UIScrollView - How to reload data on second page of subview? - ios

I have a scrollview that is set up to scroll back and forth between 2 pages. Each page uses different data for labels, etc... on the same view controller.
I need to re-load the data on each page, without exiting the 'sub' view.
For example, I navigate to page 1 in the scroll view. My web svc sends me updated data via notification. I need to reload the data that is on page 2, while still sitting on page 1... or at least reload that data the instant I start scrolling to page 2.
I hope this makes sense. Thanks in advance!
(snippet from my scrollView.. but I would think I need to add something in my subview..?)
- (void)loadScrollViewWithPage:(int)page {
if (page < 0) return;
if (page >= kNumberOfPages) return;
if ([controllerName isEqualToString:#"ClassicViewController"]){
ClassicViewController *controller = [viewControllers objectAtIndex:page];
if ((NSNull *)controller == [NSNull null]) {
controller = [[ClassicViewController alloc] initWithPageNumber:page];
controller.referringObject = self.referringObject;
controller.user = self.user;
controller.pushedFromScroll = kTrue;
controller.theirRoll = self.theirRoll;
NSLog(#"page replaced # = %d", page);
[viewControllers replaceObjectAtIndex:page withObject:controller];
[controller release];
}
if (nil == controller.view.superview) {
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
controller.view.frame = frame;
[scrollView addSubview:controller.view];
}
}
}

You have some options, but I think if your data is posting a notification that it's been updated, you should have the view controller for each page be responsible for updating the elements of their view. So -
Have each view controller subscribe to the notification you describe with NSNotificationCenter's addObserver:selector:name:objet method.
Implement the notification handler whose selector you passed to addObserver... to update the view based on the changes.
Hope this helps!

Related

How can I alternate view controller and not lose data

I have two UIViewControllers, one is a UIPickerViewController, the Other a UITableViewController. Ideally the Picker should get a request from the user to add x amount of some item to the tableView. The Picker gets user inputs and assigns them to variables val1, val2, val3, where val1 is the number of items (number of rows) and val2 is the name or label for the item.
PickerViewController.m
- (IBAction)add:(id)sender
{
TableViewController *tvc = [[TableViewController alloc] init];
[tvc setValues:self.val1 :self.val2 :self.val3];
[self presentViewController:tvc animated:YES completion:nil];
}
TableViewController.m
-(void)setValues:(NSString *)newVal1 :(NSString *)newVal2 :(NSString *)newVal3
{
self.val1 = newVal1;
self.val2 = newVal2;
self.val3 = newVal3;
}
- (void)viewDidLoad
{
[super viewDidLoad];
[self.tableView registerClass:[UITableViewCell class] forCellReuseIdentifier:#"UITableViewCell"];
// This is just a header which holds my "Add" button
UIView *header = self.headerView;
[self.tableView setTableHeaderView:header];
[self addNew:self.val1 :self.val2 :self.val3];
}
- (void)addNew:(NSString *)newVal1 :(NSString *)newVal2 :(NSString *)newVal3
{
if(!self.numberOfRows){
NSLog(#"Initially no of rows = %d", self.numberOfRows);
self.numberOfRows = [self.val1 intValue];
NSLog(#"Then no of rows = %d", self.numberOfRows);
}
else
{
self.numberOfRows = self.numberOfRows + [newVal1 intValue];
NSLog(#"New no rows = %d", self.numberOfRows);
}
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:self.numberOfRows inSection:0];
// Only run when called again .. not initially
if(self.run != 0){
[self.tableView beginUpdates];
[self.tableView insertRowsAtIndexPaths:#[indexPath]withRowAnimation:UITableViewRowAnimationBottom];
self.run ++;
[self.tableView endUpdates];
}
}
// "ADD" button which should go back to the picker and get new items to add to the table
- (IBAction)testAdd:(id)sender
{
PickerViewController *pvc = [[PickerViewController alloc] init];
[self presentViewController:pvc animated:YES completion:nil];
}
Now, I realize every time I call the next view controller I am creating a new instance of it, but I don't know how else to do it, I figure this is the main problem. As of right now, I expect when I leave the tableview for the picker view and return the console should log "New no of rows = x" but that doesn't happen.
I know val3 isn't used and my addNew: may not be the best, but I just need it to handle the basic logging mentioned above and I should be able to take it from there.
Been stuck on this for days
Create a property for TableViewController, and only create it the first time you present it,
- (IBAction)add:(id)sender {
if (! self.tvc) {
self.tvc = [[TableViewController alloc] init];
}
[self.tvc setValues:self.val1 :self.val2 :self.val3];
[self presentViewController:self.tvc animated:YES completion:nil];
}
It's not entirely clear from you question, whether it's this presentation or the one you have in the table view class that you're talking about. It also looks like you're doing something wrong in terms of presentation -- you're presenting the picker view from the table view controller, and also presenting the table view controller from the picker. That's not correct, you should present which ever controller you want to appear second, and that controller should use dismissViewControllerAnimated to go back, not present another controller.
In testAdd you don't need to create a new instance and present it. If you want to go back to the presentingViewController, just use dismissViewControllerAnimated .
And you will go one controller up in the stack.

ObjC: ARC releasing dynamically created view controller too early

I have a view controller, named AllThingsViewController that dynamically creates other view controllers, named ThingViewController, and adds their top level view to a UIScrollView. (I'm writing proprietary code so I've changed the names of my classes, but the structure of my code is exactly the same.)
Here's what its loadView method contains:
NSArray *things = [[ThingDataController shared] getThings];
if ([things count] == 0) {
// code in this block is not relevant as it's not being executed...
} else {
for(unsigned int i = 0; i < [things count]; ++i) {
ThingViewController *thingViewController = [[ThingViewController alloc] init];
[thingViewController loadView];
[scrollView addSubview:thingViewController.topView];
thingViewController.topView.frame = CGRectNewOrigin(thingViewController.topView.frame,
0, thingViewController.topView.frame.size.height*i);
[thingViewController displayThing:thing[i]];
}
}
ThingViewController's loadView method looks like this:
- (void)loadView
{
NSArray *topLevelObjs = nil;
topLevelObjs = [[NSBundle mainBundle] loadNibNamed:#"ThingView" owner:self options:nil];
if (topLevelObjs == nil)
{
NSLog(#"Error: Could not load ThingView xib\n");
return;
}
}
When my app starts up everything displays correctly, until I try to tap one of the buttons that exists in the xib being loaded by ThingViewController, at which point it crashes due to an exception: "unrecognized selector sent to instance". It seems that ARC is releasing my ThingViewController instances too early.
Looking at my code, I figured it was because they weren't being held on to anything, so I created an NSMutableArray as an instance variable in my AllThingsViewController class, and started adding the ThingViewControllers to it thusly:
NSArray *things = [[ThingDataController shared] getThings];
if ([things count] == 0) {
// not being executed...
} else {
for(unsigned int i = 0; i < [things count]; ++i) {
ThingViewController *thingViewController = [[ThingViewController alloc] init];
[thingViewController loadView];
[scrollView addSubview:thingViewController.topView];
thingViewController.topView.frame = CGRectNewOrigin(thingViewController.topView.frame,
0, thingViewController.topView.frame.size.height*i);
[thingViewController displayThing:thing[i]];
[allThingsViewControllers addObject:thingViewController];
}
}
However, it didn't change anything, even though those objects are being added to the array. Finally, just to confirm that this is ARC releasing it early, I changed "thingViewController" to be an instance variable in AllThingsViewController and changed:
ThingViewController *thingViewController = [[ThingViewController alloc] init];
to be:
thingViewController = [[ThingViewController alloc] init];
Sure enough, the last item in the scrollable list doesn't crash when I tap its buttons, but the other ones do, because its ThingViewController isn't being deallocated.
I'm still relatively new to ARC, but after a bunch of Googling I have no idea how to fix this. What do I do?
Couple of things.
Problem 1:
This looks like the cause of your bug:
[allBillViewControllers addObject:billViewController];
It should be:
[allBillViewControllers addObject:thingViewController];
Right?
Problem 2
You are not properly adding the view controller to your view hierarchy. It should be this:
[self addChildViewController:childViewController];
[childViewController.view setFrame:targetFrame];
[scrollView addSubview:childViewController.view];
[childViewController didMoveToParentViewController:self];
And similarly when removing a child view controller:
[childViewController willMoveToParentViewController:nil];
[childViewController.view removeFromSuperview];
[childViewController removeFromParentViewController];
Problem 3
Never call loadView explicitly on a view controller. It gets called by UIKit whenever you access the view property of a view controller.
Problem 4
You must add the view of the child view controller to your scroll view, not an arbitrary subview topView in its view hierarchy. Refactor your ThingViewController class to make this simpler for yourself. :-)
Let's look at your code:
for(unsigned int i = 0; i < [things count]; ++i) {
ThingViewController *thingViewController = [[ThingViewController alloc] init];
[thingViewController loadView];
[scrollView addSubview:thingViewController.topView];
thingViewController.topView.frame = CGRectNewOrigin(thingViewController.topView.frame,
0, thingViewController.topView.frame.size.height*i);
[billViewController displayThing:thing[i]];
[allBillViewControllers addObject:billViewController];
}
After each loop of the for loop executes, nothing will have a strong reference to the ThingViewController. Thus, it gets released and destroyed.
If ThingViewController is a subclass of UIViewController, then it should be made a "child view controller" of the scrollview's view controller. I recommend reading the section on from the View Controller Programming Guide on creating custom container view controllers (i.e., a view controller that encapsulates and displays other view controllers).

iOS: Memory Management in UIScrollView with many UIViewControllers

i've got a question regarding a UIScrollView with paging enabled that contains many UIView, each managed by an own UIViewController.
Right now there are about 20 to 30 UIViewControllers that COULD be contained in the UIScrollView. It's a catalog app on the iPad, and I started preloading all the views at the beginning, but with the amount of UIViewControllers getting bigger and bigger, that is not an option any more.
I'm looking for the perfect solution in terms of memory usage. It's no problem to reload the UIViewControllers when the ContentOffset of the ScrollView reaches a specific controller. And I think to nil the UIViewControllers when the ContentOffset tells me that the UIViewControllers is not needed any more isn't that hard as well.
What is the correct way to handle this? Is it enough to alloc the UIViewControllers when needed, putting them into a NSMutableDictionary or NSMutableArray and nil them when they are not needed any more? A little bit of help from someone already having done something similar would be great!
Thanks for your help!
I'm sure there are some good infinite scrolling classes out there, but if you were going to "roll your own", here is a minimalist bit of code that demonstrates the process of infinite scrolling, keeping the current, previous, and next pages in memory, but letting go of anything else. This assumes that:
you're doing horizontal scrolling and have turned on paging;
that you're using view controllers for the child views;
your child view controller class has a page property to keep track of what page it's for; and
you've made your view controller the delegate for your scroll view
Thus, it might look like:
- (void)viewDidLoad
{
[super viewDidLoad];
// my underlying model is just an array of strings, which I'll show on my child
// view; your model will be more elaborate, but I just want to illustrate the concept
self.objects = #[#"1", #"2", #"3", #"4", #"5", #"6", #"7", #"8", #"9"];
// set the `contentSize` for the scrollview
CGRect content = self.view.bounds;
content.size.width *= [self.objects count]; // make it wide enough to hold everything
self.scrollView.contentSize = content.size;
// set our current page and load the first pages (the first and the next pages)
self.currentPage = 0;
[self addChildPage:0 toScrollView:self.scrollView];
[self addChildPage:1 toScrollView:self.scrollView];
}
- (void)addChildPage:(NSInteger)page toScrollView:(UIScrollView *)scrollView
{
// create the child controller
ChildViewController *controller = [self.storyboard instantiateViewControllerWithIdentifier:#"child"];
// set whatever properties you need to in order for it to present its information correctly
controller.text = self.objects[page];
controller.page = page;
// now do the stuff to add it to the right place in the scrollview
CGRect frame = self.view.bounds;
frame.origin.x = frame.size.width * page;
controller.view.frame = frame;
[self addChildViewController:controller]; // containment call for adding child view controller
[scrollView addSubview:controller.view];
[controller didMoveToParentViewController:self]; // containment call when done adding child
}
- (ChildViewController *)childControllerForPage:(NSInteger)page
{
for (ChildViewController *controller in self.childViewControllers)
{
if (controller.page == page)
return controller;
}
return nil;
}
- (void)addChildIfNecessary:(NSInteger)page toScrollView:(UIScrollView *)scrollView
{
if (page < 0 || page >= [self.objects count])
return;
ChildViewController *controller = [self childControllerForPage:page];
if (controller == nil)
[self addChildPage:page toScrollView:scrollView];
}
- (void)removeChildController:(UIViewController *)controller
{
[controller willMoveToParentViewController:nil]; // containment call before removing child
[controller.view removeFromSuperview];
[controller removeFromParentViewController]; // containment call to remove child
}
- (void)updateChildrenViewsForPage:(NSInteger)page forScrollView:(UIScrollView *)scrollView
{
if (page == self.currentPage)
return;
// add child pages as necessary
[self addChildIfNecessary:page toScrollView:scrollView];
[self addChildIfNecessary:(page-1) toScrollView:scrollView];
[self addChildIfNecessary:(page+1) toScrollView:scrollView];
// find any pages that need removing
NSMutableArray *pagesToRemove = [NSMutableArray array];
for (ChildViewController *controller in self.childViewControllers)
{
if (controller.page < (page - 1) ||
controller.page > (page + 1))
{
[pagesToRemove addObject:controller];
}
}
// remove them if they need removing
for (UIViewController *controller in pagesToRemove)
{
[self removeChildController:controller];
}
// update our "current page" index
self.currentPage = page;
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
NSInteger page = scrollView.contentOffset.x / scrollView.frame.size.width + 0.5;
[self updateChildrenViewsForPage:page forScrollView:scrollView];
}
This demonstrates the appropriate custom container calls and the handling of the scroll events. I hope this helps.

Releasing memory of multiple view controllers inside a scrollview

I have an app the loaded many view controllers in a scroll view depending on the number of objects the user has in a tableview. So when I flip between the tableview and the scroll view, the number of view controllers in the scroll view changes according to how many objects the user has in the tableview.
I use the code in Apple's PageControl sample code to build the scroll view with many view controllers inside it, after some modification of course.
- (void)loadScrollViewWithPage:(int)page
{
if (page < 0) return;
if (page >= kNumberOfPages) return;
// replace the placeholder if necessary
MainViewController *countdownController = [viewControllers objectAtIndex:page];
if ((NSNull *)countdownController == [NSNull null])
{
id occasion = [eventsArray objectAtIndex:page];
countdownController = [[MainViewController alloc] initWithPageNumber:page];
[countdownController setOccasion:occasion];
[viewControllers replaceObjectAtIndex:page withObject:countdownController];
[countdownController release];
}
// add the controller's view to the scroll view
if (nil == countdownController.view.superview)
{
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
countdownController.view.frame = frame;
[scrollView addSubview:countdownController.view];
}
}
The problem is the number of living view controllers (MainViewController here) keeps increasing when I flip between the table view and the scroll view (according to Instruments) even though I didn't add any new objects which causes memory problems of course.
I tried so many things in viewWillDisappear of the scroll view like:
- (void) viewWillDisappear:(BOOL)animated
{
//test unloading all views
//Remove all subviews
[[scrollView subviews] makeObjectsPerformSelector:#selector(removeFromSuperview)];
//[[scrollView subviews] makeObjectsPerformSelector:#selector(release)];
//[viewControllers removeAllObjects];
for (unsigned m = 0; m < [viewControllers count]; m++)
{
//[[viewControllers objectAtIndex:m] makeObjectsPerformSelector:#selector(release)];
[viewControllers removeObjectAtIndex:m];
}
}
But it didn't work.
Here is a recording of how the app works youtube.com/watch?v=5W8v_smZSog
And this is the viewWillAppear method of the scroll view:
- (void)viewWillAppear:(BOOL)animated
{
eventsArray = [[NSMutableArray alloc] init];
kNumberOfPages = [self.dataModel occasionCount];
//update the eventsArray from the dataModel
//Fill in the events Array with occasions form the data model
for (unsigned r = 0; r < kNumberOfPages; r++)
{
Occasion* occasion = [self.dataModel occasionAtIndex:r];
[eventsArray insertObject:occasion atIndex:r];
}
// view controllers are created lazily
// in the meantime, load the array with placeholders which will be replaced on demand
NSMutableArray *controllers = [[NSMutableArray alloc] init];
for (unsigned i = 0; i < kNumberOfPages; i++)
{
[controllers addObject:[NSNull null]];
}
self.viewControllers = controllers;
[controllers release];
// a page is the width of the scroll view
scrollView.pagingEnabled = YES;
scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * kNumberOfPages, scrollView.frame.size.height);
scrollView.showsHorizontalScrollIndicator = NO;
scrollView.showsVerticalScrollIndicator = NO;
scrollView.scrollsToTop = NO;
scrollView.delegate = self;
pageControl.numberOfPages = kNumberOfPages;
pageControl.currentPage = currentPage;
[self loadScrollViewWithPage:0];
[self loadScrollViewWithPage:1];
}
UPDATE: Video recording of Instruments http://www.youtube.com/watch?v=u1Rd2clvMQE&feature=youtube_gdata_player
And a screen shot showing the responsible caller:
Thank you.
This is for you if you don't want to use UIPageViewController (read my other answer).
The sample project is designed for a constant number of pages (kNumberOfPages). The scrollview content size and the size of the view controller array depends on the number of pages. The sample code set this up in awakeFromNib, which is called only once.
So in order to make this dynamic you could recreate the whole ContentController when the number of pages changes. You just need to add a property for the number of pages.
The other option would be to reset the scrollview and view controller array when the number of pages changes.
I'm assuming you have defined a property for the events:
#property(nonatomic,retain) NSArray* eventsArray;
You could then add a setter method like this:
-(void)setEventsArray:(NSArray *)eventsArray
{
if (eventsArray != _eventsArray) {
[_eventsArray release];
_eventsArray = [eventsArray retain];
NSUInteger eventCount = [eventsArray count];
//reset scrollview contentSize
scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * eventCount, scrollView.frame.size.height);
// reset content offset to zero
scrollView.contentOffset = CGPointZero;
//remove all subviews
[[scrollView subviews] makeObjectsPerformSelector:#selector(removeFromSuperview)];
pageControl.numberOfPages = eventCount;
// reset viewcontroller array
NSMutableArray *controllers = [[NSMutableArray alloc] init];
for (unsigned i = 0; i < eventCount; i++)
{
[controllers addObject:[NSNull null]];
}
self.viewControllers = controllers;
[controllers release];
[self loadScrollViewWithPage:0];
[self loadScrollViewWithPage:1];
}
}
You call this method from the table view controller at the time when the user switches to the scroll view.
Apple's PageControl sample code is 2 years old and you can consider it as deprecated because there is a new container view controller in iOS 5 that does all this: UIPageViewController.
You should really start using UIPageViewController, then you don't need that loadScrollViewWithPage method at all. It would be less code and more easy.
Take a look at the PhotoScroller sample code. It has been updated to take full advantage of UIPageViewController.
It doesn't look like you are implementing Apple's View Controller Containment pratices. It would make memory management that much easier and safer.
Plus, hoping that it might save you a lot of future headaches, there is already an open source project that does what you are describing (implementing a self-managing scrollview of an arbritary number of view controllers).
You might want to take a look at it: RHHorizontalSwipe.
The concept of a UIScrollView containing multiple UIViewController views sounds sketchy at best, that design does not sound good at all.
That being said, one potential issue could be this line:
if ((NSNull *)countdownController == [NSNull null])
You would be better off with something like this:
if (!countdownController || [countdownController isKindOfClass:[NSNull class]])
Also, you should call [super viewWillDisappear:animated] in your viewWillDisappear method.

ios multiple views with a scroll view deallocated instance

I am have an issue with my scrollview which holds multiple views. I think the problem is that subviews are being released. I have buttons in the subviews and when I click the buttons I get this error, [GraphDisplayViewController performSelector:withObject:withObject:]:
message sent to deallocated instance
. If there is only one subview then I can just use a property and this works, but since the number of subviews varies(one or more), it does not work and I don't know how to solve this.
I currently load all the views at once in the beginning. I'm working on only loading one subview at a time and assigning the property to that view, but I'm not sure if that will work.
My layout is as follows, a parent view(DetailViewController) contains a scrollview, I add views(GraphDisplayViewController) to the scrollview, the subviews each load a view(GraphView).
Any help or advice would be greatly appreciated. If you need any more details please let me know. Thank you for your time.
Code sample of how I add the subviews,
DetailViewController
- (void)loadScrollViewWithPage:(int)page
{
if (page < 0) return;
if (page >= pageControl.numberOfPages) return;
subView = [viewControllers objectAtIndex:page];
NSString *description;
NSString *packsize;
if ((NSNull *)subView == [NSNull null])
{
subView = [[GraphDisplayViewController alloc] initWithNibName:#"GraphDisplayViewController" bundle:nil];
[viewControllers replaceObjectAtIndex:page withObject:subView];
subView = [[GraphDisplayViewController alloc] init];
subView.molecule = moleculeName;
subView.description = description;
subView.dataArray = moleculePrices;
}
else
{
return;
}
// add the controller's view to the scroll view
if (nil == subView.view.superview)
{
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
subView.view.frame = frame;
[scrollView addSubview:subView.view];
}
}
UPDATE
There was a mistake in the code, testing to see if that solves anything
subView = [[GraphDisplayViewController alloc] initWithNibName:#"GraphDisplayViewController" bundle:nil];
[viewControllers replaceObjectAtIndex:page withObject:subView];
subView = [[GraphDisplayViewController alloc] init]; <- Mistake
you are not retaining the GraphDisplayViewController assigned to subView variable. and hence you are loosing it at some point of time.
as we can see you are fetching the subView object like subView = [viewControllers objectAtIndex:page];
then you should also store it in viewControllers (though i am not sure what logic you have implemented but in ur code for each allocated subView this must be executed : [viewControllers replaceObjectAtIndex:page withObject:subView]; and you need to be sure that viewControllers variable is also retained for everything to work smoothly.) array so that it can be retained to avoid the crash you are facing.
I hope this will work for you..best of luck
There was a simple error in my code, I init the view twice.
subView = [[GraphDisplayViewController alloc] initWithNibName:#"GraphDisplayViewController" bundle:nil];
subView = [[GraphDisplayViewController alloc] init]; <- Mistake

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