This is for an addition to a legacy iPhone app with the architecture already defined (years ago, by somebody else.)
The main limitation is that the functionality of the main menu system is based on configuration files, so I can't call any specific initialisation code from the main menu.
This means that the view I am developing is stand-alone, and has to somehow manage its states with the information from the system.
Further, on each screen there is a "Settings" button, taking the user to a Settings pane, that is pushed on the navigation stack on top of "my" view. When the user closes the settings pane, my view reappears, as per normal navigation.
OK, so here is my problem:
When the user enters my view from the menu I want it to be reset so all input fields are empty.
If the user goes to the settings screen and returns to my screen, I want all previous input to be preserved, i.e., not reset to empty fields.
If the user then goes back to the main menu, and re-enters my screen, fields should be empty again.
Is there a robust, documented and preferably simple way to know if I should reset the fields in this scenario?
Can you check the navigation stack to see if the settings page is currently on the stack?
- (void)viewWillAppear:(BOOL)aAnimated
{
[super viewWillAppear:aAnimated];
NSArray* stack = [[self navigationController] viewControllers];
UIViewController* last = [stack lastObject];
}
Presumably viewDidDisappear is called when your view is hidden for some reason. You could presumably get the UIWindow and work up the view chain to find where your view is in the chain (if it is at all) and what is hiding it.
Non-trivial, though, and the sort of thing that will likely need to be "maze bright" vs robust.
(Though if a navigation controller is consistently used it becomes much simpler.)
In the view controller in question, how about you set up a delegate.
id delegate;
#property (nonatomic, assign) id delegate;
for the header, then synthesize in the implementation.
Whenever you push to this view controller, set self as the delegate from the pushing view. Then in this view controller, you can perform a check in the viewDidLoad or viewDidAppear: (or wherever you feel it would be necessary) with something like the following:
if ([self.delegate isKindOfClass:[SomeClass class]]) {
// now you can find which class sent to this view;
}
That should do the trick, so I hope it helps you out
EDIT: considering you are switching views without always using a nav controller, the above won't be valid all the time. In that case, you are probably better off using an internal property as well as an outlet to your settings pane. So in this view controller, you'll want something like this in the header:
BOOL shouldReset;
#property (readwrite) BOOL shouldReset;
In your viewDidLoad, you'll want to initialize this as shouldReset = YES. You should also put this in your viewDidDisappear: since it is your default behavior. When you present the settings pane, give the settings an outlet to the current view controller so you can, from within the settings (when you press the back button) set [self.otherViewController setShouldReset:NO]. Then in your viewDidAppear: for the original view controller in question, you can check to see if it should reset its fields or not
Related
I am building an iPad application that uses Jeremy Fox's JFDepthView library. For those that aren't familiar it basically allows a new view controller to brought front and center, sending the parent view to the background and applying a blurring algorithm to it to bring the user focus to the presented top view. That all works perfectly but I am having issues setting the value of an int and passing it back to the parentViewController from the presented topView.
I have TTViewController which is the originating view controller. A button is tapped on this view and JFDepthView kicks in and presents a new view on top of TTViewController called IndustryViewController. When a button on IndustryViewController is tapped I want that view to be dismissed and a specific action to happen on the parent TTViewController depending on the int passed back that I set when the button is pressed.
I have created a property for my int in the originating (parent) viewController.
#interface TTViewController : UIViewController <JFDepthViewDelegate> {
}
#property (nonatomic, assign) int defence;
#end
In my child view controller (the one presented over the top by JFDepthView) I am trying to gain access to the parent and set the value of the variable then dismiss the view.
#implementation IndustryViewController
- (IBAction)defenceBtnPressed:(id)sender
{
TTViewController *viewController = (TTViewController *)self.parentViewController;
viewController.defence = 1;
[self.depthViewReference dismissPresentedViewInView:self.presentedInView animated:YES];
}
I get no errors or warnings, everything builds fine. But the value of the int 'defence' is always 0. I am obviously doing something wrong and have a lack of understanding of the parentViewController setup. Can anyone fill in the blanks or point me in the right direction?
EDIT: It seems that if I log out parentViewController and presentingViewController they are both NULL. I have also logged out the defence variable immediately after setting it and it never actually gets set to '1'.
Check if self.parentViewController is nil. I conjecture that JFDepthView doesn't set the parentViewController automatically for you.
If self.depthViewReference is the parent view controller (i.e. the one on which you called presentViewController:xxx inView:self.view to present the current VC), then simplify cast it to the desired class TTViewController and set defence = 1 on that.
I have seen a lot of posts on stack overflow stating that the viewDidLoad method of controllers is only called the first time the controller is accessed and not necessarily every time but always at least once.
This is not what I am seeing at all! I put together a simple test to highlight this:
https://github.com/imuz/ViewDidLoadTest
It seems for navigation controller segues and modal views viewDidLoad is always called. The only time it is not called is when switching between tabs.
Every explanation of viewDidLoad I can find contradicts this:
When is viewDidLoad called?
UIViewController viewDidLoad vs. viewWillAppear: What is the proper division of labor?
http://www.manning-sandbox.com/thread.jspa?threadID=41506
And apples own documentation indicate that a view is only unloaded when memory is low.
I am currently doing initialisation in viewDidLoad making the assumption that it is called with every segue transition.
Am I missing something here?
Phillip Mills' answer is correct. This is just an enhancement of it.
The system is working as documented.
You are seeing viewDidLoad because the view controller being pushed onto the navigation controller is a new instance. It must call viewDidLoad.
If you investigate a little further, you would see that each of those view controllers are deallocated when they are popped (just put a breakpoint or NSLog in dealloc). This deallocation has nothing to do with the view controller container... it does not control the life of the controller it uses... it is just holding a strong reference to it.
When the controller is popped off the navigation controller stack, the nav controller releases its reference, and since there are no other references to it, the view controller will dealloc.
The navigation controller only holds strong references to view controllers that are in its active stack.
If you want to reuse the same controller, you are responsible for reusing it. When you use storyboard segues, you relinquish that control (to a large extent).
Let's say you have a push segue to view controller Foo as the result of tapping some button. When that button is tapped, "the system" will create an instance of Foo (the destination view controller), and then perform the segue. The controller container now holds the only strong reference to that view controller. Once it's done with it, the VC will dealloc.
Since it creates a new controller each time, viewDidLoad will be called each time that controller is presented.
Now, if you want to change this behavior, and cache the view controller for later reuse, you have to do that specifically. If you don't use storyboard segues, it's easy since you are actually pushing/popping the VC to the nav controller.
If, however, you use storyboard segues, it's a bit more trouble.
There are a number of ways to do it, but all require some form of hacking. The storyboard itself is in charge of instantiating new view controllers. One way is to override instantiateViewControllerWithIdentifier. That is the method that gets called when a segue needs to create a view controller. It's called even for controllers that you don't give an identifier to (the system provides a made-up unique identifier if you don't assign one).
Note, I hope this is mostly for educational purposes. I'm certainly not suggesting this as the best way to resolve your problems, whatever they may be.
Something like...
#interface MyStoryboard : UIStoryboard
#property BOOL shouldUseCache;
- (void)evict:(NSString*)identifier;
- (void)purge;
#end
#implementation MyStoryboard
- (NSMutableDictionary*)cache {
static char const kCacheKey[1];
NSMutableDictionary *cache = objc_getAssociatedObject(self, kCacheKey);
if (nil == cache) {
cache = [NSMutableDictionary dictionary];
objc_setAssociatedObject(self, kCacheKey, cache, OBJC_ASSOCIATION_RETAIN);
}
return cache;
}
- (void)evict:(NSString *)identifier {
[[self cache] removeObjectForKey:identifier];
}
- (void)purge {
[[self cache] removeAllObjects];
}
- (id)instantiateViewControllerWithIdentifier:(NSString *)identifier {
if (!self.shouldUseCache) {
return [super instantiateViewControllerWithIdentifier:identifier];
}
NSMutableDictionary *cache = [self cache];
id result = [cache objectForKey:identifier];
if (result) return result;
result = [super instantiateViewControllerWithIdentifier:identifier];
[cache setObject:result forKey:identifier];
return result;
}
#end
Now, you have to use this storyboard. Unfortunately, while UIApplication holds onto the main storyboard, it does not expose an API to get it. However, each view controller has a method, storyboard to get the storyboard it was created from.
If you are loading your own storyboards, then just instantiate MyStoryboard. If you are using the default storyboard, then you need to force the system to use your special one. Again, there are lots of ways to do this. One simple way is to override the storyboard accessor method in the view controller.
You can make MyStoryboard be a proxy class that forwards everything to UIStoryboard, or you can isa-swizzle the main storyboard, or you can just have your local controller return one from its storyboard method.
Now, remember, there is a problem here. What if you push the same view controller on the stack more than once? With a cache, the exact same view controller object will be used multiple times. Is that really what you want?
If not, then you now need to manage interaction with the controller containers themselves so they can check to see if this controller is already known by them, in which case a new instance is necessary.
So, there is a way to get cached controllers while using default storyboard segues (actually there are quite a few ways)... but that is not necessarily a good thing, and certainly not what you get by default.
I believe the Apple documentation is describing a situation where the view controller is not being deallocated. If you use a segue, then you are causing the instantiation of a new destination controller and, being a new object, it needs to load a view.
In xib-based apps, I have sometimes cached a controller object that I knew I might re-use frequently. In those cases, they behaved in keeping with the documentation in terms of when a view had to be loaded.
Edit:
On reading the links you included, I don't see any contradiction in them. They, too, are talking about things that happen during the lifespan of a view controller object.
It is called every time the controller's view is loaded from scratch (i.e. requested but not yet available). If you deallocate the controller and the view goes along with it, then it will be called again the next time you instantiate the controller (for example when you create the controller to push it modally or via segue). View controllers in tabs are not deallocated because the tab controller keeps them around.
Ok I am trying to refresh the tab content of each of my tabs after a web call has been made, and I have tried soo many different methods to do this that I have lost count. Could someone please tell me how this is possible?
The web call just calls JSON from a server and uses it to update the content of the tabs. For testing purposes I have a button set up inside my settings class. Settings class is a view within the home tab which has a button called refresh. When clicked this takes JSON stored on the device which is different to the one called from the web call on application start up. This saves me having to change the JSON on the server.
I will take you through some of the techniques I have tried and would be grateful if someone could tell me what I am doing wrong.
I tried making an instance of the class and calling the refresh method like this
DashboardVC *db = [[DashboardVC alloc] init];
[db refreshMe];
The refresh method in dashboard class is this
-(void) refreshMe
{
[self loadView];
[self viewDidLoad];
}
However no luck. This method will work if I call it inside the Dashboard class, but wont work if I call it from another class. I think it is become I am instantiating a new class and calling refresh on that. So I dropped that technique and moved onto the next method
This loops through all the tabBars and changes the tabTitles without any issues, so it I know it is definitely looping through the ViewControllers properly.
I also tried every varient of the view methods like ViewDidAppear, viewWillAppear etc, no luck.
I also tried accessing the refreshMe method I made in the dashBoard class through the tabController like this
[[[self.tabBarController viewControllers] objectAtIndex:0] refreshMe];
But again no luck, this just causes my application to crash.
I read through this guide
https://developer.apple.com/library/ios/#documentation/WindowsViews/Conceptual/ViewControllerPGforiOSLegacy/TabBarControllers/TabBarControllers.html
on the apple website but it doesn't seem to cover how to refresh individual tab content.
All I want is to have each individual tab refresh its content after the web call is made, and have spent ages trying to figure this out, but nothing is working.
So would be very grateful if someone could show me what I am doing wrong?
Thanx in advance....
EDIT:
Expand on what I have tried
After discussion with Michael I realised you should never call loadView as against Apple guidelines. So I removed any references to LoadView. I have now placed a method in all the main ViewControllers called RefreshMe which sets up the views, images texts etc in the class. And this method is placed inside the ViewDidLoad. Now I want to be able to call these methods after a web call has taken place, so effectively refreshing the application.
My viewDidLoad now looks like this in all my the main classes.
- (void) viewDidLoad {
[super viewDidLoad];
[self refreshMe];
}
And then the refreshMe method contains the code which sets up the screen.
The JSON data pulled from the web call will set up the content of each of the 5 tabs, so need them all to be refreshed after web call.
I tried looping through the viewControllers and calling viewDidLoad, which should in turn call the refreshMe method which sets up the class, however nothing happens. Code I used was this
NSArray * tabBarViewControllers = [self.tabBarController viewControllers];
for(UIViewController * viewController in tabBarViewControllers)
{
[viewController viewDidLoad];
}
For the time being I have also included
NSLog(#"Method called");
in the viewDidLoad of each class to test if it is being called. However the message is only being printed out when I first load the application or if I re-enter the application. This method should be called after I click the refresh button in the settings screen but it isn't and I have no idea why.
Anyone have any idea why this is not working?
From the question and your comments, it sounds like there are at least two problems:
You're having trouble accessing the view controllers managed by your app's tab bar controller.
You seem to be working against the normal operation of your view controllers.
The first part should be straightforward to sort out. If you have a pointer to an object, you can send messages to that object. If the corresponding method doesn't execute, then either the pointer doesn't point where you think it does or the object doesn't have the method that you think it does. Let's look at your code:
NSArray * tabBarViewControllers = [self.tabBarController viewControllers];
for(UIViewController * viewController in tabBarViewControllers)
{
[viewController viewDidLoad];
}
This code is supposed to call -viewDidLoad on each of the view controllers managed by some tab bar controller. Leaving aside the wisdom of doing that for a moment, we can say that this code should work as expected if self.tabBarController points to the object that you think it does. You don't say where this code exists in your app -- is it part of your app delegate, part of one of the view controllers managed by the tab bar controller in question, or somewhere else? Use the debugger to step through the code. After the first line, does tabBarViewControllers contain an array of view controllers? Is the number of view controllers correct, and are they of the expected types? If the -viewDidLoad methods for your view controllers aren't being called, it's a good bet that the answer is "no," so figure out why self.tabBarController isn't what you think.
Now, it's definitely worth pointing out (as Michael did) that you shouldn't be calling -viewDidLoad in the first place. The view controller will send that method to itself after it has created its view (either loaded it from a .xib/storyboard file or created it programmatically). If you call -viewDidLoad yourself, it'll either run before the view has been created or it'll run a second time, and neither of those is helpful.
Also, it doesn't make much sense to try to "refresh" each view controller's view preemptively. If your app is retrieving some data from a web service (or anywhere else), it should use the resulting data to update its model, i.e. the data objects that the app manages. When a view controller is selected, the tab bar controller will present its view and the view controller's -viewWillAppear method will be called just before the view is displayed. Use that method to grab the data you need from the model and update the view. Doing it this way, you know that:
the view controller's view will have already been created
the data displayed in the view will be up to date, even if one of the other view controllers modified the data
you'll never spend time updating views that the user may never look at
Similarly, if the user can make any changes to the displayed data, you should ensure that you update the model either when the changes are made or else in your view controller's -viewWillDisappear method so that the next view controller will have correct data to work with.
Instead of refreshing your view controllers when updating your tab bar ordering, why not simply refresh your views right before they will appear by implementing your subclassed UIViewController's viewWillAppear: method?
What this means is that each time your view is about to appear, you can update the view for new & updated content.
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.
I shift to my view by
[[self navigationController] popToViewController:controller animated:YES];
In that ViewController, I'm not able to get a notice, that it comes back to front (e.g. by viewWillAppear). I want to reload a table, as soon as the view is visible again.
How do I get a notice, that the view comes back on the screen?
----> solved: See my last comment on Corey's answer
viewWillAppear should be called if you are using a UINavigationController.
Are you sure you have added it correctly to the view hierarchy?
Did you check if viewWillDisappear gets called when it goes offscreen?
Did you try viewDidAppear just to make sure?
Did you spell the method name correctly?
To add:
Is the instance of UINavigationController added directly to the UIWindow instance?
The delegate methods like viewWillappear are sent from UIApplication (I believe). UIApplication only "knows" about viewControllers whose views are either:
Added Directly to UIWindow.
Added to a
UINavigationController/UITabBarCOntroller
that is added directly to UIWindow
(or a chain of these that leads to UIWindow).