How to update text in a UITextField programmatically in a loop

Question

I am trying to dynamically update the text in a UITextField while in a loop and the text does not show up in real time. When the loop is complete it will display the final value. How do I get the text to display each time it is updated in the loop? I have found many threads on updating in a tableview but this text field is just on the main app. Here is a simple app with a text field and a button.

in ViewController.h #import

@interface ViewController : UIViewController<UITextFieldDelegate>
@property (weak, nonatomic) IBOutlet UITextField *myText;
@property (weak, nonatomic) IBOutlet UIButton *myButton;
- (IBAction)pressMe:(UIButton *)sender;
@end

in ViewController.m #import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize myButton,myText;

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    myText.delegate = self;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)pressMe:(UIButton *)sender {

    for (int i=0;i<10;i++){
        NSString *m = [[NSString alloc] initWithFormat:@"%d",i];
        NSLog(@"%@",m);
        [myText setText:m];
        [NSThread sleepForTimeInterval:.05];
    }
}
@end

The texfield delegate is connected to the view controller. This is a simple app to illustrate what I am trying to do. My actual app is trying to display lat lon from the gps to the screen with continual updates. Any help is appreciated.

Answer 1

If your intention is to update the text in the fields with GPS coordinates, I'd suggest setting the text in CLLocationManagerDelegate method locationManager:didUpdateLocations: (assuming you are using CLLocationManager to track user location). This method is called as and when location is updated. No need for GCD here.

Sample Code:

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations {

    CLLocation *mostRecentLocation = [locations lastObject];

    latitudeTextField.text = [NSString stringWithFormat:@"%f", mostRecentLocation.coordinate.latitude];
    longitudeTextField.text = [NSString stringWithFormat:@"%f", mostRecentLocation.coordinate.longitude];
}

Answer 2

You should use dispatch_async(dispatch_get_main_queue(), ^{ }); for UI updates in different thread. [textfield setNeedsDisplay] also can work if you are already in main thread

Answer 3

Try This Once..

-(IBAction)btnPress:(id)sender
{

    for (int i=0;i<10;i++){
        NSString *m = [[NSString alloc] initWithFormat:@"%d",i];
        NSLog(@"%@",m);

        [NSThread detachNewThreadSelector:@selector(call:) toTarget:self withObject:m];
        sleep(1);
    }
}

-(void)call:(NSString *)str
{
    _myText.text = str;
}

Answer 4

@interface ViewController ()
{
    NSTimer *timer;
    NSInteger i;
}
@end

- (void)viewDidLoad {
   [super viewDidLoad];

   i=0;       

   timer = [NSTimer scheduledTimerWithTimeInterval:1.0
       target:self
       selector:@selector(targetMethod:)
       userInfo:nil
       repeats:YES];    


   myText.delegate = self;
 }

 - (IBAction)StopUpdate:(UIButton *)sender {
    [timerinvalidate]
 }
 -(void)targetMethod{
    NSString *m = [[NSString alloc] initWithFormat:@"%d",i];
    i++;
    [myText setText:m];
 }

Answer 5

-(IBAction)btnPressed:(id)sender
{
dispatch_queue_t Queue = dispatch_queue_create("",0);
    dispatch_async(Queue, ^{
        for (int i=1 ; i<=10;i++) {
            sleep(1);
            dispatch_async(dispatch_get_main_queue(),^{

                myTxtFld.text = [NSString stringWithFormat:@"%d",i];
            }
            );
        }
    });
}