1. Reflection SoftUni Team Technical Trainers C# OOP Advanced
Software University

2. Table of Contents What? Why? Where? When? Reflection API Type Class*
Table of Contents
What? Why? Where? When?
Reflection API
Type Class
Reflecting Fields
Reflecting Constructors
Reflecting Methods
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3. Questions
sli.do #CSharp-OOP

4. Reflection
What? Why? Where? When?

5. What is Metaprogramming?
Programming technique in which computer programs have the ability to treat other programs as their data
Programs can be designed to:
Read
Generate
Analyze
Transform
Modify itself while running.

6. What is Reflection?
The ability of a programming language to be it’s own metalanguage
Programs can examine information about itself

7. Why, Where Reflection? Code becomes more extendible
Reduces code length significantly
Easier maintenance
Testing
Tools for programmers

8. When Reflection?
If it is possible to perform an operation without using reflection, then it is preferable to avoid using it
Cons from using Reflection
Performance overhead
Security restrictions
Exposure of internals

9. Reflecting Class and Members
Reflection API
Reflecting Class and Members

10. You need fully qualified class name as string
Type Class
Primary way to access metadata
Obtain at compile time if you know it’s name
Obtain at run time if the name is unknown
Type myType = typeof(ClassName);
Type is the root of the System.Reflection functionality and is the primary way to access metadata. Use the members of Type to get information about a type declaration, about the members of a type (such as the constructors, methods, fields, properties, and events of a class), as well as the module and the assembly in which the class is deployed.
Type describes data types. It stores type information in a variable, property or field. The Type class represents the program's metadata, which is a description of its structure but not the instructions that are executed.
Type myType = Type.GetType("Namespace.ClassName")
You need fully qualified class name as string
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11. Class Name Obtain Class name
Fully qualified class name - Type.FullName
Class name without the package name - Type.Name
string fullName = typeOf(SomeClass).FullName;
string simpleName = typeOf(SomeClass).Name;
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12. Base Class and Interfaces
Obtain base class
Obtain interfaces
Only the interfaces specifically declared implemented by a given class are returned
Type baseType = testClass.BaseType;
Type[] interfaces = testClass.GetInterfaces();
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13. New Instance
CreateInstance - creates an instance of a type by invoking the constructor that best matches the specified arguments
Type sbType =
Type.GetType("System.Text.StringBuilder");
StringBuilder sbInstance =
(StringBuilder) Activator.CreateInstance(sbType);
StringBuilder sbInstCapacity = (StringBuilder)Activator
.CreateInstance(sbType, new object[] {10});
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14. Reflect Fields Obtain public fields Obtain all fields
FieldInfo field = type.GetField("name"); FieldInfo[] publicFields = type.GetFields();
FieldInfo[] allFields = type.GetFields(
BindingFlags.Static | BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
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15. Field Type and Name Get field name and type
FieldInfo field = type.GetField("fieldName");
string fieldName = field.Name;
Type fieldType = field.FieldType;
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16. Field Altering Type testType = typeof(Test); Test testInstance =
(Test) Activator.CreateInstance(testType);
FieldInfo field = testType.GetField("testInt");
field.SetValue(testInstance, 5);
int fieldValue =
(int) field.GetValue(testInstance);
WARNING: use with extreme caution as you could alter an objects internal state!
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17. Access Modifiers
Each modifier is a flag bit that is either set or cleared
Check access modifier of a member of the class
field.IsPrivate //private
field.IsPublic //public
field.IsNonPublic //everything but public
field.IsFamily //protected
field.IsAssembly //internal
etc…
IsPrivate – check if field is
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18. Reflect Constructors Obtain constructors
Obtain all non static constructors
ConstructorInfo[] publicCtors =
type.GetConstructors();
ConstructorInfo[] allNonStaticCtors =
type.GetConstructors(
BindingFlags.Instance |
BindingFlags.Public |
BindingFlags.NonPublic);
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19. Reflect Constructors(2)
Obtain a certain constructor
Get parameters type
ConstructorInfo constructor =
type.GetConstructor(new Type[] parametersType);
Type[] parameterTypes = constructor.GetParameters();
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20. Instantiating Objects
Instantiating objects using constructor
StringBuilder builder =
(StringBuilder)constructor.Invoke(new object[] params);
Supply an array of object parameters for each argument in the constructor you are invoking
The .Invoke method takes an array of objects and you must supply exactly one parameter per argument in the constructor you are invoking. In this case it was a constructor taking a string, so one string must be supplied.
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21. Reflect Methods Obtain public methods Obtain certain method
MethodInfo[] publicMethods = sbType.GetMethods();
MethodInfo appendMethod =
sbType.GetMethod("Append");
MethodInfo overloadMethod = sbType.GetMethod( "Append", new []{typeof(string)});
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22. Method Invoke Obtain method parameters and return type Invoke methods
ParameterInfo[] appendParameters =
appendMethod.GetParameters();
Type returnType = appendMethod.ReturnType;
Parameters for the method
appendMethod.Invoke(
builder, new object[] { "hi!“ });
Target object instance
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23. Live Exercises in Class (Lab)
Reflection
Live Exercises in Class (Lab)
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24. Summary What are the: Benefits Drawbacks Of using reflection?
Main benefit:
code becomes easy to extend and maintain because it adapts at runtime
Main drawback:
- performance is sacrificed

25. Reflection https://softuni.bg/courses/
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26. License
This course (slides, examples, demos, videos, homework, etc.) is licensed under the "Creative Commons Attribution- NonCommercial-ShareAlike 4.0 International" license
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