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Diffstat (limited to 'macosx/README')
| -rw-r--r-- | macosx/README | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/macosx/README b/macosx/README index 69be037..202dbbd 100644 --- a/macosx/README +++ b/macosx/README @@ -388,3 +388,64 @@ make overrides to the tk/macosx GNUmakefile, e.g. sudo make -C tk${ver}/macosx install \ TCL_FRAMEWORK_DIR=$HOME/Library/Frameworks TCLSH_DIR=$HOME/usr/bin The Makefile variables TCL_FRAMEWORK_DIR and TCLSH_DIR were added with Tk 8.4.3. + +4. About the event loop in Tk for Mac OSX +----------------------------------------- + +The main program in a typical OSX application looks like this (see *) + + void NSApplicationMain(int argc, char *argv[]) { + [NSApplication sharedApplication]; + [NSBundle loadNibNamed:@"myMain" owner:NSApp]; + [NSApp run]; + } + +The run method implements the event loop for the application. There +are three key steps in the run method. First it calls +[NSApp finishLaunching], which creates the bouncing application icon +and does other mysterious things. Second it creates an +NSAutoreleasePool. Third, it starts an event loop which drains the +NSAutoreleasePool every time the queue is empty, and replaces the +drained pool with a new one. This third step is essential to +preventing memory leaks, since the internal methods of Appkit objects +all assume that an autorelease pool is in scope and will be drained +when the event processing cycle ends. + +Mac OSX Tk does not call the [NSApp run] method at all. Instead it +uses the event loop built in to Tk. So we must take care to replicate +the important features of the method ourselves. Here is how this +works in outline. + +We add a private NSAUtoreleasePool* property to our subclass of +NSApplication. (The subclass is called TKApplication but can be +referenced with the global variable NSApp). The TkpInit +function calls [NSApp _setup] which initializes this property by +creating an NSAutoreleasePool. A bit later on, TkpInit calls +[NSAPP _setupEventLoop] which in turn calls the +[NSApp finishLaunching] method. + +Each time that Tcl processes an event in its queue, it calls a +platform specific function which, in the case of Mac OSX, is named +TkMacOSXEventsCheckProc. In the unix implementations of Tk, including +the Mac OSX version, this function collects events from an "event +source", and transfers them to the Tcl event queue. In Mac OSX the +event source is the NSApplication event queue. Each NSEvent is +converted to a Tcl event which is added to the Tcl event queue. The +NSEvent is also passed to [NSApp sendevent], which sends the event on +to the application's NSWindows, which send it to their NSViews, etc. +Since the CheckProc function gets called for every Tk event, it is an +appropriate place to drain the main NSAutoreleasePool and replace it +with a new pool. This is done by calling the method +[NSApp _resetAutoreleasePool], where _resetAutoreleasePool is a method +which we define for the subclass TKApplication. + +One minor caveat is that there are several steps of the Tk +initialization which precede the call to TkpInit. Notably, the font +package is initialized first. Since there is no NSAUtoreleasePool in +scope prior to calling TkpInit, the functions called in these +preliminary stages need to create and drain their own +NSAutoreleasePools whenever they call methods of Appkit objects +(e.g. NSFont). + +* https://developer.apple.com/library/mac/documentation/Cocoa/\ +Reference/ApplicationKit/Classes/NSApplication_Class |