I've done this delegation pattern a million times. On the million and one-th time I'm getting a nil delegate:
CatViewController *vc = [[UIStoryboard storyboardWithName:#"Cat" bundle:nil] instantiateInitialViewController];
vc.delegate = self;
[self presentViewController:vc animated:YES completion:^{
DDLogWarn(#"[%# %#] delegate: %#", THIS_FILE, THIS_METHOD, vc.delegate); //here the delegate is valid
}];
#protocol CatViewControllerDelegate;
#interface CatViewController : UIViewController
#property (weak, nonatomic) id <CatViewControllerDelegate> delegate;
#end
#protocol CatViewControllerDelegate <NSObject>
#required
- (void)catViewController:(CatViewController*)catVC didFinishWithSuccess:(BOOL)success;
#end
However, in viewDidLoad of CatViewController, self.delegate is already nil, and of course is nil when I try to do this:
[self.delegate catViewController:self didFinishWithSuccess:YES];
Why is the catViewController's delegate becoming nil?
The problem was that the CatViewController was embedded in a Navigation Controller in the Storyboard. Therefore instantiateInitialViewController was not returning a CatViewController, although everything appeared fine on screen. The fix:
UINavigationController *navVC = [[UIStoryboard storyboardWithName:#"Cat" bundle:nil] instantiateInitialViewController];
CatViewController *catVC = navVC.viewControllers[0];
catVC.delegate = self;
You have:
vc.delegate = self;
Whatever self is, it is being deleted by the time your new view controller's viewDidLoad gets called. To test this theory, put a dealloc method in that class and put a breakpoint in it.
Did you try to declare the delegate like this instead?
#property (unsafe_unretained, nonatomic) id <CatViewControllerDelegate> delegate;
Related
My first view in the viewDidLoad has the following code
UIStoryboard *sb = [UIStoryboard storyboardWithName:#"Dialpad" bundle:nil];
self.vc = [sb instantiateViewControllerWithIdentifier:#"DialpadBoard"];
self.vc.delegate = self;
The header file contains the definition of the view controller
#property (nonatomic, retain) DialpadTableViewController *vc;
after catching an event the view loads a new modal view
- (void)handleEvent:(UIGestureRecognizer*)recognizer {
[self presentViewController:self.vc animated:YES completion:NULL];
}
The view also contains the method to dismiss the modal view:
- (void) dialpadControllerDidCancel:(SearchDialpadTableViewController *)controller {
[self dismissViewControllerAnimated:YES completion:nil];
}
The last method never gets called.
The problem is that the modal view when it is loaded has nil self.delegate. The new modal view is loaded from the storyboard as seen below. Why the delegate is nil? I cannot how a segue since the view is in another storyboard.
you can try this
UIStoryboard *sb = [UIStoryboard storyboardWithName:#"Dialpad" bundle:nil];
UINavigationController *nav= [sb instantiateViewControllerWithIdentifier:#"DialpadBoard"];
((SearchDialpadTableViewController *)[nav viewControllers][0]).delegate = self;
[self presentViewController:nav animated:YES completion:NULL];
Since we have the nav let's take the first controller and assign the delegate
the trick ;)
((SearchDialpadTableViewController *)[nav viewControllers][0]).delegate = self;
Does SearchDialpadTableViewController define a delegate protocol and does it have a property that is specific to that protocol?
The header for that file should look something like:
#protocol ViewControllerDelegateProtocol <NSObject>
- (void)dialpadControllerDidCancel:(SearchDialpadTableViewController *)controller;
#end
#interface ViewController : UIViewController
#property (weak, nonatomic) id<ViewControllerDelegateProtocol> searchPadDelegate;
#end
Then when the user taps Done which is I'm assuming what you're trying to do (send a delegate message when that happens). You would write something like
- (IBAction)donePressed:(id)sender
{
if ([self.searchPadDelegate respondsToSelector:#selector(dialpadControllerDidCancel)]) {
[self.searchPadDelegate dialpadControllerDidCancel:self];
}
}
you must be certain, that self.vc is a class, that you expected. It can be also NavigationController
line presentViewController crash app
#interface VVPassbook : NSObject
#property (nonatomic, retain) id delegate;
-(void)gotPassbookFromUrl:(NSURL *)passbookUrl;
#end
#import "VVPassbook.h"
#implementation VVPassbook
-(void)gotPassbookFromUrl:(NSURL *)passbookUrl
{
//present view controller to add the pass to the library
PKAddPassesViewController *vc = [[PKAddPassesViewController alloc] initWithPass:pass];
[vc setDelegate:(id)self.delegate];
[self.delegate presentViewController:vc animated:YES completion:nil];
}
#end
im call this method in AppDelegate.m in method
- (void)application:(UIApplication*)application didReceiveRemoteNotification:
(NSDictionary*)userInfo
{
VVPassbook *pass = [[VVPassbook alloc] init];
pass.delegate = self.window.rootViewController;
[pass gotPassbookFromUrl:MYURL ];
}
all times error
reason: 'Application tried to present a nil modal view controller on target <VVRightManuViewController: 0x15dd28460>.'
you should present a viewController from a UIViewController, i.e., self
(if self is a viewcontroller).
Note that you will get a "Attempt to present on whose view is not in the window hierarchy"-warning when self (this viewcontroller) is detached from the Main Window.
Solution: always use addChildViewController: to child viewcontrollers.
Why are you using self.delegate to push the view Controller,
simple write
[self presentViewController:vc animated:YES completion:nil];
in the place of
[self.delegate presentViewController:vc animated:YES completion:nil];
Just when I thought I had my head around how delegates work, it seems I am missing something.
I've setup a delegate like so:
ViewControllerA.h
#protocol LoginDelegate <NSObject>
-(void)userLoginSuccessful;
#end
#interface BBLoginViewController : BBBaseViewController
#property (weak, nonatomic) id <LoginDelegate> delegate;
#end
ViewControllerA.m
-(void)someMethod
{
if ([self.delegate respondsToSelector:#selector(userLoginSuccessful)]){
[self.delegate userLoginSuccessful];
}
[self dismissViewControllerAnimated:YES completion:nil];
}
ViewControllerB.m
#import "ViewControllerA.h"
#interface ViewControllerB () <UITableViewDataSource, UITableViewDelegate, LoginDelegate>
-(void)viewWillAppear:(BOOL)animated
{
ViewControllerA *loginViewController = [[ViewControllerA alloc]init];
loginViewController.delegate = self;
}
#pragma mark - Login Delegate
-(void) userLoginSuccessful
{
NSLog (#"Delegate fired!");
}
After all this my delegate method does not fire. What am I doing wrong? I looked at this SO answer and when checking the delegate is not nil - it is not. Its set to ViewControllerB.
This code:
-(void)viewWillAppear:(BOOL)animated
{
ViewControllerA *loginViewController = [[ViewControllerA alloc]init];
loginViewController.delegate = self;
}
Will create a ViewControllerA object and then (almost) immediately destroy it and is not what you intended.
You probably want to be setting the delegate in the prepareForSegue: method anyway...
Set the delgate before presenting ViewControllerB. The below code is not required anymore
-(void)viewWillAppear:(BOOL)animated
{
ViewControllerA *loginViewController = [[ViewControllerA alloc]init];
loginViewController.delegate = self;
}
Dont do like that. It will give you unexpected results. Remember always set the delegate before moving to the next view. If you are presenting modally just before presentViewController of if you are using segue in prepareForSegue
I've got a view in a xib file that I load to my viewController - its a temp view and thus isn't on screen all the time. However the temp view and the main view, use the same view controller class as they both are doing the same job.
Now, in the xib view I load up a second viewControoler - lets call it viewControllerB - which is a UITableView with 197 cells. Once a cell is selected, the view is dismissed and the value of the cell is returned to viewControllerA.
viewControllerB is on the storyboard.
Here is the code I have used:
viewControllerB (The VC I need data back from)
Delegate Protocol:
#protocol CountrySelectedDelegate <NSObject>
-(void)selectedCountry: (id)countryReturned;
#end
#property (strong, nonatomic) id <CountrySelectedDelegate> myDelegate;
Then in the .m file:
Set the delegate:
ViewControllerA *viewA = [[ViewControllerA alloc]init];
self.myDelegate = viewA;
Then I call the delegate in the same file;
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
[[self myDelegate] selectedCountry:indexPath.row];
[self dismissViewControllerAnimated:YES completion:nil];
}
Now in viewControllerA:
pragma mark - CountrySelected Delegate
-(void)selectedCountry:(id)countryReturned
{
self.testInt = countryReturned;
}
Now this method does get called by the delegate. Looking in the console: countryReturned is the correct value. Once this method has finished, self.testInt is also the correct value.
Then, in my viewWillAppear method, I simply check the value again to see if its still the same with a NSLog print.
the value is always nil in the viewWillAppear method (Or anywhere else I check it) - I have tried with NSMutableString and NSString - always nil.
Why are my properties / instance variables getting set to nil?
Update:
This is how I show viewControllerB
- (IBAction)countrySelect:(UIButton *)sender
{
UIStoryboard *sb = [UIStoryboard storyboardWithName:#"Main_iPhone" bundle:nil];
UITableViewController *vc = [sb instantiateViewControllerWithIdentifier:#"CountrySelection"];
vc.modalTransitionStyle = UINavigationControllerOperationPop;
[self presentViewController:vc animated:YES completion:NULL];
}
On ViewB do the below I guess you have already done
#protocol CountrySelectedDelegate <NSObject>
-(void)selectedCountry: (NSInteger)countryReturned;
#end
#property (week, nonatomic) id <CountrySelectedDelegate> myDelegate;
and in didSelectRowAtIndexPath
if ([[self myDelegate] respondsToSelector:#selector(selectedCountry:)])
{
[[self myDelegate] selectedCountry:indexPath.row];
}
On ViewA
Conform the protocol
#interface ViewA : UIViewController < CountrySelectedDelegate >
create the call ViewB
ViewB *viewBObjc=[[ViewB alloc] init];
[viewBObjc setMyDelegate:self];
[[self navigationController] presentViewController:ViewB animated:YES completion:Nil];
implement the delegate on ViewA
-(void)selectedCountry: (NSInteger)countryReturned
{
NSLog(#"Country Id is :%d", countryReturned);
}
Try this,
Set delegate by
//in ViewControllerB
self.myDelegate = [self parentViewController];
or
- (IBAction)countrySelect:(UIButton *)sender
{
UIStoryboard *sb = [UIStoryboard storyboardWithName:#"Main_iPhone" bundle:nil];
ViewControllerB *vc = (ViewControllerB *)[sb instantiateViewControllerWithIdentifier:#"CountrySelection"];
vc.modalTransitionStyle = UINavigationControllerOperationPop;
vc. myDelegate = self;
[self presentViewController:vc animated:YES completion:NULL];
}
I'm fairly new to Objective-C, programming. The one thing, I'm currently putting up with is passing a value from the first ViewController to the next one.
I've read this entry here and it didn't help me. Which is funny, since his answer has nearly 500 votes, so I must be the problem. What I did was the following.
I opened my PreviewViewController.m and added the following line #import "MainViewController.h" since I wanted to pass a value from the PreviewViewController to the `MainViewController. Then, when I switch the layouts ( which successfully works ) I want to pass a value.
MainViewController *mainViewController = [[MainViewController alloc] initWithNibName:#"MainViewController" bundle:nil];
mainViewController.userId = #"539897197";
As you can see, I want to pass the userId. For that, I also created a property in the MainViewController.h
#property ( nonatomic, strong ) NSString *userId;
Now, In my MainViewController.m I want to access the userId. But when I log it, the console tells me it is null. However, when I set the variable right before the NSLog it works, so it seems like the passing is the problem.
Additionally in the MainViewController.m I have the following line
#synthesize userId = _userId;
but even when I removed that line and changed the NSLog to NSLog(#"%#",self.userId); the same problem occurred.
How can I successfully pass the variables? Which step am I doing wrong?
EDIT
This is how I switch the layouts
UIViewController *viewController = [[MainViewController alloc]init];
MainViewController *mainViewController = [[MainViewController alloc] initWithNibName:#"MainViewController" bundle:nil];
mainViewController.userId = #"539897197";
[self presentViewController:viewController animated:YES completion:NULL];
Why not create a custom initializer and pass it in that way? Something like
- (id)initWithUserId:(NSString *)aUserId {
self = [super initWithNibName:#"MainViewController" bundle:nil];
if (self) {
self.userId = aUserId
}
return self;
}
Then you can just do:
MainViewController *mvc = [[MainViewController alloc] initWithUserId:#"1234"]
[self presentViewController:mvc animated:YES completion:nil];
If you are using storyboard then you should use prepareForSegue: method to pass data between view controllers. First Create the segue from your PreviewViewController to MainViewController, just control drag from your view controller to next viewcontroller to create segue. Use UINavigationController if you are using push segue. Use this method to segue and pass data
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if([segue.identifier isEqualToString:#"yourSegueIndentifier"]){
MainViewController *mvc = (MainViewController *) segue.destinationViewController;
mvc.userId = #"539897197";;
}
}
UIViewController *viewController = [[MainViewController alloc]init];
MainViewController *mainViewController = [[MainViewController alloc] initWithNibName:#"MainViewController" bundle:nil];
mainViewController.userId = #"539897197";
[self presentViewController:mainViewController animated:YES completion:NULL];
use mainViewController rather than viewController when presenting the view controller
Here we have two ways for passing data.
First is Custom Delegate
Second is NSNotification
Here we have two view controllers.
ViewController
and
SecondViewController
in SecondViewController
.h
#import <UIKit/UIKit.h>
#class SecondViewController;
#protocol SecondViewControllerDelegate <NSObject>
- (void)secondViewController:(SecondViewController *)secondViewController didEnterText:(NSString *)text;
#end
#interface SecondViewController : UIViewController
#property (nonatomic, assign)id<SecondViewControllerDelegate> delegate;
#property (nonatomic, strong) IBOutlet UITextField *nameTextField;//It must connect as outlet connection
- (IBAction)doneButtonTapped:(id)sender;
#end
.m
#import "SecondViewController.h"
#interface SecondViewController ()
#end
#implementation SecondViewController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
}
//Either use NSNotification or Delegate
- (IBAction)doneButtonTapped:(id)sender;
{
//Use Notification
[[NSNotificationCenter defaultCenter] postNotificationName:#"passingDataFromSecondViewToFirstView" object:self.nameTextField.text];
//OR Custom Delegate
[self.delegate secondViewController:self didEnterText:self.nameTextField.text];
[self.navigationController popViewControllerAnimated:YES];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
in ViewController
.h
#import <UIKit/UIKit.h>
#import "SecondViewController.h"
#interface ViewController : UIViewController<SecondViewControllerDelegate>
#property (nonatomic, strong) IBOutlet UILabel *labelName; //You must connect the label with outlet connection
- (IBAction)gotoNextView:(id)sender;
#end
.m
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
//addObserver here...
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(textFromPreviousViewControllerNotificationReceived:) name:#"passingDataFromSecondViewToFirstView" object:nil];
// Do any additional setup after loading the view, typically from a nib.
}
//addObserver Method here....
- (void)textFromPreviousViewControllerNotificationReceived:(NSNotification *)notification
{
// set text to label...
NSString *string = [notification object];
self.labelName.text = string;
}
- (IBAction)gotoNextView:(id)sender;
{
//If you use storyboard
SecondViewController *secondViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
//OR If you use XIB
SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:#"SecondViewController" bundle:nil];
secondViewController.delegate = self;
[self.navigationController pushViewController:secondViewController animated:YES];
}
//Calling custom delegate method
- (void)secondViewController:(SecondViewController *)secondViewController didEnterText:(NSString *)text
{
self.labelName.text = text; //Getting the data and assign the data to label here.
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
For your understanding the code I create a simple passing data from one second view controller to first view controller.
First we navigate the view from first view controller to second view controller.
After that we send the data from second view controller to first view controller.
NOTE : You can either use NSNotification or Custom Delegate method for sending data from One View Controller to Other View Controller
If you use NSNotification, you need to set the postNotificationName for getting data in button action method.
Next you need to write addObserver in (sending data to your required View Controller) ViewController and call the addObserver method in same View Controller.
If you use custom delegate,
Usually we go with Custom Protocol Delegate and also we need to Assign the delegate here.
Very importantly we have to set the Custom Delegate Method in the Second View Controller.Because where we send the data to first view controller once we click the done button in second view controller.
Finally we must call the Custom Delegate Method in First View Controller, where we get the data and assign that data to label.Now you can see the passed data using custom delegate.
Likewise you can send the data to other view controller using Custom Delegate Methods
I tried and got the solution for passing the value between viewcontroller.
MainViewController *mainVC = [[self storyboard] instantiateViewControllerWithIdentifier:#"MainViewController"];
mainVC.userId = #"539897197";
[self presentViewController:mainVC animated:YES completion:Nil];
or using this way . You don`t use the storyboard use the following its working fine
MainViewController *mainVC = [[MainViewController alloc] init];
mainVC.userId = #"539897197";
[self presentViewController:mainVC animated:YES completion:Nil];