Short hand for [[UIApplication sharedApplication]

问题:

I stored global variables in my AppDelegate and access them by:

AppDelegate *d = [[UIApplication sharedApplication] delegate];
d.someString = ...

What's the recommend way to save some typing and so I don't need to AppDelegate *d = [[UIApplication sharedApplication] delegate]; again and again? Thanks!

回答1:

As Shaggy Frog said, define a macro in your YourAppDelegate.h file, an example like this:

#define AppDelegate (YourAppDelegate *)[[UIApplication sharedApplication] delegate]

Then you can get the app delegate in your code like this:

[AppDelegate ......];

回答2:

Since your app delegate never really changes, you can create an external that you define in the app delegate code, very similar to the NSApp external for Mac OS X Cocoa applications.

So, define the external in your AppDelegate header (or something else that you would include everywhere):

extern AppDelegate* appDelegate;

Then create it and set it in your implementation file:

AppDelegate* appDelegate = nil;

// later -- i can't recall the actual method name, but you get the idea
- (BOOL)applicationDidFinishLaunchingWithOptions:(NSDictionary*)options
{
  appDelegate = self;
  // do other stuff
  return YES;
}

Then other classes can just access it:

#import "AppDelegate.h"

// later
- (void)doSomethingGreat
{
  NSDictionary* mySettings = [appDelegate settings];
  if( [[mySettings objectForKey:@"stupidOptionSet"] boolValue] ) {
    // do something stupid
  }
}

回答3:

You could just create a C-style macro and put it in a header file somewhere.

(As for using your app delegate as a giant global variable catch-all, that's another rant for another day.)

回答4:

I create a category called UIApplication+delegate with some convenience messages in it. Getting my specific delegate being one of the convenience messages. So, for instance, if my app delegate was called MyAppDelegate, it would look like this:

UIApplication+delegate.h

#import "MyAppDelegate.h"

@interface UIApplication(delegate)
+ (MyAppDelegate *)thisApp;
@end

and UIApplication+delegate.m

#import "UIApplication+delegate.h"


@implementation UIApplication(delegate)

+ (MyAppDelegate *)thisApp {
    return (MyAppDelegate*)[[UIApplication sharedApplication] delegate];
}

@end

In a class that needs the delegate, I do this:

#import "UIApplication+delegate.h"

...

- (void)doStuff {
    MyAppDelegate *app = [UIApplication thisApp];
    // use "app"
}

回答5:

I also created a category, except that I applied mine to NSObject so any object in the application can easily get to the delegate.

---

#import "MyAppDelegate.h"

@interface NSObject(delegate)
- (MyAppDelegate *) appDelegate;
@end

---

#import "NSObject+delegate.h"

@implementation UIApplication(delegate)

- (MyAppDelegate *)appDelegate {
    return (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
}

@end

---