I have a view controller that then has a button that passes to an option menu.
When options are set they need to be past back to the previously allocated viewcontroller.
How is this possible without 'alloc and init another' instance of the object?
You can achieve this by using a delegate protocol. First view controller should become the delegate of the second view controller and then you can call this delegate method in your first view controller once the selection is done.
You can lookup google for implementation of delegates in objective-c. Its pretty simple. Add a
#protocol <delegatename>
<declare delegate method>
#end
Create a member variable in the second view controller for assigning the delegate. And define the method in the class implementing the delegate.
When you init your option viewController, pass it a reference to its parent.
I.E.
[[OptionViewController alloc] initWith...: parent:];
Use a #property or a method or somesuch to call on the parent to pass the data back.
You could use a shared singleton?
http://cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html
Or save the parameters to nsuserdefaults and read them back in in your first viewcontroller
or some other temporary store such as your appdelegate
I've used all three of the above approaches before.
Related
I have a subclass of UIViewController that I want to add from the storyboard.
So I'm using what seems the standard methodology:
SubViewController *svc = [self.storyboard instantiateViewControllerWithIdentifier:#"SubViewControllerID"];
[self addChildViewController:svc];
[self.view addSubview:svc.view];
Which is fine but what if I want to call a custom init method on the subview?
I can do something like:
svc = [svc initWithFoo:#"Hello"];
Which seems to have to go after the addSubview call inorder for it to work.
Is this the best way to do this?
Seems a bit unorthodox. Calling an init method on an object that has already been created seems like its no longer truly an init method.
Maybe I should call it setWithFoo: or something and not have it return anything?
SubViewController *svc = [self.storyboard instantiateViewControllerWithIdentifier:#"SubViewControllerID"];
will cause the SubViewController to be inited with it's - (id)initWithCoder:(NSCoder *)decoder {} method.
Override that method (don't forget to call super)
If you want to do additional setup to your view controller after you instantiate it form the storyboard you can create some methods in the view controller's class and call them after the instantiate method fo the storyboard.
But be careful, if you try to make changes on any UI component in those methods, they wont be applied, and probably the app will crash. So use those methods to set params to the View Controller like array of objects, or any kind of data, and apply the UI changes for the view controller's view in viewDidLoad/viewWillAppear/viewDidAppear methods of your view controller.
Essentially I think the answer is that you can't use custom initialisers on ViewControllers added from the storyboard. Instead you have to set properties directly or through a method at the appropriate time in the life cycle as stated above.
Also as mentioned, the VC will be instantiated through initWithCoder, so calling an additional initialiser might be superfluous(?).
I encountered problems trying to use a custom initialiser that contains a call to super if I called it before the subview was added. I would just get a blank view added, I think because the superclass doesn't seem to know about the storyboard at that point. I had more success removing the call to super but that seems wrong.
This case would be more pertinent when adding subviews to a scrollview. For simplicity I left this out of my example.
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.
My understanding about passing data back to a delegate completely revolves around making a new view controller and having it conform to a protocol.
I am trying to get a time input back from a UIDatePicker set with the UIDatePickerModeCountDownTimer mode and I am running into issues.
Inside of Main1.m I create a UIActionSheet *action, and set everything up so that it presents itself with a UIDatePicker on a click. Inside of Main.m I also say:
main.delegate = self;
If this were not a UIActionSheet, I would make a protocol reference inside the new ViewController and then have the new vc pass data to a method that Main has, but I can't do that with a UIActionSheet!!
What am I missing? I assume there is something inherently different about Action Sheets, ut I can't figure it out.
Thanks for your help!!!
EDIT:
Sorry! I was giving a generic name to my view controller. It isn't actually Main.m, its FirstViewController.h/m
I didn't realize that my generic reference was getting mixed up with the Main.m file that is completely different than a vc.
I don't exactly understand why you're putting your delegate assignment in Main.m. I assume that you're setting up your UIActionSheet in a ViewController, and launching it from there. In this case, your ViewController is your delegate object. So you need to make sure that your ViewController implements the UIActionSheetDelegate. ie:
#interface SomeController : UIViewController <UIActionSheetDelegate>
Then you simply implement the required methods of that delegate in your view controller class, and that should do it. If I'm missing something about how you're implementing this, then you need to provide more code examples to examine.
Prior to asking this question here, I have googled aroung. In general, people suggest two ways to pass values/parameters between NavigationControllers:
Via properties in the root ViewController
Via Data Models
I know already that the first choice may not be the best practice. A lot of people seem to adopt this practice. However, I still don't understand how the second practice may be implemented. Does anyone happen to know any tutorial?
Moreover, is it possible to pass the value/parameter downward through constructors? I guess the only problem with that is to get back value/parameter from sub-viewcontrollers.
This file defines the delegate protocol:
#protocol VCDelegate
- (void)notifyParent:(NSString*)someString;
#end
You can include it in the .h of any view controller you define. In that view controller you declare an ivar:
id<VCDelegate> delegate;
In the view controller in which you create the child view controller you include your child view controller's .h as usual. However you add
<VCDelegate>
to indicate that it implements the protocol you have defined, just as you would if you were indicating that it implemented UITableViewDelegate - you're defining a delegate that works just the same way.
When you create your child view controller:
MyChildViewController* myCVC = [[MyChildViewController alloc] initWithString:(NSString*)someString];
myCVC.delegate = self;
So now the child view controller has a delegate which is the parent view controller, the one you are creating the child in and the one that will push it on the nav stack. You have to implement the delegate function in the parent view controller of course:
Incidentally here's where you can pass information down the stack - just set ivars after creation, same as you do the delegate ivar. You'll notice there's an initWithString that is passing a string to a custom init method, that's another way to pass information. You still do all the normal init things, just pass data additionally.
- (void)notifyParent:(NSString*)someString
{
NSLog(#"Child view controller says %#", someString);
}
And then in the child view controller you can do
[self.delegate notifyParent:#"Hello"];
presto - parent VC gets data from child VC.
This seems like the job for NSNotificationCenter. Have a look at this.
sending data to previous view in iphone
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.