1. Programming in C#
Lesson 5. Exceptions.

2. Defining “Exception”
An exception is when a class member fails to complete the task it is supposed to perform as indicated by its name.

3. Exceptions Characteristics
A classic implementation of the OOP exception model
Deliver powerful mechanism for centralized handling of errors and unusual events
Substitute procedure-oriented approach, in which each function returns error code
Simplify code constructions and maintenance
Allow the problematic situations to be processed at multiple levels

4. Handling Exceptions
In C# exception can be handled with try-catch-finally construction

5. Handling Exceptions: Complete Example

6. Exceptions in .NET
System.Exception is a base class for all exceptions in .NET

7. System.Exception class
System.Exception provides information about the cause of the error or unusual situation via properties:
Message – text description of the exception
StackTrace – a snapshot of the stack at the moment the exception is thrown
InnerException – an exception that caused the current exception (if any)

8. Custom Exceptions
To define a custom exception class it needs to be inherited from System.Exception

9. Mind the hierarchy!
When catching an exception of a particular class all derived exceptions are caught too.

10. Order catch blocks from specific to general!

11. Throwing Exceptions
Exceptions are thrown by using throw keyword.

12. How Exceptions Work?

13. Re-throwing Exceptions

14. Choosing Exception Type
When an invalid parameter is passed to a method:
ArgumentException
ArgumentNullException
ArgumentOutOfRangeException
When requested operation is not supported:
NotSupportedException
When a method is not implemented:
NotImplementedException
If no suitable standard exception class is available:
Create your own exception class

15. try-finally block

16. using block

17. Best Practices Order catch blocks from more specific to more general
Do not handle all exceptions disregarding their type
When raising an exception always pass to the constructor good explanation messages and the inner exception (if any)
Do not swallow exceptions
Avoid throwing exceptions for normal situations (as they affect performance)