Can i have a single NSMutableArray in my multiple views application?

问题

I have a navigational based application which has multiple views. Is it possible to use one single NSMutableArray for the whole applicaiton? Can i add objects to that NSMutableArray in one view and then remove object from the same NSMutableArray from some other view? I tried

 myappAppDelegate *appDelegate = (myappAppDelegate *)[[UIApplication sharedApplication] delegate];

but it gives me null when i try to access appDelegate's array. If anyone can give me any idea or helping link or tutrorial. Thanks in advance.

回答1:

If you are having multiple views in your application, and in that case you want to have a variable accessible to every view, you should always create a Model/Data(singleton) class and define the variable in it. Something like this :

//DataClass.h      

@interface DataClass : NSObject {    

NSMutableArray *arrGlobal;     

}    
@property(nonatomic,retain)NSMutableArray *arrGlobal;   
+(DataClass*)getInstance;    
@end  



//DataClass.m    
@implementation DataClass    
@synthesize arrGlobal;    
static DataClass *instance =nil;    
+(DataClass *)getInstance    
{    
    @synchronized(self)    
    {    
        if(instance==nil)    
        {    

            instance= [DataClass new];    
        }    
    }    
    return instance;    
}    

Now in your view controller you need to call this method as :

DataClass *obj=[DataClass getInstance];  
obj.arrGlobal = arrLocal; 

This variable will be accessible to every view controller. You just have to create an instance of Data class.

回答2:

For your type of issue I would use a singleton.

http://en.wikipedia.org/wiki/Singleton_pattern

The appdelegate is a singleton too but you can reduce a bit the number of coded lines if you use your own singleton.

回答3:

The AppDelegate approach should work, and you should probably figure out why it's not working, even if you go with a singleton.

The statement to get your appDelegate pointer appears to be correct, so I'm guessing that the pointer to the array is either not getting set (and retained) in your myappDelegate class, or you did not create the AppDelegate instance correctly in the first place.

回答4:

On the Singleton approach add this

instance.arrGlobal = [[NSMutableArray alloc] init];

this way:

@synchronized(self)    
{    
    if(instance==nil)    
    {    

        instance= [DataClass new];
        instance.arrGlobal = [[NSMutableArray alloc] init];
    }    
}    
return instance;

This way you can initilize the array and use it properly.

来源：https://stackoverflow.com/questions/7636057/can-i-have-a-single-nsmutablearray-in-my-multiple-views-application