I have an application where I was using buttons on a toolbar to call up the views, but I am switching it over to using a tab bar.
When using the buttons I was using the following code in MainViewController.m to update the values on the page and it was working just fine:
-(IBAction) loadSummaryView:(id) sender {
[self clearView];
[self.view insertSubview:summaryViewController.view atIndex:0];
//Update the values on the Summary view
[summaryViewController updateSummaryData];
[summaryViewController calculateData];
}
However, with the Tab Bar I can not figure out how to do this. I tried putting all of the necessary code in the Summary Views viewDidLoad and it loads the initial values, but it will not update the values when I change them in another view.
Any help is appreciated. I am a bit new at this, so please don't be cryptic as I may not understand the response.
Thank you.
By placing your code in viewDidLoad, it will only be called when the view is loaded from the nib. Unless you're running low on memory, this view will remain loaded for the duration of the life of your app.
So if you need to update values every time the view will appear, consider moving that code to an override of viewWillAppear
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// your stuff goes here...
[self updateSummaryData];
[self calculateData];
}
You can update your current view in the viewWillAppear:animated message of the view:
If you have everything setup correctly, there is nothing to do, the UITabBarController will show your view, an your UIViewController will receive a viewWillAppear message, where you can do your update:
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[self updateSummaryData];
[self calculateData];
}
I strongly recommend reading the View Controller Programming Guide for iOS which describes in detail the main interface paradigms supported by the iPhone.
Related
I have a view controller that just shows progress during calculations. I put the method calls
in viewDidLoad but the problem is the view only appears once the calculations are done! How
could I automatically launch the calculations after the view has appeared on screen?
You may use GCD. Here is Raywenderlich tutorial
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
//Calculations
dispatch_async(dispatch_get_main_queue(), ^{
//Update UI must be here
});
});
}
viewDidLoad: triggers when the view is loaded. This is different from when the view is displayed.
Try starting the calculations in the - (void)viewDidAppear:(BOOL)animated callback method on UIViewController instead.
If these calculations take a while, considering running them on a background thread. This will prevent the UI from locking up while the calculations are running. This has the bonus of not only allowing the view to show, but it can be interacted with while the user waits.
[self performSelectorInBackground:#selector(doCalc)
withObject:nil];
From that doCalc method you would call back to the main thread with the result.
[self performSelectorOnMainThread:#selector(didCalcValue:)
withObject:result
waitUntilDone:NO];
As others have correctly pointed out, viewDidAppear let's you know when the view has appeared on screen. *Also, don't forget to call super when you use these event methods.
Example:
// Tells the view controller that its view was added to the view hierarchy.
- (void)viewDidAppear:(BOOL)animated
{
// makes sure it's also called on the superclass
// because your superclass may have it's own code
// needing to be called here
[super viewDidAppear:animated];
// do your calculations here
}
Commonly used UIViewController events:
– (void)viewDidLoad
Called when your view first loads in memory.
– (void)viewDidAppear:
Called after your view has appeared on screen.
– (void)viewWillDisappear:
Called before your view will disappear from the screen.
See the full list on the UIViewController Class Reference page.
I'm stuck! I can't see why viewWillAppear doesn't run in my code but viewDidLoad runs. If I understand it correctly viewDidLoad runs once on the first instance and viewWillAppear runs every time a view is added to the stack of views to display.
I see others have had this issue but some how their solutions of calling viewWillAppear directly causes my app to crash. Other solutions were related to Navigation Controller and pushingView's but thats not what i'm using either! What am I missing?
Thanks in advance for your help! :)
See below:
View Controller #1 - Currently being displayed on screen
-(IBAction)someButtonPressed:(id)sender{
NSLog(#"FirstViewController - someButtonPressed");
SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:#"SecondViewController" bundle:nil];
secondViewController.myLocation = self.myLocation;
secondViewController.myDatabase = self.myDatabase;
[self.view addSubview:secondViewController.view];
//[secondViewController viewWillAppear:YES];
}
SecondViewController:
- (void)viewWillAppear:(BOOL)animated {
NSLog(#"SecondViewController - viewWillAppear");
[super viewWillAppear:animated];
// updating ivars with data
}
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
NSLog(#"SecondViewController - viewDidLoad");
[super viewDidLoad];
}
If I understand it correctly viewDidLoad runs once on the first instance and viewWillAppear runs every time a view is added to the stack of views to display.
-viewDidLoad is called every time a UIViewController's view is loaded. That may be many times during a single controller's life as the view may be unloaded to free up memory when it is not visible and reloaded, triggering another call to -viewDidLoad, when needed.
-viewWillAppear: is called when a UIViewController's view becomes visible. However UIKit assumes that UIViewController's views will fill their window. Nesting UIViewControllers' views is an example of abusing UIViewControllers and will result in unexpected behavior. As you have seen.
See About Custom View Controllers in the View Controller Programming Guide for iOS:
Each custom view controller object you create is responsible for managing all of the views in a single view hierarchy. In iPhone applications, the views in a view hierarchy traditionally cover the entire screen, but in iPad applications they may cover only a portion of the screen. The one-to-one correspondence between a view controller and the views in its view hierarchy is the key design consideration. You should not use multiple custom view controllers to manage different portions of the same view hierarchy. Similarly, you should not use a single custom view controller object to manage multiple screens worth of content.
If you wrote a custom UIViewController Container you might have overwritten the following method, which leads to your described behavior.
- (BOOL)shouldAutomaticallyForwardAppearanceMethods{
return NO;
}
In this case you have to manually handle beginAppearanceTransition/endAppearanceTransition.
See Apples View Controller Containment article
viewWillAppear: is called when a view controller is displayed in one of the normal ways (e.g. by selecting a tab in a UITabBarController, by pushing onto a UINavigationController, by being popped back to in a UINavigationController, by being presented with presentModalViewController:animated, by being uncovered after dismissModalViewControllerAnimated:, etc). Just displaying a view with addSubview: does not call the method.
It is possible to correctly call viewWillAppear: manually, but in general it's better to use one of the normal ways mentioned above.
Just try this.. I got it working :)
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
NSLog(#"SecondViewController - viewWillAppear");
// updating ivars with data
}
When you push view or present a view controller by pushViewController:animated or presentModelViewController:animated:, they will call viewWillAppear:animated:, and else method for you. But if you addSubview: manually, you need to call those method by self.
I've got a weird problem with a TableViewController.
In the doc it says that a tableViewController deals also with the method
-flashScrollIndicators when the table is "oversized" respect the visible area.
My app consists in 3 nav controller loaded in a tab controller. Each nav controller has as root view controller a subclass of a table view controller.
Each "model" is populated from a plist file, that loads its contents into an array in the -viewDIdLoad, later everything is passed to the table. Everything is loaded programmatically no IB.
I've found out in my app that when it loads the first view (a nav controller with a table view controller as root) the scroll bar isn't flashing even if the number of cell it's great enough.
If I choose another tab, that loads another nav controller (with a t.v.c. as root) scroll bar isn't shown again. When I press the tab corresponding to the first nav controller loaded the scrollbar flashes.
So I've tried to make it flash programmatically but no way, the code seems simple:
[self.tableView flashScrollIndicators];
I've tried to put it almost everywhere. First in the -viewDidLoad (As suggested in the doc), then in viewDidAppear and in -viewWillAppear.
Also tried use that code tring to cast the view of the t.v.c. as a table view.
[((UITableView*)self.view) flashScrollIndicators];
..without result.
I've started looking at Apple sample and I've found that in Apple's table view custom sample (the one with different times) scroll bar doesn't flash also there.
Tested both on sim and device.
Is a bug?, is there a correct way to show it programmatically?
Can someone help me?
Regards,
Andrea
Or more concisely:
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
[self.tableView performSelector:#selector(flashScrollIndicators) withObject:nil afterDelay:0];
}
I had exactly the same problem. I got around it in the end by putting a delayed selector in the viewDidAppear: method. Weirdly, I can set it to 0 seconds and it still works fine.
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
[self performSelector:#selector(flashTableScrollIndicators) withObject:nil afterDelay:0.0];
}
- (void)flashTableScrollIndicators
{
[self.tableView flashScrollIndicators];
}
It is not displayed when you show section index titles.
- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView;
My solution was to send the "flashScrollIndicators()" message with a slight delay using "dispatch_after":
let delayTime = dispatch_time(DISPATCH_TIME_NOW, Int64(0.4 * Double(NSEC_PER_SEC)))
dispatch_after(delayTime, dispatch_get_main_queue(),
{ () -> Void in
myScrollView.flashScrollIndicators()
})
Going through many tutorials and with the help of everyone here, I am trying to wrap my head around using multi view controllers with their own xib files.
I have one example where there is a : multiViewController and two others: aboutViewController, rulesViewController.
In both aboutViewController.m and rulesViewController.m files, I have placed the following code:
- (void)viewDidLoad {
NSLog(#"rules View did load"); // (Or About View did load, depending on the .m file)
[super viewDidLoad];
}
The mainViewController.m file contains:
-(IBAction) loadRules:(id) sender {
[self clearView];
[self.view insertSubview:rulesViewController.view atIndex:0];
}
-(IBAction) loadAbout:(id) sender {
[self clearView];
[self.view insertSubview:aboutViewController.view atIndex:0];
}
My question is, why is it when I run the application does the ViewDidLoad for both About and Rules fire? Meaning, I get the NSLog messages. Does this mean that regardless of the separate xib files, all views are loaded on start up?
My point of all this is: I want the multiViewController to be my main menu which will have separate buttons for displaying the other xib files when clicked. I had been placing my "initalize" code in the viewDidLoad but this seems wrong now as I don't want to hit until the users presses the button to display that view.
An example was to have a view that is: playGameViewController. In the viewDidLoad I was checking to see if a prior game was in progress and if so, prompt the user if they would like to resume. In the above case, when the app starts, it prompts right away (because the viewDidLoad is firing) even though I only wanted to display the main menu first.
Any explanation is greatly appreciated. Thanks in advance.
Geo...
My question is, why is it when I run
the application does the ViewDidLoad
for both About and Rules fire?
Meaning, I get the NSLog messages.
Does this mean that regardless of the
separate xib files, all views are
loaded on start up?
When you call
[self.view insertSubview:rulesViewController.view atIndex:0];
it's going to first call viewDidLoad for the initial view and then viewDidLoad once again for RulesViewController.
When your MainViewController, or any view for that matter loads, viewDidLoad is called automatically. ViewDidLoad is there in order for you to override or modify any objects in the nib, or you can create objects yourself. Views are only loaded on an as needed basis. If you were to load all your views initially when the app boots up, the user would just see a black screen until all the views are processed.
You say you are going through some tutorials, I don't know your area of expertise yet, but have you looked into navigation based apps using UINavigationController?
Just an example as your request if you want to have a button load a view you can do something like.
- (IBAction)pushSecondView:(id)sender {
SecondViewController *secondView = [[SecondViewController alloc] initWithNibName:#"SecondViewController" bundle:nil];
if (secondView != nil) {
secondView.title = #"Second View";
[self.navigationController pushViewController: secondView animated: YES];
}
}
I'm trying to detect a shake on the iPhone device, so for what i've read I need to set my view controller as first responder on the viewDidAppear method. This method is supposed to be called automatically, but for some reason this method is never called. Only viewDidLoad is called.
this is my code (I put only the relevant parts):
BuildHouseViewController.h:
#interface BuildHouseViewController : UIViewController {
BuildHouseViewController.m:
- (void)viewDidLoad {
[super viewDidLoad];
[self.view becomeFirstResponder];}
-(void)viewDidAppear:(BOOL)animated{
[self becomeFirstResponder];
[super viewDidAppear:animated];}
-(BOOL)canBecomeFirstResponder {
return YES;}
- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event{
NSLog(#"shake");
if ( event.subtype == UIEventSubtypeMotionShake )
{ }
if ( [super respondsToSelector:#selector(motionEnded:withEvent:)] )
[super motionEnded:motion withEvent:event];
}
I added breakpoints on the viewDidAppear method and it is never called. Shakes are never detected, I suppose it is because as this methods are never called, so the view controller can never become first responder. I don't understand why this is happening.
Any help will be appreciated.
Edit:
I call the view from another view using:
[self.view addSubview:nextScreen.view];
The view is displayed on screen
Thanks for the quick answers.
I've found something interesting. I tried loading the same view I'm having problems with in different ways and I'm getting different results
-As I said before if I call it from another view using:
[self.view addSubview:nextScreen.view];
viewDidLoad is never called and I cannot detect shakes.
-Now if I call it from the AppDelegate using:
[window addSubview:nextScreen.view];
viewDidLoad is called!! and I am able to detect shakes, however this solution is not possible, I should be able to call it from another view
-If I call it from another view using:
[self presentModalViewController:nextScreen animated:YES];
viewDidLoad is called!! However I don't want to use a modal view controller, but it appears to be the only solution to my problem, shakes are detected.
It is strange that the first method doesn't load the view correctly, is it a bug??
The [self becomeFirstResponder] and the like don't actually make that become the first responder. The method gets called when the view is going to become the first responder. So that's not doing what you think it is.
Secondly, the viewDidAppear will only be called when the view, well, did appear. Is it showing up on the screen? Where are you telling it to be displayed? You need to either add the view controller's view as a subview of another view, or pushed onto a navigation controller stack, or pushed as a modal view.
viewDidAppear:(BOOL)animated only gets called when the view is shown by UINavigationController or UITabBarController. If you add a view controller's view to a subview (such as a scrollview or what have you), it won't get called. You would think it would but you'd be wrong. Just got bit by this myself.
Further to #Genericrich's comments, you can manually call viewDidAppear after you put the subview in yourself.
[self.view addSubview:theViewController.view];
[theViewController viewDidAppear:FALSE];
This worked for me. Hope it helps someone else.