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Exception handling in C# .Net

 

Screenshot_80

 

Try

{

Int s = int Parse  (t1. text)

S = S + 1000;

MBS  (S + “”);

}

 

  1. Compile Time Problems are called as errors.

EX: – Syntax errors

 

  1. Runtime problems are called as exception.
  2. Exception is a run time condition which stops the normal execution of a program abnormally.
  3. Generally Exceptions will be raised

 

  1. While Typecasting
  2. While working with Files
  3. While working with Data bases
  4. While managing the memory

5.To work with exception handling .net introduced 4 keywords

 

 

Try, Catch, finally and throw

 

  1. When an exception is expected from a block of code, then recommended writing this logic within try block.

 

  1. Syntax for try, catch, finally

 

Try{

 

}

Catch  (Type of exception obj)

{

}

Catch (Type of exception obj)

{

}

Finally

{

}

  1. Try block must be followed either with one catch, many catches or ONE finally or ALL.

 

  1. Catch will be executed only when exception is raised.
  2. Finally will be executed always irrespective of exception.
  3. In an exception is raised in line 2 then line 3 and 4 will not be executed.
  4. To handle exception, Micro soft introduced – 400 predefine classes.

 

 

 Screenshot_81

 

 Exception class Hierarchy

 

 

arrrowFile not formatted exception

arrrowInvalid   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

  1.  Working with System. Io namespace is called “File handling”
  2. 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.

 

  1. 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) ;

}

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