In an iOS app, how can I determine whether a back button is displayed? Ideally, I'd like to know this in my controller's loadView method.
Here's what I've tried in loadView, viewDidLoad, and viewWillAppear:
if (self.navigationItem.backBarButtonItem)
and this:
if (self.navigationItem.leftBarButtonItem)
Neither of those work - they're always nil (the expression evaluates to false), even when there is a back button on the screen. What I'd ultimately like to do is set a Cancel button as the self.navigationItem.leftBarButtonItem, but only if there's no back button. If there is a back button, we don't need the Cancel button. As it is, setting the leftBarButtonItem is overriding the back button, so we're seeing a Cancel button all the time - even when there should be a back button.
You're asking the wrong object for its backBarButtonItem. This property controls how an object is represented when it is the "back" item in the navigation stack.
Therefore, you need to be asking the view controller at the level below where you are in the navigation stack what its backBarButtonItem is:
int n = [self.navigationController.viewControllers count] - 2;
if (n >= 0)
if ([(UIViewController*)[self.navigationController.viewControllers objectAtIndex:n]navigationItem].backBarButtonItem == nil)
// Do your thing....
You may need to check if the navigation controller has added your viewController to the stack at the time you are executing this code, the top view controller may still be the previous one. I've checked in viewWillAppear and the stack does contain the new top controller at this point.
NSLog(#"%#",self.navigationController.navigationBar.backItem);
if (self.navigationController.navigationBar.backItem == NULL) {
UIBarButtonItem *cancelButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:#selector(addLaunch)];
self.navigationItem.leftBarButtonItem = cancelButton;
[cancelButton release];
}
this code works, its in the viewDidAppear, if your controller is null, theres no button, so i add the cancel button, its not a back item though, just a regular:] hope this helps
loadView is too early. The earliest you could check this is in viewDidLoad. You may need to wait for viewWillAppear.
Search for the following
self.navigationController.navigationBar.backItem
instead of backBarButtonItem.
If backItem exists then you are on navigation stack further than rootViewController.
Just use this code:
if (![[[self.parentViewController childViewControllers] firstObject] isKindOfClass:[self class]]) {
}
Related
When a view loads, i want to see if it's because the user pressed the back button. How can i check this?
The best solution I've found to detect a UINavigationController's back button press (pre-iOS 5.0) is by verifying that the current view controller is not present in the in the navigation controller's view controller stack.
It is possibly safer to check this condition in - (void)viewDidDisappear:(BOOL)animated as logically, by the time that method is called it would be extremely likely that the view controller was removed from the stack.
Pre-iOS 5.0:
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
if (![[self.navigationController viewControllers] containsObject:self]) {
// We were removed from the navigation controller's view controller stack
// thus, we can infer that the back button was pressed
}
}
iOS 5.0+ you can use -didMoveToParentViewController:
- (void)didMoveToParentViewController:(UIViewController *)parent
{
// parent is nil if this view controller was removed
}
in your viewWillDisappear method check
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
if ([self isMovingFromParentViewController]) {
//specific stuff for being popped off stack
}
}
This is only for post iOS 5
UINavigationController has a delegate property that issues delegate callbacks. Please see the iOS reference here.
The delegate doesn't have a "back button pressed" callback, but instead it tells you when something is going to appear on the navigation stack. When you press back, you are "popping" the top view controller off the stack, so it will tell you that the view is about to appear. I think this is the callback you'd be looking for.
You could have some simple logic to check if it's the view controller that's "interested", and then you could send a notification, et al.
For the sake of completeness, mix of two most upvoted answers (1, 2) in Swift:
override func willMoveToParentViewController(parent: UIViewController?) {
super.willMoveToParentViewController(parent)
if parent == nil {
// view controller is popping
}
}
This is a slightly different scenario, but I thought the solution might help others out.
In my situation, I had a UINavigationController within a UIPopoverController. I needed to detect whether the user clicked the back button, or clicked outside of the popover. To do this I checked the visibleViewController property in viewWillDisappear. If the view controller is still the visibleViewController when closing, then the popover is being closed by another means. If the view controller is not the visibleViewController when closing, then the back button was pressed.
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
if (self.navigationController.visibleViewController != self) {
<Do something since we're closing using something else>
} else {
<Do something since we're closing because of the back button>
}
}
I tried using zach's solution, but isMovingFromParentViewController returns true for both cases.
I verified this works in iOS 5+
I hope this helps.
Create a custom back bar button and set the target,
Step 1: Add these methods to your class
- (void)backButtonClicked :(id)sender{
[self.navigationController popViewControllerAnimated:YES];
}
- (void)addBackBarButton{
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(0, 0, 55, 35);
[button setTitle:#"back" forState:UIControlStateNormal];
[button addTarget:self action:#selector(backButtonClicked:) forControlEvents:UIControlEventTouchUpInside];
UIBarButtonItem *customBarItem = [[UIBarButtonItem alloc] initWithCustomView:button];
self.navigationItem.leftBarButtonItem = customBarItem;
}
Step 2: Call [self addBackBarButton]; in viewDiDLoad method
You will get the action in backButtonClicked method. You can play around with it the way you want.
Cheers!
The only way to do this so you know for sure that it was the back button is to create a custom button. If you don't know how to do that, check out this tutorial. It won't look exactly like the normal back button, but close. If you need more help, post a comment
I got a NavigationController(short for nv) and a ViewController(short for vc).
nv's RootViewController is vc.
My Goal
I just want to set the NavigationItem , I want the left bar button to be BACK button(customized).since this left button shared in all ViewControllers so I don't want to write the code in the ViewController , otherwise I have to write it many times. And I can't just subclass a ViewController, since I only need my customized left bar item in just a few ViewController.
So I try adding the generating button code in my nv , but i failed.
The result is , only the original vc got customized left bar button. other vc which is push on it all got the default one.
My Code
Here is my NavigationController's code:
- (void) viewWillAppear:(BOOL)animated{
[self createBackButton];
- (void) createBackButton{
UIViewController* vc = [self.viewControllers lastObject];
vc.navigationItem.leftBarButtonItem = nil;
vc.navigationItem.leftBarButtonItem =
[[UIBarButtonItem alloc]initWithTitle:#"Roll Back"
style:UIBarButtonItemStyleBordered
target:self
action:backButtonPressedSelector];
}
But if I put my createBackButton method in my ViewController , everything works just fine. But I also Have to write this method many times. Even the sentence like [self createBackButton]
it seems that viewWillAppear isn't a good time to call my createBackButtonMethod
My Question
In what order does the method below be called when I am pushing and hoping view controller , and where should I add my createBackButtonMethod in order to got some of the ViewController have the same left bar button without writing unnecessary code?
1、NavigationController's didload
2、NavigationController's willappear
3、ViewController(the one being pushed) 's didload
4、ViewController's willappear
Answer
The the method calling order is this:
1、vc's didload
2、nv's didload
3、nv's will appear
4、vc's will appear
and then when I continue to push vc, there are only
vc's didload and vc'didload being called repeatedly.
That's why I failed, because the nv's didload will only be called once here.
Instead of writing a common parent class, I think of the pretty solution below.
just do the adding things in the pushingViewController:method
So I override my pushViewController: method
- (void) pushViewController:(UIViewController *)viewController animated:(BOOL)animated{
viewController.navigationItem.leftBarButtonItem = nil;
viewController.navigationItem.leftBarButtonItem =
[[UIBarButtonItem alloc]initWithTitle:#"Roll Back"
style:UIBarButtonItemStyleBordered
target:self
action:backButtonPressedSelector];
}
try to make parent view controller and extend all your view controllers from it and add the needed code in there all the view controller will have it
hope i understand your question right and this answer help you with your problem good luck
--> Put all your code in viewcontroller's viewdidload or viewwillappear.
-->Viewdidload calls only once when you push the controller and viewwillappear will call every time in any case push, pop, present, dismiss etc.
--> First will call viewdidload and then will call view will appear.
I have storyboard of several view controllers embedded in Navigation Controller.
Due to navigation logic in later views of storyboard, the back button (in the left upper corner, in navigation bar) does not go back to the first view. I am wondering where and how to change this behaviour of Back button of second view only. Appreciate any ideas, examples.
Of course you could implement a custom back button. But there is also a nice way to keep using the default button.
Simply check if the current viewController is still in the navigation stack in viewWillDisappear before you call super.viewWillDisappear(). If it is not, the back button has been pressed. Then you can do the popToRootViewControllerAnimated.
override func viewWillDisappear(animated: Bool) {
if (navigationController?.viewControllers)!.contains(self) {
// back button was pressed
self.navigationController?.popToRootViewControllerAnimated(animated)
}
super.viewWillDisappear(animated)
}
The custom back button appears to be the best solution. The code inside your action method would look like the following in swift:
self.navigationController?.popToRootViewControllerAnimated(true)
//Just change the true to false if you don't want it animated.
I hope this helps (if you had not already found the answer). Cheers!
If you meant to say: Prevent Back Button Navigating to Previous Controller and move to first view controller:
You could do this by creating a custom back button - drag a button in storyboard to the top left of the navigation bar, and wire it up to your view controller. In your custom back button's selector write:
[self.navigationController popToRootViewControllerAnimated:YES]
Assuming you have a view controllers stack like : VC1 > VC2 > VC3, and you want to back to VC1 when tapping back on VC3, then you could set this code in VC2 :
[self.navigationItem setBackBarButtonItem:[[UIBarButtonItem alloc] initWithTitle:#"Back" style:(UIBarButtonItemStylePlain) target:self action:#selector(backToVC1)]];
Then, always in VC2 :
- (void)backToVC1
{
[self.navigationController popToRootViewControllerAnimated:YES];
}
I have a navigation controller that has a hidden navigation bar on the first view, and then appears for all children views. Problem is, I can't seem to hide it again if you go back to the first view.
I created a back button (so I could rename it) in the first view's init:
self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc]
initWithTitle:#"Logout" style:nil target:self
action:#selector(hideNavigationBar:)];
But the method never gets called. Why?
In your first controller, in -(void)viewWillAppear, say:
[self.navigationController setNavigationBarHidden:YES animated:NO];
What does this error indicate:
"Popovers cannot be presented from a view which does not have a window."
the thing that saved my life:
if (self.view.window != nil)
[popoverController presentPopoverFromRect:CGRectMake(44, yCoord, 111, 111) inView:self.view permittedArrowDirections:UIPopoverArrowDirectionUp animated:YES];
by adding if condition it doesn´t crash anymore. I don´t really get it because the presentPopoverFromRect function is ALWAYS called. There is no situation where window would be nil but anyway it did the trick.
edit: I have this code in viewDidAppear.
Nevertheless in most cases it's enough to move presentPopoverFromRect to viewDidAppear or didMoveToWindow but in my case for some reason the if condition was necessary.
the view you're adding the popover to has to already have been added to a window with the "addSubview:" method.
Try waiting until
- (void) didMoveToWindow
is called for the view and then load the popover
I got this problem.
I had a UITabBarController as the detail view, and I set the barButtonItem as the leftBarButtonItem on all three navigation controllers in the tab bar.
vcChart.navigationItem.leftBarButtonItem = barButtonItem;
vcAnalysis.navigationItem.leftBarButtonItem = barButtonItem;
vcTechnicals.navigationItem.leftBarButtonItem = barButtonItem;
Turns out only the last one added is valid, and the previous two would throw the exception when tapped on.
To fix it, I only set the leftBarButtonItem for the visible view controller, and just switched the barButtonItem to the visible view controller every time the user switched tabs.
Just encountered this issue. Turned out that the inView: parameter was using an IBOutlet that wasn't connected in IB. Thus, an attempt was made to launch the popover in nil. That doesn't work.
So, make sure you are using a valid view.
There are many ways to get to this error. Basically you need to wait to call the presentPopover command until your calling view is added to a window. I did it this way.
- (void)viewDidAppear:(BOOL)animated
{
[self methodThatDisplaysPopOver];
}
My presentPopoverFromRect call is inside my methodThatDisplaysPopOver function.
You could protect every presentPopover call like MobiMaciek suggests with this.
if (self.view.window != nil)
[popoverController presentPopoverFromRect:CGRectMake(10, 10, 100, 100) inView:self.view permittedArrowDirections:UIPopoverArrowDirectionUp animated:YES];
However, I think it would be better to understand when self.view.window gets assigned and make sure that you present you popover after the view has a window.
I received the same error message when assigning the same UIBarButtonItem to multiple navigation items as did Lewis. My example was slightly more complicated as I was using a UISplitViewController.
In my RootViewController I have an array of arrays to accomplish multiple sections within my table. Each time that the user clicks a row in the table, a new "detail" view controller is placed in the right pane of my splitViewController. Prior to setting the leftBarButtonItem = nil, I would receive a segfault after 3-4 clicks of the "Menu" button with the same error as a111. I updated my code to actually retrieve the previous detail view controller and set the leftBarButtonItem item to nil.
allData is my NSMutableArray that contains several other NSMutableArrays as objects.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// Retrieve the new detail view controller
UIViewController *detailViewController = [[self.allData objectAtIndex:indexPath.section] objectAtIndex:indexPath.row];
// Add the detail view controller to a navigation controller and set the bar style
UINavigationController *detailNavigationController = [[UINavigationController alloc] initWithRootViewController:detailViewController];
detailNavigationController.navigationBar.barStyle = [[NSUserDefaults standardUserDefaults] integerForKey:#"UIBarStyle"];
// Retrieve previous detail view controller and remove the leftBarButtonItem
UINavigationController *previousDetailNavigationController = [splitViewController.viewControllers objectAtIndex:1];
UIViewController *previousDetailViewController = [[previousDetailNavigationController viewControllers] lastObject];
previousDetailViewController.navigationItem.leftBarButtonItem = nil;
// Update the split view controller's view controllers array.
NSArray *viewControllers = [[NSArray alloc] initWithObjects:self.navigationController, detailNavigationController, nil];
splitViewController.viewControllers = viewControllers;
[detailNavigationController release];
[viewControllers release];
// Dismiss the popover if it's present.
if (popoverController != nil) {
[popoverController dismissPopoverAnimated:YES];
}
// This sets the left bar to nil when in landscape and equal to "Menu" when in portrait.
// We need to remove rootPopoverButtonItem from the previous viewController...
detailViewController.navigationItem.leftBarButtonItem = rootPopoverButtonItem;
}
The error message was slightly deceiving at first but the answers above helped me out. I wonder why I could click the "Menu" button up to 3-4 different times before the segfault... I'll investigate further.
This error also occurred when the inView: Parameter is incorrect - to test try self.view
yes, you are right but still we can add subview from parent class in it. so it can be represented from a view which have a window:
[popoverController.contentViewController.view addSubview:mySubView];
I had the same error message as the OP, in a very similar situation to that reported by TPoschel, except I had a split view controller with an embedded tab bar controller in the detail pane, and a navigation controller within this. The bar button item is added as the navigation bar leftBarButtonItem.
Only on iOS5.0 (not 5.1) does it seem to require you invalidate the bar button item on the tab bar you are leaving by setting it to nil. Before then adding the bar button to the navigation bar on the tab you are going to.
If I don't do that, from debugging my own code, the window property of the bar button item stays set to nil, and causes the exception, on returning to a screen you'd previously been to. I'm guessing as a side effect of setting the leftBarButtonItem in the navigation item, it goes off and sets the frame. But it doesn't seem to bother unless the button is different from what is currently set there. Hence, the need to set it to nil when leaving a tab, even though it is technically the same button that's being passed around.
I would upvote TPoschel's answer, except SO won't let me.
I had a problem like this. Received this message when clicking a customized UIBarButton item that invoked a selector method with did performSeque.
The problem was my segue was still attached to the UIBarButton item. It should have been attached to the main view of of the view controller. Changed this and worked fine.
P.S., all this got started because I wanted to add and "info" button to my UIToolBar. This isn't one in the system provided list and should be.
There will be a view from which you asks to display your popover.The reason for this error is because you didn't made this view as a subview of the window.
[self.view addSubview:displayPopOverVC];
where displayPopOverVC is the view controller from which the popOver appears
i had the same problem, after adding PresentPopOver in viewDidAppear this was solved
- (void) viewDidAppear:(BOOL)animated{
CGRect popoverRect = screenBounds;
popoverRect.size.width = MIN(popoverRect.size.width,0) ;
popoverRect.origin.x = screenBounds.origin.x;
[popoverController
presentPopoverFromRect:popoverRect
inView:self.view
permittedArrowDirections:UIPopoverArrowDirectionAny
animated:YES];
}
this was happening as inView:self.view should be called after viewDidLoad as suggested by #hey68You and MobiMaciek..
I replaced
[actionSheet showFromBarButtonItem:self.navigationController.navigationItem.leftBarButtonItem animated:YES];
with
[actionSheet showInView:self.view];