Week 7 : Debugging and Error Handling

C#4.0Week 7:

Debugging and Error Handling

Debugging methods available in the ID Error-handling techniques available in C#

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Debugging methods available in the ID

Week 7: Debugging and Error Handling

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DEBUGGING IN VS AND VCE

Both VS and VCE(express) allow you to build applications in two configurations: Debug (the default) and Release.

Windows Programming 1 Chapter 7: Debugging and Error Handling Slide 3

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DEBUGGING IN VS AND VCE

In debug configuration and execute it in debug mode, more is going on than the execution of your code. Debug builds maintain symbolic information about your application, so that the IDE knows exactly what is happening as each line of code is executed

In release configuration, application code is optimized. However, release builds also run faster; and when you have finished developing an application, you will typically supply users with release builds because they won’t require the symbolic information thatdebug builds include


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Outputting Debugging Information

First, an additional using directive appears at the beginning of the code: using System.Diagnostics;

Then Debug.WriteLine() Trace.WriteLine()

System.Diagnostics.Debug.WriteLine("Bananas");


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Debug Menu and Toolbar Breakpoints


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Breakpoints Breakpoints


Toggle Breakpoints On/Off by clicking in Editor's gray left margin indicator

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Debugging in Break Mode Breakpoints


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Monitoring Variable Content

Monitoring variable content is just one example of how VS and VCE help you a great deal by simplifying things.

The easiest way to check the value of a variable is to hover the mouse over its name in the source code while in break mode.

A yellow tooltip showing information about the variable appears, including the variable’s current value.


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Viewing Current Values During Program Execution


Place mouse pointer over variable or property to view current value

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Monitoring Variable Content

Autos (VS only): Variables in use in the current and previous statements (Ctrl+D, A)

Locals: All variables in scope (Ctrl+D, L) Watch N: Customizable variable and

expression display (where N is 1 to 4, found on Debug WindowsWatch)


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Locals window


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The Watch window


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Immediate and CommandWindows

The Command (VS only) and Immediate windows (found on the DebugWindows menu) enable you to execute commands while an application is running.

The Command window enables you to perform VS operations manually (such as menu and toolbar operations).

The Immediate window enables youto execute additional code besides the source code lines being executed, and to evaluate expressions.


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Immediate and CommandWindows


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Error-handling techniques available in C#

Week 7: Debugging and Error Handling

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Slide 17

UNDERSTANDING EXCEPTIONS

An exception occurs when a program encounters any unexpected problems.

Your program should be able to handle these exceptional situations and, if possible, gracefully recover from them. This is called exception handling.

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Slide 18

STEP BY STEP 3_1

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Slide 19

STEP BY STEP 3_1

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UNDERSTANDING EXCEPTIONS

The FCL provides two categories of exceptions ApplicationException Represents exceptions

thrown by the applications SystemException Represents exceptions thrown

by the CLR

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Slide 21

Try Block - General Form

The try Block

Try{

statements that may cause error}catch [ExceptionType VariableName ]{

statements for action when an exception occurs}

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Slide 22

HANDLING EXCEPTIONS The catch Block

DivideByZeroExceptionArithmeticExceptionOverflowExceptionFormatException

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Slide 23

HANDLING EXCEPTIONS

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Slide 24

HANDLING EXCEPTIONS

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Slide 25

HANDLING EXCEPTIONS The throw Statement

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Slide 26

The throw Statement

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Slide 27

The throw Statement

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Slide 28

HANDLING EXCEPTIONS The finally Block: contains code that always executes,

whether or not any exception occurs.

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Slide 29

VALIDATING USER INPUT

Field-Level Validation 1. Enter (Occurs when a control is entered.) 2. GotFocus (Occurs when a control receives

focus.) 3. Leave (Occurs when focus leaves a control.) 4. Validating (Occurs when a control is validating.) 5. Validated (Occurs when a control is finished

validating.) 6. LostFocus (Occurs when a control looses

focus.)

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Slide 30

The Validating Event

Inside the Validating event, you can write code to do the following: Programmatically correct any errors or omissions

made by the user. Show error messages and alerts to the user so

that the user can fix the problem Use the Focus() method of the control to transfer

the focus back to the field. Set the Cancel property of CancelEventArgs to

true. This cancels the Validating event, leaving the focus in the control.

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Slide 31

VALIDATING USER INPUT • 1. KeyDown• 2. KeyPress• 3. KeyUp• The KeyPress event happens after the KeyDown

event but before the KeyUp event• KeyPress event match keys include any alphabetic

and numeric characters (alphanumeric a–z, A–Z, and 0–9), not raise this event include Ctrl, Alt, and the function keys

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Slide 32

VALIDATING USER INPUT EXAM private void textBoxAge_KeyPress(object sender, KeyPressEventArgs e)

{

if ((e.KeyChar < 48 || e.KeyChar > 57) && e.KeyChar != 8)

e.Handled = true;

}

private void textBox1_KeyUp(object sender,

System.Windows.Forms.KeyEventArgs e)

{

if (e.Alt == true)

MessageBox.Show("The ALT key is still down");

}

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Slide 33

The CausesValidation Property

The default value of the CausesValidation property for a control is true for all controls

When you want a control to respond, regardless of the validation status of other controls, you should set the CausesValidation property of that control to false

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Slide 34

9:06:37 AM

The ErrorProvider Component

The ErrorProvider component can set a small icon next to a field when it contains an error

When the user moves the mouse pointer over the icon, an error message pops up as a ToolTip

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Slide 35

9:06:37 AM

The ErrorProvider Component

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Slide 36

Using the ErrorProvider Component andOther Validation Techniques

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Slide 37

The Validating Event and Sticky Form

The CausesValidation property of the btnExit control to false.

Declare the following variable outside a method block in the class:

private bool closingFlag = false; Add the following code to the Click event handler of the

Exit button:

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Slide 38

The Validating Event and Sticky Form

Attach the following event handling code to the Validating events of both the txtMile controls

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Methods

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Slide 40

Math Class Methods The Math class

Allows the user to perform common math calculations

Using methodsClassName.MethodName( argument1,

arument2, … ) Constants

Math.PI = 3.1415926535…Math.E = 2.7182818285…

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Slide 41

Math Class Methods

Method Example Abs( x ) Abs( 23.7 ) is 23.7

Ceiling( x ) Ceiling( 9.2 ) is 10.0 Ceiling( -9.8 ) is -9.0

Cos( x ) Cos( 0.0 ) is 1.0

Exp( x ) Exp( 1.0 ) is approximately 2.7182818284590451

Floor( x ) Floor( 9.2 ) is 9.0 Floor( -9.8 ) is -10.0

Log( x ) Log( 2.7182818284590451 ) is approximately 1.0

Max( x, y ) Max( 2.3, 12.7 ) is 12.7 Max( -2.3, -12.7 ) is -2.3

Min( x, y ) Min( 2.3, 12.7 ) is 2.3 Min( -2.3, -12.7 ) is -12.7

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Slide 42

Math Class Methods

Method Example Pow( x, y ) Pow( 2.0, 7.0 ) is 128.0

Pow( 9.0, .5 ) is 3.0 Sin( x ) Sin( 0.0 ) is 0.0 Sqrt( x ) Sqrt( 900.0 ) is 30.0

Sqrt( 9.0 ) is 3.0 Tan( x ) Tan( 0.0 ) is 0.0

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Method Definitions

Writing a custom method HeaderReturnType Properties Name( Param1, Param2, …) Body

Contains the code of what the method does Contains the return value if necessary

For uses call elsewhere in program Pass parameters if needed

All methods must be defined inside of a class

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Slide 44

Method Definitionspublic void MethodName ( ) {

// Contains the code of what the method does}

public ReturnType methodName(Param1, Param2, … ){

//Contains the code of what the method does

//Contains the return value }

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Slide 45

User-defined method Maximum

public double Maximum( double x, double y, double z ){

double maximumValue = x; if ( y > maximumValue )

maximumValue = y; if ( z > maximumValue )

maximumValue = z; return maximumValue;

} // end method Maximum

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9:06:37 AM

User-defined method Maximum

public void DetermineMaximum(){ Console.WriteLine( "Enter three floating-point values,\n"

+ " pressing 'Enter' after each one: " );double number1 = Convert.ToDouble( Console.ReadLine() ); double number2 = Convert.ToDouble( Console.ReadLine() ); double number3 = Convert.ToDouble( Console.ReadLine() );

double result = Maximum( number1, number2, number3 ); Console.WriteLine( "Maximum is: " + result ); }

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Slide 47

Argument Promotion

Implicit Conversion Object is converted to a needed type implicitly Only done if complier knows no data will be lost

Explicit Conversion Object is manually converted Required if there could be a loss of data Widening

Make an object that of a derived class and more complex Narrowing

Make an object that of a base class and cause some data loss

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Slide 48

Argument PromotionType Can be Converted to Type(s)

bool object

byte decimal, double, float, int, uint, long, ulong, object, short or ushort

sbyte decimal, double, float, int, long, object or short

char decimal, double, float, int, uint, long, ulong, object or ushort

decimal object

double object

float double or object

int decimal, double, float, long or object

uint decimal, double, float, long, ulong, or object

long decimal, double, float or object

ulong decimal, double, float or object

object None

short decimal, double, float, int, long or object

ushort decimal, double, float, int, uint, long, ulong or object

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Slide 49

Passing Arguments: Call-By-Value vs. Call-By-Reference

Passing by value Send a method a copy of the object When returned are always returned by value Set by value by default

Passing by reference Send a method the actual reference point

Causes the variable to be changed throughout the program When returned are always returned by reference The ref keyword specifies by reference The out keyword means a called method will initialize it

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Slide 50

Reference and value parameters

void SquareRef( ref int x ){ x = x * x; }

void Square( int x ){ x = x * x; }

void SquareOut( out int x ){ x=5;

x = x * x; }

int z=5;Square ( z );

int z=5;SquareRef (ref z );

int z;SquareOut (out z );

Value of z after Square: 5

Value of z after SquareRef: 25

Value of z after SquareOut: 25

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Slide 51

Random Number Generation Class Random

Within namespace System randomObject.Next()

Returns a number from 0 to Int32.MaxValue Int32.MaxValue = 2,147,483,647

randomObject.Next ( x ) Returns a value from 0 up to but not including x

randomObject.Next ( x, y ) Returns a number between x and up to but not including y

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Slide 52

Class Random_ ExampleRandom rand = new Random();

int value;

value = rand.Next();

// phát sinh 1 số trong [0; 2,147,483,647]value = rand.Next( 6 );

// phát sinh 1 số trong [0; 5]

value = rand.Next( 1, 7 );

// phát sinh 1 số trong [1,6]

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Finish


Week 7 : Debugging and Error Handling

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