Lecture Windows programming: Chapter 5 - Châu Thị Bảo Hà

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Chapter 5 of lecture Windows programming introduce about debugging and error handling. In this chapter presents the contents: Introduction to the errors in program, debugging, error handling. Inviting you to refer.

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Nội dung Text: Lecture Windows programming: Chapter 5 - Châu Thị Bảo Hà

Debugging and Error Handling Chapter 5 Ebook: Beginning Visual C# 2010, chapter 7 Reference: CSharp How to Program, part D
Contents  Introduction  Debugging  Error handling Slide 2
Introduction  Errors in program: a program can have three types of errors:  compile-time errors: The compiler will find syntax errors and other basic problems  run-time errors: A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally  logical errors: A program may run, but produce incorrect results, perhaps using an incorrect formula 1-3
Debugging  Debugging is the process of finding and correcting logic errors in applications  applications are executed in two ways: with debugging enabled (F5) or without debugging enabled (Ctrl+F5)  Techniques  debugging in nonbreak mode  outputting debugging information: Console.WriteLine(), Debug.WriteLine()  debugging in break mode  using Breakpoints  Some windows in Debug\Windows: Autos, Locals, Watch  demo… Slide 4
Error handling  An exception is an indication of a problem that occurs during a program's execution  format error,  arithmetic overflow,  out-of range array subscripts,  division by zero,  invalid method parameters  running out of available memory,  …  Your program should be able to handle these exceptional situations. This is called exception handling Slide 5
Error handling (cont.) int tu = Convert.ToInt32( txtNumerator.Text ); int mau = Convert.ToInt32( txtDenominator.Text ); int result = tu / mau; lblOutput.Text = result.ToString(); Slide 6
Exception handling: try…catch try{ // code that may cause exception } catch ( ExceptionTypeA e ){ // statement to handle errors occurring // in the associated try block } catch ( ExceptionTypeB e ){ // statement to handle errors occurring // in the associated try block } Slide 7
Exception handling: try…catch...finally try{ // code that may cause exception } catch ( ExceptionTypeA e ){ // statement to handle errors occurring // in the associated try block } catch ( ExceptionTypeB e ) { … } finally{ // statements always excuted } Slide 8
Exception types  Some common exception classes Exception Class Cause DivideByZeroException An attempt was made to divide by zero. FormatException The format of an argument is wrong. IndexOutOfRangeException An array index is out of bounds. An attempt was made to cast to an invalid InvalidCastExpression class. OutOfMemoryException Not enough memory to continue execution. StackOverflowException A stack has overflown. Slide 9
Example: try…catch private void divideButton_Click( object sender, System.EventArgs e ) { try { lblOutput.Text = ""; int x = Convert.ToInt32( txtX.Text ); int y = Convert.ToInt32( txtY.Text ); int result = x / y; lblOutput.Text = result.ToString(); } catch ( FormatException ) { MessageBox.Show( "You must enter two integers", "Invalid Number Format", MessageBoxButtons.OK, MessageBoxIcon.Error ); } catch ( DivideByZeroException er ) { MessageBox.Show( er.Message, "Attempted to Divide by Zero", MessageBoxButtons.OK, MessageBoxIcon.Error ); Slide 10
The throw statement  A throw statement explicitly generates an exception in code  There are two ways you can use the throw statement  rethrow the exception in a catch block: catch( Exception e ) { // Add code to create an entry in event log throw; }  throw explicitly created exceptions: string strMessage = “EndDate should be greater than the StartDate”; ArgumentOutOfRangeException exp = Slide 11 new ArgumentOutOfRangeException( strMessage );
Deﬁning properties with throw statement [1]  What should you public class DiemMonHoc { do if an invalid private string mMaSV; value is used? private string mMaMon; private int mDiem;  do nothing public int Diem  assign a default { value to the ﬁeld get { return mDiem; } set {  continue as if if (value >= 0 && value
Deﬁning properties with throw statement [2] set This can be handled using { try ... catch ... finally if (value >= 0 && value
.NET Exception hierarchy  The FCL provides two categories of exceptions  ApplicationException : represents exceptions thrown by the users program  SystemException : represents exceptions thrown by the CLR Exception ApplicationException SystemException Slide 14
Programmerdefined Exception classes  Creating customized exception types  should derive from class ApplicationException  should end with “Exception”  should define three constructors  a default constructor  a constructor that receives a string argument  a constructor that takes a string argument and an Exception argument Slide 15
Programmerdefined Exception classes: Example [1]
Programmerdefined Exception classes: Example [2] class NegativeNumberException : ApplicationException { public NegativeNumberException() : base( "Phai nhap vao so khong am" ) { } public NegativeNumberException( string message ) : base( message ) { } public NegativeNumberException( string message, Exception inner ) : base( message, inner ) {
Programmerdefined Exception classes: Example [3] private void squareRootButton_Click( object sender, System.EventArgs e ) { outputLabel.Text = ""; try { double input = Double.Parse(inputTextBox.Text); if ( input < 0 ) throw new NegativeNumberException( “Không tính được căn bậc hai âm." ); double result = Math.Sqrt(input); outputLabel.Text = result.ToString(); } // BẮT lỗi định dạng số không hợp lệ catch ( FormatException error ) { MessageBox.Show( error.Message, "Lỗi nhập liệu", MessageBoxButtons.OK, MessageBoxIcon.Error ); } // BẮT lỗi nhập số âm catch ( NegativeNumberException error ) { MessageBox.Show( error.Message, “Lỗi nhập liệu", MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
Validating user input  When getting data from the user, you must ensure that the entered data is valid  You can use various techniques for validating data:  by using standard controls such as comboboxes, listboxes, radiobuttons, checkboxes, numericupdown, trackbar,...  by enabling or disabling data fields, depending on the state of other fields  by capturing the user’s keystrokes and analyze them for validity (Keystroke-level validation)  by analyzing the contents of the data field as a whole and warn the user of any incorrect values when the user attempts to leave the field or close the window (Field-level validation) Slide 19
Keystrokelevel validation  When pressing a key on a control, three events occur in the following order:  KeyDown event  KeyPress event  KeyUp event Slide 20