In C#, the catch clause takes an exception class name, and a variable to use in referring to this class. The block is executed if one of the statements in the try block throws this class as an exception. The catch clause can leave this class name out to catch any exception. Here, we catch all Exception class objects, which is generally all exceptions in .NET. For example, the OpenFileDialog.OpenFile method can throw a file I/O exception using the IOException class. Since this class derives from the Exception class, it will be caught by our handler. Other exceptions such as OutOfMemoryException may also occur, and are caught by our block as well.3

HANDLE EXCEPTIONS IN THE BTNLOAD_CLICK METHOD

This code uses a class we have not seen before: the MessageBox class. This class is used to display a simple dialog box. We discuss this class in detail in chapter 8. For now, just copy the code and trust me.

The Message property for the ex variable is used in our dialog to insert the message string describing the exception provided by the Exception object. This and other members of the Exception class are summarized in .NET Table 2.1.

We will use exceptions throughout the book to handle errors in a similar manner. Other concepts associated with exceptions will be presented as they are required by our sample program.

Our MyPhotos application is now in line with our MyForm application from section 1.3, with the slight improvement of handling any exception that occurs while opening the file. Our last task in this chapter is to enable the form to resize gracefully using the Anchor property.

2.4Resizing forms

Our final task in this chapter is to set the behavior for resizing using the Anchor property for our controls, and establish a minimum size for the form so that our PictureBox control does not disappear. This will finish our duplication of the application created in chapter 1. The remainder of this book will use Visual Studio

.NET when discussing applications changes, so we will carry the MyPhotos application into chapter 3 and beyond.

3 A more formal discussion of exceptions and the exception handling syntax appears in appendix A.

Figure 2.6

The application is resized here via the PictureBox.Anchor property.

.NET Table 2.1 Exception class

The Exception class represents a generic exceptional condition, and serves as the base class for all exception classes in .NET. This class is part of the System namespace, and provides information required to raise (throw) and process (catch) exceptions. Note that it is possible for unmanaged code to throw exceptions that will not be seen as Exception objects. These exceptions can be caught using an empty catch clause.