Crash when closing window in a MacOS application?-CodePudding

I am attempting to create a functional MacOS application but with absolutely no xib or storyboard file just to see how it is done.

In the AppDelegate.m I create and show a window and set the application to terminate after last window closed:

#import "AppDelegate.h"
@implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)Notification {
    NSWindow *const Window = [[NSWindow alloc] initWithContentRect:(NSRect){.size = {800, 512}} styleMask:NSWindowStyleMaskTitled|NSWindowStyleMaskClosable|NSWindowStyleMaskMiniaturizable|NSWindowStyleMaskResizable backing:NSBackingStoreBuffered defer:YES];
    [Window center];
    [Window makeKeyAndOrderFront:Window];
    // Insert code here to initialize your application
}
- (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication *)Sender {
    return YES;
}
@end

AppDelegate.h:

#import <Cocoa/Cocoa.h>
@interface AppDelegate : NSObject<NSApplicationDelegate>
@end

In the Main.m file is the following:

#import <Cocoa/Cocoa.h>
#import "AppDelegate.h"
int main(void) {
    @autoreleasepool {
        [NSApplication sharedApplication].delegate = (AppDelegate *){[[AppDelegate alloc] init]}; // I also tried using setDelegate to no avail
        [NSApp run];
    }
    return 0;
}

A window is created, but the issue is that when I close the window, the app crashes, showing an Thread 1: EXC_BAD_ACCESS (code=1, address=0x20) at the [NSApp run] line in Main.m. Somehow the application does not terminate properly and crashes instead. Clearly I am missing something but the question is what?

Edit: I noticed an odd occurance which is that the crash only occurs when ARC (Automatic Reference Counting) is enabled.

CodePudding user response：

The problem is the window is automatically released (and thus deallocated) upon closure. This, combined with the automatic reference counting, presumably creates a sort of double free error. To solve this problem without disabling ARC or disabling releaseWhenClosed, Window is made a global or instance variable. Doing so will prevent ARC from releasing the window after already having been released by being closed.

NSWindow *Window;
// ...
- (void)applicationDidFinishLaunching:(NSNotification *)Notification {
    Window = [[NSWindow alloc] initWithContentRect:(NSRect){.size = {800, 512}} styleMask:NSWindowStyleMaskTitled|NSWindowStyleMaskClosable|NSWindowStyleMaskMiniaturizable|NSWindowStyleMaskResizable backing:NSBackingStoreBuffered defer:YES];
    [Window center];
    [Window makeKeyAndOrderFront:Window];
    // Insert code here to initialize your application
}