AN OVERVIEW OF .NET ERROR HANDLING in Font

Creation PDF-417 2d barcode in Font AN OVERVIEW OF .NET ERROR HANDLING

4. Open the code window for Form1 and replace the code in the GetAnswer() method with code that includes a Try-Catch block around the statements that have been causing you problems. Your code will look like Listing 4-7 when you are done. Listing 4-7. Using Your Own Custom Class VB .NET 'Create a Method to calculate Mileage Public Sub GetAnswer() 'Create three variables to work with Dim Mileage, Distance, Gallons As Decimal Try 'Add this line to start Try-Catch Block ' Set values from the UI Distance = txtDistance.Text Gallons = txtGallons.Text 'Check for zeros If Distance = 0 Then 'Cause an Exception to be Thrown Throw New MyCustomException End If 'Calculate the mileage Mileage = Distance / Gallons Catch ex As DivideByZeroException 'Catch Divide by Zero errors and use the object from Microsoft's 'DivideByZeroException Class to show a Message MessageBox.Show(ex.Message) Catch ex As MyCustomException 'Catch all MyCustomException errors, 'Use the Object to show a Custom error Message MessageBox.Show(ex.Message) Catch 'Catch any other type of Exception MessageBox.Show("There was an Error") Finally 'Put code here that you want to always run MessageBox.Show("Inside Finally") End Try MessageBox.Show(Mileage.ToString, "Answer") End Sub

C# //Create a Method to calculate Mileage public void GetAnswer() { //Create three variables to work with Decimal Mileage = 0, Distance = 0, Gallons = 0; try { //Add code to set these values from the UI Distance = Convert.ToDecimal(txtDistance.Text); Gallons = Convert.ToDecimal(txtGallons.Text); //Check for zeros if (Distance == 0) { //Cause an Exception to be Thrown throw new MyCustomException(); } Mileage = Distance / Gallons; }//end if catch (DivideByZeroException ex) { //Catch Divide by Zero errors and use the object from Microsoft's //DivideByZeroException Class to show a Message MessageBox.Show(ex.Message); } catch (MyCustomException ex) { //Catch all MyCustomException errors, //Use the Object to show a Custom error Message MessageBox.Show(ex.Message); } catch { //Catch any other type of Exception MessageBox.Show("There was an Error"); } finally { //Put code here that you want to always run MessageBox.Show("Inside Finally"); } //End Try-Catch Block

MessageBox.Show(Mileage.ToString(), "Answer"); }//end of GetAnswer 5. With a breakpoint set on the start of the GetMileage() method, start the application and step into the code using the default values, Distance being 100 and Gallons being 10. The application should work as expected and give you an answer of 10. Note that the code in the Finally clause still runs even though there were no errors. 6. Change the value of Gallons to 0 in the txtGallons textbox and click the button again. Step into the code line-by-line and watch how it jumps to the DivideByZeroException Catch clause when the application attempts to divide by zero. Note that the Finally clause still runs its code. 7. Change the value of Distance to 0 and click the button again. Step into the code line-by-line until it enters the If statement block and throws the error. Continue stepping into the code and watch how, this time, it jumps to the Catch clause that matches your custom Exception. The Finally block will run once again. In this exercise, you saw how the Try-Catch-Finally statement block is used to catch errors. You also saw how you can create your own custom Exception class, how to throw that Exception, and how to catch it. As you go through the book, you will see more of these types of statements, which will help you understand when and how to use this knowledge in practice.

In addition to using Visual Studio to debug applications, Microsoft has long had a set of Debug commands that you could use to get information about what is happening in your program while it is running. The way it works is this: You put Debug commands in your code to print out information about what is going on at specific points in your code. This information can be things like line numbers reached, the value of variables, or the status of a conditional statement. These types of statements can be used while you have Visual Studio open in front of you, but you already have breakpoints for that. The Debug messages really come in handy when you have just merged two or more code files, like an .exe and a .dll, and you want to see how they work together. This works even when you have access to some or none of the actual code files.