Exception handling in C# .Net
Try
{
Int s = int Parse (t1. text)
S = S + 1000;
MBS (S + “”);
}
- Compile Time Problems are called as errors.
EX: - Syntax errors
- Runtime problems are called as exception.
- Exception is a run time condition which stops the normal execution of a program abnormally.
- Generally Exceptions will be raised
- While Typecasting
- While working with Files
- While working with Data bases
- While managing the memory
5.To work with exception handling .net introduced 4 keywords
Try, Catch, finally and throw
- When an exception is expected from a block of code, then recommended writing this logic within try block.
- Syntax for try, catch, finally
Try{
---
---
---
--
}
Catch (Type of exception obj)
{
}
Catch (Type of exception obj)
{
}
Finally
{
}
- Try block must be followed either with one catch, many catches or ONE finally or ALL.
- Catch will be executed only when exception is raised.
- Finally will be executed always irrespective of exception.
- In an exception is raised in line 2 then line 3 and 4 will not be executed.
- To handle exception, Micro soft introduced – 400 predefine classes.
Exception class Hierarchy
File not formatted exception
Invalid formatted exception
Example on Exception handling where multiple catches and finally :-
- Open WFAP
- Place a text box and a Button
- Code for Button1 _ click
{
Try
{
Int S = int . Parse (text Box1.Text)
S =s + 1000;
Message Box. Show (“Salary is ” + s);
String [] X = new String [] {“C #”, “VB”};
Message Box. Show (X [0]);
Message Box. Show (X [1]);
Message Box. Show (X [2]);
}//try
Catch (Format Exception fe)
{
Message Box. Show ( fe. Message);
}
Catch (Exception cd)
{
Message Box. Show (ed. Message );
}
Finally {
Message Box. Show (“From finally”);
}
Working with File handling
- Working with System. Io namespace is called “File handling”
- Generally File handling is used
- To find Drives Information
- To find Directory and files Information.
- To crate and delete files and directories.
- To manipulate Files and folders.
- Classes of System. Io namespace
- Directory: used to find Drives information
- Directory info: To find the meta data of a directory or drive
- File: used to do to operations like copy, delete, etc….
- File Info
- Stream Reader
- Stream writer
Methods of directory class
Directory . Get Logical Drive () à returns all drive names.
Directory . Get Directories (path) à returns all directory names.
Directory . Get Files (path) à returns all files names.
Example on Directory class:-
- Place a combo box and two List Boxes on form
- Using System .Io;
- Code for form 1 _ load Event
String [] X = Directory . Get Logical Drives ();
For (int I = 0; I < x. length ; I ++)
Combo Box 1. Items . Add (X [1] )
à Code for combo Box 1 Selected Index changed event
List Box 1.Items . Clear ();
String P = Combo box 1. Selected Item . To string ();
Try
{
String [] x = Directory. Get Directories (p);
For (int I = 0; I < x. length ; I ++)
List box1. Items a Add (X[i]);
}
Catch (Io Exception)
{
Message Box. Show (I .e Message) ;
}