I'm trying to learn more about Objective C blocks and how they work. I've set up a simple project with two UIViewControllers embedded in a UINavigationController in Storyboard. I'm attempting to change the background color of the first ViewController's view from the second view controller. Here's some code:
ViewController.m
#implementation ViewController{
ColorBlock _colorBlock;
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if([segue.identifier isEqualToString:#"theSegue"]){
SecondViewController *vc = [self.storyboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
vc.colorBlock = _colorBlock;
}
}
- (IBAction)moveToSecondViewController:(id)sender {
__weak id weakSelf = self;
_colorBlock = ^{
[[weakSelf view] setBackgroundColor:[UIColor redColor]];
};
}
SecondViewController.h
typedef void (^ColorBlock)(void);
#interface SecondViewController : UIViewController
#property (readwrite, copy) ColorBlock colorBlock;
#end
SecondViewController.m
- (IBAction)buttonTapped:(id)sender {
if(self.colorBlock){
self.colorBlock();
}
}
The first ViewController's background color isn't being changed because in the buttonTapped: method of SecondViewController.m, self.colorBlock is nil, causing the block invocation not to be called. I thought I had successfully set the block in prepareForSegue:sender:. Why is my block property nil?
In your prepareForSegue, the destination has already been instantiated. So assuming that SecondViewController is the destination, you can do:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if([segue.identifier isEqualToString:#"theSegue"]){
SecondViewController *vc = segue.destinationViewController;
NSAssert([vc isKindOfClass:[SecondViewController class]], #"destination is not SecondViewController class");
vc.colorBlock = _colorBlock;
}
}
Related
Ok this really makes me headache. I have ViewController (using replace) that I assign its delegate property
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"spoSelectionDemoPlanSegue"])
{
SPOSelectionViewController * vc = [segue destinationViewController];
vc.delegate = self;
NSLog(#"spo segue %#", vc.delegate); //returns current ViewController
}
}
SPOSelectionViewController.h
#property (nonatomic, assign) id<SPOInputDelegate> delegate;
SPOSelectionViewController.m
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(#"delegate didload spo %#", delegate); //returns (null)
}
Somehow it prints null! However there is my other ViewController (using popover) that I try to assign its delegate and it does not null. Anyone can give me suggestion?
As I expected and this is silly, since the storyboard's segue is to a navigationController, so actually the destinationViewController is the navigationController not SPOSelectionViewController.
So I solved it by this way:
UINavigationController* navController = segue.destinationViewController;
SPOSelectionViewController * vc = (SPOSelectionViewController*)navController.topViewController;
vc.delegate = self;
I created a subclass of UIStoryboardSegue in order to achieve a modal segue with optional animation.
(subclass of UIStoryboardSegue):
.h
#import <UIKit/UIKit.h>
#interface ModalSegue_OptionalAnimation : UIStoryboardSegue
#property (readwrite) BOOL withAnimation;
#end
.m
#import "ModalSegue_OptionalAnimation.h"
#implementation ModalSegue_OptionalAnimation
-(void) perform{
BOOL _withAnimation_Va = self.withAnimation;
[[[self sourceViewController] navigationController] pushViewController:[self destinationViewController] animated:_withAnimation_Va];
}
#end
But I am unsure now how to call this property from the outside.
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if([[segue identifier] isEqualToString:#"segue_qVC_to_cVC_checkAnswer"]) {
CheckAnswerViewController *cVC = [segue destinationViewController];
if(segue_QVC_ISEXAM) {
//Something like this:
//segue.withAnimation = NO;
//Settings the property to NO is like 'I dont animation when performing the segue'
}
....
In my storyboard I already set the segue to custom with the just created class.
Try something like this:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if([[segue identifier] isEqualToString:#"segue_qVC_to_cVC_checkAnswer"]) {
CheckAnswerViewController *cVC = [segue destinationViewController];
if(segue_QVC_ISEXAM) {
ModalSegue_OptionalAnimation *customSegue = (ModalSegue_OptionalAnimation *)segue;
customSegue.withAnimation = NO;
//Something like this:
//segue.withAnimation = NO;
//Settings the property to NO is like 'I dont animation when performing the segue'
}
....
I wanna to pass data between controller, but I am getting this error, and I am blocked here :s
Error :
[UITabBarController setUID:]: unrecognized selector sent to instance
Code :
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
NSString *test = (NSString *)sender;
if ([segue.identifier isEqualToString:#"segueno"]) {
FirstViewController *VC = (FirstViewController *)[segue destinationViewController];
VC.uID = test;
NSLog(#"%#",VC.uID);
}}
Here is storyboaard
Check what is actual type of VC during runtime. Looks like you cast to wrong type.
To check real type during runtime set breakpoint on line VC.uID = test;. In debug window you should have something like:
VC = (RealClass *) 0x312321312
Real class is not what you expected.
The most possible reason, that VC is UITabBarController. So you have to replace
FirstViewController *VC = (FirstViewController *)[segue destinationViewController];
with
UITabBarController *tabBarController = (UITabBarController *)[segue destinationViewController];
// replace 1 with real index of your FirstVC
FirstViewController *VC = [[tabBarController viewControllers] objectAtIndex:1];
segue destination is UITabBarController. so you need to check viewcontrollers list. then based on that u can look for uID.
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
NSString *test = (NSString *)sender;
if ([segue.identifier isEqualToString:#"segueno"]) {
FirstViewController *firstVC ;
UITabBarController *destinat = [segue destinationViewController];
if ([destinat isKindOfClass:[UITabBarController class]]) {
for (id listOfViewControllers in [destinat viewControllers]) {
if ([listOfViewControllers isKindOfClass:[FirstViewController class]]) {
firstVC = listOfViewControllers;
break;
}
}
}
firstVC.uID = test;
NSLog(#"%#",firstVC.uID);
}}
Here is how I pass managedObjectContext between segues
In your class where you will pass the data use prepareForSegue call. (The assumption is this class has a variable called _managedObjectContext which can be passed along to the segue class)
Class to Segue From:
.h file:
#property (weak, nonatomic) NSManagedObjectContext *managedObjectContext;
.m file:
#synthesize managedObjectContext
The call to #synthesize will make the following:
a local variable called _managedObjectContext
a method to getManagedObjectContext
a method to setManagedObjectContext
Additionally add the following method to your class
// Pass on managedObjectContext
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
// If the destination VC is able to take the setManagedObjectContext method the current objectContext will be passed along.
if ([segue.destinationViewController respondsToSelector:#selector(setManagedObjectContext:)]) {
[segue.destinationViewController performSelector:#selector(setManagedObjectContext:)
withObject:_managedObjectContext];
} else {
NSLog(#"Segue to controller [%#] that does not support passing managedObjectContext", [segue destinationViewController]);
}
}
Then in my "class" to receive the data I do:
in the .h file i have
#property (weak, nonatomic) NSManagedObjectContext *managedObjectContext;
and in the .m file i have:
#synthesize managedObjectContext;
What this does (with syntehsiation) is make a setManagedObjectContext and getManagedObjectContext call. Upon being about to segue I check to make sure the destinationController will "respond to" this method, if so the data gets set.
clear?
I have a ViewController1 with a UILabel that can present a ViewController2 with a Modal Segue. I have a UITextField in ViewController2 that I need to access from ViewController1 so I can set my UILabel with the collected text.
I've tried working with the prepareForSegue without success. What should I do?
EDIT:
I'm using a Delegate, but I'm doing something wrong. Here's the code I'm using in ViewController2.h:
#class ViewController2;
#protocol VCProtocol
-(void)setName:(NSString *)name;
#end
#interface ViewController2 : UIViewController
#property (nonatomic, weak) id<VCProtocol> delegate;
#property (strong, nonatomic) IBOutlet UITextField *nameField;
- (IBAction)setButton:(id)sender
#end
ViewController2.m
-(IBAction)setButton:(id)sender
{
[self.delegate setName:nameField.text];
}
I conform to VCProtocol in my ViewController1.h. Then, in my ViewController1.m, I have this code:
- (void)setName:(NSString *)name
{
self.firstSignatureNameLabel.text = name;
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqual:#"Sign"])
{
ViewController2 *VC = [segue destinationViewController];
VC.delegate = self;
}
}
You can create a protocol and set VC1 as delegate of VC2, and using prepareForSegue to set VC1 as VC2's delegate should work. I know that you said it didn't work, but I can't see why. Have a try with this :
Give an identifier to your segue (on storyboard), and implement prepareForSegue as shown below :
VC2Delegate.h :
#protocol VC2Delegate
- (void)updateLabel:(NSString *)text;
#end
VC1.h :
#import "VC2Delegate.h"
#interface VC1 : UIViewController <VC2Delegate>
// All your stuff
#end
VC1.m :
- (void)updateLabel:(NSString *)text {
[_label setText:text];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([[segue identifier] isEqualToString:#"YourSegueIdentifier"]) {
VC2 * vc = [segue destinationViewController];
[vc2 setDelegate:self];
}
}
VC2.h :
#import "VC2Delegate.h"
#interface VC2 : UIViewController
#property (weak, nonatomic) id<VC2Delegate>delegate;
#end
VC2.m
- (void)textWasUpdated { // or whatever method where you detect the text has been changed
if (_delegate)
[_delegate updateLabel:[_textView text]];
}
Tell me if it works. Else, is prepareForSegue even been called ?
EDIT : Updated my answer (wasn't exactly what you needed).
But as you say it doesn't work :
Is prepareForSegue called ?
If so, is the delegate method called ?
If the delegate method isn't called, check that delegate is not nil.
You might want to remove the segue, and present it modally by yourself, using presentViewController:animated:completion:, like that :
- (IBAction)buttonWasTapped {
static NSString * const idModalView = #"modalView";
static NSString * const storyBoardName = #"MainStoryBoard"
UIStoryboard * storyboard = [UIStoryboard storyboardWithName:storyBoardName bundle:nil];
VC2 * vc = [storyboard instantiateViewControllerWithIdentifier:idModalView];
[vc setDelegate:self];
[self.navigationController presentViewController:vc2 animated:YES completion:nil];
}
When I ran into this problem, I chose the singleton approach and it works.
I have a HomeViewController which has a tableView populated with the array tableViewArray (originally empty). When I tap on a barButton, I segue modally to another View Controller called OutsideViewController which has another tableView populated by a different array.
What I would like to do is the following:
When I tap on a row in my OutsideViewController, I would like to add the selected string value to the tableViewArray so that when I go back to HomeViewController, the tableView has that new item listed in the tableView.
So far, this is what I have tried:
In the -didSelectRowAtIndexPath method of my OutsideViewController.m I have this piece of code:
NSString *selectedRow = [outsideArray objectAtIndex:indexPath.row];
NSMutableArray *temporaryArray = [NSMutableArray arrayWithObject:selectedRow];
HomeViewController *homeVC = [[HomeViewController alloc] init];
homeVC.tableViewArray = temporaryArray;
That code works but the tableView in HomeViewController is still empty when I return. Do I have to reload the tableView data?
Am I doing this right?
This is how I have set up my View Controllers in Storyboard:
HomeViewController -(modal segue)-> Navigation Controller --> OutsideViewController
Also, the return from OutsideViewController to HomeViewController is done by this line of code:
[self dismissViewControllerAnimated:YES completion:^{ }];
What you're doing wrong is you're allocationg a new HomeViewController. What I would do is keeep a reference to your HomeViewController in your OutsideViewController. Here is how.
First, in OutsideViewController.h, create a property, like this :
#property (nonatomic, weak) HomeViewController *homeVC;
Don't forget to add #class HomeViewController; in your .h, and #import "HomeViewController.h" in your .m
In HomeViewController, implement the prepareForSegue: method like this (replace ModalSegueIdentifier with your segue's identifier) :
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"ModalSegueIdentifier"]) {
OutsideViewController *modalVC = (OutsideViewController*)segue.destinationViewController;
modalVC.homeVC = self;
}
}
Then, in OutsideViewController.m, instead of doing :
HomeViewController *homeVC = [[HomeViewController alloc] init];
homeVC.tableViewArray = temporaryArray;
Do this :
_homeVC.tableViewArray = temporaryArray;
When you leave your modal VC, your HomeVC will have the correct array. Don't forget to refresh your UITableView !
NB: Of course, there are many other ways, and it's maybe not the best one. But still, it should work.
You can achieve this too using delegation. You have to create a protocol in your OutsideViewController with a method that is responsible for sending the new object to your HomeViewController. Do this in OutsideViewController.h:
#protocol OutsideViewDelegate <NSObject>
- (void)OutsideViewController:(OutsideViewController *)controller didAddObject:(NSString *)object;
#end
In the implementation file you have to change a little bit the didSelectRowAtIndexPath: method:
NSString *selectedRow = [outsideArray objectAtIndex:indexPath.row];
[self.delegate OutsideViewController:self didAddObject:selectedRow];
In your HomeViewController.h you have to make your class conforms to the protocol:
#interface HomeViewController : UIViewController <OutsideViewDelegate>
After, create a property for the delegate:
#property (nonatomic, weak) id <OutsideViewDelegate> delegate;
To finish the process, implement the protocol in your HomeViewController.m to receive the new object from the OutsideViewController:
- (void)OutsideViewController:(OutsideViewController *)controller didAddObject:(NSString *)object
{
if (object != nil)
{
[self.tableViewArray addObject:object];
}
[self dismissViewControllerAnimated:YES completion:nil];
}
The code above depends of if your tableViewArray object is mutable or not. If it's not, you can change the type of the object argument in the protocol method to an inmutable array object and just assign tableViewArray to the new array.
EDIT:
In the prepareForSegue: method don't forget to set the delegate:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"SEGUE_IDENTIFIER"]) {
OutsideViewController *outsideVC = (OutsideViewController *)[segue destinationViewController];
[outsideVC setDelegate:self];
}
}
First of all make sure you alloc, init your tableViewArray in HomeViewController
Second , In this line
HomeViewController *homeVC = [[HomeViewController alloc] init]
you are creating a new reference to your HomeViewController which is not correct, you need to pass correct reference, possibly creating HomeViewController variable in your OutsideViewController
Even though you correctly do first and second suggestion you will still see an empty tableview because you dont reload the tableview, somehow you need to fire [self.tableview reloadData]; method.
That means; you need to learn Delegate or NSNotifications pattern to communicate between child->parent scenarios
How do I set up a simple delegate to communicate between two view controllers?
http://mobile.tutsplus.com/tutorials/iphone/ios-sdk_nsnotificationcenter/
For your question just create a delegate in your Outside;
in your OutsideViewController.h
#import <UIKit/UIKit.h>
#protocol OutsideDelegate;
#interface{}//bunch of interface stuff
// Declare a property for the delegate
#property (weak) id <OutsideDelegate> delegate;
#end
// Protocol Header
#protocol OutsideDelegate <NSObject>
#optional
- (void)dismissPop:(NSMutableArray *)list;
#end
in your OutsideViewController.m
#synthesize delegate;
//run delegate method
[delegate dismissPop:temporaryArray];
[self dismissViewControllerAnimated:YES completion:^{ }];
in your HomeViewController.h
#import "OutsideViewController.h"
#interface OutsideViewController : UITableViewController<OutsideDelegate>
{}
#property (strong, nonatomic) OutsideViewController *pvc;
in your HomeViewController.m
#synthesize pvc;
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([[segue identifier] isEqualToString:#"your segue"]) {
pvc = [segue destinationViewController];
[pvc setDelegate:self];
}
}
// delegate callback function
- (void)dismissPop:(NSMutableArray *)list {
self.tableViewArray=list;
[self.tableView reloadData];
}
Another Solution Would be
Change your view stack to this:
Navigation Controller --> HomeViewController -(push segue)--> OutsideViewController
and apply rdurand's answer
and add this to your HomeViewController :
-(void)viewDidAppear:(BOOL)animated
{
[self.tableview reloadData];
}
In this solution since you are just push-pop viewcontrollers in a nabigation stack viewDidAppear will be called in HomeViewController everytime when you pop OutsideViewController.