I have to show a navigation view where number of views are server dependent. So I cannot hardcode the view controllers. Is there any way I can use 1 view controller and the data will be sent by server. So essentially it will work like this:
1. Get data from server... show on nav view using nav controller.
2. Once I tap on one entity... I get another set of data from server... using the same controller show that on the screen... ans so on... as I am not sure till what level we can drill down.
3. Once user tap on the back button... I will use the data cached locally to present in the same view...
Do see any issue here. I am wondering if I can push the same controller class' object multiple times in the stack.
Please guide.
As long as they're different objects it will work fine.
YourNavViewController *firstNavViewController = [[YourNavViewController alloc] initWithNibName:#"YourViewXib" bundle:nil];
[self.navigationController pushViewController:firstNavViewController animated:YES];
[firstNavViewController release];
then later onto that one:
YourNavViewController *secondNavViewController = [[YourNavViewController alloc] initWithNibName:#"YourViewXib" bundle:nil];
[self.navigationController pushViewController:secondNavViewController animated:YES];
[secondNavViewController release];
etc.
No problem at all. You can dynamically push UIViewControllers into your UINavigationControllers viewController array. You should, as you mentioned, implement a mechanism for caching content on the device, so you don't have to reload everything all the time.
One approach would be through an xml structure that you load from the server only if it differs from what you have stored locally on the device (compare e.g. through hashes, version numbers of update timestamps).
You can't push the same object on the stack multiple times, but it sounds like you want to instantiate the same class multiple times, and push each of those objects.
So if the data you were collecting was XML (for example) and you had a hierarchy of objects you were parsing from an NSXMLParser class, for each level in the hierarchy, you could create a new view object containing the data at that level, and push that.
Related
I have read that UINavigationController are best option when you want to jump from n number of screen to first screen. It takes following code to do so:
NSMutableArray *array=[[NSMutableArray alloc]initWithArray:self.navigationController.viewController];
[array removeObjectAtIndex:1];
[array removeObjectAtIndex:1];
[array removeObjectAtIndex:1];
self.navigationController.ViewController=array;
[self.navigationController popViewController:YES];
by using this code I can go directly from fourth screen to first screen directly .
If I don't using navigation controller then also by making the object of firstSCreen in fourth screen I can achieve the same thing within couple of lines.Then why one should go for navigation controller? If answer is for memory optimization then we are autoreleasing the the object of firstViewController and now we are using auto referencing.
first thing this is wrong approach to pop. true one is
[self.navigationController popToRootViewController:YES];
and second thing is that if you are at 4 screen, then by poping to a specific viewcontroller will no pop all screens. here is memory issue.
another issue is that some times you don't want to lose parent screens data. if you use method of pop to specific viewcontroller, the data will be lost as the object having data is released. you made a new one.
point is that this depends on your conditions what is suit able in your scenario. but the normal and usual approach is that don't use specific popout techniqu as it may cause problems
You can use
[self.navigationController popToViewController:(UIViewController *) animated:(BOOL)];
You just need to pass ViewController's object on which you want to move directly... And between view controller's will pop-out automatically
Hope this helps you...
agreed with 'The Saad'
one more thing is that if you have various screens with the data coming from server.
it will be quite difficult to render(user interection) screen second while loding data on first.
same with all other sibling views.
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 a tab bar controller with different view controllers all using the same managed object context, being set up as follows:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
RootViewController *rootVC = [[RootViewController alloc] initWithStyle:UITableViewStyleGrouped];
rootViewController.managedObjectContext = self.managedObjectContext;
UINavigationController *rootNavCon = [[UINavigationController alloc] initWithRootViewController:rootVC];
[rootVC release];
SettingsTableViewController *settingsVC = [[SettingsTableViewController alloc] initWithStyle:UITableViewStyleGrouped];
settingsVC.managedObjectContext = self.managedObjectContext;
UINavigationController *settingsNavCon = [[UINavigationController alloc] initWithRootViewController:settingsVC];
[settingsVC release];
tabBarController = [[UITabBarController alloc] init];
NSArray *controllers = [NSArray arrayWithObjects:rootNavCon, settingsNavCon, nil];
tabBarController.viewControllers = controllers;
[self.window addSubview:tabBarController.view];
[self.window makeKeyAndVisible];
return YES;
}
The idea is similar to the Recipes sample code if there were another tab called Settings which offered an option to managed the Category objects. The problem is that if you navigate to the view where the user can select the Category, but then go to the settings tab and delete, add, or edit a Category, when returning to the Recipes tab the changes will not be immediately reflected. Thus selecting a deleted Category would raise an exception.
What is the best way to deal with this? I was thinking about setting up an NSNotification to alert the views whenever an important change had occurred, but wasn't sure if there is a better way to do this, such as querying [managedObjectContext hasChanges] when a view appears. (Although that wouldn't seem to work if the context had already been saved.)
There's really no answer to your question other than "It's a design decision that you must make." Think carefully about your use cases and do the appropriate thing.
In your sample code, you are pushing a global managed object context into each controller. Each controller then does something with that managed object context, presumably. One thing that is not clear from the code is whether you are pushing additional view controllers onto the navigation stack or modally displaying other views. My assumption is that you are, and that any of the controllers and associated views can mutate a managed object.
In this situation, using a single managed object context might not be what you want when used with a tab view controller. Tabs allow the user to freely roam around the application so that he or she may see the appropriate view for whatever action he or she wants to perform. Allowing them to modify managed objects from a single context will potentially show changes in the wrong places, or cause an assumption to fail. It sounds like this is the situation you are in.
My advice to you would be to create multiple managed object contexts for each workflow that could mutate data. Then I would guess that you could share one managed object context for all read-only screens. Another alternative would be to use a managed object context dedicated for each tab. This would ensure that changes are made in isolation, and propagated out whenever necessary, but you will have to register the contexts to receive change notifications and then merge those changes as appropriate.
To illustrate, picture that the following diagram is an iPhone with multiple tabs, and each respective controller is handling some activity at given times.
Tab A: Controller M |--------------- ,------->
Controller N `-------+
| via NSNotificationCenter
v
Tab B: Controller O |-----------------------+-------->
Controllers M and O are members of the viewController array in the tab bar controller. The user starts on Tab A looks around, then navigates to Tab B. Then the user goes back to Tab A an pushes Controller N onto the navigation stack of Tab A and makes some change (like your your category deletion example). The deletion may or may not need to be propagated to Tab B. You can make this happen by having two managed object contexts where one listens for change notifications that the other has broadcasted via the notification manager.
Determining these use cases is probably the hard part, because I'm sure you understand how NSManagedObjectContext works in general (if not you should spend some time understanding it more thoroughly). As you can see from that simple diagram, for an extremely simple use case it introduces another dimension of complexity. So my point is that you must plan in advance if you don't want to have to tear down and reconstruct bits and pieces of your code base as it matures.
If you want changes to your managed object context to be propagated to your interface automatically and you're using table views (or even custom views), you could be using NSFetchedResultsController. This class watches a context for changes and triggers its delegate methods, allowing you to reload your views only when necessary.
I should know this by now, but I am still a bit confused. When my app navigates from one view controller to the next (via the navigation controller) I want to "finalize" the data for the current VC before going to the next VC. The only way I see to intercept the "page swap" is in the [old view viewWillDisappear] -> [newView viewWillAppear] transition. It seems weird, though I guess it works okay.
Is that really the right way to handle navigation transitions? My app is a bunch of VCs which collectively build a database file. Each VC deals with a different aspect of the data.
I don't know your exact setup, so this may not be useful to you, but I have good experiences with saving data in -(void)textFieldDidEndEditing:(UITextField*)tf, using tf.tag to index the fields. From there I commit the data to a storage class, and have no worries about what happens in the UI.
What exactly is involved in the "finalizing" part? I assume you are storing some state in the view controller for various fields and then you want to write that to the database file before going on to the next view?
When it comes to "edit view controllers" I find a nice way to do it is to have the view controller directly write to a simple model object which is injected through a property before pushing it to the nav controller.
So something like:
/* Somewhere in the app delegate, like application:didFinishLaunching */
DatabaseFileModel *model = ...;
viewController1.model = model;
viewController2.model = model;
/* ... */
[self.window makeKeyAndVisible];
Then each view controller writes to this model by setting properties etc. when a text field ends editing or whatever. Having the view controller write straight to the object means you don't need to handle viewWillDisappear etc.
If you do still need to do this however you can add a delegate to the navigation controller and handle these two methods:
– navigationController:willShowViewController:animated:
– navigationController:didShowViewController:animated:
See the UINavigationControllerDelegate documentation for more information.
This will let you keep the logic in one place rather than spread out in each view controller.
I have following problem:
I have built a tabbar application with 4 tabs. I want to pass a object/variable from the first tab controller to the third one and initialize this controller with the corresponding object.
I've already done some research. The best way, corresponding to a clean model approach, would be to call some initWithObject: method on the called viewcontroller.
How can I achieve this? How can I call the init method of the receivercontroller within the callercontroller? Can you give me some code example?
Edit:
To pass data between several views/classes etc simply create some Kind of data class which holds the data beeing shared between several classes. For more information follow the link:
Singleton
You need a data model object that stores the data for application.
A data model is a customized, standalone object accessible from anywhere in the application. The data model object knows nothing about any views or view controllers. It just stores data and the logical relationships between that data.
When different parts of the app need to write or read data, they write and read to the data model. In your case, view1 would save its data to the data model when it unloads and then view2 would read that data from the data model when it loads (or vice versa.)
In a properly designed app, no two view controllers should have access to the internal data of another controller. (The only reason a view controllers needs to know of the existence of another controller is if it has to trigger the loading of that other controller.)
The quick and dirty way to create a data model is to add attributes to the app delegate and then call the app delegate from the view controllers using:
YourAppDelegateClass *appDelegate = [[UIApplication sharedApplication] delegate];
myLocalProperty = appDelegate.someDataModelProperty;
This will work for small project but as your data grows complex, you should create a dedicated class for your data model.
Edit:
To clarify for your specific case, you would add the call to the data model when the receiver viewController becomes active.
Placing the data in an init method or a viewDidLoad won't work because in a UITabBar the users can switch back and forth without unloading the view or reinitializing the view controller.
The best place to retrieve changing data is in the viewWillAppear controller method. That way the data will be updated every time the user switches to that tab.
You might want to consider NSNotificationCenter (Reference); you register the one viewcontroller with the application notification center, and send a notification when a selection is made. When the notification is received, the other viewcontroller updates itself accordingly.
I don't think this is best practice (also check syntax) however I have got away with:
in the .h
otherclassref *otherclassname
#property (assign) otherclassname otherclassref;
and in the .m
#synthesize otherclassref;
then I just assign the reference from somewhere convenient e.g. the app delegate or wherever you are instantiating your viewcontrollers.
then the view controller can get a reference to the other view controller.
I add #class secondviewcontroller to the .h file for the firstviewcontroller and put put the #imports "secondviewcontroller.h" in the .m file of the first view controller. These are called forward references and prevent compiler errors resulting from having .h files referencing each other.