I'll start with a confession here... I'm a real newbie to Objective-C & iPhone programming (started studying in February & coding in March), I have a project that's very ambitious for that level of experience & a very tight deadline to catch an opportunity to give my app a field trial.
My app is Core Data driven & downloads all of it's data on first run which is a choice made because it will be used on sites where 3G network access may not be reliable. I'd like to present a modal view while this happens, nothing fancy just a bit of text to explain, a progress bar or activity indicator, a graphic to pretty it up & button becoming visible when the job is done. I've tried a couple of approaches & failed dismally so no code for that as all but the XIB has been trashed.
At the moment I'm running this code in applicationDidFinishLaunching ...
[self checkDataAndLoadIfNeeded];
[window addSubview:rootController.view];
[window makeKeyAndVisible];
rootController is a TabBarController with nested NavigationControllers. checkDataAndLoadIfNeeded is a method that checks a default for the data being loaded & if it is not YES presents an alert. The delegate method for dismissing the alert then a custom class, DataLoader, which goes about downloading & importing the data.
What's happening is that the rootController view becomes visible before the alert does & the table on the first tab doesn't load any data until the next run of the app. I'm wondering if that data not loading is because I'm doing that in viewDidLoad & whether I'd do better to have it in viewWillAppear or viewDidAppear. When I tried loading the modal view I've built my rootController view still became visible first & my modal view didn't become visible until the data had finished (or almost finished) downloading (the Done button became visible immediately).
Can anyone offer suggestions as to how I can make this work?
Cheers & TIA, Pedro :)
Sounds like your rootController is not watching for changes in the data. It should not matter if the element is displayed already or if the data loads first. If the data loads later then the UI element should notice that the data is updated and then refresh itself.
Depending on your app design, you should look at the NSFetchedResultsController class and implement it along with its delegate methods. This class is designed to watch the NSManagedObjectContext for changes and when data is saved out to disk, update its delegate with what has changed.
Related
I have read the apple guidelines and I know it says you shouldn't do that but hear me out as I would like to know if what I am doing is bad practice.
When my application loads up, in the app delegate, a web call is made which sets up the order of the tabs, as well the content within it. Web call is like this
WebCalls *wc = [[WebCalls alloc] init];
[wc setWebCallDidFinish:^(NSString * json) {
// set up tab order here, as well as stores the JSON in a file on the phone
// Also code here to download images and cache them on phone
self.window.rootViewController = self.tabBarController;
[self.window makeKeyAndVisible];
}
[wc getData:phoneNumber];
Now this code works great but the problem is what will happen when app starts is
Launch image shows for a second (which is not very long, sometimes it's half a second or less so just annoying)
Screen goes black for about 2 seconds while json is parsed and images downloaded etc
Then first tab controller is shown
What I want is a seamless transition between the splash screen and the first screen so the user never sees black screen.
What I was thinking of doing is something like this
Change iPhone splash screen time
In the answer given, the guy pushes a view forward to be the splash screen. Would it be bad practice to push that view forward, and then in that screen do the web calls which gets json data, and downloads images, then dismiss the view and have the tabcontroller view become main view?
Or how else would I prevent this delay? Is it bad practice to have a large enough web call like this in AppDelegate?
If this is bad practice to push a view forward while doing background loading, what else would you recommend? Would it be better if I just make the tabController the main rootViewController first and do the webCall in the first tab shown instead, then update the tabs when this web call finished? I was considering this one, but the tab order could be in any order after the web call is made, so not sure what tab will be shown first.
Would be grateful for your input
In the answer given, the guy pushes a view forward to be the splash screen. Would it be bad practice to push that view forward, and then in that screen do the web calls which gets json data, and downloads images, then dismiss the view and have the tabcontroller view become main view?
This is the way to do it. It's generally bad practice to download stuff from applicationDidFinishLaunching, what happens if the phone is not connected to the internet?
Present a simple view controller (using presentModalViewController:controller animated:NO with a UIActivityIndicator and a label describing what's going on, and then dismiss it when loading finishes (or it it fails, just display an error and deny access to the app). Remember to also check for airplane mode and notify the user.
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'm doing an app that uses a TabBarController and each Tab uses its own navigation controller.
The app has dynamic content and I use viewDidDisappear viewDidAppear methods to create or destroy the objects that I need each time I enter or exit into the ViewController.
My problem is when I start to sail very fast and I don't give time to load the Threads that I use for uploading content such as XML peta app or destroy objects when I leave the ViewController.
How I could control the tabs of the navigationbar or tabbarviewcontroller for not respond until the viewcontroller has loaded all contents?
Excuse me if I'm not well expressed. Thanks!
No matter you use synchronous request or asynchronous request, just show an UIAlertView while loading the data. This will both serve as a notification to the user that something is being loaded, and the it will block the interactions with all the other views on the screen.
As others have suggested in comments, I believe that what you want to do is rearrange the order in which things are triggered. Perhaps something like this:
On viewWillAppear:, clear (or disable or whatever is appropriate) your objects that are no longer valid and begin the load-new-content thread. Perhaps display a UIActivityIndicator or similar.
On viewWillDisappear:, tell the load-new-content thread that it can stop, its results are no longer needed. If you put up an activity indicator, take it down.
At the end of the load-new-content thread, take down any activity indicator, update the UI with the new contents and activate.
I don't really see any way around this -- if the UI is not valid until the new content is loaded, then you have to wait for it.
Another solution might be to cache the contents from the previous fetch, and always display those on viewDidLoad. Then, at the end of your new-content-thread, cache the new contents, and update the UI.
Any advice on how to fix this issue I have, or a better implementation design perhaps?
Requirement
Needed a way for the application at start up to take the user to the previous details page, if this was what they were on prior to quiting the application in their last session
If they were on the main screen of the app, then at restart they can stay here
The assumption is I'm working with UINavigationController and the main screen and details screen are built on a UITableViewController
My Implementation Concept
Put a check in "viewdidLoad" to see whether they were on a detailed screen, and then if so jump to this (refer to code below)
Issue
Works fine normally, however when I trigger a memory warning things screw up and I get nav bar weird behavior. For example I see the main page nav buttons, when it looks like I'm on the detail page content (UITableView)
My Analysis
From what I see when I am on the details page (appointmentsListController) and cause a memory warning in the simulator I see:
(a) the main page "viewDidLoad" actually gets called, which my concept didn't expect, so whilst I had hit the BACK button from the detailed view (UINavigationController) to go to the main view (RootViewController), in fact my code is run and it try's to throw the user back to the details page again
(b) I note in my logs after this point that [AppointmentListController viewDidLoad] seems to get called before the previous AppointmentListController dealloc method is called (i.e. like I was in controller A, went back to controller B, but got thrown back to A - and the initial dealloc for the first part didn't kick in until late...)
So I guess it's obvious my idea isn't too great
Question
Any suggestions on how to better implement my requirement? (how to check, which method to put them in)
Code
- (void)viewDidLoad {
[super viewDidLoad];
// My Implementation of the Requirements which seems flawed in the case there is memory warning triggered
if ( previousSelectedScreen >= 0 ) {
// Setup New Controller
AppointmentListController *appointmentListController = [[AppointmentListController alloc] initWithNibName:#"AppointmentListController" bundle:nil];
appointmentListController.screenToShow = previousSelectedScreen;
// Push new view onto stack
[[self navigationController] pushViewController:appointmentListController animated:NO];
[appointmentListController release];
}
}
Here's what I'd suggest: rather than having this logic in your view controller, but it in your application delegate. By constructing your navigation stack before displaying it you will hopefully avoid some of the weird things that can happen with nav bars, etc. To get rid of the memory warnings you may need to look at how your app allocates memory: it may not necessarily be to do with this.
Anyway - in your application delegate you can perform your check to see if the user was on a detail page when they exited. If they are, you can create an array containing the navigation stack (ie, Main Screen -> Details Page). You can then pass this into a navigation controller using its setViewControllers method. Once this is done, you can display your window and finish launching the app.
Resolution: While trying to recreate this bug in a fresh project to submit to Apple, I discovered that it is specific to iPhone OS 2.1, and compiling for 2.2 fixes the problem. Stephen, thanks for your help; I'll be accepting your answer since it would have worked if the bug still existed or I wasn't willing to compile for 2.2.
I have an app which is radically changing its database schema in a way that requires me to transform old-style records to new-style ones in code. Since users may store a lot of data in this app, I'm trying to display a modal view controller with a progress bar while it ports the data over (i.e. as the very first thing the user sees). This view controller's viewDidAppear: begins a database transaction and then starts a background thread to do the actual porting, which occasionally uses performSelectorInMainThread:withObject:waitUntilDone: to tell the foreground thread to update the progress bar.
The problem is, viewDidAppear: is being called twice. I noticed this because that "start a transaction" step fails with a "database busy" message, but setting a breakpoint reveals that it is indeed called two times—once by -[UIViewController viewDidMoveToWindow:shouldAppearOrDisappear:], and again by -[UIViewController modalPresentTransitionDidComplete]. Those names appear to be private UIViewController methods, so I'm guessing this is either a framework bug, or I'm doing something UIKit isn't expecting me to do.
Two relevant code excerpts (some irrelevant code has been summarized):
- (void)applicationDidFinishLaunching:(UIApplication *)application {
(register some default settings in NSUserDefaults)
// doing this early because trying to present a modal view controller
// before the view controller is visible seems to break it
[window addSubview:[self.navigationController view]];
// this is the method that may present the modal view
[self.databaseController loadDatabaseWithViewController:self.navigationController];
if(!self.databaseController.willUpgrade) {
[self restoreNavigationControllerState];
}
}
And from my DatabaseController class:
- (void)loadDatabaseWithViewController:(UIViewController*)viewController {
(open the new database)
(compute the path the old database would live at if it existed)
if([[NSFileManager defaultManager] fileExistsAtPath:oldDBPath]) {
(open the old database)
[viewController presentModalViewController:self animated:NO];
}
}
So, is there something I'm screwing up here, or should I file a bug report with Apple?
I saw this in my app too. I never got it entirely confirmed, but I think this is what's happening:
Load root view
Load modal view
OS sends view did appear notification for the view in step 1
The current view controller, which in this instance happens to be your DatabaseController class, picks it up
OS sends the view did appear notification for the modal view
The current view controller gets the notification. In this case it's the exact same controller as last time
In my case I just reset what happened in the first call to viewDidAppear:.
In your case two options spring to mind: a static variable to track whether you've started the upgrade already; or look at the UIView* parameter passed in before starting.