STRUCTURED ERROR HANDLING
Visual Basic .NET uses the Try Catch block to provide structured error handling. The syntax is as follows:
Try try_statements ... [Catch ex As exception_type_1 exception_statements_1 ... ] [Catch ex As exception_type_2 exception_statements_2 ... ] ... [Catch final_exception_statements ... ] [Finally finally_statements ... ] End Try
The program executes the code in the try_statements block. If any of that code throws an exception, the program jumps to the first Catch statement.
If the exception matches exception_type_1, the program executes the code in exception_statements_1. The exception type might match the Catch statement’s exception class exactly, or it might be a subclass of the listed class. For example, suppose that the code in the try_statements block performs a calculation that divides by zero. That raises a DivideByZeroException. That class inherits from the ArithmeticException class, which inherits from SystemException, which inherits from Exception. That means the code would stop at the first Catch statement it finds that looks for DivideByZeroException, ArithmeticException, SystemException, or Exception.
If the raised exception does not match the first exception type, the program checks the next Catch statement. The program keeps comparing the exception to Catch statements until it finds one that applies, or it runs out of Catch statements.