Load macOS Preference Pane into application

PrefPaneLoader.m

#import "AppDelegate.h"
#import "PreferencePanes/NSPreferencePane.h"

@interface AppDelegate ()

@property (strong) IBOutlet NSWindow *window;
@property (strong) NSPreferencePane *prefPaneObject;
@property (strong) NSView *prefView;

@end

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSBundle *prefBundle = [NSBundle bundleWithPath: @"/System/Library/PreferencePanes/Appearance.prefPane"];
    
    Class prefPaneClass = [prefBundle principalClass];
    
    _prefPaneObject = [[prefPaneClass alloc] initWithBundle:prefBundle];
    
    if ( [_prefPaneObject loadMainView] ) {
    
        [_prefPaneObject willSelect];
        
        _prefView = [_prefPaneObject mainView];
        
        /* Add view to window */
        
        [_prefPaneObject didSelect];
                
        [_window.contentView addSubview:_prefView];
        _window.contentMinSize = NSMakeSize(0, 0);
        _window.contentMaxSize = NSMakeSize(CGFLOAT_MAX, CGFLOAT_MAX);
        _window.styleMask |= NSWindowStyleMaskResizable;
        
        NSView *contentView = self.window.contentView;
        self.prefView = [self.prefPaneObject mainView];
        
        self.prefView.translatesAutoresizingMaskIntoConstraints = NO;
        [contentView addSubview:self.prefView];
        
        [NSLayoutConstraint activateConstraints:@[
            [self.prefView.leadingAnchor constraintEqualToAnchor:contentView.leadingAnchor],
            [self.prefView.trailingAnchor constraintEqualToAnchor:contentView.trailingAnchor],
            [self.prefView.topAnchor constraintEqualToAnchor:contentView.topAnchor],
            [self.prefView.bottomAnchor constraintEqualToAnchor:contentView.bottomAnchor],
        ]];
    }
}

@end