In my UIViewController I have a UINavigationController with a default back button. When the user clicks the back button, a warning message should appear: "Do you really want to go back?". I know, that it is not possible to trap the back button event. It's only possible the use viewWillDisappear and set a flag:
- (void)viewWillDisappear:(BOOL)animated {
if (backBtnPressed) {
UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:#"Question" message:#"Do you really want to go back?" delegate:self cancelButtonTitle:#"No" otherButtonTitles: #"Yes", nil] autorelease];
[alert show];
}
}
- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex {
if (buttonIndex == 0) {
// don't go back!
// cancel the back button event
}
else if (buttonIndex == 1) {
// go back
}
}
But with this code I have no chance! I can't stop the back button event, isn't it?
Do I have to write my own back button and set it as leftBarButtonItem? Or is there anybody with a great idea? :-)
Thanks for your help!
My answer from another thread matches this question. So I repost it here:
I've implemented UIViewController-BackButtonHandler extension. It does not need to subclass anything, just put it into your project and override navigationShouldPopOnBackButton method in UIViewController class:
-(BOOL) navigationShouldPopOnBackButton {
if(needsShowConfirmation) {
// Show confirmation alert
// ...
return NO; // Ignore 'Back' button this time
}
return YES; // Process 'Back' button click and Pop view controller
}
Download sample app.
What you need to do is to use the delegate of the navigation bar, and not the navigation controller.
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPushItem:(UINavigationItem *)item; // called to push. return NO not to.
- (void)navigationBar:(UINavigationBar *)navigationBar didPushItem:(UINavigationItem *)item; // called at end of animation of push or immediately if not animated
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item; // same as push methods
- (void)navigationBar:(UINavigationBar *)navigationBar didPopItem:(UINavigationItem *)item;
viewWillDisappear is a delegate method for the event that the view is going to disappear - and there's nothing the developer can do about that! If you could, it would be a viewShouldDisappear delegate method.
So I guess the only way is as you suggest, to use a custom leftBarButtonItem.
I must say this is one of the common use cases that Apple doesn't seem to make easy, and I see a lot of effort trying to get this working. I thought maybe I should summarize my findings here.
As many have pointed out, the method below in UINavigationBarDelegate is key to implementing this feature.
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item;
Many have subclassed UINavigationController and implemented the method above to make it easy to use without direct access to the UINavigationBar.
Unfortunately, there still remain some issues.
The swipe back gesture does not invoke this method.
Although it seems necessary, crashes are reported calling popViewControllerAnimated: in this method.
The Back button remains grayed out, when pop is cancelled.
Swipe back gesture
We need to intercept the gesture by setting the delegate as is done in https://stackoverflow.com/a/23173035/2400328 .
If the UINavigationController is subclassed, that would be:
self.interactivePopGestureRecognizer.delegate = self
and implementing:
- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
Take care in when you modify the delegate property, as it gets modified after the initializer is called.
Not calling popViewControllerAnimated:
Although undocumented, calling popViewControllerAnimated: can be avoided as in https://stackoverflow.com/a/26084150/2400328.
It involves calling navigationBar:shouldPopItem: of UINavigationController (from the subclass).
The Back button
Although this may be a minor detail (especially, if you have designed your own Back button), there is a simple solution (written by me :) https://stackoverflow.com/a/29440633/2400328
You only need to set a property YES and NO.
auto item = navigationBar.topItem;
item.hidesBackButton = YES;
item.hidesBackButton = NO;
You can use a custom button with a graphics, which looks exactly like "Back" button and create a custom leftBarButtonItem view as UIButton with this graphics. Add target self to your button with custom back: selector and pop your alert there. If the user presses "yes" to quit dismiss this view controller, if not - do nothing. The trick here is the button which looks exactly as navigation bar's back button.
Its better if u make your own back button and make it the left button of the Navigation controller. That can definitely help u to perform any action
If you're looking for a way to do this in Swift on iOS 10, you can create a custom UINavigationController and then a UINavigationBarDelegate extension:
class MyNavigationController : UINavigationController {
}
extension MyNavigationController : UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
return false
}
}
The Method
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item;
is doing what you want. Unfortunately we are not supposed to delegate UINavigationBar to our own objects :(
The Apple Documentation states :
... In addition, a navigation controller object automatically assigns itself as the delegate of its UINavigationBar object and prevents other objects from changing that relationship. ...
One/The? way to do what you want is to put in your own back-button.
In that Method you do your tests and call
[self.navigationController popViewControllerAnimated:true];
if the user is allowed to go back.
Related
I have an educational app working fine with tab bars. One of the tabs is a test for the user. If a user taking the test selects another tab, I would like an action sheet to display to confirm they really want to exit the test since their test results will be lost.
I can't get the action sheet to display. I am getting syntax errors with the first three examples below. The 4th example will compile OK but the app aborts. I can't figure out what should go after the self. Or possibly one of the other examples would work if I had the syntax correct.
- (void)tabBarController:(UITabBarController *)tabBarController
didSelectViewController:(UIViewController *)viewController {
NSLog(#"Tab Bar Controller reached");
UIActionSheet *actionSheet = [[UIActionSheet alloc]
initWithTitle:#"This will end the test.
Are you sure you want to leave?"
delegate:self
cancelButtonTitle:#"Cancel"
destructiveButtonTitle:#"Yes,
cancel the test."
otherButtonTitles:nil];
[actionSheet showInView:self.view];
[actionSheet showInView:elements1AppDelegate.window];
[actionSheet showFromTabBar:self.tabBarController.tabBar];
[actionSheet showFromTabBar:self];
Ultimately, once I get the action sheet to display, I will either proceed to the tab selected or stay in the test view depending on whether the user decides to exit or not. Any help/suggestions would be appreciated. Thanks.
The name of the method tabBarController:didSelectViewController: should indicate that it's too late to stop the selection. Its return type void indicates there is not much you can do about it. Instead focus on method names that have "will" or "should" in them, and return types like BOOLs such as tabBarController:shouldSelectViewController:. So here is some basic code that does what you want.
I don't know the actual classname of your test's view controller so I'll use QuizController as a classname. QuizController is a UIViewController subclass.
QuizController.m
#interface QuizController () <UITabBarControllerDelegate,UIActionSheetDelegate>{
BOOL _testInProgress;
}
#end
#implementation QuizController
-(void)viewDidAppear:(BOOL)animated{
[super viewDidAppear:animated];
// When a tabs view controller is presented viewDidAppear: will be called so here we will set this view controller as the tabBarController delegate so we get the callback.
self.tabBarController.delegate = self;
}
-(void)startQuiz{
_testInProgress = YES;
// Begin testing code
}
-(void)stopQuiz{
// Score test record results
_testInProgress = NO;
}
-(void)cancelQuiz{
// Throw out results
_testInProgress = NO;
}
-(BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController{
if (!_testInProgress) return YES;
// If trying to select this controller then who cares?
if (viewController == self) return YES; // Or NO. Just don't show the sheet.
UIActionSheet *action = [[UIActionSheet alloc] initWithTitle:#"You are in the middle of a test. Are you sure you want to switch tabs?"
delegate:self
cancelButtonTitle:#"Continue Test"
destructiveButtonTitle:#"Abort Test"
otherButtonTitles:nil];
// Lets cheat and use the tag to store the index of the desired view controller.
action.tag = [self.tabBarController.viewControllers indexOfObject:viewController];
[action showFromTabBar:self.tabBarController.tabBar];
return NO;
}
-(void)actionSheet:(UIActionSheet *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex{
if (buttonIndex == actionSheet.destructiveButtonIndex){
[self cancelQuiz];
// The above cheat pays off.
[self.tabBarController setSelectedIndex:actionSheet.tag];
}
}
EDIT (In response to comment quoted)
I'm a little confused about your example. Currently, my "take test"
class is a UIViewController. Are you suggesting I replace that with
your QuizController above?
No. I am suggesting that you take this code and integrate the design pattern into your UIViewController subclass that handles your test. Although this is a working example (providing you supply UI to toggle the _testInProgress ivar.)
Do I leave my current UITabBarController in place?
Yup.
That is currently my appdelegate and rootController.
Huh? Your UITabBarController is almost certainly your rootViewController. But unless you have done something very odd like AppDelegate : UITabBarController <UIApplicationDelegate>, by the way don't do that, then it is extremely unlikely that your "appdelegate" and your UITabBarController are the same. Much more likely your AppDelegate is your tabBarController's delegate.
If just setting the tabBarController.delegate property on appearance is bad (and it could very well be), i.e. some other object needs to be the tabBarController's delegate, then you'll have to forward a message to that view controller to see if a test is in progress. For this you could actually leave almost all of the code in the example unchanged. Of course you would have to remove the self.tabBarController.delegate = self; in viewDidAppear:. And put the following in your AppDelegate(presuming that's the tabBarController's delegate):
-(BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController{
if ([tabBarController.selectedViewController respondsToSelector:#selector(tabBarController:shouldSelectViewController:)]){
return [(NSObject <UITabBarControllerDelegate>*)tabBarController.selectedViewController tabBarController:tabBarController shouldSelectViewController:viewController];
}
return YES;
}
This implementation essentially forwards the responsibility to answer the question to the view controller, provided it will answer the question.
I check in there if the "take test" tab was selected and call an
initialization method in my "take test" class.
In my opinion the "take test" view controller should simply become selected when the user taps the tab for it. And its view should contain a button with something to the effect of 'start test' on it. But that's just my opinion.
But whatever the case is the application's knowledge of whether the user is taking a test should reside in the view controller that administers the test.
[actionSheet showInView:[[[UIApplication sharedApplication] windows] objectAtIndex:0]];
Did you try this One Link
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 create custom login page by using UIAlerView subclass. Now when i click on button it opens up UIAlertView I want to change the main view based on which button is pressed.
But as all implementation of UIAlerView is in another class though i change the view it doesn't retain that as that class variable doesn't get it's value.
Can anyone please help me with this? I can post the code if required.
Thank you,
Ankita
You can use a custom init method like below for alertView and store the _sender in global or class variable. like
id sender;
- (id)initWithSender:(id)_sender
{
self = [super init];
if (self) {
sender=_sender;
}
return self;
}
from RootVC/bgview initialize alertView as follows and define a method named
-(void) alertIndexSelected:(NSInterger) index;
{
//change the backgound view based on button selected
}
in rootvc/your main view.
alertViewobj =[[alertView alloc] initWithSender:self];
when the button is selected on alertview call the below method, this will notify your rootvc about which index of alert is pressed. use following alertview delegate.
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
[sender alertIndexSelected: buttonIndex];
}
If you are planning to use delegate methods then I think you need to referrer to some of these links.
How to use custom delegates in Objective-C
How do I create delegates in Objective-C?
http://iosdevelopertips.com/objective-c/the-basics-of-protocols-and-delegates.html
I hope this will help you a great deal in understanding delegates.
I have one delegate file, one View Controller and one UIPopoverController
My PopoverController is defined in delegate file.
when I click on the view controller's button, the popover is shown.
The view controller also contains one method named "refreshviewnow".
When I click on the PopoverController "submit button", I want to call that refreshviewnow function.
What should I have to write on submit button event ?
You need to make sure and set the delegate property of the PopoverController to the View Controller. Then in the "submit button" you can invoke the method on the delegate.
- (void) submit {
[delegate refreshAction];
}
Good Luck.
I am not sure what you mean by "submit button" (maybe you should post some of the code you are using), but if you are trying to call a method that is in the same controller, you would do it like this:
- (void) methodToDisplayPopover
{
[self refreshViewNow];
}
EDIT:
MySecondView *second = [[MySecondView alloc] init];
[second refreshViewNow];
[second release];
I got the answer now.
add observer in View Controller file for method refreshviewnow.
post the notification when popover is going to dismiss.
I have a button inside the content of a UIPopoverController. This button runs a method called myAction.
MyAction has the form
- (void) myAction:(id)sender
so, myAction receives the id of the caller button.
Now, inside this method I would like to dismiss the UIPopoverController, but the only thing I have is the ID of the caller button. Remember that the button is inside the UIPopoverController.
Is there a way to discover the ID of the UIPopoverController, given the button ID I already have?
thanks.
Unfortunately no. At least, not within the standard practices. You might be able to travel up the responder stack to find it, but it's a hack, it's buggy, and it's really, really messy.
If you want to dismiss a popover by pushing a button, some place relevant should keep a reference to the popover. Usually that would be the owner of the popover (not the controller showed within the popover). When the button is pressed, it can send a message to the owner controller, which can then dismiss the popover.
You might be tempted to have the controller displayed inside of the popover be the owner of its own popover, but coding this way is brittle, can get messy (again), and may result in retain loops so that neither ever gets released.
You can access the presenting popoverController by accessing "popoverController" with KVC.
[[self valueForKey:#"popoverController"] dismissPopoverAnimated:YES]
I have this working, and I do not think it is a hack. I have a standard split view iPad app. I then added a method on my detail controller (the owner of the pop over) to handle the dismissal.
On the standard split view architechture, both the root and detail view controllers are available via the app delegate. So I bound a button click inside the pop over to call a method which gets the app delegate. From there I call the method on the detail controller to dismiss the pop over.
This is the code for the method on the View Controller that is displayed inside the popover:
- (void) exitView: (id)sender {
MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
[appDelegate.detailViewController exitDrill];
}
Then the simple method to dismiss on the Detail View Controller:
- (void) exitDrill {
if(dtController != nil){
[dtController dismissPopoverAnimated: YES];
[dtController release];
}
}
I like the ability to do this because it give me a way to show a user how they can exit a pop over. This may not be necessary in future versions of the app; for right now, while this paradigm is still new to the platform, I prefer to let the users gexit a display in a couple fo different ways to make sure I minimize frustration.
As Ed Marty already wrote
If you want to dismiss a popover by pushing a button, some place relevant should keep a reference to the popover
This is very true; however, when showing a UIPopoverController, the class opening the popovercontroller keeps this resource already. So, what you could do is to use this class as the delegate class for your Popover Controller.
To do so, you could do the following, which I use in my code.
In the class opening the popover, this is my code:
- (void)showInformationForView:(Booking*)booking frame:(CGRect)rect
{
BookingDetailsViewController *bookingView = [[BookingDetailsViewController alloc] initWithStyle:UITableViewStyleGrouped booking:booking];
[bookingView setDelegate:self];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:bookingView];
self.popController = [[UIPopoverController alloc] initWithContentViewController:navController];
[self.popController setDelegate:self];
[self.popController setPopoverContentSize:CGSizeMake(320, 320)];
rect.size.width = 0;
[self.popController presentPopoverFromRect:rect inView:self.view permittedArrowDirections:UIPopoverArrowDirectionLeft animated:YES];
}
- (void)dismissPopoverAnimated:(BOOL)animated
{
[self.popController dismissPopoverAnimated:animated];
}
So what I am doing here is creating a UINavigationController and setting a BookingDetailsViewController as its rootViewController. Then I am also adding the current class as delegate to this BookingDetailsViewController.
The second thing I added is a dismissal method called dismissPopoverAnimated:animated.
In my BookingDetailsViewController.h I added the following code:
[...]
#property (nonatomic, strong) id delegate;
[...]
And in my BookingDetailsViewController.m I added this code:
[...]
#synthesize delegate = _delegate;
- (void)viewDidLoad
{
UIBarButtonItem *closeButton = [[UIBarButtonItem alloc] initWithTitle:#"Close" style:UIBarButtonItemStylePlain target:self action:#selector(closeView)];
[self.navigationItem setRightBarButtonItem:closeButton];
[super viewDidLoad];
}
- (void)closeView
{
if ([self.delegate respondsToSelector:#selector(dismissPopoverAnimated:)]) {
[self.delegate dismissPopoverAnimated:YES];
}
else {
NSLog(#"Cannot close the view, nu such dismiss method");
}
}
[...]
What happens is that when the "Close" button in the UINavigationController is pressed, the method closeView is called. This method check if the delegate responds to dismissPopoverAnimated:animated and if so, it calls it. If it does not respond to this method it will show a log message and do nothing more (so it wont crash).
I have written my code using ARC, hence there is no memory management.
I hope this helped you.