In Visual FoxPro, the name of the constructor is always Init. This makes programming by exception difficult. This means that the original constructor doesn't fire anymore unless it's called explicitly. Whenever you create a subclass in C++, the class gets new name, and therefore the constructor has a new name. Doing so in the Init would be too late, because member objects that are linked to data would have already failed to instantiate at that point.įoxPro's handling of the constructors has a couple advantages over the C++ way, one of which is subclassing. This particular event allows changing settings or opening tables that are needed by member objects. Form classes, for instance, have a Load event that fires even before the Init.
However, some classes feature other events in addition to the regular constructor. This is especially true for the event-firing sequence, which I'll discuss later.Īll FoxPro base classes support the constructor and destructor events. However, there are some differences between the events FoxPro fires, and real constructors and destructors as they are used in C++. The constructor event is called Init() and the destructor event is called Destroy(). FoxPro simply fires events that occur whenever the object is instantiated or dies. Visual FoxPro also supports constructors and destructors, but they are implemented a bit differently. The constructor uses the same name as the class itself. C++ simply uses a naming convention that allows you to attach code to a class that runs whenever the object is created or destroyed. Visual C++, for example, has a concept called constructors and destructors. Most object-oriented languages support this in one way or another. Often the constructor sets properties of the current object based on certain conditions, while the destructor removes things the object created in order to leave the system as it was when the object was created. A typical task would be to bring the environment to a proper state or clean up after the object. Often it's helpful to do something whenever a class is created or destroyed. Now I'll take a closer look at how to create those objects and discuss what strings are attached. In Chapter 1, I discussed how to define classes and I assumed objects could be created out of these classes.
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