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Launching Other Applications
Launching Other Applications
The information in this section about launching applications replaces the
corresponding discussion in the Programmer'Ës Guide to MultiFinder.
You can launch other applications using the high-level LaunchApplication
function. The LaunchApplication function lets your application control
various options associated with launching an application. For example, you can
• allow the application to be launched in a partition smaller than the
preferred size but greater than the minimum size, or allow it to be
launched only in a partition of the preferred size
• launch an application without terminating your own application,
bring the launched application to the front, and get information about
the launched application
• request that your application be notified if any application that it has
launched terminates
Earlier versions of system software used a shorter parameter block as a
parameter to the _Launch trap macro. The _Launch trap macro still supports
the use of this parameter block. Applications using the LaunchApplication
function should use the new LaunchParamBlockRec . Use the Gestalt
function and specify the selector gestaltOSAttr to determine which launch
features are available. See the Compatibility Guidelines for information
on how to use the Gestalt function.
Most applications do not need to launch other applications. However, if your
application includes a desk accessory or another application, you might use
either the high-level LaunchApplication function to launch an application
or the LaunchDeskAccessory function to launch a desk accessory. For
example, if you have implemented a spelling checker as a separate application,
you might use the LaunchApplication function to open the spelling checker
when the user chooses Check Spelling from one of your application's menus.
You specify a LaunchParamBlockRec as a parameter to the
LaunchApplication function. You use the LaunchParamBlockRec to
specify the filename of the application to launch, to specify whether to allocate
the preferred size for the application's heap or to allow a partition size less
than the preferred size, and to set various other options-for example, whether
your application should continue or terminate after it launches the specified
application.
The LaunchApplication function launches the application from the
specified file and returns the process serial number, preferred partition size,
and minimum partition size if the application is successfully launched.
Note that if you launch another application without terminating your
application, the launched application does not actually begin executing until
you make a subsequent call to WaitNextEvent or EventAvail.
The launch parameter block is defined by the LaunchParamBlockRec.
Specify the constant extendedBlock in the launchBlockID field to identify the
parameter block and to indicate that you are using the fields following it in the
LaunchParamBlockRec.
The code example shows the use of the LaunchApplication function
// Launching an application
// Assuming inclusion of
#include <Processes.h>
void LaunchAnApplication (StandardFileReply *mySFReply);
void DoError (OSErr myErr);
void LaunchAnApplication (StandardFileReply *mySFReply)
{
LaunchParamBlockRec myLaunchParams;
ProcessSerialNumber launchedProcessSN;
OSErr launchErr;
long prefSize;
long minSize;
long availSize;
myLaunchParams.launchBlockID = extendedBlock;
myLaunchParams.launchEPBLength = extendedBlockLen;
myLaunchParams.launchFileFlags = 0;
myLaunchParams.launchControlFlags = launchContinue + launchNoFileFlags;
myLaunchParams.launchAppSpec = &(mySFReply->sfFile);
myLaunchParams.launchAppParameters = nil;
launchErr = LaunchApplication(&myLaunchParams);
prefSize = myLaunchParams.launchPreferredSize;
minSize = myLaunchParams.launchMinimumSize;
if (!launchErr)
launchedProcessSN = myLaunchParams.launchProcessSN;
else if (launchErr == memFullErr)
availSize = myLaunchParams.launchAvailableSize;
else
DoError(launchErr);
}
In the code example above, the application file to launch is specified by using
a file system specification record returned by the StandardGetFile routine
and specifying a pointer to this record in the launchAppSpec field. The
launchControlFlags field indicates that LaunchApplication should extract
the Finder flags from the application file, launch the application in the
preferred size, bring the launched application to the front, and that
LaunchApplication should not terminate the current process.
Specifying Launch Options
When you use the LaunchApplication function, you specify the launch
options in the launchControlFlags field of the LaunchParamBlockRec. These
are the constants you can specify in the launchControlFlags field.
launchContinue = 0x04000,
launchNoFileFlags = 0x00800,
launchUseMinimum = 0x00400,
launchDontSwitch = 0x00200,
launchInhibitDaemon = 0x00080
Set the launchContinue flag if you want your application to continue after the
specified application is launched. If you do not set this flag,
LaunchApplication terminates your application after launching the
specified application, even if the launch fails.
Set the launchNoFileFlags flag if you want the LaunchApplication function
to ignore any value specified in the launchFileFlags field. If you set the
launchNoFileFlags flag, the LaunchApplication function extracts the Finder
flags from the application file for you. If you want to extract the file flags,
clear the launchNoFileFlags flag and specify the Finder flags in the
launchFileFlags field of the LaunchParamBlockRec.
Clear the launchUseMinimum flag if you want the LaunchApplication
function to attempt to launch the application in the preferred size (as specified
in the application's 'SIZE' resource). If you set the launchUseMinimum flag,
the LaunchApplication function attempts to launch the application using the
largest available size greater than or equal to the minimum size but less than
the preferred size. If the LaunchApplication function returns the result
code memFullErr or memFragErr, the application cannot be launched given the
current memory conditions.
Set the launchDontSwitch flag if you do not want the launched application
brought to the front. If you set this flag, the launched application runs in the
background until the user brings the application to the front-for example, by
clicking in one of the application's windows. Note that most applications expect
to be launched in the foreground. If you clear the launchDontSwitch flag, the
launched application is brought to the front, and your application is sent to the
background.
Set the launchInhibitDaemon flag if you do not want LaunchApplication to
launch a background-only application. (A background-only application has the
onlyBackground flag set in its 'SIZE' resource.)
Controlling Launched Applications
When your application launches another application using
LaunchApplication , the launched application is automatically brought to
the front, sending the foreground application to the background. If you do not
want to bring the application to the front when it is first launched, set the
launchDontSwitch flag in the launchControlFlags field of the
LaunchParamBlockRec.
In addition, if you want your application to continue to run after it launches
another application, you must set the launchContinue flag in the
launchControlFlags field of the LaunchParamBlockRec.
You can control the scheduling of the launched application in a limited way by
using the Process Manager routines SetFrontProcess and
WakeUpProcess .
If you want your application to be notified when an application it has launched
terminates, set the acceptAppDiedEvents flag in your 'SIZE' resource. If you
set this flag and an application launched by your application terminates, your
application receives an
Application-Died event ('aevt' 'obit').
See the Apple Event Manager for information on receiving the
Application-Died event and other Apple events.
Launching Desk Accessories
In version 7.0, when a desk accessory is opened, the Process Manager
launches the desk accessory in its own partition. The Process Manager
gives it a process serial number and an entry in the process list. The
Process Manager puts the name of the desk accessory in the list of open
applications in the Application menu and also gives the active desk accessory
its own About menu item in the Apple menu that contains the name of the desk
accessory. This makes desk accessories more consistent with the user interface
of small applications.
Your application can launch desk accessories using the
LaunchDeskAccessory function. However, you should use this function
only when your application needs to launch a desk accessory for some reason
other than in response to the user choosing a desk accessory from the Apple
menu. In version 7.0, the Apple menu can contain any Finder object that the
user chooses to add to the menu. When the user chooses any item from the Apple
menu that you did not add specifically for your application, use the
OpenDeskAcc function.
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