I have a problem in my application. Any help will be greatly appreciated. Basically it is from view A to view B, and then come back from view B.
In the view A, it has dynamic data loaded in from the database, and display on the table view. In this page, it also has the edit button, not on the navigation bar. When user tabs the edit button, it goes to the view B, which shows the pick view. And user can make any changes in here. Once that is done, user tabs the back button on the navigation bar, it saves the changes into the NSUserDefaults, goes back to the view A by pop the view B.
When coming back to the view A, it should get the new data from the UIUserDefaults, and it did. I used NSLog to print out to the console and it shows the correct data. Also it should invoke the viewWillAppear: method to get the new data for the table view, but it didn't. It even did not call the tableView:numberOfRowsInSection: method. I placed a NSLog statement inside this method but didn't print out in the console.
As the result, the view A still has the old data. the only way to get the new data in the view A is to stop and start the application.
Both view A and view B are the subclass of UIViewController, with UITableViewDelegate and UITableViewDataSource.
Here is my code in the view A :
- (void)viewWillAppear:(BOOL)animated {
NSLog(#"enter in Schedule2ViewController ...");
// load in data from database, and store into NSArray object
//[self.theTableView reloadData];
[self.theTableView setNeedsDisplay];
//[self.theTableView setNeedsLayout];
}
In here, the "theTableView" is a UITableView variable. And I try all three cases of "reloadData", "setNeedsDisplay", and "setNeedsLayout", but didn't seem to work.
In the view B, here is the method corresponding to the back button on the navigation bar.
- (void)viewDidLoad {
UIBarButtonItem *saveButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self action:#selector(savePreference)];
self.navigationItem.leftBarButtonItem = saveButton;
[saveButton release];
}
- (IBAction) savePreference {
NSLog(#"save preference.");
// save data into the NSUSerDefaults
[self.navigationController popViewControllerAnimated:YES];
}
Am I doing in the right way? Or is there anything that I missed?
When a view is first loaded, it calls the viewDidLoad method. If you create a stack, drill down into it (from A to B) and then return (B to A) the viewDidLoad does not get called again on A. What you may want to try is passing A into B (by passing in self) and call the viewDidLoad method to get the new data and then reloadData method on the the tableView to refill the table view.
What you may want to try is taking the data fetching and setting functionality out of the viewDidLoad method and place it in its own getData method. At the end of the getData method, you could place a [self.tableView reloadData]; to reset/refill the table view. From class B, you could call [self getData] and minimize the amount of work you would do in class B. This would help increase reuse-ability of that code and may prevent side effects from calling the viewDidLoad method.
You could also use viewDidAppear. It is called every time the screen appears. For performance reasons, set a flag so you don't repeat the same functionality in viewDidLoad with viewDidAppear for the first screen view.
Related
I have a the first application controller, MAViewControllerMenu, and when that controller loads, I already allocate the next controller, imageControllerView.
- (void)viewDidAppear{
[super viewDidAppear:(YES)];
if (!imageControllerView)
imageControllerView = [[self storyboard] instantiateViewControllerWithIdentifier:#"chosenImageController"];
}
Then, I select an image from the image picker, and want to move to the next controller,imageControllerView, where the image would be displayed. I set the next window's image property as follows:
imageControllerView.image = [[self.pageViews objectAtIndex:(centered_image_ind)] image];
This line works, I checked that there's a value in imageControllerView.image.
However, when I move to the next controller,imageControllerView , I notice that the memory address of imageControllerView changes, or in other words, imageControllerView's properties that I change before moving to that controller, specifically image, reset when I move there.
Instead of throwing code here, I was hoping you could let me know what I should provide.
I think it's a common problem people know of:
Controller's objects re-init'ing when moving from one controller to another.
Here's a screen shot that might give a hint of what Im trying to do
Left most one is where I select pictures which in turn go into the slide show scrollview. Then I click next, and the image is supposed to appear in the centered ImageView
Thanks
OK...
You cannot "already allocate the next view controller" this won't work. There is no point in creating it like this at all. You can delete the imageViewController property (or iVar) completely.
The arrows that you have between the view controllers in your storyboard are segues. In Interface Builder you can select a segue and give it an identifier. For instance you would use something like #"ImageViewSegue".
I guess the segue is attached to the Next button. This is fine.
Now, in your MAViewControllerMenu you need to put this method...
- (void)prepareForSegue:(UIStoryBoardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:#"ImageViewSegue"]) {
// the controller is CREATED by the segue.
// the one you create in view did load is never used
ImageViewController *controller = segue.destinationController;
controller.image = [[self.pageViews objectAtIndex:(centered_image_ind)] image];
}
}
Now for the segues in the other direction...
You appear to be using segues to dismiss the modal views. You can't do this. What it will do is create a new view controller and present that instead of dismissing the presented view.
i.e. you'll go...
A -> B -> C -> B -> A -> B
// you'll now have 6 view controllers in memory
// each segue will create a fresh view controller with no values set.
What you want is...
A -> B -> C
A -> B
A
// now you only have one view controller because the others were dismissed.
// when you dismiss a view controller it will go back to the original one.
// the original one will have all the values you set previously.
To do this you need to create a method something like...
- (IBAction)dismissView
{
[self dismissViewControllerAnimated:YES completion:nil];
}
Then whatever the button is for your dismiss action attach it to this method.
Now delete all the backwards curly segues.
Passing info back
To pass info back to the original view controller you need a delegation pattern or something similar.
You can read more about creating a delegate at This random Google Search
Create a delegate method something like...
- (void)imageViewSelectedImage:(UIImage *)image;
or something like this.
Now when you do prepareForSegue you can do...
controller.delegate = self;
and have a method...
- (void)imageViewSelectedImage:(UIImage *)image
{
// save the method that has been sent back into an array or something
}
I might be wrong, but seems you go to your second view controller using a segue, it is normal your controller instance isn't the same than the one retrieved by [[self storyboard] instantiateViewControllerWithIdentifier:#"chosenImageController"]
you should take a look at - (void) prepareForSegue:(UIStoryboardSegue *)segue
(UIViewController method)
inside this method set your image property to the segue destination controller (check the identifier of the segue)
I have a project in xcode that uses storyboards. The first view that loads is an "accept terms and conditions" view in which the user must click an accept button to proceed. After clicking it, it segues to the next view. After the user clicks accept the first time the program launches, I never want them to see that view again - I want it to go straight to the next view. I have some code but its not working. Here is what I have exactly:
In app delegate: (inside applicationDidFinishLaunchingWithOptions)
if([[NSUserDefaults standardUserDefaults] boolForKey:#"TermsAccepted"]!=YES)
{
[[NSUserDefaults standardUserDefaults] setBool:NO forKey:#"TermsAccepted"];
}
Inside the accept terms and conditions view implementation: (viewDidLoad)
if ([[NSUserDefaults standardUserDefaults] boolForKey:#"TermsAccepted"]){
[self.navigationController pushViewController: self animated:YES];
//I want it to go to the next screen
}
else {
//I want to show this screen, but I don't know what goes here
}
Also Inside the accept terms and conditions view implementation (in the accept button)
- (IBAction)acceptButton:(id)sender {
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:#"TermsAccepted"];
}
I run it and get the error: 'Pushing the same view controller instance more than once is not supported'. How do I fix this?
In your first code snippet, you basically say "if TermsAccepted is not YES (so it is NO), then set it to NO. This does not make sense
In your 2nd code snippet, you wrote [self.navigationController pushViewController:self animated:YES];. So basically you ask the current UIViewController (self) to push itself on its own navigationController… which does not make sense either.
That's why you have this error. You try to push the current viewController self whereas it is already on screen in your navigationController. So you try to push the same instance (self) twice on the same navigationController.
You obviously meant to push another viewController (probably an instance of a TermsAndConditionViewController or something that shows the terms and conditions of your app) on the navigation controller, and not the current viewController itself, which doesn't make sense.
First, you want to have the next view controller, the one you always want to show, be the root view controller of your window. In that controller's viewDidLoad method, put your if clause to show the accept terms and conditions controller -- you can show that one using presentModalViewController. The if clase can be like this:
If([[NSUserDefaults standardUserDefaults] BoolForKey:#"TermsAccepted"] !=YES) {
// instantiate your terms and conditions controller here
// present the controller
}
Then, in the method where you dismiss the terms and conditions controller, set the value of that key to YES.
I have set up a demo application with a simple UITableViewController with no contents, but an 'Add' button in the toolbar. This launches a modal view controller which is again empty other than a 'cancel' button. The cancel button just tells its delegate (the UITableViewController) to dismiss the modal.
I then added an NSLog statement in the UITableViewController's numberOfSectionsInTableView method.
Ordinarily, when the table view controller loads I see two calls to numberOfSectionsInTableView. When I open and dismiss the modal (which returns to the UITableViewController) I see no further calls to numberOfSectionsInTableView.
However, if I return 0 from numberOfSectionsInTableView, in addition to the two calls on display, I also see an additional numberOfSections call when the modal is dismissed.
This only happens when numberOfSectionsInTableView returns 0, and I have added no additional code to my project besides that mentioned. This is easily verifiable by setting up a couple of controllers as I've described and modifying the result from numberOfSectionsInTableView.
My questions:
Why is the UITableView calling numberOfSectionsInTableView on return from a modal view?
Why is it only doing this if numberOfSectionsInTableView returns 0?
In addition to numberOfSectionsInTableView, the UITableViewController is also calling cellForRowAtIndex: when the modal is dismissed. In fact, it is attempting to display the new contents of its dataSource. How am I meant to manually animate a row insertion if the first row added is going to already be updated automatically? Shouldn't it be left to me to make sure that my UITableView is consistent with its dataSource?
What property is the UITableViewController checking to know that there is one or more sections (and therefore ask my delegate how many sections)? It can't be numberOfSectionsInTableView itself, since I would see it called whenever I return from the modal, not only when numberOfSections = 0.
From UITableViewController docs:
When the table view is about to appear the first time it’s loaded, the
table-view controller reloads the table view’s data... The
UITableViewController class implements this in the superclass method
viewWillAppear:
If you watch in the debugger, the second call upon app launch is from UITableViewController's viewWillAppear: implementation - specifically the part referred to above, where tableView is sent the reloadData message.
Now, the first call to numberOfSectionsInTableView: on launch is also from UITableViewController's implementation of viewWillAppear: but not directly from that implementation's call to -[UITableView reloadData]. I'm not sure what the first call is all about.
But, to your question, the call to numberOfSectionsInTableView: that happens when dismissing the modal has exactly the same call stack as the second call from applicationDidFinishLaunching:withOptions:. My hypothesis then is that UITableView interprets having zero sections as being in a state where it has not loaded at all. That does make some sense actually. I'd consider an "empty" table view to be one without any rows, but one without any sections seems almost "uninitialized" to me. Furthermore the UITableViewDataSource documentation implies UITableView has by default one section. Returning zero from this method would be inconsistent with that assumption of the docs as well.
Now, to your concern about animation - if you give the table an empty section to work with, you will be able to have full control over inserting the first row with whatever animation you'd like, and not be locked in to when you need to reload.
I think the moral of the story is, don't return zero sections unless you really, really need to for some reason. The title of your post refers to this table view being "empty" as well but I think it's clear the framework finds zero sections to not be empty but unloaded.
Hope this helps! And thanks for posting the sample project for me to play around with.
Perhaps the delegate just couldn't believe its eyes. But seriously, since a table view has to have at least one section, passing 0 doesn't make any sense. Why do it? You pass it an invalid argument and it gives you back a weird response. As to why it doesn't ask for number of sections when you pass 1, I think it's because it doesn't need to know at that point (coming back from the modal view controller) -- the table view has already been populated (if there were some data) and you haven't changed anything in the model, so it doesn't need to update.
I added a few lines to your example project to slide in a row each time you return from the modal view controller, which is what I think you're trying to do. I added an int property num for the return value of numberOfRowsInSection, added an array to populate the table, and a call to insertRowsAtIndexPaths from the modal view controller dismissal method.
- (void)viewDidLoad
{
_num = 0;
self.theData = #[#"one",#"two",#"three"];
[super viewDidLoad];
self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self
action:#selector(addRecipe)];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
NSLog(#"# sections requested");
//when 0, this fires on return from the modal. When 1, it does not.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSLog(#"in numberOfRows in section");
return _num;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"in cellForRowAtIndexPath");
UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:nil];
cell.textLabel.text = [self.theData objectAtIndex:indexPath.row];
return cell;
}
- (void)addRecipe
{
//create the modal and suscribe for delegate notifications
AddRecipeViewController *addRecipeController = [[AddRecipeViewController alloc]initWithStyle:UITableViewStyleGrouped];
addRecipeController.delegate = self;
//display the modal in a navigation controller
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:addRecipeController];
[self.navigationController presentModalViewController:navController animated:YES];
}
- (void)addRecipeVC:(AddRecipeViewController *)addRecipeVC didAddRecipe:(NSString *)recipe
{
[self dismissModalViewControllerAnimated:YES];
_num += 1;
[self performSelector:#selector(addRow) withObject:nil afterDelay:.5];
}
-(void)addRow {
[self.tableView insertRowsAtIndexPaths:#[[NSIndexPath indexPathForRow:_num-1 inSection:0]] withRowAnimation:UITableViewRowAnimationRight];
}
The tableview checks number of sections when it's populating the table view with data!
Since the table can be divided into sections, it has to know specifically how many sections to divide it into.
When you reload the data, the number of sections is also checked.
Because every time the table view has to take action in accessing either the data of the table, like what row you tapped, and in what section, or populating the data table, the number of sections has to be known!
Hope this helped!
Similar to this question: Adding subview, gets delayed?
But I don't think you can pushViewController in a separate thread so is this really impossible?
Here is what I'm trying to do:
I have a TableView and when a cell is pressed, I want to call
[self.view addSubview:LoadingView]
to display an overlay with a spinner. Then I call
self.navigationController.navigationBar.hidden = NO;
[self.navigationController pushViewController:newGameViewController animated:YES];
However, the subview only displays for a split second (~1-4 seconds after the cell selection occurs while it waits for the new viewcontroller to initialize).
Is there any way to get some sort of loading indicator to occur at the instant the cell is selected?
Okay. What about this. In your didSelectRowAtIndexPath start your spinner (via addSubview ...) and start loading your stuff from the server. If that's finished remove the spinner an push your new view controller onto the stack. Make sure the user can't touch any other cell during that time. By the way. From a users perspective I'd find it mor intuitive if the new controller is loaded immediately and displays some waiting message.
Or the other way around: The newGameViewController displays the spinner and starts loading the data from the server in a background thread. When the data is complete, remove the spinner and display the data. That way the user could even go back if she doesn't want to wait.
You do not need to add code before pushing newGameViewController.
Inside viewDidLoad of newGameViewController, write the code of displaying spinner. To get the updated UI, just insert a delay before calling a web API.
inside GameViewController.m
-(void) viewDidLoad
{
[self.view addSubview:LoadingView];
[self performSelector:#selector(callWebAPI) afterDelay:0.1];
}
-(void) callWebAPI
{
//Handle network activity here..
}
This one is probably something simple, still learning the ins-and-outs on this but I've run out of searches for this one with no available answer.
I've got a UIViewController with several elements displayed on it, one such element is a UITableView. The UITableView has it's own class and is allocated in the UIViewControllers viewWillAppear
- (void)viewWillAppear:(BOOL)animated
{
UITableView *insideTableView = [[UITableView alloc] init];
tableView.delegate = insideTableView;
tableView.dataSource = insideTableView;
}
Everything is working fine in regards to the tableview. Today I am experimenting with a few additions, one of which is a new view popup on cell selection within that tableview.
Inside my TableView Class, I have the following:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"Cell Pressed, Present View");
PopupView *popupView = [[PopupView alloc] initWithNibName:#"PopupView" bundle:nil];
popupView.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController:popupView animated:YES];
}
Now it gets called fine, verified by the NSLog, however the view doesn't appear. I know the problem is related to the fact that I want PopUp to appear over the TableViews Parent rather than itself.
I'm just not sure how to properly call it in this instance.
The delegate is a UIViewController which doesn't have its view property set, which is why presentModalViewController:: doesn't work.
You need the view controller containing the table view to present the modal view controllers, but note that that view controller is not the parent of the table view delegate. This is because you have no view controller hierarchy in place.
The easiest way to fix this is to put those methods inside the view controller whose view contains the table view. Alternatively the table view delegate needs to hold a reference to the view controller so it can call presentModalViewController:: on it.
The latter approach can lead to retain cycle, so you have to use a non-retaining reference. The nicest implementation is the delegate pattern.
Also, you don't want to do the instantiation in viewWillAppear: because that can be called multiple times during the lifecycle of a view controller. Put the code in viewDidLoad and balance it in dealloc. Right now you are leaking memory every time your view appears, which when your modal view controller is working will be every time the modal view controller is presented and dismissed.