--- a/PDFViewer/appdelegate/AppDelegate.h
+++ b/PDFViewer/appdelegate/AppDelegate.h
@@ -9,9 +9,7 @@
 #import <Cocoa/Cocoa.h>
 #import "ViewController.h"
 
-@interface AppDelegate : NSObject <NSApplicationDelegate> {
-    NSWindow *window;
-    ViewController *controller;
-}
-
+@interface AppDelegate : NSObject <NSApplicationDelegate>
+@property (weak) NSWindow* window;
+@property (weak) ViewController* controller;
 @end