I have two view controllers, one is MainViewController, the other is SetupViewController. I want a UILabel on MainViewController to set the text to the contents of a UITextField from the SetupViewController when a button is pressed in the SetupViewController.
In SetupViewController, I have this in the IBAction:
- (IBAction)donePressed:(id)sender {
MainViewController *mvc = [[MainViewController alloc] init];
[mvc.testLabelOnMVC setText:testTextFieldOnSVC.text];
[release mvc];
}
testLabelOnMVC (and testTextFieldOnSCV, with respective terms) is
#property (nonatomic, retain) UILabel *testLabelOnMVC;
and is also synthesized.
Every time I try, it doesn't work. Nothing happens, nothing changes. I have no errors or warnings. Can anyone help me out?
The view of your MainViewController does not exist until you reference the MainViewController's view property (which forces viewDidLoad to execute). You must reference the view (or otherwise force the view to be constructed) before you attempt to modify any UI objects in the MainViewController.
You are allocating a new MainViewController when you press the button, then you are setting the text of the label on this new controller, not on the MainViewController that your app is showing.
To fix this, create either and IBOutlet or iVar that points to the original MainViewController and set the text on that instead.
Easiest way is to create a #property in the main view controller and write the text in there. Then just read it in the second MVC's viewDidLoad.
The only views that MainViewController should worry about are the ones that it owns; it shouldn't be trying to access the view hierarchy managed by SetupViewController. Likewise, SetupViewController should not directly modify views in MainViewController's view graph.
The right way to do what you're asking is for the two controllers to talk to each other, either directly or via the data model. For example, let's say that your MainViewController instantiates SetupViewController. If that's the case, it'd be natural for mvc to set itself as svc's delegate, so that svc sends it a messages like -setupController:didUpdateTestStringTo:. MainViewController's implementation of that method could then save the new test string somewhere and update it's testLabel field.
Another example: MainViewController instantiates SetupViewController. SetupViewController contains a field where the user can enter a new value for the test string. Before exiting, SetupViewController writes the contents of that field into NSUserDefaults or some other common data storage. When control returns to MainViewController, that object reads the shared data and updates itself as necessary, including setting the new value for testLabel.
There are other variations on the same theme, but the common thread here is that neither view controller has to directly access views that it doesn't own.
You can change the text of the label if the view is already loaded. Instead of initializing the viewcontroller, retrieve it from the view stack if you are using navigation controller.
I dont know if your viewController is already loaded or not.
Related
I am following this tutorial: http://www.appcoda.com/ios-programming-sidebar-navigation-menu/
However, I need to be able to access the side menu from the classes view controller as seen in the image . While my first view controller is a login screen that the user needs to login to a a server with. To fix the problem I have made a property inside the reveal view controller #property (strong, atomic, retain) NSString *SWSegueFrontIdentifier;. Then I use the getters and setters to assign which view controller is should to/from. I assign the first value sw_first in view controller and everything is fine. In ViewDidLoad of the classmates view controller, seen in the second image, i assign sw_front. However, even when that is set in the same function, if i try to print the property from the reveal controller, it ends up returning null. However, if I manually switch the SWSegueFrontIdentifier inside the view controller to sw_front it segues just fine, but ends up skipping my view controller, which is my login controller. I just need a way for the side menu to be accessed from my classmates view controller and have not had any luck, because it seems most things on www.cocoacontrols.com are made to use without storyboards and I can't seem to get them to work.
This code returns null:
[self.revealViewController setSWSegueFrontIdentifier:#"sw_front"];
tempMenuButton.target = self.revealViewController;
tempMenuButton.action = #selector(revealToggle:);
NSLog(#"reveal view controller prop2: %#", self.revealViewController.SWSegueFrontIdentifier);
Any ideas on what I can do to get this to work?
EDIT: Only thing that I can think of is some sort of memory retention problem, but I can't seem to figure it out.
after declaring the property
#property (strong, atomic, retain) NSString *SWSegueFrontIdentifier;
ave you used a synthesize to create the getters and setters
#synthesize SWSegueFrontIdentifier = _SWSegueFrontIdentifier;
and then you just do it like this
self.revealViewController.setSWSegueFrontIdentifier =#"sw_front";
This is what I came up with.
Hello everyone — I am a beginner in iPhone programming and Core Data. I am currently trying to learn some of the theory behind Core Data, and have been using this tutorial to help me implement it in my app.
The tutorial teaches by making the main view a UITableViewController that lists the saved objects and another UITableViewController that saves objects (where you enter in the attributes).
The app that I am creating has 3 views. The main view is a plain UIViewController (it handles calculations), you are able to save your calculations by tapping a UIBarButtonItem that brings you to the second view where you enter in more specific attributes. Once you tap save, you are taken BACK to the main view, where you are able to tap a Show Saved button to access the UITableViewController containing saved objects.
I have included #imported the UITableViewController files into my main view's interface file, but when I run the program, I get an error on this line in my prepareForSegue method:
addShoeSizeTVC.managedObjectContext = self.managedObjectContext;
The error is "Property managedObjectContext not found on object of type 'SSFViewController*'" I understand the meaning of this error — I don't have any object called managedObjectContext in my SSFViewController class, but I figured that if I included my file that DOES contain managedObjectContext that it would still be recognized. I should add, that in the tutorial, the prepareForSegue method was contained in the list view for the segue to the add new object UITableViewController. I moved this method to my mainViewController.
I also get an error in my App Delegate in my ApplicationDidFinishLaunchingWithOptions method:
controller.managedObjectContext = self.managedObjectContext;
I understand that this stems from the same problem with the other error (it gives the same error message).
I do not understand how to pass data going from my viewA (mainView), to viewB (add object), back to viewA, then to viewC (view saved objects). I have heard about delegation and am using it in my prepareForSegue method in my SSFViewController main view:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"Add Object Segue"]) {
NSLog(#"Setting ObjectsTVC as a delegate of AddObjectTVC");
AddObjectTVC *addObjectTVC = segue.destinationViewController;
addObjectTVC.delegate = addObjectTVC.self;
addObjectTVC.managedObjectContext = addObjectTVC.self.managedObjectContext;
}
}
Also on the addObjectTVC.delegate = addObjectTVC.self; line I get a warning that says "Passing 'AddObjectTVC*' to parameter of incompatible type 'id'"
Do I have to set up an NSManagedContext or another delegation method in my main view? Or is it something that I must add to any of my Table views???
Thank you very much. I feel like this is a simple problem to solve, if provided with the right information. I am happy to post any other methods that I used if needed to solve the problem. I am a beginner, so it would be great if you could explain in a beginner-friendly way.
Thanks!
First of all, if you want data from ViewA to ViewB, insert a property in the ViewB and you can pass data from ViewA to this #property
Example
ViewB:
#property (nonatomic, strong) NSString *yourName;
(don't forget to call #synthesize yourName )
ViewA: (in prepareForSegue method)
"ViewB-Controller" *controller = segue.destinationViewController;
controller.yourName = self.name
--> name will be passed to ViewB
Second:
I prefer a delegate which send from ViewB to ViewA "Hey please save your data". It keeps your controller easy and smart, and you don't have to manage the save method from all view controllers. Delegate is an important chapter in iOS and it can be very frustrated for a beginner. (I was in the same situation 9 months before ;))
Search for a delegate example and try to understand how it works (learning by doing), if you have further question about delegate, I will friendly respond to your question.
It isn't the view controller that has the managedObjectContext property, but your UIManagedDocument.
The context is typically described as the 'scratch pad' in which your app will work with the data store.
I'm having this problem because I originially made everything in the main NIB, but then after reading learned that it is better to use subviews.
I've got my IBActions in the AppDelegate, and I've successfully connected and loaded my subviews. However, when I try to connect my buttons in the subviews to the IBActions in the AppDelegate, the IBActions appear under the "First Responder". They seem to connect fine, but when running the application they do not trigger the IBActions (I've confirmed this with some NSLogs, it's not an error in the code within the IBActions). What am I doing wrong?
Thanks!
The AppDelegate should only be used for very specific items such as implementing the UIApplicationDelegate protocol (i.e. methods like applicationDidFinishLaunching) or in some cases storing global variables.
You should keep IBActions and other outlets in their respective view controller files (i.e. if you created MyViewController.h and MyViewController.m which are linked with MyViewController.xib where you have some buttons, images, etc.). They can then be hooked up via dragging the inspector control you want (i.e. TouchUpInside) to the File's Owner.
Something you should read to better understand view controllers: http://developer.apple.com/iphone/library/featuredarticles/ViewControllerPGforiPhoneOS/Introduction/Introduction.html
Typically it is best to create a unique view controller for each view you will present to the user. For instance, if I had a main screen and then an "about" or a settings screen, I would make each of those their own view controller. It helps organize things better than using one view with a whole bunch of subviews that you hide/show and will also improve loading times and general performance.
Update for your 2nd question in the comments about accessing the app delegate:
First, you need to import the .h file (i.e. #import "AppDelegate.h") for the app delegate into whichever view controller .m file you wanna use to access whatever variables, arrays, etc you have stored in the app delegate files. Make sure you synthesize whichever objects you create in the app delegate's .h file in the app delegate's .m file so the getters and setters are created (so you can access them).
Then in the view controller .m file, in whichever method you are using:
-(void)someMethod {
// here we just create a shortcut to the app delegate called "theAppDelegate"
YourAppDelegateFileNameHere *theAppDelegate = (YourAppDelegateFileNameHere *)[[UIApplication sharedApplication] delegate];
// now you can use the dot notation if you wanna access a variable
int SomeNewInteger = theAppDelegate.someIntegerYouHaveStored;
// or some array you have stored
return [theAppDelegate.someArrayYouCreated count];
}
Hope that helps!
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...
Edited for brevity:
How does a subview access properties in its superview and its superview's view controller? Easy enough to go down the chain. How do we go back up?
Original (verbose) post:
The immediate problem I'm trying to solve is simplifying the "birth" of a somewhat complex view. The large picture has to do with Nibs and how subclasses (of UIView in particular) that have beyond trivial initializers are reconstituted when the view loads.
I have some custom UIViews - subviews of a subview of my viewcontroller's view. When I instantiate these views in particular they need a reference to some properties (NSNumberFormatter, & NSDictionary) of the View Controller.
Currenty I use a method to instantiate them:
- (id)initWithFrame:(CGRect)frame items:(NSDictionary *)dictionary forEditingMode:(EditingMode)mode
I'm experimenting with moving them into a Nib to let them reconstitute themselves and running into basic design issues. One being I think I'm limited to initWithFrame as the default initializer?!? If so how can these objects look into the parent view controller and get a reference to the dictionary and some other properties?
Are there methods I could call within initWithFrame (similar to the ones that retrieve the UIApplication delegate) but would instead allow the child view to send methods to it's parent views and/or controllers?
Send in the MVC police, I'm sure I'm breaking something...
It should work the other way round.
The views only contain controls (text fields, etc.). The data lives in a model, and the view/window controllers mediate, accessing and setting the view controls values, synchronizing with the model.
OK, sometimes you may need to have a dictionary shared between the controller and the view. Then create a dictionary property in the view and set it in the awakeFromNib method of the nib owner.
You can set up outlets that get connected to the view's superview or view controller and pull out the info in awakeFromNib. You need to use awakeFromNib instead of init* because the connections won't be created until then.
FYI, if you instantiate via a Nib, your designated initializer is initWithCoder:, not initWithFrame: (but don't use either for this).
You should probably be doing this through the view controller manually just after the nib is loaded. This means that you will have to set the shared dictionary AFTER the view has been initialized. You might do it like so:
#interface MyViewController : UIViewController {
IBOutlet MyView* view1;
IBOutlet MyView* view2;
IBOutlet MyView* view3;
}
#end
#implementation MyViewController
-(void) viewDidLoad;
{
NSDictionary* sharedDict = //make the shared dictionary here;
view1.sharedDict = sharedDict;
view2.sharedDict = sharedDict;
view3.sharedDict = sharedDict;
}
#end