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C# Try catch .

n  If you need handling errors in your program use try/catch block .

n   try/catch block can control the errors without exit program .

n  try/catch block consists of two part

o   Try Block : put all your code in this block .

o   Catch Block : write code that will handling the error when it's occurred .

§  you can use type of Catch to control specific error.

·         ArithmeticException : this catch specialized in numerical errors

·         IndexOutOfRangeException : this catch specialized errors that occurred when an index is outside the boundary of an array .

§  You can have multi catch in your code each one specialized in specific error . in this case one block of catch can be occurred .

Example 1:

        public void action()

        {

            try

            {

                int x = 5;

                int y = 0;

                int z = x / y;

            }

            catch

            {

                Console.WriteLine("an error occurred");

            }

        }

or

            try

            {

                int x = 5;

                int y = 0;

                int z = x / y;

            }

            catch(ArithmeticException ex)

            {

                Console.WriteLine("your error is :");

                Console.WriteLine(ex.Message);

            }

Example 2 :

            try

            {

                int[] x = new int[2];

                x[0] = 85;

                x[1] = 44;

                x[2] = 33;

                Console.WriteLine(x[2]);

            }

            catch(IndexOutOfRangeException e)

            {

                Console.WriteLine("your error is :");

                Console.WriteLine(e.Message);

            }

Example 3 :

 public void action()

        {

            try

            {

                // write your code here

            }

            catch (IndexOutOfRangeException  err)

            {

                Console.WriteLine("your error is :");

                Console.WriteLine(err.Message);

            }

            catch (ArithmeticException ex)

            {

                Console.WriteLine("your error is :");

                Console.WriteLine(ex.Message);

            }

            catch

            {

                Console.WriteLine("an error occurred");

            }

        }

Using StringBuilder

 

Example 1

     StringBuilder My_StringBuilder = new StringBuilder();

            for (int x = 0; x < 10; x ++ )

            {

                My_StringBuilder.Append(x);

            }

            MessageBox.Show(My_StringBuilder.ToString());

Example 2

            StringBuilder My_StringBuilder = new StringBuilder();

            for (int x = 0; x < 10; x ++ )

            {

                My_StringBuilder.Append(x).Append(", ");

            }

            MessageBox.Show(My_StringBuilder.ToString());

Example 3

            StringBuilder My_StringBuilder = new StringBuilder();

            My_StringBuilder.AppendLine("list of Categories:");

            My_StringBuilder.AppendLine("-------------------");

            My_StringBuilder.Append("1-Category1").AppendLine();

            My_StringBuilder.Append("2-Category2").AppendLine();

            My_StringBuilder.Append("3-Category3").AppendLine();

            MessageBox.Show(My_StringBuilder.ToString());

Example 4

     StringBuilder My_StringBuilder = new StringBuilder("my string in my code");

            My_StringBuilder.Replace("my", "your");

            MessageBox.Show(My_StringBuilder.ToString());

Example 5

            StringBuilder My_StringBuilder = new StringBuilder("my string in my code");

            My_StringBuilder.Remove(9, 11);

            MessageBox.Show(My_StringBuilder.ToString());

Working with LINQ

Working with LINQ (1)

Write the following code inside button in windows form .

string[] names = { "Burke", "Connor", "Frank",

                       "Everett", "Albert", "George",

                       "Harris", "David" };

    IEnumerable<string> query = from s in names

                               where s.Length == 5

                               orderby s

                               select s.ToUpper();

    foreach (string item in query)

      MessageBox.Show(item);

Working with LINQ (2)

Step 1 : Create database

create database HRDB

Step 2 : creating the following table

create table People (

    Name nvarchar(32) primary key not null,

    Age int not null,

    CanCode bit not null

)

Step 3 : Add the following data into People table

Step 4 : Add the following two lines above class form .

using System.Data.Linq;

using System.Data.Linq.Mapping;

Step 5 : Write the following block of code into project 

[Table(Name = "People")]

    public class Person

    {

        [Column(DbType = "nvarchar(32) not null")]

        public string Name;

        [Column]

        public int Age;

        [Column]

        public bool CanCode;

    }

Step 6 : Design  form .

Step 7 : inside Show Data button, write the following code .

DataContext context = new DataContext(

     "Data Source=.;Initial Catalog=HRDB;Integrated Security=True");

            Table<Person> custs = context.GetTable<Person>();

            var query = from c in custs

                      

                      

                        select new

                        {

                            c.Name,

                           

                            c.Age

                        };

            foreach (var item in query)

            {

                listBox1.Items.Add(item.Name + "-" + item.Age);

            }

Project Layers

Any project should consist of three layer, Dataabase, Classes and forms layer. Each one of these layer contain objects that need to create and develop.

Application Life cycle developing components

Database Layer, Contains objects such as Database files, tables, View, Functions and Stored procedures. Programmer will create and develop each of these objects.

Database Layer Components.

1-DatabaseFiles: that will store all objects of the project.

2- Tables: tables created to storing row data and normalize it.

3-Stored Procedures: SPs or Stored Procedures keeps the actions that needed to be fired when project want.

4- Functions: Keeps all answers for all questions needed to be answered for project.

5- Views: project needs Views for displaying Reports.

After finishing Database layer, programmer needs to call these objects from application. To do that, programmer need to developing Classes Layer.

Classes Layer, created in the application development environment by Classes files. Each of class refer to one object in the database Layer.

For example, Emp_Tbl is a table object in the database layer. For manipulate with this object its need to create Class with name Cls_Emp, and so on with all tables in the database.

Classes Layer Components.

Create Class file for each table in the Database. Each class will contain blocks of code that will work with Store Procedures and Functions that associated with specific table.

ID	Database Layer		Classes Layer
	Table Name	Associated Objects (Store Procedures, Functions)	Blocks of code in Class (Methods)	Class Name
1	Dep_Tbl	Dep_Insert_SP	Dep_Insert	Cls_Dep
		Dep_Update_SP	Dep_Update
		Dep_Delete_SP	Dep_Delete
		Dep_SelectALL_Fun	Dep_SelectALL
		Dep_GetInfo_Fun	Dep_GetInfo
		Dep_GetMax_Fun	Dep_GetMax
2	…	…	…	…

On the other hand, Working with Forms layer need first finish the previous layer in order to avoid errors, change Requests issues and Work around.

Forms Layer, means Working with User interface of the project and how to let the application interface to communicate with database layer throw classes layer. Forms layer contains a set of files. Each file consists of set of controls that will display for user to let him interacting with data of project.

Forms layer Components.

One or more classes in the class's layer will be act with one form in the forms layer.

ID	Table Name	Class Name	From Name	Form Search
1	Dep_Tbl	Cls_Dep	Frm_Dep	Frm_Dep_Search
2	…	…	…	…