如何在Object-C中将字符串发送到AppDelegate？

Question

I've create a class 'Datetool' inherit from NSObject to record the date when the application was launched. But I need to show the startTime string in the AppDelegate.

I tried to use the Block to send the string with a variable declared in 'AppDelegate.h', however, I couldn't get it in Datetool's method initialize .

Datetool.m

static NSString *startTime2;

+(void)initialize
{

   if (self == [DateTool self])
   { 
       NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
       [formatter setDateStyle:NSDateFormatterNoStyle];
       [formatter setTimeStyle:NSDateFormatterMediumStyle];
       startTime2 = [formatter stringFromDate:[NSDate date]];
    }
}

Answer 1

Why not simply call a function in the AppDelegate when the app starts.(warning I have not tried compiling this).

- (NSString*)getStartDate {

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterNoStyle];
    [formatter setTimeStyle:NSDateFormatterMediumStyle];
    return [formatter stringFromDate:[NSDate date]];
}

Answer 2

You can get at your AppDelegate from anywhere by using the UIApplication's singleton method: [UIApplication sharedApplication].delegate Just cast it as your custom class to access specific methods: (AppDelegate*)[UIApplication sharedApplication].delegate

That said, I don't think that's the right approach to take here. Your Datetool is a utility class and shouldn't be reliant on references to the AppDelegate, which makes for very tightly coupled code. Instead, Datetool should be able to be called from the AppDelegate and return the desired value. Since you're already using a class method, it doesn't seem like Datetool needs an instance at all. You can scrap storing the static value and just return what you need:

+ (NSString*)startTime
{ 
   NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
   [formatter setDateStyle:NSDateFormatterNoStyle];
   [formatter setTimeStyle:NSDateFormatterMediumStyle];
   return [formatter stringFromDate:[NSDate date]];
}

Now you're pulling a value from the tool rather than trying to push it onto the AppDelegate, which makes it reusable for other purposes.

Answer 3

将类定义导入AppDelegate.h并在AppDelegate中实例化对象会是个坏主意吗？

Answer 4

I suggest that you provide a delegate protocol in your DateTool which is implemented by your AppDelegate. For example (not tested):

DateTool.h:

/** The delegate protocol of DateTool. */

@protocol DateToolDelegate <NSObject>

/** The start date was set. */
- (void)startDateSet:(NSDate)startDate;

@end

@interface DateTool : NSObject

/** The delegate of DateTool. */
@property (weak) id<DateToolDelegate> delegate;

@end

DateTool.m:

+(void)initialize
{

   if (self == [DateTool self])
   { 
       NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
       [formatter setDateStyle:NSDateFormatterNoStyle];
       [formatter setTimeStyle:NSDateFormatterMediumStyle];
       startTime2 = [formatter stringFromDate:[NSDate date]];
       if ([_delegate conformsToProtocol:@protocol(DateToolDelegate)]) {
           [_delegate startDateSet:startTime2];
       }
    }
}

In AppDelegate.h you need to add the protocol:

#import "DateTool.h"
@interface AppDelegate : UIResponder <DateToolDelegate>

In your AppDelegate.m you need to register itself as delegate:

...    
dateTool.delegate = self;
...

and implement the protocol:

- (void)startDateSet:(NSDate)startDate
{
// Do something with startDate
}

Hope that helps.

PS: Why is initialize a class method? I'd suggest to instantiate an object.