Inspecting methods and properties in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the type of the object.

C Sharp (C#)

Type type = obj.[1]();

Drag options to blanks, or click blank then click option'

AEquals

BToString

CGetType

DGetHashCode

Attempts:

3 left

💡 Hint

Common Mistakes

Using ToString() instead of GetType()

Trying to access a property instead of calling a method

The GetType() method returns the runtime type of the current instance.

2fill in blank

medium

Complete the code to get all public methods of a type.

C Sharp (C#)

MethodInfo[] methods = type.[1]();

Drag options to blanks, or click blank then click option'

AGetProperties

BGetConstructors

CGetFields

DGetMethods

Attempts:

3 left

💡 Hint

Common Mistakes

Using GetProperties() instead of GetMethods()

Using GetFields() which returns fields, not methods

The GetMethods() method returns an array of MethodInfo objects representing all the public methods of the type.

3fill in blank

hard

Fix the error in the code to get the name of the first property.

C Sharp (C#)

string propName = type.GetProperties()[[1]].Name;

Drag options to blanks, or click blank then click option'

A-1

B0

Cnull

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as index causing IndexOutOfRangeException

Using null which is invalid as an index

Array indexes start at 0, so to get the first property, use index 0.

4fill in blank

hard

Fill both blanks to get all public properties and filter those with a specific type.

C Sharp (C#)

PropertyInfo[] props = type.[1]();
var stringProps = props.Where(p => p.PropertyType == typeof([2]));

Drag options to blanks, or click blank then click option'

AGetProperties

BGetMethods

Cstring

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using GetMethods() instead of GetProperties()

Using int instead of string for filtering

GetProperties() gets all properties, and filtering by typeof(string) selects properties of type string.

5fill in blank

hard

Fill all three blanks to get method names that have no parameters.

C Sharp (C#)

MethodInfo[] methods = type.[1]();
var noParamMethods = methods.Where(m => m.GetParameters().[2] == [3]);

Drag options to blanks, or click blank then click option'

AGetMethods

BLength

C0

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using Count instead of Length on the parameters collection

Using 1 instead of 0 to check for no parameters

GetMethods() gets all methods, GetParameters() returns parameters, and Length == 0 filters methods with no parameters.

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