WriteLine(p.Name); calls GetProperties() directly on the class name, which is invalid syntax.

4. Final Answer:

   var props = typeof(Person).GetProperties(); foreach(var p in props) Console.WriteLine(p.Name); -> Option A

5. Quick Check:

   Use typeof(Type).GetProperties() and loop to print names [OK]

Hint: Use typeof(Class).GetProperties() and loop to print names [OK]

Common Mistakes:

• Calling GetProperties() on an instance
• Using GetMethods() instead of GetProperties()
• Calling GetProperties() directly on class name