I'm trying to learn how delegates work and wrap my head around the concept. I'm finding I get some of the ideas. I understand you use it to pass data from one view controller to another, however wouldn't it work the same if I just sent data from a segue and every time the 1st view controller would appear, it would use that data?
So for example I have 2 view controllers.
1 is homeViewController and
2 is editViewController.
I have a variable titled "addressOfHome" which is a string in homeViewController(1).
In homeViewController under the method "viewDidAppear"
I also set the addressLabel = addressOfHome.
Then I just pass the data from editViewController(2) to homeViewController(1)
when the segue's destination vc is homeViewController ?
I'm terrible at explaining things so I apologize for that, but I gave it my best shot. Thanks for your time!
Delegates are mainly used to "trigger action" on an object from another one.
An object delegates a way to handle something to someone else, for example when you click on an UIAlertView button, if its delegate is set on a viewController, alertView:clickedButtonAtIndex will be executed on the VC, which can so react as it want
I'm terrible at explaining things
Haha, yes, you are !
A delegate isn't for that - a delegate is a way to over-ride the default behaviour of some feature(s) of a class, without creating your own sub-class. See this post : How does a delegate work in objective-C?
Are you trying to understand how delegates work (in which case, I don't think your example is one that requires a delegate) or are you trying to implement the functionality you describe, and think that a delegate is the way to do it? (I think you actually want a data source).
Related
I need to send an object (data) from a view controller (embedded in a navigation controller) to a class (or struct) which should manage this data.
How can I get a reference to this viewController from the class (which has no link of any kind (no segue), or better the struct) with the set of viewControllers in order to implement a delegation protocol?
I use swift, a storyboard, and I look for any pointer or documentation which could help me to understand how to address this problem. I'm a beginner and I am sorry if this question is far too trivial.
I just need a link to appropriate documentation, many thanks.
This answer might help you. You might wanna read up more on delegation pattern in iOS.
https://stackoverflow.com/a/42977875/2396199
First of all, I am not Objective-c developer, however I have 4 years of experience in C and C++.
I am trying to make a few demo programs for an (iPad) app camp. For one of these programs I want to pass data between two UIViewControllers.
I have tried various examples, among the example below.
Passing Data between View Controllers
The code is written in an older version of Xcode so I took a bit of tweaking to get it through the compiler. Now I am facing the following problems:
It seems the prepareForSegue is not being called when I open a new view? (Or am I doing something wrong?) I have tried various ways.
In the same post there is a way to pass a delegate to a new class and back to the calling class. When I run this all goes good but there is the last part:
In ViewControllerA.m implement the following method from our protocol
(void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item
{
NSLog(#"This was returned from ViewControllerB %#",item);
}
Does net execute... I have no idea what is wrong. I followed the example exactly. I can see the second view opening and closing, only the delegate code won't run. Do I have to do this in a different way in Xcode 7?
P.S. I know this is a basic question but I cant seem to find the answer or a good Xcode 7 guide anywhere.
following method from our protocol.. Does net execute...
Are you sure that you assign your first view controller's reference to your target view controller's delegate property like,
secondViewController.delegate = self;
You can do this in where you create the second view controller, e.g prepareForSegue method. If you forgot this your delegate method simply not work, because your second view controller doesn't know who's its delegate.
I have created a custom class for my UIBarButtonItem (refreshIndicator.m). This button will be on many different view controllers, all push-segued from my MainViewController/NavigationController.
Instead of dragging an outlet onto every single ViewController.m file for iPhone storyboard THEN iPad storyboard (ugh, still targeting iOS7), I want to know if there is a way to complete my task simply within my UIBarButtonItem custom class. I've looked around everywhere but I haven't quite found an answer to this,
All I need to do is check which UIViewController is present, check the last time the page was refreshed, and then based on that time, set an image for the UIBarButtonItem. (I've got this part figured out though, unless someone has a better suggestion). How can I check for the current UIViewController within a custom button class? Is this possible?
Does it need to know which view controller its on so it can tell that vc it was pressed? If that's the case, then use your button's inherited target and action properties. On every vc that contains an instance of the button, in view did load:
self.myRefreshIndicator.target = self;
self.myRefreshIndicator.action = #selector(myRefreshIndicatorTapped:);
- (void)myRefreshIndicatorTapped:(id)sender {
// do whatever
}
More generally, its better to have knowledge about the model flow to the views from the vc, and knowledge of user actions flow from the views. Under that principal, your custom button could have a method like:
- (void)timeIntervalSinceLastRefresh:(NSTimeInterval)seconds {
// change how I look based on how many seconds are passed
}
And your vcs:
NSTimeInterval interval = [[NSDate date] timeIntervalSinceDate:self.lastRefreshDate];
[self.myRefreshIndicator timeIntervalSinceLastRefresh:interval];
If you really must go from a subview to a view controller, you could follow the responder chain as suggested in a few of the answers here (but I would go to great lengths to avoid this sort of thing).
It is possible to achieve this, but the solution is everything but elegant. It is one way of getting around the basic principles of iOS and is strongly discouraged.
One of the ways is to walk through the responder chain, posted by Phil M.
Another way is to look through all subviews of view controllers until you find the button.
Both ways are considered a bad practice and should be avoided.
For your particular case, I would rethink the structure of having a separate instance of the bar button. For example, you could rework it into a single UIButton instance that gets displayed over every view controller and it can also act as a singleton.
Can anyone tell me how I can phrase an if () statement to discover if a segue's destination view controller will appear in the Detail Split or in the Master Split?
I want to put the if() statement inside my prepareForSegue:sender: methods.
EDIT
All my detail views that are relevant to this question (at the moment) conform to a protocol and I am currently performing introspection on the destination controller using:
if ([segue.destinationViewController conformsToProtocol:#protocol(myProtocol)])...
I can see that this would not work if I wanted:
To be able to show the same class in either Master or Detail of the splitView from time to time, and at the same time...
I only want the if() statement to be true when the view is to be presented in the detail split.
Things like segue.destinationViewController.navigationController == ... don't appear to be any use either.
I was hoping that since we need to set "Master Split" or "Detail Split" when we set the segue up... there would be a way to access that information less circuitously.
SECOND EDIT:
The way I have this set up with using introspection does "work". It just doesn't seem very "Object Oriented". I don't think I should be querying the View Controller at all for this information, I can't see why the VC should know anything about which side of the splitView it will be displayed. Surely the object that should hold onto this information is the Segue and, as I say, it appears this is being "set" in the storyboard when we select "Detail" or "Master" split.
Maybe it isn't a property of anything, but I can't see how to get at it.
I suppose I could query the destinationViewController in its viewWillAppear to discover which NavigationController it is in after it appears on screen but, again, it seems a bit "hacky".
There is probably a better more abstract and reusable way to do this that I'm not aware of, but here is a suggestion that could help in your specific project that requires just a bit of special knowledge of your specific project.
If you use introspection in your prepare for segue, you can check to see if methods exist by using the responds to approach.
So for example, in typical implementations of a splitview controller (note - not all) the detail view will implement the methods to handle rotation. So if this is true in your project, you could do something like this:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.destinationViewController respondsToSelector:#selector(splitViewController:shouldHideViewController:inOrientation:)]) {
//do something
}
}
You could use this same approach based upon something that was unique but constant in your project related to either the master or detail view.
hope that helps,
be well
My experience is a little limited, but most times I've seen prepareForSegue used, the if() block checks segue.identifier to do anything that needs to be done specifically to handle building the new page. If you set the identifier for all your segues, you could just have code to handle each segue from that controller, and change what the code is depending on if that segue goes to a masterViewController or a detailViewController. Not really a well automated way, but it'll get the job done.
EDIT: oh geez, that wording is kinda confusing. If you want me to I can put a code example up, but it'll have to wait until Monday, as I don't have access to a Mac until then.
The talk of classes and protocols gave me another idea, but again, not sure if it will work - I wanted to test it before posting, but I'm not going to have the time to test anytime soon.
I think you should be able to create 2 new classes, UIMasterViewController and UIDetailViewController, that are subclasses of just UIViewController. Then, for each of your actual screens, instead of making them subclasses of UIViewController directly, make them either a UIDetailViewController or UIMasterViewController. Then, in your prepareForSegue,
if ([segue.destinationViewController isKindOfClass:UIMasterViewController])
{
//do master view specific stuff
}
else if ([segue.destinationViewController isKindOfClass:UIDetailViewController])
{
//do detail view stuff here
}
This should be a pretty dependable way to tell where your segue is sending you, as long as you can set up the custom view controller classes right. This still won't solve the first issue noted in the question
"To be able to show the same class in either Master or Detail of the
splitView from time to time, and at the same time..."
This could be overcome by making 2 copies of all of the views you want to be able to show as either or both, then make one a UIMasterViewController and the other a UIDetailViewController - copy-paste should be good for most of the rest.
Let me know if this works - I'm not exactly sure how to set up the controllers off the top of my head, but I'm pretty sure it could be done. If it can, I can see this being a very useful thing.
I would like to be able to add a score, in a different view controller then the main. So what is the best way to replace self in this call?
[self.gameCenterManager reportScore: self.currentScore forCategory:self.currentLeaderBoard];
I thought about passing it in to the view controller, but it is the third view controller, so i would need to pass it twice, feels wrong to me.
I thought about a NSManagedObjectContext, but then I saw in the sample has GameCenterManagerDelegate.
Is there a way to use that anywhere in the game?
Check out GKTapper to see this, but the VC that you call that function from should have a GameCenterManager declared.
Then your call will work, check out GKTapper.
http://developer.apple.com/library/ios/#samplecode/GKTapper/Introduction/Intro.html