Exception Handling in .NET Framework презентация

Structured Exceptions Handling in .NET V'yacheslav Koldovskyy SoftServe University 2014

Contents

1. Introduction to structured exception handling

Main task – correct operation of the application There are possible situations during the application execution when predetermined plan of actions may be changed Developer should provide ways to ensure correct execution despite possible errors

Obsolete check-based method Obsolete error handling method is based on multiple checks of input data and operation return codes. Drawbacks: difficulties; bloated code; unreliable.

Structured exception handling Modern way to handle errors provides using of special mechanism – structured exception handling which is the part of programming language Exception is an event which happens during software execution and changes normal way of code execution Exceptions in .NET Framework are instances of classes inherited from base class Exception. Only instances of this class and inherited classes may participated in structured exception handling.

2. Construct «try..catch»

Simplest "try..catch" constuct try { // Code which may result in exception } catch { // Code executed only in case of exception }

"try..catch" construct with specific exception try { // Code which may result in exception } catch (DivideByZeroException) { // Code executed in case of exception }

Cascade sections of catch try { // Code which may result in exception catch (DivideByZeroException) { // Code executed in case of exception type DivideByZeroException } catch (Exception) { // Code executed in case of exception type Exception // Means "any exception" }

"try..catch" construct with instance of exception

3. «Exception» class and exception hierarchy in.NET Framework

Exception class Exception is a base class for all exceptions исключений Important properties: Message – user-oriented message about error Source – name of an error source (application or object) InnerException – inner exception (if called from other) StackTrace – call stack to the point of exception call TargetSite – method name which raised an exception HelpLink – URL-address to information about exception Data – dictionary with additional information with exception (IDictionary)

Exception hierarchy in .NET Framework

4. Exception throwing and re-rising

Exception throwing

Exception re-rising

5. Creating own exceptions

Exception declaration

MSDN recommendations for exception declarations

6. Construct «try..finally»

Using finally «try..finally» used when it is required to guarantee execution of some code May be used together with catch

7. Best practices for exception handling

Best practices for exception handling Do not catch general exceptions (do not use catch without parameters or catch(Exception) ) Create own exceptions based on ApplicationException class but not on SystemException Do not use exceptions for application execution control flow as exception handling is heavy resource usage task. Exceptions should be used to manage errors only Do not mute exceptions which can’t be handled in application context (system errors and failures). Do not raise general exceptions: Exception, SystemException, ApplicationException Do not generate reserved system exceptions: ExecutionEngineException, IndexOutOfRangeException, NullReferenceException, OutOfMemoryException Do not return an exception instance as a method return result instead of using throw. Do not create exceptions used only for debugging purposes. Do define debug-only exceptions use Assert.

8. References to additional sources MSDN recommendations for creating exceptions: http://msdn.microsoft.com/en-us/library/ms173163.aspx MSDN recommendation for exception generation: http://msdn.microsoft.com/en-us/library/ms182338.aspx Full hierarchy of Microsoft .NET Framework exceptions (code sample in comments): http://stackoverflow.com/questions/2085460/c-sharp-is-there-an-exception-overview

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