Howto get access to another controller/view (iOS)

Question

I have three separated class, UIViewController (A) and two UITableViewControllers (B and C).

I add table B and C into A.

[A.view addSubview:B.tableView];

[A.view addSubview:C.tableView];

Now I need to change/reload one table by the selection in another table. For example, select "meat" in B then C become "chicken, pork...", select "fruit" then get "apple, tomato...".

My question is generally Howto get access to another controller/view. What should I write in didSelectRowAtIndexPath in B to access another controller (A, C)?

vikingosegundo · Accepted Answer · 2012-01-27 02:03:45Z

2

You are looking for delegation. Add a protocol to B and C and let the other implement it.

I wrote a sample code quite along time ago.

In there the CheckTableController can inform the ShowFavoritesTableController, as the second implements the delegate protocol of the first.

answered Jan 27, 2012 at 2:03

vikingosegundo

52.3k14 gold badges140 silver badges184 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

ThinkChris Over a year ago

Thanks @vikingosegundo. what is the difference between delegation and notification in this case, in a view of programming principles. I think their principles are quite similar, which are let someone else to do it for them.

vikingosegundo Over a year ago

There are similarities. But big differences as well. Notifications do broadcasting: They can inform many objects, that "tuned-in" on an object, but their sender can't receive any message or objects from it listeners. Delegations is a 1-to-1 communication, but the delegate methods can return objects. You are free to use methods with signatures of any kind. Notification broadcasting is expensive, while delegations is just normal message sending.

vikingosegundo Over a year ago

developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/…

MobileOverlord · Accepted Answer · 2012-01-27 02:20:01Z

2

I usually do this through the NSNotificationCenter. In the

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath

broadcast a message using NotificationCenter.

[[NSNotificationCenter defaultCenter]postNotificationName:@"NotificationName" object:myObj];

On the class that has the receiving end set it to listen for this notification in the viewDidLoad or init method

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reloadTable:) name:@"NotificationName" object:nil];

Have your method declared in the .m file

-(void)reloadTable:(NSNotification*)n {
[tableView reloadData];
}

Remember to remove the observer when the object is destroyed in the dealloc method If you're using ARC

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

If you're not using ARC remember to super

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [super dealloc];
}

edited Jan 27, 2012 at 2:20

answered Jan 27, 2012 at 1:36

MobileOverlord

4,6003 gold badges25 silver badges32 bronze badges

3 Comments

ThinkChris Over a year ago

Thanks @Justin. This seems a good way to do it. Lets see if there are other ways. Just want to know the best method.

MobileOverlord Over a year ago

I also like @asops's strategy for handling multiple table views in the same class. I have also done that before and it works well. Sometimes I switch which table is which by setting the tableView's tag(int) property so I don't have to hold weak references to the tableView when using Interface Builder. The notification center way works well when you are talking across objects and don't want to force rigidity into the structure of your code. In addition, you don't have to worry about retain cycles this way.

vikingosegundo Over a year ago

Notifications are considered expensive. They are good for situations, where you can't know, if any (or many) objects need to be informed — and if they exists yet. also they can be used, if you pass informations from a distance part of your application to another instead of using a custom singleton. But the question does not describe such a scenario.

aopsfan · Accepted Answer · 2012-01-27 01:48:17Z

0

I think the best way to do this is, instead of using three separate controllers, just to use one. This one controller will be a subclass of UIViewController, and its .h file should look something like this:

@interface MyController : UIViewController <UITableViewDataSource, UITableViewDelegate>
    UITableView *firstTableView;
    UITableView *secondTableView;
@end

Now, in your .m file, set the tables up like so:

- (id)init {
    if ((self = [super init])) {
        firstTableView = [[UITableView alloc] initWithFrame:/*desired frame*/ style:/*desired style*/];
        secondTableView = [[UITableView alloc] initWithFrame:/*desired frame*/ style:/*desired style*/];

        firstTableView.delegate = self;
        firstTableView.dataSource = self;

        secondTableView.delegate = self;
        secondTableView.dataSource = self;
    }
}

- (void)dealloc {
    [firstTableView release];
    [secondTableView release];
    [super dealloc];
}

Then, implement desired UITableViewDataSource methods like so:

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    if (tableView == firstTableView) {
        // Do something
    } else if (tableView == secondTableView) {
        // Do something else
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    if (tableView == firstTableView) {
        // Configure the cell
    } else if (tableView == secondTableView) {
        // Configure the cell a different way
    }
}

Finally, in didSelectRowAtIndexPath:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    if (tableView == firstTableView) {
        // Update something that is linked to the return values of secondTableView's dataSource methods
        [secondTableView reloadData];
    }
}

This approach ensures that your controller gets the right -viewDidLoad, -viewWillAppear, and so on, automatically. Remember, just adding view controller's views as subviews means that your controller will not receive these calls.

answered Jan 27, 2012 at 1:48

aopsfan

2,44119 silver badges30 bronze badges

6 Comments

vikingosegundo Over a year ago

Personally I think, this is a very messy way, as you will have to maintain a jungle of if/else-statements.

ThinkChris Over a year ago

Thanks @aopsfan, a huge class is powerful, but also hard to maintain, use it with care

sosborn Over a year ago

I agree with the idea that only one view controller should be used (OF COURSE!), but I think it is best to create separate files for each tableview that handles the approprate datasource/delegate methods.

ThinkChris Over a year ago

@aopsfan just adding view controller's views as subviews means that your controller will not receive these calls - is there other ways to add those table in? for example, add the controller B and C in A so they can access to each other?

aopsfan Over a year ago

@ThinkChris Yes, there is. I'll add another answer for this solution when I get the time. Note that it is iOS5 specific.

|

Collectives™ on Stack Overflow

Howto get access to another controller/view (iOS)

3 Answers 3

3 Comments

3 Comments

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

3 Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related