I need to check if viewWillDisappear: is called because I am presenting another UIViewController as modal or not. Does anyone know if this is possible?
UPDATE
I want to know why it is being called. For example, if its being popped or if another viewcontroller is shown as modal. I need to differentiate the both.
This is only a partial answer to your question, but have a look at "Determining Why a View’s Appearance Changed" in the "View Controller Programming Guide for iOS".
For example, you can call [self isBeingDismissed] from within viewWillDisappear to determine if the view controller was just dismissed (e.g. popped from the navigation stack).
You can set a breakpoint in that method or do NSlog(#"ViewwillDisapper"); So, you can verify whether that method is calling or not.
Related
New to iOS, kindly bare if the question is very basic? When I press the tab button multiple times, it is not invoking viewWillAppear function? If I am wrong, then which function gets invoked, each time a tab button is pressed being on the same tabview?
You are correct, viewWillAppear is a little special, it is usually called automatically but in some cases including when you are adding a view controllers view manually (view addSubview:), and also when adding this as a view controller to a UITabViewController it doesn't get messaged.
This however is only for the root view, as you navigate (maybe with a navigation controller) back and forth, that root view's viewWillAppear will get triggered as some point.
In short, if you need to implement something in viewWillAppear in these cases, you should message it yourself when you know it's going to be presented. You can handle this case in your view controller, check out the following article about the matter:
http://www.touchthatfruit.com/viewwillappear-and-viewdidappear-not-being-ca
Good luck.
I am experimenting with the splitViewController, introduced for iPads and am stuck at a point. I have a button on my detail view of the splitViewController, clicking on which a modal view opens. Now I want to change the positoning of UI controls on the detail view when the modal view gets dissmissed.
A pretty obvious way of doing this would be to catch the view transition in the ViewWillAppear method of the detailView. But it's not being called in this case. I remember facing the same problem in tabBarController where [tabBarController viewWillAppear:animated] was needed to be set before viewWillAppear of views in each tab item got called. I tried doing this with the splitViewController as well, but this doesn't seem to to work.
Any Ideas??
If the positioning is required due to an action that occurred in the modal view, you should use an explicit delegate callback. That will allow you to clearly specify the control flow and resulting behaviour of your app.
You should then define a protocol that has specific methods that carry pertinent information about the action taken. When the action occurs in the modal, perform the protocol method on the delegate, and it can react to that event (for you it seems to be a re-layout of button positioning).
To get an idea of the methods that are abstract enough to handle generic modal behaviour, look at UIAlertViewDelegate protocol. Here the delegate will get an alertViewCancel: message when the user decides to take no action, or alertView:didDismissWithButtonIndex: when they selected one of the options presented to them.
That is a good start for how to define the protocol.
If you need a many view controllers to react to the action taken in the modal, say a Sign In modal, then a better mechanism is notifications.
Using a UINavigationViewController, how do I find out how a view has appeared?
The view has either appeared in a straightforward manner, as the first view in the UINavigationController stack. Or it has appeared because a second view has been popped and the first view has revealed itself again. How do you find out which of these happened?
The only reliable way to do this, as far as I'm aware, is to subclass UINavigationController and override the UINavigationBarDelegate methods:
– navigationBar:shouldPushItem:
– navigationBar:didPushItem:
– navigationBar:shouldPopItem:
– navigationBar:didPopItem:
Don't forget to call super, of course.
Simple approach is to add a property to your RootViewController to track whether or not it has pushed another view onto the navigationController.
-(BOOL)hasPushedSecondView;
Initialize to NO in your init method.
Before pushing secondViewControllers view onto the stack, update the property to YES.
In viewWillAppear, check the value and update your view accordingly. Depending on how you want the application to behave you may need to reset the hasPushedsecondview property back to NO.
you could take a look at the leftBarButtonItem or backBarButtonItem, based on how your application is written and determine how the view appeared. If it is on top, unless you have a custom leftBarButtonItem, there would be no object there.
You can determine this directly via a couple of methods on your UIViewController subclass.
From Apple's documentation:
Occasionally, it can be useful to know why a view is appearing or
disappearing. For example, you might want to know whether a view
appeared because it was just added to a container or whether it
appeared because some other content that obscured it was removed. This
particular example often appears when using navigation controllers;
your content controller’s view may appear because the view controller
was just pushed onto the navigation stack or it might appear because
controllers previously above it were popped from the stack.
The UIViewController class provides methods your view controller can
call to determine why the appearance change occurred.
isMovingFromParentViewController: view was hidden because view controller was removed from container
isMovingToParentViewController: view is shown because it's being added to a container
isBeingPresented: view is being shown because it was presented by another view controller
isBeingDismissed: view is being hidden because it was just dimissed
In the iPhone, I have a tableview, and touching the cells, I have one method calling presentModalViewController, and opening another view, with email and this kind of stuff.
When the user press the cancel button, the viewWillAppear method in the previous view is called.
So far, so good. But in the iPad, the viewWillAppear is only called the first time that the view appears, anyone knows if this is a bug or it's right?
I tried to implement the
- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated{
with no success.
Does anybody know how to fix this without doing any delegate method from scratch?
Thanks in advance
Since view controllers presented modally don't necessarily completely cover up the underlying view on iPad, the viewWillAppear method does not fire when said modal view controllers get dismissed. I rely on delegate methods to announce to the original view controller the actions of the modal view controller. I think it's the best way to go.
Based on guesswork, rather than reading, testing or anything useful really, but therefore not covered under the NDA...
Is viewWillDisappear being called when you presentModalViewController ? It may be that it doesn't think the modal view obscures the original view fully, therefore (unlike the iPhone) both exist at once ?
Chances are it's a bug, I would file a bug report with apple here.
So the the problem is that when someone touches the back button on the UINavigationControler, I would like to run some code to update the datasource.
The problem is that i cant seem to find the right delegate to do it. only these are available on the nav controller delegate, and i want the 'didfinishshowing' type method.
– navigationController:willShowViewController:animated: optional method
– navigationController:didShowViewController:animated: optional method
The next best place i thought was the nav bar but when i try that.
Terminating app due to uncaught
exception
'NSInternalInconsistencyException',
reason: 'Cannot manually set the
delegate on a UINavigationBar managed
by a controller
This makes sense retrospectively, as you don't want some hacker messing around with the internals of the nav controller and stopping it from working.
This must is a common problem, and i have missed something simple.
Just so we're clear: view A is the starting point. User taps something and you slide right to view B. User taps the back button and you're going from B back to A and you want to do something as a result of the 'back' action.
There are three ways to do it (and on neither do you have to go near the navigationController -- these apply to the underlying viewControllers themselves):
As dmercredi suggests override viewWillAppear on view controller A so when you're heading back to it, it refreshes itself. Problem is that viewWillAppear is also called when A is called the very first time. So you'll have to set some sort of flag to distinguish between the first viewWillAppear and any subsequent ones when returning from B.
Override viewWillDisappear on view controller B and do your refreshing there. This will only get called when B is about to go away. If there's something on B that goes one level deeper or brings up a modal dialog on top, viewWillDisappear is going to get called so again you'll have to distinguish between the coming and the going.
Decouple the various views and use the delegate pattern. View controller A sets itself as a delegate of B and when B updates something it invokes the delegate method, so A is notified of the change and can update whatever it needs to. You can invoke the delegate method any time the user makes a change inside B or override viewWillDisappear and just do it one time on the way out.
Add your refresh code to the viewWillAppear:(BOOL)animated method on the view controller that is about to be displayed. In your case, that is the view controller that's already on the navigation stack.