minimal macos app that can snap

  // main.m
  #import <Cocoa/Cocoa.h>

  @interface AppDelegate : NSObject <NSApplicationDelegate>
  @property (strong, nonatomic) NSWindow *window;
  @end

  @implementation AppDelegate
  - (void)applicationDidFinishLaunching:(NSNotification *)notification {
    [self createMainMenu];
    NSRect frame = NSMakeRect(0, 0, 400, 300);
    NSUInteger style = NSWindowStyleMaskTitled | NSWindowStyleMaskResizable;
    self.window = [[NSWindow alloc] initWithContentRect:frame
                                              styleMask:style
                                                backing:NSBackingStoreBuffered
                                                  defer:NO];
    [self.window setTitle:@"Foobar"];
    [self.window center];

    NSTextField *label = [[NSTextField alloc] init];
    [label setStringValue:@"Hello, world!"];
    [label setBezeled:NO];
    [label setDrawsBackground:NO];
    [label setEditable:NO];
    [label setSelectable:NO];
    [label setAlignment:NSTextAlignmentCenter];
    [label setFont:[NSFont systemFontOfSize:24 weight:NSFontWeightMedium]];
    [label setTranslatesAutoresizingMaskIntoConstraints:NO];

    [self.window.contentView addSubview:label];

    [NSLayoutConstraint activateConstraints:@[
                                              [label.centerXAnchor constraintEqualToAnchor:self.window.contentView.centerXAnchor],
                                              [label.centerYAnchor constraintEqualToAnchor:self.window.contentView.centerYAnchor]
                                              ]];


    [self.window.contentView addSubview:label];
    [self.window makeKeyAndOrderFront:nil];
    [[NSApplication sharedApplication] activateIgnoringOtherApps:YES];
  }

  - (void)createMainMenu {
    NSMenu *mainMenu = [[NSMenu alloc] init];

    // Application menu
    NSMenuItem *appMenuItem = [[NSMenuItem alloc] init];
    [mainMenu addItem:appMenuItem];

    NSMenu *appMenu = [[NSMenu alloc] init]; // XXX: initWithTitle doesn't set the
                                             // title for this one for some
                                             // reason.
    [appMenuItem setSubmenu:appMenu];

    NSMenuItem *quitItem = [[NSMenuItem alloc] initWithTitle:@"Quit"
                                                      action:@selector(terminate:)
                                               keyEquivalent:@"q"];
    [quitItem setTarget:NSApp];
    [appMenu addItem:quitItem];

    // Window menu
    NSMenuItem *windowMenuItem = [[NSMenuItem alloc] init];
    NSMenu *windowMenu = [[NSMenu alloc] initWithTitle:@"Window"];

    [windowMenuItem setSubmenu:windowMenu];
    [mainMenu addItem:windowMenuItem];
    [NSApp setWindowsMenu:windowMenu];
    [NSApp setMainMenu:mainMenu];
  }

  - (void)buttonClicked:(id)sender {
    NSLog(@"Button was clicked!");
  }
  @end

  int main(int argc, const char * argv[]) {
    @autoreleasepool {
      // XXX: some carbon api? cool.
      ProcessSerialNumber psn = { 0, kCurrentProcess };
      TransformProcessType(&psn, kProcessTransformToForegroundApplication);

      NSApplication *app = [NSApplication sharedApplication];
      AppDelegate *delegate = [[AppDelegate alloc] init];
      [app setDelegate:delegate];
      [app run];
    }
    return 0;
  }