捆绑包中NSApplication委托的使用

Question

I am trying to create a plugin for Unity using Objective-C for an app running on Mac. I need to get the URL when launching my app from a link using an url protocol. I haven't used Objective-C before, so I am having trouble trying to make it work.

I am using an example provided by Unity ( download example ) and changing the methods to the ones I need to get the URL, but my app crashes on the line nsApplication = [[NSApplication alloc] init]; on the _GetUrl method. I have no idea what I am missing/doing wrong. Also, _GetUrl is the method called from Unity when I want to ask for the url (which is called at the first frame), but I am afraid it might be called after applicationWillFinishLaunching. So where should I actually set the delegate so that applicationWillFinishLaunching happens after the delegate is set?

I use an .h and a .m script and then compile the bundle and import it into Unity as a plugin. This is my code:

PluginUrlHandler.h

#import <Foundation/Foundation.h>
#import <AppKit/AppKit.h>

@interface NSApplicationDelegate : NSObject
{
    NSString* urlString;
}

// NSApplication delegate methods
- (void)applicationWillFinishLaunching:(NSNotification *)aNotification;
- (void)handleGetURLEvent:(NSAppleEventDescriptor *)event withReplyEvent:(NSAppleEventDescriptor *)replyEvent;

//Other methods
- (NSString *)getUrl;
@end

PluginUrlHandler.m

#import <Foundation/Foundation.h>
#import "PluginUrlHandler.h"

@implementation NSApplicationDelegate

- (id)init
{
    self = [super init];
    urlString = @"nourl";
    return self;
}

- (void)applicationWillFinishLaunching:(NSNotification *)aNotification
{
    NSAppleEventManager *appleEventManager = [NSAppleEventManager sharedAppleEventManager];
    [appleEventManager setEventHandler:self
                           andSelector:@selector(handleGetURLEvent:withReplyEvent:)
                         forEventClass:kInternetEventClass andEventID:kAEGetURL];

}

- (void)handleGetURLEvent:(NSAppleEventDescriptor *)event withReplyEvent:(NSAppleEventDescriptor *)replyEvent
{
    [event paramDescriptorForKeyword:keyDirectObject] ;

    NSString *urlStr = [[event paramDescriptorForKeyword:keyDirectObject] stringValue];

    urlString = urlStr;
}

- (NSString *)getUrl
{
    return urlString;
}

@end

static NSApplicationDelegate* delegateObject = nil;
static NSApplication* nsApplication = nil;


// Helper method to create C string copy
char* MakeStringCopy (const char* string)
{
    if (string == NULL)
        return NULL;

    char* res = (char*)malloc(strlen(string) + 1);
    strcpy(res, string);
    return res;
}

#if c__plusplus
extern "C" {
#endif

    const char* _GetUrl ()
    {
        if (delegateObject == nil)
        delegateObject = [[NSApplicationDelegate alloc] init];

        if (nsApplication == nil)
            nsApplication = [[NSApplication alloc] init];

        [nsApplication setDelegate:delegateObject];

        return MakeStringCopy([[delegateObject getUrl] UTF8String]);
    }

#if c__plusplus
}
#endif

Answer 1

If your application is crashing, you need to provide some information, such as a stack trace or error message so we can best help. I'm assuming the error you're receiving looks like this:

2016-03-06 10:07:14.388 test[5831:230418] *** Assertion failure in -[NSApplication init], /Library/Caches/com.apple.xbs/Sources/AppKit/AppKit-1404.34/AppKit.subproj/NSApplication.m:1980
2016-03-06 10:07:14.391 test[5831:230418] An uncaught exception was raised
2016-03-06 10:07:14.391 test[5831:230418] Creating more than one Application

You shouldn't create your own NSApplication object. Just use the system one by referencing [NSApplication sharedApplication] .

Generally speaking, you shouldn't need an NSApplication (or NSApplicationDelegate ) for a plugin, though. The program that's loaded you should already have one, and you don't want to mess with that. Just create a custom NSObject subclass to be your AppleEvent handler. You don't need NSApplication (or it's delegate) at all for this. Any object can be the target of an AppleEvent.

You can't use things like applicationDidFinishLaunching:withOptions: from a plugin in any case. It's too late. The application has long since launched. You'll need to add your AppleEvent handler in some function called from Unity. I'm not particularly familiar with Unity's plugin engine, so I don't know if there's a particular "load" function that gets called automatically (I don't see one in the sample code). You may have to call something yourself. It would have to occur after the plugin is loaded, but before the Get URL Apple Event happens (it's unclear what you expect to generate that).

Just curious what you're trying to pull off with this. I've never seen a protocol handler used this way.

Answer 2

Creation of NSApplication instance looks very suspicious. Normally you don't create it as it is a singleton by definition.

So instead of this:

if (nsApplication == nil)
   nsApplication = [[NSApplication alloc] init];

you should have rather this (getting current NSApplication instance):

if (nsApplication == nil)
   nsApplication = [NSApplication sharedApplication];

Answer 3

I made a tutorial on this, see Override app delegate in Unity for iOS and OSX (4/4) Inject code to Mach-O binary .

It uses code injection to set an Objective-C class to respond the corresponding Apple Event.