CS193P UITabBarController MVC Help on Assignment 4

问题

I'm going through the Stanford CS193P course on iTunesU and am a little puzzled on how to do the recently viewed photos portion on assignment 4.

In the assignment we are to have a tab bar controller with two tabs. 1st tab is a navigation controller that will show a table of places, which will push a table of photo names, which will push a scroll view with a photo 2nd tab is a navigation controller that will show a table of recently viewed photos, which will push a scroll view with a photo.

I have the first tab working, and now when I push the scroll view with the image, I also want to add that photo to an array of recent photos, which MVC should own this recent photos array?

The Tab View Controller (if so the docs say that this class is not intended for sub classing)
The root Table View Controller of the 2nd Tab (how do I pass the current photo to the instance is in another tab) (and quite frankly should the first tab know about the second tab)
The root Table View Controller of the 1st Tab (then how does the second tab pull this data from the first tab?)
Something else

I guess I'm still hazy about MVC's, protocols, delegates and data sources. If you have your solution to this task that I could look through I would greatly appreciate it.

I ended up pushing and pulling the data from user defaults. Although I'm curious why the tab bar controller is not intended for sub classing. That seems like the most logical place for data to be owned when it is needed by multiple tabs.

回答1:

I've done something similar and if I don't missundestood your question completely, you could create a Singelton whichcould act like some kind of shared database. It will never be initialized in a normal fashion, just created when you use it the first time. This singelton could contain your array and you could then call it from everywhere by writing just:

[SingeltonType main].sharedPhotos

The following example is from my own code where I have a "User" which is the owner of the app. There I store a database with info that will be available from anywhere during runtime.

header:

@interface User : NSObject {
Database *_storage;
}

@property (nonatomic, retain) Database *storage;

+(User*)owner;

main file:

#import "User.h"

@implementation User

@synthesize password = storage = _storage;

static User* _owner = nil;

+(User*)owner {
    @synchronized([User class]) {
        if(!_owner) [[self alloc] init];

        return _owner;
    }
    return nil;
}

+(id)alloc {
    @synchronized([User class]) {
        NSAssert(_owner == nil, @"Attempted to allocate a second instance of a singleton.");
        _owner = [super alloc];

        return _owner;
    }
    return nil;
}

-(id)init {
    self = [super init];

    if(self != nil) {
        self.storage = [[[Database alloc] init] autorelease];
    }
    return self;
}

Then I just call it like this:

[User owner].storage // which gives me access to it

Hope that helps! Really useful if you need to access data from different places :)

Note: You will only have ONE instance of this object and cannot create more.

回答2:

After a bunch of additional searching, I didn't find any one consistent way to pass data from tab to tab.

Since we are only storing a relatively small amount of data, I decided to make a class, with class methods (for convenience) to push and pull the data into user defaults.

回答3:

I have messed around with that question a bit by using protocol. I created the protocol in the class displaying the image (and UIScrollView). I then adopted the protocol in the "viewed photos" tableController class and implemented that protocol method that passes the viewed image. The problem I have is how do you define the "viewed Photos" tableController class as the delegate, given that 1) it has not been loaded yet and might not be loaded until after viewing pictures 2) how do you work your way though the nav controllers and tab controller to point to the class declaring the protocol. Would love to hear from experts here on whether protocol or class method is the right way here from a programming methodology?

Thanks KB

来源：https://stackoverflow.com/questions/9629168/cs193p-uitabbarcontroller-mvc-help-on-assignment-4

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objective-c

model-view-controller

uitabbarcontroller

cs193p