如何从另一个UIViewController更改UIViewController的UILabel

Question

i have a two UIViewController named FirstUIViewController and SecondUIViewController and i want to change the text of a UILabel on the SecondtUIViewController from the FirstUIViewController when i pressed the button from the FirstUIviewController. i don't know how to do it i am new to objective-c and ios development.

here is what i currently have

FirstUIViewController.h

#import <UIKit/UIKit.h>

@interface FirstUIViewController

IBAction Button1:(id)sender;
@end

FirstUIViewController.m

#import "MainViewController.h"

@implementation FirstUIViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewdidload {
//some codes here.
}

SecondUIViewController.h

#import <UIKit/UIKit.h>

@interface SecondUIViewController {
IBOutlet UILabel *label;
}

@end

SecondUIViewController.m

#import "SecondUIViewController.h"

@implementation FirstUIViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewdidload {
//some codes here.
}

Answer 1

You will need to declare a delegate protocol for your class. An example of a delegate protocol and interface for class Foo might look like this:

@class Foo;
@protocol FooDelegate <NSObject>
@optional
- (BOOL)foo:(Foo *)foo willDoSomethingAnimated:(BOOL)flag;
- (void)foo:(Foo *)foo didDoSomethingAnimated:(BOOL)flag;
@end

@interface Foo : NSObject {
     NSString *bar;
     id <FooDelegate> delegate;
}

@property (nonatomic, retain) NSString *bar;
@property (nonatomic, assign) id <FooDelegate> delegate;

- (void)changeLabelText;

@end

Don't forget to synthesize your properties in the @implementation .

The last step is for a Foo object to be instantiated in the class that conforms to FooDelegate , and for this Foo object to have its delegate property set:

Foo *obj = [[Foo alloc] init];
[obj setDelegate:self];

Now, your class is prepared to receive messages from Foo objects that have their delegates set correctly.

Answer 2

if you are not using storyboard you just have to create an instance of the second screen and then you can refer to the secondviewcontroller properties.

on the .h file of the first screen: creating an instance of the secondviewpage

@property (nonatomic,retain)SecondViewController *detailcontroller;

on the .m file of the first view (when you want to load the page).

self.detailcontroller = [[SecondViewController alloc]initWithNibName:@"SecondViewController" bundle:nil];

self.detailcontroller.label

//str as some nsstring variable in the secondViewController

now you cant access the "SecondViewController" from the first view by the dot notation

hope i helped you.

idan

Answer 3

Easy method is store the property in the AppDelegate and set/get it there.

In AppDelegate.h @property (nonatomic, strong) NSString *transferString; In AppDelegate.m @synthesize transferString

In both your first and second v iewcontrollers.m import "AppDelegate.h" create a property for it @property (nonatomic, strong) AppDelegate *appDelegate;

in the viewcontrollers viewDidLoad set it self.appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

then just get or set the string value in the appDelegate in your viewcontrollers

to set it: self.appDelegate.transferString = aString; to get it: NSString *theString = self.appDelegate.transferString;