I have a class: MainViewController
An instance of that controller is controlling the current view.
I have another class: DetailClass in which I have an instance of MainViewController, myMainViewController.
How can I set myMainViewContoller equal to the instance of MainViewController currently controlling the view seen by the user?
I think you're confusing "instance" and "pointer to instance." Your question would make much more sense if you said that DetailClass has an instance variable that's a pointer to an instance of MainViewController. I'll assume that's what you meant.
Usually in these situations, one of the controllers has created the other one, or some other object has created both of them. The first case is common in navigation-based apps, while the second is likely if the two controllers are managed by a tab bar controller. Either way, there's generally some object that knows about both controllers. So, let's say that your MainViewController creates an instance of DetailClass. If that's the case, it can simply pass a pointer to itself as part of the initialization, or perhaps after the DetailClass instance has been created. Does DetailClass have a -setMyMainViewController: method? If yes, MainViewController might have some code that looks like this:
//...
DetailClass *detailController = [[DetailClass alloc] initWithNibName:nil bundle:nil];
[detailController setMyMainViewController:self];
//...
Related
I have one single MainViewController which has of course it's one main UIView. I have this main view comprised of many different subviews.
Some of these subviews have their very own ViewController.
Lets say the MAIN view (whose delegate is primarily MainViewController) has a container which loads another UIView that uses a separate UIViewController- SecondaryViewController as the delegate for most it's actions.
This container view is of course loaded in MainViewController via
MyContainerViewController *myContainerController =
[[MyContainerViewController alloc] ...];
[self addSubView: myContainerController.view];
the controller for myContainerController.view though is MyContainerViewController. How inside this controller do I access MainViewController properties? Specifically I need to access MainViewController's - self.navigationController property to push a new ViewController? :)
Does this make any sense? I assume there's going to be casting of some sort involved since it seems I need to somehow retain a reference to MainViewController inside SecondaryViewController?
It doesn't make sense to push a new ViewController from the SecondaryViewController in the MainViewController.
This screws up the design of the code. A child object will access its parents method to call a method. By other words: bad code.
Make a delegate call from the SecondaryViewController to the MainViewController that it state has changed. Then the MainViewController can decide to do with the call and the SecondaryViewController will not know anything about the implementation of the MainViewController.
So:
Make a protocol in SecondaryViewController.
Let the MainViewController be SecondaryViewController's delegate.
Implement the delegate method in MainViewController which pushes the new ViewController.
Expose the desired sub-view controllers as properties of the view controller that contains them.
Expose your root view controller(s) as properties of your app delegate, and synthesize them also.
When you want to access a different UIViewController, first obtain a reference to your appDelegate:
MyAppDelegate* myAppDelegate = [[UIApplication sharedApplication] delegate];
Then just use your chain of properties to get access to your desired view controller.
SubSubViewController* ssvc = myAppDelegate.rootViewController.subViewController.subSubViewController;
Some folks frown upon the use of the sharedApplication class method to obtain the reference to a delegate, but I've used it in multiple apps and not suffered for it (yet). The alternative is to pipe your appDelegate through your hierarchy of viewControllers.
I am able to pass a variable forward from view controller to view controller by pushing its view controller onto the navigation stack. An example of how I do it would be this:
MyViewController *controller = [[MyViewController alloc] initWithNibName:#"MyViewController" bundle:nil];
controller.myString = stringToPass;
[self.navigationController pushViewController:controller animated:YES];
[controller release];
However, what do I do if I want to pass a variable BACK UP the navigation stack? Using popViewControllerAnimated rather than pushViewController does not pass the variable up like I thought it would.
I need to be able to access the variable several pops up from the view controller it is defined in.
Any help will be greatly appreciated :)
You're passing values, not variables.
A view controller should not be responsible for popping itself. With Apple's view controllers (e.g. UIImagePicker), it is the parent view controller's responsibility to do the popping; the parent VC can also obtain the current value. (Not entirely correct; it might access the value before a keyboard autocompletion is applied)
Alternatively, if it's a value that can be shared globally, you can store it in your application delegate.
You can get a hold of the navigation controller in the VC stack using self.navigationController. You can just call some method like
[self.navigationController setMyString:stringToPassUp];
There are several more ways, e.g. self.tabBarController for the tabbarcontroller up in the stack, or most simply
[self.parentViewController setMyString:stringToPassUp];
edit given the downvotes on the examples above, and nobody giving a better explanation, let's discuss the proper way to do this.
If you have some object (like your MyViewController *controller) and that object has something to tell you, the usual approach is this:
MyViewController gets a delegate property, of type (id)
the view controller instantiating the MyViewController, sets this delegate property, like so:
controller.delegate = self;
MyViewController will, when it has something to say, do something like:
[self.delegate delegateMessage:arg1]; to "pass the message up" as you put it.
To do it perfectly, you may want to create your own #protocol MyViewControllerDelegate, and declare the class which would be setting controller.delegate = self; to adopt this protocol, by putting <MyViewControllerDelegate> on the #interface line. The delegate property of MyViewController should then be declared id<MyViewControllerDelegate> delegate;, so that the [self.delegate ...] messages can be matched to the protocol specification.
Basically the whole Cocoa Touch API works like this. Just have a look around for ideas how to implement your interaction.
I hope that you will succeed in at least a little to clarify me how and what to do, I'm sure I'm wrong, so I really need an expert opinion.
I have two viewcontroller together with nibs what I want is to call function that is in first class from another ViewController, the problem is that another viewcontroller manages to call this function but the only thing I can see that is done is NSlog which outputs in the console (which I put in that position to know that the function is called)
example:
FirstViewController.m
-(void)drawingFunction:(NSString*)inputText{
NSLog("Feature was launched");
/* showing stuff in FirstView.xib */
}
SecondViewController.m
-(void)turnOnFunction:(id)sender{
FirstViewController *stuff= [[PrviViewController alloc] init];
[stuff drawingFunction:#"ShowAll"];
}
Basically when I call that function in the PrviViewController.m meaning without reference to the outside e.g.
[self drawingFunction:#"ShowAll"];
everything is well displayed, but when I try to call this function from SecondViewController.m all I see is just a "feature was launched" on the console
I really don't know what to do ...
if i get you right, the FirstViewController is on top of the view controller hierarchy (either within a navigation controller or presented modal)? So, if that is the case just creating an instance of SecondViewController and calling a function which should change the user interface on the view which corresponds to SecondViewController will do nothing at all.
You have to present the SecondViewController and its view with presentModalViewController:animated: for instance. After that the view of SecondViewController will be shown and you can do any changes on that view. Also calling the method drawingFunction: will act as you expect it.
Cheers,
Andreas
You're confusing instances with classes. You don't send messages (call functions) to classes, you send them to instances.
In this case, you have two entirely separate instances of FirstViewController. The first is created by loading the nib and the second is created in -[SecondController turnOnFunction:]. The drawingFunction: message is being sent to the second instance when you want it to be sent to the first.
You need to link the nib instance of FirstViewController to the SecondController instance. You can do that with an outlet in interface builder or you can assign it when you create the display the SecondController.
An iphone app I'm working on is terminating periodically ... and I have a feeling it is because of how I'm accessing a shared NSArray amongst several view controllers. So ...
What is the best way to pass NSArray/NSMutableArray amongst several ViewControllers ... all of which can modify and/or set it to nil or whatever?
Thanks
There are two approaches, generally speaking.
In the first approach, when you instantiate your next view controller, you could set an array property to "inherit" from the current (soon-to-be previous or parent) view controller:
MyNextViewController *_myNextViewController = [[MyNextViewController alloc] initWithNibName:#"MyNextViewController" bundle:nil];
_myNextViewController.myViewControllerArray = self.myViewControllerArray;
...
In the second approach, you could create a myAppDelegateArray property in your application delegate, instantiating the array when the application initializes (or instantiated somewhere else, on demand).
You can then call the getter for this property from any class — including view controllers.
For example, within an instance of MyNextViewController, you might have a property called myViewControllerArray and you would set it as follows:
self.myViewControllerArray = [UIAppDelegate myAppDelegateArray];
You would add a #define statement somewhere in your application constants file, e.g.:
#define UIAppDelegate ((MyAppDelegate *)[UIApplication sharedApplication].delegate)
or use the full [UIApplication sharedApplication].delegate call, if you prefer.
As a general approach, people seem to prefer the app delegate approach, as it decentralizes access to the desired property.
With this approach, if you rearrange your view controllers or insert new view controllers into your VC hierarchy, you wouldn't need to debug child view controller properties inherited from parent view controllers, because a reference is always available from the app delegate.
you are probably not retaining it, it gets deallocated and you are trying to access it again. try to send a [myArray retain] where you are using it (in each of the controllers), and [myArray release] when you are done with it
I've finally had to give up the relentless search for an answer to this question, as I just can't find anyone that's asked it before! So hope someone can provide some insight. I'll start by explaining what I can do, then compare that with what I can't figure out how to do.
Suppose I have a custom VC called RootViewController. It contains an outlet of type MyViewController. My RootViewController has an .xib which contains a generic VC object dragged out of IB's palette which is given the class type of MyViewController, I set the right bar button item to a UIBarButtonItem called 'Cancel'. The RootViewController unarchives it's .xib, hooks up the outlet to the MyViewController object, I push said object on to the navigation stack which displays as expected, I have a view and a button on the navigation bar that says 'Cancel'.
The problem I have with this approach is that I want MyViewController to be re-usable across any object that might want to create a MyViewController. This therefore means that the "File's Owner" could be any object. Previously it was RootViewController, but what if another object wanted to instantiate a MyViewController? The Files Owner will be different every time. I also want it to be able to completely initialise itself from a nicely self-contained .xib. Basically, I want to do this:
MyViewController *myVC = [[MyViewController alloc] init];
And in the implementation of MyViewController, I write this:
- (id)init
{
if ( self = [super initWithNibName:#"MyViewController" bundle:nil] )
{
// Initialisation
}
}
This neatly hides the name of the .xib used to intialise the VC, uses all the goodness IB gives me in configuring the controller and view, and with MyViewController always being the owner, it means I solve the File's Owner problem too - it will work for any type of class that creates it.
So, in order to achieve this, I create a .xib, set the File's Owner to be of type MyViewController, drop in a UINavigationItem and add the UIBarButtonItem. I now have a .xib structurally the same as before, except it does not use IB's generic VC object as separate top level object, the .xib is the VC definition, rather than something that contains a VC definition.
So, given that File's Owner is a MyViewController and as such a subclass of UIViewController (supposedly inheriting everything you get by using a UIViewController from IB's palette), then I should inherit all the functionality of it's superclass... Except it doesn't.
When the .xib in unarchived, it does not hook up the UINavigationItem. Therefore, when it's pushed on to the navigation stack, none of the bar button items are displayed.
UIViewControllers navigationItem property is read-only, creating an outlet for it in iPhone OS 3.0 is therefore deprecated.
So, at the end of all this, how on earth does the nib loading code manage to connect IB's version of the VC object to the navigation item? And why, even though my object is a UIViewController through inheritance, will it not do it for my object? I am completely at a loss to fathom this out...
Thanks for reading this far! Hope to hear from you guru's
Only a UINavigationController sets UIViewController's navigationItem property. Do something like this:
MyViewController *viewController = [[MyViewController alloc] init];
[self.navigationController pushViewController:viewController animated:YES];
[viewController release];
Assuming you are in a view controller that already has a navigation controller. After you have pushed it, you will be able to access navigationItem from inside MyViewController.
Right, I think I get it now. I thought I'd post an answer to my own question as I've seen at least one other person ask a similar question, and both seem to point to the same conclusion, so I hope this will be of help to others.
Essentially (and this will sound obvious) a UIViewController is not a Proxy Object! It's not instantly obvious as we're all used to the idea that if any two objects inherit from the same base class, then their implementations are the same and they will behave in exactly the same way (assuming no customisation in the inheriting class). But an IB object's type is distinct from the class attribute you can assign to these objects.
They are not both UIViewController objects because their class attribute it set in such a way.
Simply setting the class attribute of these objects in IB does not mean that these objects are now UIViewController objects. A View Controller object remains a View Controler object, and a Proxy Object remains a Proxy Object. As far as IB is concerned, they are both very different beasts, they just happen to have the same class attribute.
Just take a look in to the .xib and you'll find your IB View Controller objects have been archived like this:
<object class="IBUIViewController" id="...">
...
</object>
And the Proxy Object (that is set to a subclass of a UIViewController) is archived like this:
<object class="IBProxyObject" id="...">
...
</object>
As you can see they are both very different types, one is a IBUIViewController and the other is a IBProxyObject - and then it starts to makes sense - you can't impose VC controller attributes on an object of type IBProxyObject.
It is also interesting to note the class type is an IBUIViewController object and not just a UIViewController object. Whether this is just a naming convention or not I don't know, but it could also imply that IB's view controller objects wrap the instantiated VC object, or is a factory object for it. For example, you can set a "Resize View From NIB" attribute in IB's view controller object - but I can find no equivalent property or methods in the UIViewController reference docs.
So in conclusion, if you're trying to instantiate an object programatically instead of using outlets to an IB object, be prepared to implement some of the initialisation that the IB version would otherwise provide for you...