QuickTime Movies and File Handling

This chapter is from the book

Mac OS X Programming

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This chapter is from the book

This chapter is from the book 

Mac OS X Programming

Learn More Buy

At 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 Services

A 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 hard-coding 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 Box

You'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:

struct NavDialogCreationOptions {
  UInt16                version;
  NavDialogOptionFlags  optionFlags;
  Point                 location;
  CFStringRef           clientName;
  CFStringRef           windowTitle;
  CFStringRef           actionButtonLabel;
  CFStringRef           cancelButtonLabel;
  CFStringRef           saveFileName;
  CFStringRef           message;
  UInt32                preferenceKey;
  CFArrayRef            popupExtension;
  WindowModality        modality;
  WindowRef             parentWindow;
  char                  reserved[16];
};
typedef struct NavDialogCreationOptions NavDialogCreationOptions;

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:

OSStatus                  err;
NavDialogCreationOptions  dialogAttributes;

err = NavGetDefaultDialogCreationOptions( &dialogAttributes )

After setting the values of the members of a structure to default values, you can customize 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:

dialogAttributes.modality = 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:

pascal void MyNavEventCallback(
               NavEventCallbackMessage callBackSelector, 
               NavCBRecPtr             callBackParms, 
               void*                   callBackUD );

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:

NavEventUPP  gNavEventHandlerPtr;

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:

NavCreateGetFileDialog(
  const NavDialogCreationOptions *  inOptions,
  NavTypeListHandle                 inTypeList,
  NavEventUPP                       inEventProc,
  NavPreviewUPP                     inPreviewProc,
  NavObjectFilterUPP                inFilterProc,
  void *                            inClientData,
  NavDialogRef *                    outDialog );

Using the previously declared dialogAttributes and gNavEventHandlerPtr variables, here's how a call to NavCreateGetFileDialog could look:

NavDialogRef  openDialog;

err = NavCreateGetFileDialog( &dialogAttributes, NULL, 
                              gNavEventHandlerPtr, NULL, NULL, 
                              NULL, &openDialog );

The inOptions parameter is a pointer to the set of Open dialog box features that was returned by a prior call to NavGetDefaultDialogCreationOptions. In the preceding code snippet, dialogAttributes holds that set of default values, with the exception of the modality that was altered after NavGetDefaultDialogCreationOptions was called.

The inTypeList is a list of file types to display in the Open dialog box's browser; pass NULL to display all file types.

The inEventProc parameter is the procedure pointer that points to the Open dialog box's event handler routine. In the preceding snippet, the global UPP variable gNavEventHandlerPtr, which was assigned its value from a call to NewNavEventUPP, is used.

The next three arguments each can be set to NULL. The inPreviewProc parameter is a pointer to a custom file preview routine. The inFilterProc parameter is a pointer to a custom file filter routine. The inClientData parameter is a value that gets passed to either of the just-mentioned custom routines (if present). The preceding snippet uses NULL for each of these three arguments.

The last argument is a pointer to a variable of type NavDialogRef. After NavCreateGetFileDialog executes, this argument will hold a reference to the newly created Open dialog box.

NavCreateGetFileDialog creates an Open dialog box, but it doesn't display or control it. To do those chores, call the Navigation Services routine NavDialogRun:

err = NavDialogRun( openDialog );

NavDialogRun handles the user's interaction with the Open dialog box, so you don't need to write any code to follow the user's actions as he or she uses the dialog box to browse for a file to open. When the user clicks the Cancel or Open button, the application-defined event handler associated with this Open dialog box is called. In doing this, Navigation Services passes on information about the event that initiated the event handler call.

As you'll see a little later in this chapter, the event handler takes care of the opening of the selected file and the dismissing of the Open dialog box. Control then returns to the code that follows the call to NavDialogRun. That code should look something like this:

if ( err != noErr )
{
  NavDialogDispose( openDialog );
  DisposeNavEventUPP( gNavEventHandlerPtr );
}

If NavDialogRun completes without an error, your work is done. If there was an error, the variable err will have a nonzero (non-noErr) value. Your code should call the Navigation Services routines NavDialogDispose to dispose of the Open dialog box reference and DisposeNavEventUPP to dispose of the pointer to the Open dialog box event handler.

Whew. That covers the process of displaying and running the Open dialog box. Now it's time to take a look at all the code as it might appear in an application-defined routine that is used to enable a user to choose a file to open:

void DisplayOpenFileDialog( void )
{
  OSStatus                 err;
  NavDialogRef             openDialog;
  NavDialogCreationOptions dialogAttributes;

  err = NavGetDefaultDialogCreationOptions( &dialogAttributes );

  dialogAttributes.modality = kWindowModalityAppModal;   

  gNavEventHandlerPtr = NewNavEventUPP( MyNavEventCallback );   

  err = NavCreateGetFileDialog( &dialogAttributes, NULL, 
                 gNavEventHandlerPtr, NULL, NULL, 
                 NULL, &openDialog );

  err = NavDialogRun( openDialog );

  if ( err != noErr )
  {
   NavDialogDispose( openDialog );
   DisposeNavEventUPP( gNavEventHandlerPtr );
  }
}

Open Dialog Box Event Handler

After the user of an Open dialog box makes a final decision (by clicking the Cancel or Open button), the Open dialog box event handler is automatically invoked. When the system invokes this handler, the system passes information about the event initiated by the user's action:

pascal void MyNavEventCallback( 
                NavEventCallbackMessage callBackSelector,
                NavCBRecPtr             callBackParms, 
                void*                   callBackUD )

Your event handler uses the information in the callBackSelector argument to determine the action with which to deal. The bulk of the event handler consists of a switch statement that determines which of the primary dialog box-related tasks needs handling:

switch ( callBackSelector )
{
  case kNavCBUserAction: 
   // further determine which action took place (open or save)
   // handle the action (open or save selected file)
   break;

  case kNavCBTerminate:
   // clean up after the now-dismissed dialog
   break;
}

The main two tasks handled in the switch consist of a user action (kNavCBUserAction), such as the request to open a file, and the memory clean up (kNavCBTerminate), which is in response to the dismissal of the dialog box.

To respond to a user action, call the Navigation Services routine NavDialogGetReply. Pass this routine a reference to the dialog box that initiated the event and a pointer to a reply record. NavDialogGetReply will fill the reply record with information about the user's action (such as the file to open). The context field of the event handler argument callBackParms holds the dialog reference. Declare a variable of type NavReplyRecord to be used as the reply record:

OSStatus        err;
NavReplyRecord  reply;
NavUserAction   userAction = 0;   

err = NavDialogGetReply( callBackParms->context, &reply );

Now call NavDialogGetUserAction, passing this routine a reference to the affected dialog box. Once again, the context field of the callBackParams event handler argument is used. NavDialogGetUserAction tells your program the exact action the user took. In the case of an Open dialog box, you're looking for a user action of kNavUserActionOpen. Note that similar code is used to handle a Save dialog, and in such a case, you'd look for a user action of kNavUserActionSaveAs. Finish with a call to NavDisposeReply to dispose of the reply record.

userAction = NavDialogGetUserAction( callBackParms->context );

switch ( userAction )
{
  case kNavUserActionOpen:
  // open file here using reply record information
  break;
}
err = NavDisposeReply( &reply );

You can put the just-described Open dialog box event handler code into a routine that looks like the one shown here:

pascal void MyOpenDialogEventCallback(
               NavEventCallbackMessage callBackSelector,
               NavCBRecPtr             callBackParms, 
               void*                   callBackUD )
{
  OSStatus     err;
  NavReplyRecord  reply;
  NavUserAction  userAction = 0;   

  switch ( callBackSelector )
  {
   case kNavCBUserAction:    
     err = NavDialogGetReply( callBackParms->context, &reply );
     userAction = NavDialogGetUserAction( callBackParms->context );   

     switch ( userAction )
     {
      case kNavUserActionOpen:
      // open file here using reply record information
      break;
     }
     err = NavDisposeReply( &reply );
     break;

   case kNavCBTerminate:
     NavDialogDispose( callBackParms->context );
     DisposeNavEventUPP( gNavEventHandlerPtr );
     break;
  }
}

The MyOpenDialogEventCallback routine is generic enough that it should work, with very little alteration, in your own file-opening program. Now all you need to do is replace the routine's one comment with a call to an application-defined function designed to open a file of the appropriate type. In the next section, you see how to write such a routine. The code for the application-defined function OpenOneQTMovieFile opens a QuickTime movie file. The OpenPlayMovie example then uses the MyOpenDialogEventCallback routine with a call to OpenOneQTMovieFile.