Create Protocol, prepareForSegue
prepareForSegue
When we connect two view controllers from storyboard, the following method will be called when first view wants to transmits to the second view.- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
}
Because this method is called before transition, so we can initialize or set some value for the next view controller. segue has two important property:
1)segue.identifier
In storyboard click on the arrow that links two view controllers then in attribute inspector tab on right side toolbar give the name in identifier field. Now in prepareForSegue we can check if the identifier matches the one that we are looking. The following is statement goes inside of prepareForSegue just to protect our application from any exception or crash.- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:@"AddContact"])
{
//Do something
}
}
2)segue.destinationViewController
As it can be guessed destinationViewController represents the next view controller. We can cast it to the next class name.Casting in Objective-C
In order to force the compiler to consider a different type for an object we use casting. It's so simple to use. Yo just have to add a desired type inside of () and you are done. For example here we want segue.destionationViewController to have a type of AddContactVC. We should write:(AddContactVC *)segue.destinationViewControllerYou may ask why we should cast!!! If we don't cast, compiler couldn't understand what is our specific type so it cannot see the available methods.
Create Protocol
If we have two different view controllers and we want them to talk back and forth, we need to define protocol and delegate. If you remember in textField delegate methods we used some built-in protocols and delegates. In this tutorial we will create our own protocol and delegate methods.Steps to Create Protocol (Custom Delegate)
We have two view controllers in this example (Contact List) first view controller is a table view controller that shows the contact and the second view controller is the place that we add contact to the list. First view controller would be our delegate and second view controller would be our delegator. Here are the steps for delegator class:1)Create Protocol
Add the following lines inside of the .h file of delegator class (AddContactVC) before @interface:@class AddContactVC; @protocol AddContactVCDelegate - (IBAction)dismissAddContactVC:(AddContactVC *)sender; - (void)addContactName:(NSString *)name phone:(NSString *)phone; @end@class is kind of our promise to compiler that we will define AddContactVC class in the following. If we don't put @class compiler will give error that there is not a class called AddContactVC. @protocol defines the name of the protocol and start point of it's methods. @end defines the end of the protocol.
2)Create Delegate Property
Create a weak property for our delegate between @interface and @end of delegator .h file.@property (nonatomic, weak) id <AddContactVCDelegate> delegate;
3)Use delegate property in .m file
Inside of delegator .m file we should use our delegate property in appropriate place. In this example we have two delegate methods. The first method should be called when the user taps on the done button. And the second one should be used when the user taps on the add button. Open AddContactVC .m file control+drag the done button and add button to the implementation portion and create IBAction, then inside of these methods we can use our delegate property like bellow:- (IBAction)dismissAddContactVC:(UIBarButtonItem *)sender
{
[self.delegate dismissAddContactVC];
}
- (IBAction)addContactPressed:(UIButton *)sender
{
[self.delegate addContactName:self.nameField.text phone:self.numberField.text];
}
Second method not only notifies us about user interaction but also sends two parameters, which are name and phone so we can use them to add to our table.
Here are the steps for delegate class:
4)Set delegate equal to self
First step to tell the compiler that we want to implement some delegate is to put our class delegate equal to self. Most of the time the best place is when we create an instance of delegator class but in this example since we have the instance, which is(AddContactVC *)segue.destinationViewControllerSo we don't need to instantiate another instance we can use it and set the delegate equal to self like bellow:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:@"AddContact"]) {
[ (AddContactVC *)segue.destinationViewController setDelegate:self];
}
}
5)Add <delegateName> in front of @interface
The second step to tell the compiler that we want to implement some delegate methods is to declare the delegate name in fron of @interface of delegate class. Before doing that make sure you import the delegator class.#import "AddContactVC.h" @interface ContactTVC () <AddContactVCDelegate>
6)Implement the delegate methods
The last but not the least is implementing the delegate methods- (void)dismissAddContactVC
{
[self dismissViewControllerAnimated:YES completion:nil];
}
- (void)addContactName:(NSString *)name phone:(NSString *)phone
{
[self.names addObject:name];
[self.phones addObject:phone];
[self.tableView reloadData];
[self dismissAddContactVC];
}
First method uses dismissViewControllerAnimated:YES completion:nil, which is one of view controller methods for dismissing the modal view. Second method adds the arguments to the array and then it reloads the table view by a method called reloadData. Then it calls our method dismissAddContactVC to dismiss the modal view once the user add new contact.
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