How to make [NsApp run] not block? - objective-c

Question

I'm a complete Cocoa newbie.
Right now my simple Hello World app blocks after calling [NsApp run] from main().
All I need is create a window and not block main().
I want my application to behave like glfw:
https://github.com/glfw/glfw/blob/master/src/cocoa_window.m#L1022
For some reason, it doesn't block there. In fact, you can remove this line, and it will still work.
I've been playing with a glfw source to figure out what they do differently. And for example, [NsApp run] blocks if I remove [NSApp setDelegate:_glfw.ns.delegate];
But that's not it.
According to the Apple docs:
The NSApplication class sets up #autorelease block during
initialization and inside the event loop—specifically, within its
initialization (or shared) and run() methods.
Typically, an app creates objects either while the event loop is
running or by loading objects from nib files, so this lack of access
usually isn’t a problem. However, if you do need to use Cocoa classes
within the main() function itself (other than to load nib files or to
instantiate NSApplication), you should create an #autorelease block to
contain the code using the classes.
I guess that's what I need, but I have no idea how to use the #autorelease block.
Thanks for your help.

Answer 1

I figured it out.
GLFW implements its own event loop, so calling [NSApp run] is not needed:
NSEvent *event = [NSApp nextEventMatchingMask:NSEventMaskAny
untilDate:[NSDate distantFuture]
inMode:NSDefaultRunLoopMode
dequeue:YES];
[NSApp sendEvent:event];

Answer 2

I've been looking at this problem myself, and decided to organize everything everyone said and I have found into one answer.
You should probably note that the reason run blocks is because it has something functionally similar to a while(1) loop inside of it which updates the window and handles events and such. Calling [NSApp stop] stops this loop so it wont block anymore (good), but we also have no more events (bad).
Overall, what GLFW does is the following:
Create an NSApplication, create a delegate, and set the delegate to the application.
Call run and stop on the NSApp. stop is called inside applicationDidFinishLaunching of the delegate.
On each frame get the next event from queue and dispatch it down the application.
More in-depth with code: PS. All code is (altered for simplicity) from the GLFW github
// src/cocoa_init.m
int _glfwPlatformInit(void)
{
...
//setup NSApplication, then init and set delegate
[NSApplication sharedApplication];
GLFWApplicationDelegate* del = [[GLFWApplicationDelegate alloc] init];
[NSApp setDelegate:del];
//This is a guard to make sure run is only called once
if (![[NSRunningApplication currentApplication] isFinishedLaunching])
[NSApp run];
}
Note the isFinishedLaunching guard exists because applicationDidFinishLaunching in the delegate only gets called after the first run call. If for some reason the user called glfwInit() again, without the guard run would be called, causing it to block again.
// src/cocoa_init.m
#interface GLFWApplicationDelegate : NSObject <NSApplicationDelegate>
#end
#implementation GLFWApplicationDelegate
...
- (void)applicationDidFinishLaunching:(NSNotification *)notification
{
_glfwPlatformPostEmptyEvent();
[NSApp stop:nil];
}
#end
// src/cocoa_window.m
void _glfwPlatformPollEvents(void)
{
#autoreleasepool {
for (;;)
{
NSEvent* event = [NSApp nextEventMatchingMask:NSEventMaskAny
untilDate:[NSDate distantPast]
inMode:NSDefaultRunLoopMode
dequeue:YES];
if (event == nil)
break;
[NSApp sendEvent:event];
}
} // autoreleasepool
}
Note glfwPollEvents retrieves the next event from the queue, then sends the event to the application to be propogated through the responders. It functions as the main loop explained in the documentation about event architecture.
In the main event loop, the application object (NSApp) continuously gets the next (topmost) event in the event queue, converts it to an NSEvent object, and dispatches it toward its final destination

Answer 3

I just experienced the same scenario.
I and found a little different solution.
Just call [[NSApplication sharedApplication] run]; and when your window is created, call [[NSApplication sharedApplication] stop:nil];, the run call will now exit. And then you can still call the sendEvent method.