My question may be a bit stupid, but why can't any object instantiated in IB handle, say, button click? I mean I'm able to add my own object to a xib, and link outlets to cotrols and control actions to object's method, but once I press the button everything just crashes (uknown selector).
Do you guys have a hint around that?
EDIT: The code, as requested:
#interface TextController {
IBOutlet UILabel * textLabel;
IBOutlet UITextField * textField;
}
-(IBAction)buttonClicked:(id)sender;
#end
#implementation TextController
-(IBAction)buttonClicked:(id)sender {
textLabel.text = #"Ololo";
}
#end
Connections in IB are ok, just believe me. It's really hard to get them wrong with all this drag'n'drop stuff :)
EDIT 2: TextController is not a file owner (in this case it works fine). However, I just want to understand why I can't wire up an action to some object (may be even not a subclass of UIViewController).
You can wire outlets and actions to any object in the nib-file. Drag an NSObject form the library palette onto your nib-file, in Interface Builder. Then go to the Identity tab of the information palette and set the Class of your object.
This way you can instantiate any object of any class from your nib. If the target you want to hook to is statically created from the nib-file. Make sure that the file's owner have at least one reference to your object, or else it will be deallocated as soon as it has been created. Targets are not retained by the sender.
If the object you want to hook up should not be statically created from your nib, then implement awakeFromNib in a class that is instantiated from the nib-file and hook up the targets in code.
Last option is if you do not have any sub-class of your own in the nib-file at all. Then implement initWithNibName:bundle: in your UIViewController subclass, and hook up your targets in code after calling the super implementation.
post code, this usually means you dont have your connections wired up correctly. Is file's owner TextController in IB?
Related
First, I am super-new to Objective-C/iOS development and, in fact, this question is for my first, test project. Also, I come from a C#/WinForms background so I'm coming into iOS development with certain pre-conceived notions of user interface design and application state. Please bear with me and help clear up my confusion.
I just created my first iOS application project which, consists of a Single View. I allowed Xcode to create all the files for me through the Single View project wizard. When it was finished, I opened my new applications, single UIView Nib file in the designer and I dropped three sliders onto the view.
The desired purpose of this application is very simple-- each slider corresponds to either the R, G or B values associated with the background color of my view.
I have figured out how to set the background of my view but I can not figure out how to access the values of each slider objects. Yes, I can hook-up and respond to an IBAction for each slider, but my plan is that each time a slider's value changes, I want the IBAction to call a refactored method that accesses the values of all three sliders and then set's the views Background Color based of the values associated with each one.
How can I access the values of my sliders? Specifically, how can I access the value of the sliders that I created by dragging and dropping them into the Nib designer window? I've seen code explaining how to programatically add a UISlider to your UIView and then access the value, but how do you access the value of a UISlider that's added to the Nib and, I assume, will be automatically "wired" in at compile time?
Hopefully this makes since? If I'm missing an intermediate step or critical concept, please let me know.
You create UISlider ivars/properties and make them IBOutlets:
#property (nonatomic, retain) IBOutlet UISlider* yourSlider;
You synthesize it in your .m file and the connect the IBOutlet in interface builder. The yourSlider pointer is then a reference to the object you connected it to. Note that it will only be loaded with the view of the UIViewController and therefore will be nil until viewDidLoad is called. You also must set it back to nil
self.yourSlider = nil;
in your viewDidUnload method (so that it is released). In Xcode 4 you have a convenient way of doing all the above steps in one action (see the "Interface Builder is Built-in" of What's new in XCode 4)
Similar to CTRL+dragging from the UISlider to the .m file to create the IBAction, you can CTRL+drag the UISlider from your .nib designer to the associated .h file and have it create a property for you. Then, from your .m file, you can access self.mySlider (or whatever you name the property).
There's a video on this page that shows binding to a UISlider specifically.
Another approach is to use the tag property of a view.
#property(nonatomic) NSInteger tag
- (UIView *)viewWithTag:(NSInteger)tag
You can set the tag property of a view in the interface builder and later reference that view in your controller.
UIView *myViewFromTag = [self.view viewWithTag:theNumberYouSetInIB];
In general, it's better to stick with IBOutlets. However, there are certain situations where it makes more sense to use tags.
Good luck!
I guess this is basic, but I can't get my head around this.
I used to have only one ViewController in which all my variables were defined, e.g. an UITextView named myTextView. I also had methods in this ViewController for handling events that relate to myTextView, such as - ()hideKeyboard { // do something with myTextView or - (void)keyboardWillShow:(NSNotification *)notification { // do something with myTextView.
As my program became bigger and bigger, I thought about using subclasses, especially for other views. So I started a subclass, eg. mySubClass.h and mySubClass.m, in which I had another UITextView (for argument's sake myOtherTextView). In order to incorporate mySubClass, I #imported it into my ViewController and added a #class mySubClass; and could then produce instances of this class so as to use it in my App.
So far so good. As you can imagine, all the nice methods I defined in my ViewController for what should happen when an UITextView is edited (such as hiding keyboard etc.) didn't work for the UITextView in mySubClass.
It was then suggested to me that I should make another class in which I had all the keyboard events and subclass my ViewController and mySubView to it:
#interface ViewController : MyKeyboardEventsViewController
Now, the problem I am seeing is that I won't be able to access all the views, textviews, textfields etc. that I have created in my ViewController (e.g. myTextView which I mentioned earlier).
How can I achieve that all the variables that I have defined in my ViewController will also be available for MyKeyboardEventsViewController? Or is there another way to handle this?
Basically, I don't get how MyKeyboardEventsViewController will be able to access variables in my ViewController which it will need (e.g. the UITextView in question, or the accessoryView which will pop up etc. etc.).
Any suggestions would be very much welcome.
Example:
Class A contains a ivar UITextField textField
Class B subclasses Class A and thus it already contains ivar textField
Note: it's not the other way around. Class A does not "see" what ever is created in Class B.
When ever you subclass a class you give your new class the same ivars end methods of that subclassed class.
I hope this is what you were asking for.
EDIT
So for your example I would do the follwing:
Create a class "MyUIKeybordEventResponder"
Implement all the responder methods like - (BOOL)textFieldShouldReturn:(UITextField *)textField
Subclass your ViewController from "MyUIKeybordEventResponder"
Note method textFieldSHouldReturn has a parameter UITextField so it knows which textfield was pressed. So in a way it receives your textField from the subclass.
If I'm understanding this correctly, you have a UIViewController with MyKeyboardEventsViewController as an instance variable and you want to communicate between the two? If that is the case, one option would be to create a protocol.
#protocol MyKeyboardDelegate
- (void)closeAccessoryView;
#end
(Note - make whatever methods in the protocol that you need, this is simply an example)
In your MyKeyboardEventsViewController you then include the protocol file, and create an ivar
id <MyKeyboardDelegate> delegate;
Also make it a property and synthesize it.
Whatever class that is going to create the keyboardviewcontroller should delcare themselves as conforming to the protocol.
#interface MyViewController : UIViewController <MyKeyboardDelegate>
...
#end
When you create the MyKeyboardEventsViewController, set the delegate.
MyKeyboardEventsViewController *eventsVC = [[MyKeyboardEventsViewController alloc] init];
[eventsVC setDelegate:self];
Now just implement the delegate method and perform whatever action that is necessary.
In my iPhone project I have a UIViewController in which I add an instance of a subclass of UIView. From this instance I need to communicate back an integer to my view controller. My current solution is to send a message from my instance to my App Delegate which sends a message to the view controller. It works, but it feels a bit messy.
Is there anyway I can send a message straight back to the view controller?
I would love to be able to do something like [super doSomething:123];
Any ideas?
Thanks
This is the kind of thing that NSNotificationCenter was provided for. Once you get handy with sending and receiving notifications, your message-passing gets a WHOLE lot simpler.
One of the classic things people confront is how to get a pointer to the object they want, in order to tell it about something. How do I, for instance, tell the ViewController two slots back up the UINavigationController stack that the user just changed this data field? So you dig into the stack, offset back by some magic number of elements in the stack, build public setters on the fields you want talk to... It's super cumbersome.
Compared to registering as a notification receiver in one place, and then firing a notification in some complete other place when the data changes. It's kind of magical, after doing all the "dig through the view hierarchy" work.
Um, I'm not sure I understand your problem correctly. You have a class derived from UIView which needs to send a message to another class derived from a UIViewController. It sounds like you are creating the UIView instance programmatically. Is there any reason my you could not have a property on the UIView which refers to the UIVIewController and just use that to send it a message directly.
You cannot use [super ...] because the super of your UIView derived class would be UIView.
Or am I miss-understanding the issue :-)
If I understand correctly, you want to send a message from your subclass of UIView to the view controller.
That means your subclass of UIView needs to have a property or ivar which is the view controller. The easiest way to do this is to add it as an outlet and connect it to the view controller in the nib file.
Generally you should not go via the app delegate. Having a typed pointer link is also less than ideal.
The optimal way of communicating - Apple does it like this as well - is to create a delegate protocol. When creating the view controller you pass a pointer to the delegate as id . Then when it gets to sending the message you ask the delegate:
if ([delegate respondsToSelector(didFinishSomething:)])
{
[delegate didFinishSomething:info_to_pass];
}
If you want to be extra-sophisticated then you can also add a pointer to the calling class instance. Like:
[delegate myViewController:self didFinishSomething:info_to_pass];
This way you always know what kind of class the message is coming from.
If there is more than one place that needs to be notified of a change, then instead of delegation you will use notifications.
In my iPhone project I have a
UIViewController in which I add an
instance of a subclass of UIView.
This implies that you have both a reference to the instance of the UIView subclass and the UIViewController in the same scope. I.e. something equivalent to:
UIViewControllerSubclass *myViewController;
UIViewSubclass *myView;
(It doesn't matter if they are actually instance variables or, even, globals)
And once those two variables are initialized, somewhere you do something like:
myViewController.view = myView;
In your UIViewSubclass, add a property that points back to your UIViewControllerSubclass:
#property(assign) UIViewControllerSubclass *myController;
Then, when you do the above assignment, add:
myView.myController = myViewController;
From there, messaging your controller from your view is easy:
[self.myController yoManHereIsAnInt: 42];
Note that I used assign instead of retain because the controller already retains the view. If the view were to also retain the controller, you would have a cycle that would eventually lead to a leak.
No super about it. super is entirely related to the inheritance hierarchy of your Objective-C classes. What you are asking has nothing to do with inheritance and everything to do with how the various instances of objects in your application are connected together.
Simply add an outlet to your UIView subclass, connect it to its view controller in Interface Builder, and call your method on that. Here’s how that might look:
MyUIView.h:
#interface MyUIView : UIView
{
UIViewController *viewController;
}
#property (assign) IBOutlet UIViewController *viewController;
#end
MyUIView.m:
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
[[self viewController] setTitle:#"Hello from MyUIView"];
}
I've recently been doing a lot of Objective-C programming, and just got back into doing more iPhone development. I've done a lot of programming using MVC in other languages/frameworks, but I just want to make sure I'm using MVC properly in my iPhone Development.
I created a new iPhone Utility Application, which creates two views: MainView and FlipsideView. Both have a controller (FlipsideViewController and MainViewController) and XIB file of their own.
What I've been doing is putting the IBOutlet UIControl myControl variables in my MainView.h or FlipsideView.h files and then tying the controls in Interface Builder to those variables. Then I put any IBAction SomeAction myAction methods in the MainViewController.h and FlipsideViewController.h files and tying the events to those methods in Interface Builder.
This seems to be conceptually correct, but seems to cause problems. Say I have a button that when clicked it changes a label's text. So the Controller doesn't have a clue of what the variable name of the label is in the OnTouchUp event handler for my button. So I make a #property for it. But since the MainViewController.view property isn't of type MyView, I get warnings or errors whenever I try to access those properties from the view controller.
I am doing this correctly? Is there a better way to do this? If this is correct, how do I properly work with those variables without getting warnings or errors?
Thanks
Here's some code showing what I'm doing:
MainView.h
#import ...
#interface MainView : UIView
{
IBOutlet UILabel* label;
IBOutlet UIButton* button;
}
#property UILabel* label;
#property UIButton* button;
#end
MainViewController.m
-(void) buttonTouchUp:(id) sender
{
self.view.label.text = #"The button was pressed!"; //This gives error because label is not in the view structure or union
[self.view label].text = #"The button was pressed!"; //This gives a warning
}
I know I can cast the view to be of the right type, but that seems like a hack job.
I know I can live with the warning, but a warning says to me that I'm doing something that I probably shouldn't be doing. I don't believe the SDK would set me up to do have to do something like that all the time.
I must just be misunderstanding what the View is supposed to be and I'm using it incorrectly.
Most code I've seen and written myself keeps all the outlets and the actions on the controller. The button sends a message to the controller (via IBAction), then the controller updates the label (via IBOutlet). In other words, putting outlets on your views is unusual.
Views shouldn't be connected to other views unless they have some special relationship, like maybe back/forward buttons that target a UIWebView... but even then, you find out you need a controller to enable/disable the buttons as appropriate.
I have been having huge issues with this, so I drew a diagram...
alt text http://tomsfil.es/7bdead0a.png
I successfully get to the CLASS A - METHOD B but at that point, IBOutlet Z is Nil? :(
Any ideas?
note
Somebody told me it might be an Overrelease and to use NSZombieEnabled but that confused me
It's all a matter of when you call the class. Right after you create a view controller with initWithNibName, nothing is actually wired up yet - it's only after the view is created that IBOutlets are created and wired in.
One trick is that you can simply ask the view controller for .view, like so:
myViewController.view;
Then the view will be created and the IBOutlet will exist. A better method though, is to create properties on the view controller that you set, and then either in viewDidLoad, or in viewWillAppear you use those properties to set values for your outlets.