I'm creating a custom ViewController. This VC needs to load some data that is known in the event that creates it and pushes it to the top of the NavigationController that it is going to be part of.
My question is, how should I pass data from the view that handles the custom ViewController's creation into that custom ViewController.
I've thought of four possible options, and I was hoping to get feedback on why each one is good or not for this functionality.
1) Expose public properties in the custom ViewController and set the UI elements in the view based on those properties in - (void) ViewDidLoad.
2) Expose the actual UI elements themselves and set their .text/.image/.whatever attributes as the ViewController is being created.
3) Create a custom constructor for the custom view and pass in the values I need to set up the UI elements
4) Create a custom model that both views have access to, set the data before the CustomView is created/pushed, and access that data in the ViewDidLoad event.
I'm still new to all of this, and I want to make sure that I understand the proper handling of these handoffs of data. It seems like something like this is probably a simple answer, but I'm still a little confused and its probably really important to do this right to avoid memory loss/leaks.
Also, in case anyone cares, I'm using Stanford's CS193p class on iTunes U and Mark/Lamarche's "Beginning iPhone Development" to teach myself cocoa for the iPhone. I'm working on an application with a NavigationController and a couple ViewControllers (Presence 1 if you're familiar with 193p).
Well, I believe there are advantages & disadvantages to each of those methods depending on your requirements...often it will require some combination of approaches. I believe the most common, for me anyway, is to do something like this where you give it enough to get started.
MyViewController *vc = [[MyViewController alloc] init]; // (or initWithNibName:bundle:)
// transfer vc values here
vc.value1 = aValue;
vc.value2 = anotherValue;
[self.navigationController pushViewController:vc animated:YES];
[vc release];
After your view controller is instantiated you have an opportunity to pass objects to it. Say MyViewController is a detail view then you'd give it the object it will be displaying the details for. Or, if it's a table view you can give it the NSArray it will need for display. Then in viewDidLoad or awakeFromNib or awakeFromCoder, or... you can fill out the view...so to speak.
#1 is fine, with or without #3 (these two are not mutually exclusive)
#4 is my preferred solution. For instance, if I had a UserViewController, I would probably also like to have a User object and create it this way:
User *user = [self.users objectAtIndex:someIndex];
UserViewController *uvc = [[[UserViewController alloc] initWithUser:user] autorelease];
#2 is not a good idea. Objects should not access the UI elements of other objects. Much trouble comes from this when you decide to change your UI around (and you will).
Related
I am using Xcode 4.3 and need to know the parent view controller of the current view.
I am also using storyboard.
self.parentViewController always returns nil.
I saw different answers to save the parent view controller in AppDelegate class as a property. E.g., To create a variable: UIViewController parentViewController in AppDelegate and in the code write:
appDelegate.parentViewController = self;
I am afraid that it will consume memory - as this is a heavy object.
What is the best approach to know aretnViewController when using story board?
Whether or not an object is "heavy" does not matter as long as you store only a reference to it (in your case in the application delegate). Creating a second object would make a difference, but the line
appDelegate.parentViewController = self;
does not do that, it merely stores a reference to the object.
I know that this does not answer your direct question, but I think you should go ahead with the "store a reference in the app delegate" approach.
I am developing an iOS application that handles a hierarchy of UIViewController objects using a UINavigationController:
MenuViewController
|
|-ListOfAnimalsViewController
|
|-AnimalDetailsViewController
|
|-ListOfPlantsViewController
|
|-PlantDetailsViewController
The application receives local NSNotification objects with information of a certain animal or plant. The usual behavior when you touch the notification is to open the application and load the first view controller in hierarchy.
Is there a way of programmatically navigating to an instance of a UIViewController deep in the hierarchy instead?
EDIT: I am not asking for pushing the controller into the navigation stack, but for pushing the previous controllers as well, i.e. I would like to keep the navigation schema above.
I'm gonna have to disagree with Suresh. While this solution may work in a simple case like this where you only have 1 previous ViewController, what if you wanted to add a 10th ViewController and keep the entire hierarchy? First of all you'd have to pass the final piece of data you want to show (in this case the plant or animal) through every ViewController and you'd be creating 10 ViewControllers at once. The transition between the current ViewController and the 10th would be far from seamless, performance would be terrible. Also no need to go and create your own navigation system, no need to make things more complicated than they are since this issue isn't too difficult.
Just push the ViewController you want to show, that way you'll only be creating 1 ViewController. In every ViewController that can be pushed as a result of a notification (and all the ones below that), override the behavior of the back button. Check in the viewControllers property of the navigationController if the ViewController before is is the one you expect, using NSStringFromClass. If not, create an NSMutableArray as a copy of the viewControllers, create the ViewController you do expect and insert it at the second to last spot in the array. Then replace the entire stack by calling the setViewControllers:animated: method on the navigationController with the mutable array, animated NO. Finally do the pop. Again you'll have created just 1 ViewController at a time, keeping your performance optimal.
Ican't post code right now since I'm on an iPad but if you need it, just ask and I'll add an example when i have a real keyboard.
If you know the name of the class you can use the following code to navigate.
NSString *className = #"viewControllerName";
UIViewController* myClass = (UIViewController*)[[NSClassFromString(className) alloc] init];
[self.navigationController pushViewController:myClass animated:YES];
I think you will have to invent your own mechanism for following the navigation order since there's nothing in an iOS view controller's static definition that defines an ordering. (Segues seem to be as close as it gets and that's not very close.)
If I had to do this for a hierarchy of view controllers with some unknown depth, I'd consider creating a superclass that worked with a path, sort of like network routing. It would have a method such as displayNextControllerOnPath:(NSString *)path. A MenuViewController that was a RoutingController subclass would receive a path like #"ListOfAnimalsViewController.AnimalDetailsViewController", strip off the first path element, instantiate it (it being another RoutingController subclass), and send it #"AnimalDetailsViewController".
Other details would involve knowing when to stop and perhaps passing an object or dictionary as a payload for the last controller to use as content.
I would reconstruct the stack in the following way:
MenuViewController *menuController = [[MenuViewController alloc] init];
ListOfAnimalsViewController *listController = [[ListOfAnimalsViewController alloc] init];
AnimalDetailsViewController *detailsController = [[AnimalDetailsViewController alloc] init];
UINavigationController *navigationController = [[UINavigationController alloc] init];
[navigationController setViewControllers:#[menuController, listController, detailsController]];
self.window.rootViewController = navigationController;
You may need to set some properties to based on your implementations.
Let's say I have a two subclasses of UIViewController called MasterViewController and DetailViewController.
DetailViewController has a property of type NSNumber called level and a UILabel called levelLabel.
MasterViewController has a segue to DetailViewController called ToDetail. MasterViewController's prepareForSegue is like so
- (void)prepareForSegue:(UIStoryboardSegue)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:#"ToDetail"]) {
DetailViewController *detailVC = (DetailViewController *)segue.destinationViewController;
detailVC.level = [NSNumber numberWithInt:10]; // never mind the literal...pretend there was some algorithm for it
}
}
So then, in DetailViewController we implement the setter for levelLabel like so:
- (void)setLevelLabel:(UILabel *)levelLabel
{
if (levelLabel) {
_levelLabel = levelLabel;
_levelLabel.text = level.stringValue;
}
}
Is this good code design? Also, could you critique my code writing style? I pretty much wrote all this code on the fly so this is pretty much how I write code for the most part.
I thought of this question while showering because this is how I implement the setting of almost all the label texts that depend on a segue.
What follows is my own way of thinking about such relationships. Italics applies to your question.
You have the thing being controlled (the label) the controller (destination view controller) and the context it is being controlled within (the source view controller). This can also be expressed as model-view-controller, but I think thinking about a context can apply to much more specific and localised situations.
You should generally try to keep information flow going in one direction, from the context downwards. Objects should not have to be aware of the context in which they exist, ie they shouldn't have to ask for any information, they should be told everything they need to operate. So the source view controller should push the level to the destination view controller, the destination view controller should push this information to the label. This is what you already have, sort-of.
To build upon the above, not only should information flow in one direction, but I also try to ensure the relationships are causal, ie pushing information from one object to another should cause it to subsequently be pushed to the next object. Your code is not doing this which is probably why you have a bad feeling about it.
A more appropriate thing to do is set the text property of the label within the level setter, so that when you set or change the level, the label will update subsequently. The label may or may not be loaded so you will have to check whether it is using -isViewLoaded; -viewDidLoad is the appropriate place to set the text property upon first load.
(When I say 'push' that's just my way of thinking about setting properties or passing arguments because it implies directionality. It is really dependency injection. An example of pulling information would be delegates and data sources. But note here still the object isn't aware of any context, delegates and data sources are clearly defined as protocols, not classes, and usually within the same header file, and are themselves pushed onto the object from a surrounding context. So yes the object is asking for information, but on its own terms and from a system it has no knowledge of.)
Re coding style:
That's exactly how I write code but note Apple reserves the use of underscore prefixes
I feel i am totally out of my depth here, im very new to objective c but have been asked to design an iphone app as part of my uni course. I designed a sinple quiz before, but I was hoping to design a more advanced quiz game with 3 levels (each level will have a different quiz).
I dont know how to use the UIViews and I have tried a tutorial online to help me code a navigation controller. It allows gives me 3 options to go into subview 1, 2 or 3. All the subviews have the same screen though, with one label and a button.
I have 3 classes so far, RootViewController, BasicNavigationAppDelegate and SubViewOneController.
I really dont understand the code at all, im familiar with Java but this objective c is nothing like it. Could someone maybe take a minute to help out a person in distress and explain if i am doing this right by using the navigation controller to display my levels? When i check the xib interface files i dont see the button or label, or dont know where to add the quiz interface objects!! I really am confused by all this. Could anyone help?
You should search google for sample source code, and see how some of the views can be handled. There are many ways you can handle a view, whether its by a UINavigationController, UITabBarController, etc. If you are new to Objective-C, then your not really going to get an answer to this question that will instruct you on what exactly to do.
Interface Builder + View Controllers
Here's a good one for you: View Controllers Programming Guide
(Apple's) View Controller Reference Guide
Some Code Samples
Getting Started Sample Code
I recommend Head First iPhone Development: A Learner's Guide to Creating Objective-C Applications for the iPhone. Within a few chapters you'll know everything you need to build this app and you'll actually understand what you're doing.
(I don't know the authors or the publisher, I just think it's a great book for quickly getting up to speed.)
for a 3 level quiz, UINavigationController is definitely an option.
if you need to find out how to use a class, in xcode, type its name, then press -alt- and double click the class name, this will bring up a short description, with two icons, one will take you to the header file, and the other to the documentation.
to add elements to the nib/xib files, you will need to open the library window, where you will find labels, buttons etc. to use a button, you will need to define an action in your header file, and hook it up in IB, to be able to interact with UIElements in your code, you want to set up outlets in the header file, and hook them up in IB.
something you need to decide on, is how you are going to present the questions, and will also depend if the answer will be true/false, multiple choice, or text entry.
if you arent familiar with obj-c and xcode, it is probably worth picking up an ebook from someone like http://www.pragprog.com. they have an iPhone one up there by Bill Dudney which is quite good(i believe he now works for apple.)
for the standard slide out transition you could use this.
//you would probably want to call this something like level1NavBarItemWasPushed: instead
- (IBAction)lvl1pushNavBarItem:(id)sender {
//create instance of AnswersViewController class.
AnswersViewController *level1AnswersVC= [[Level1AnswersViewController alloc] init];
//pass it some kind of identifier so it can tell which quiz/question it is dealing with and pull in the answers, so that you can reuse the view
[level1AnswersVC setAnswersObject:<<insert object dictionary here>>];
//push the view controller onto the navigationController's view stack
[self.navigationController pushViewController:level1AnswersVC animated:TRUE];
//pushing it onto the view stack has given it +1 retain, so we can now release it without worrying about it disappearing prematurely.
[level1AnswersVC release];
}
for the page flip transition you could use this.
- (IBAction)lvl1pushNavBarItem:(id)sender {
//create instance of AnswersViewController class.
AnswersViewController *level1AnswersVC= [[Level1AnswersViewController alloc] init];
//pass it some kind of identifier so it can tell which quiz/question it is dealing with and pull in the answers, so that you can reuse the view
[level1AnswersVC setAnswersObject:<<insert object dictionary here>>];
//set the current viewController as the delegate, so that it can call back to us when its done
level1AnswersVC.delegate = self;
//set the modal transition style
level1AnswersVC.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
//show answers as modal view, which has been setup to use the page flip transition.
[self presentModalViewController:level1AnswersVC animated:YES];
//pushing it onto the view stack has given it +1 retain, so we can now release it without worrying about it disappearing prematurely.
[level1AnswersVC release];
}
I'm having trouble referencing one view controller from another. The code works but I get warnings which makes me think I'm going about it wrong. I'm trying to reload the data in a tableView whose controller is in a NavigationController.
What's wrong with a message like this:
From the AppDelegate:
[self.tabBarController.selectedViewController.topViewController.tableView reloadData];
Although this works, I get the warning request for member 'topViewController' in something not a structure or union because Xcode doesn't know that the selectedViewController will return a navigationController. So I could do the following:
UINavigationController *myNavigationController = self.tabBarController.selectedViewController;
[myNavigationController.topViewController.tableView reloadData];
But then I get this warning: incompatible Objective-C types initializing 'struct UIViewController *', expected 'struct UINavigationController *'
How far do I have to go with this? The first line works. To get to the "right way" is it gonna take 8 lines of code?
A major code smell here, IMO. You're trying to do action at a (great) distance. It's not exactly clear what you're trying to accomplish, nor why you need to do this action from the app delegate. I have seen some developers treat the app delegate like a giant catch-all global lump of mud, and I think this is an anti-pattern that should be eliminated from iOS development.
Back to your question: you're trying to force a table view controller, inside a tab view controller, to reload its data. I'm assuming this is in response to something happening. Why not have the view controller in charge of that table watching for that event instead of the app delegate? That way, the thing that owns the table view is directly controlling it -- which is the entire point of the MVC pattern. This is a much better approach than having the app delegate drill down through a hierarchy to find a table view... in terms of complexity, readability, and brittleness.
If, for some reason, you can't or won't have that view controller observing for the event directly (hard to fathom why offhand), you could always have the app delegate post an NSNotification and let the view controller in charge of the table register as an observer for it. Not as good as direct observation, but definitely better than your current approach.
You can't use dot-notation unless the compiler knows what type of object you are using it on, and that that object type can receive a message with that name.
You can use dot-notation with a bunch of type-casts (which in this case, is hideously ugly):
[((UITableViewController *) ((UINavigationController *) self.tabBarController.selectedViewController).topViewController).tableView reloadData];
Or you can break it up into discrete steps:
UINavigationController *navController = (UINavigationController *) self.tabBarController.selectedViewController;
UITableViewController *tableViewController = (UITableViewController *) navController.topViewController;
[tableViewController.tableView reloadData];
Note that I'm assuming that your top VC is a sub-class of UITableViewController.
You really shouldn't be accessing the .tableView property externally - you should encapsulate that behaviour with a reloadData method on the View Controller itself. Even if all it does is call reloadData on its .tableView, you should encapsulate it. This will make your code more modular (which makes it easier to understand for you and others), and make it easier to expand on and add complexity to your View Controller down the track.
Without knowing exactly how this app is structured, I would guess that you're probably better off using notifications or observers to get your VC to reload its data. If you have some global event that requires a UI refresh, an NSNotification is a good way to make the UI layer get the message while keeping your code nice and modular.