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Chapter 9: QuickTime Movies and File HandlingAt this point, you know all about interface elements such as windows, controls, and menus, and you have a firm grasp on how your program recognizes and handles a variety of types of events. So it's on to the fun stuff. In this chapter, you'll see how your program opens and plays a QuickTime movie. QuickTime is movie-playing software that is part of the system software of every Macintosh in your target audience.
It's possible for a program to cause a QuickTime movie to spring forth from (seemingly) nowhere. However, it's more likely that a movie-playing application will enable the user to select the file that holds the movie to play. Giving the user the power to open a QuickTime movie file, or any other type of file, involves the Open dialog box.We'll look at the Open dialog box first in this chapter.
Files and Navigation ServicesA file is a sequence of bytes stored on physical media, such as a hard drive, and a directory is another name for a folder. A volume can be an entire physical storage device or it can be part of the device (the result of formatting the device to consist of multiple volumes). For a program to access a file, it needs to know the file's name, the directory in which the file is located, and the volume on which that directory resides. In certain circumstances, a program that's to open a file includes these values (the file name and location) directly within its code, but that's a scenario few programs use. In addition, this hardcoding of file information prevents the user from choosing what file to open, and it also sets up an application failure should the user move or delete the sought-after file.
A better way to handle the situation is to call Navigation Services routines to make use of the Open dialog box. By displaying the Open dialog box, you enable a user to select the file to open. Handling file opening in this way also forces the system to do the work of determining a file's name and location, and it leaves it to the system to convey this important file information to your program.
The Open dialog box provides the user with a standard interface for opening a file. This same Open dialog box is used by any real-world application.You can see it by choosing Open from the File menu of programs such as Apple's TextEdit or by looking at Figure 9.1.
Navigation Services is part of the Carbon API that makes is possible for your programs to include standard dialogs such as the Open dialog box. In addition, it is an important and useful part of the Carbon API. It routines provide interface consistency for the user and removes the burden of file location determination from the programmer. In this chapter, you'll see how to make use of Navigation Services, so brace yourself for a barrage of information about key Navigation Services routines.
Implementing an Open Dialog BoxYo u 'll make use of a number of Navigation Services routines to display and handle an Open dialog box that is similar to the one TextEdit and other Mac OS X applications use. To do that, your code will perform the following:
1. Create and display the standard Open dialog box.
2. Become aware of the user's action in the Open dialog box.
3. Respond to the user's action (for instance, open the appropriate file if the user clicks the Open button).
4. Clean up by disposing of the Open dialog box when appropriate.
The overall look and behavior of an Open dialog box usually is the same. Such a dialog box includes Cancel and Open buttons and a list view of the folders and files on the user's machine. The general behavior of this type of dialog box is the same from one implementation to another as well; the user navigates through the file list, clicks the name of a file to open within the list, and then clicks the Open button to open the selected file. To promote this consistent look and behavior, Navigation Services defines the NavDialogCreationOptions data structure as the following...
...The NavDialogCreationOptions structure defines the features (such as size and location) of an Open dialog box. The Navigation Services routine NavGetDefaultDialogCreationOptions is used to fill the fields of a NavDialogCreationOptions structure with default values. Use this routine by declaring a variable of type NavDialogCreationOptions and then passing that variable's address as the routine's one argument...
...After setting the values of the members of a structure to default values, you can cus-tomize the structure by changing the value of any individual member. For instance, to make the Open dialog box take over the application and disallow other application actions to take its place, the value of the dialog box's NavDialogCreationOptions modality member can be set to the Apple-defined constant kWindowModalityAppModal:
You 've seen how a program includes an application-defined event handler routine that's associated with a window or other object. The Open dialog box also needs an application-defined event handler routine associated with it. This event handler will be called by the system when the user dismisses the Open dialog box. Navigation Services creates, displays, and runs the Open dialog box, but it is this event handler that should perform the actual work of opening a user-selected file. Like other event handlers, this Open dialog box event handler can have a name of your choosing, but it must include arguments of specific types. Here's the prototype for such a routine...
...In a moment, you'll pass a pointer to this event handler to the Navigation Services routine that creates the Open dialog box. The pointer should be of type NavEventUPP. The UPP in NavEventUPP stands for universal procedure pointer, which is a pointer that is capable of referencing procedures, or routines, in different executable formats. In this case, a NavEventUPP can point to a routine that is in native Mac OS X executable format or in pre-Mac OS X executable format.You'll also need this pointer elsewhere in your program, so declaring this pointer globally makes sense...
Use the Navigation Services routine NewNavEventUPP to set this routine pointer variable to point to the Open dialog box event handler:
gNavEventHandlerPtr =NewNavEventUPP(MyNavEventCallback );
Now it's time to make a call to the Navigation Services routine NavCreateGetFileDialog to create the Open dialog box.This routine requires seven arguments, many of which can typically get set to NULL . Here’s the function prototype...