在主窗口中显示自定义的View

@interface AppDelegate ()

@property (weak) IBOutlet NSWindow *window;

//自定义view类的对象，带xib文件

@property (nonatomic, strong) IBOutlet MainViewController *mainVC;

@end

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {

    // Insert code here to initialize your application

    self.mainVC = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];

    [self.window.contentView addSubview:self.mainVC.view];

    self.mainVC.view.frame = self.window.contentView.bounds;

}