Change label text color using delegate

问题

I have two view controller, ParentViewController have label that updated using SecondViewController. Now I want to change ParentViewController's label text color from ChildViewController, for that i am using protocol and delegate but it shows error.

My code is like this:

ChildViewController.h

@protocol ViewControllerDelegate

-(void) updateLabel;

@end
@interface ChildViewController : UIViewController<UITextFieldDelegate,UITextViewDelegate>
{
    id <ViewControllerDelegate> delegate;
}

@property (assign) id <ViewControllerDelegate> delegate;
@end

ChildViewController.m

@implementation childViewController

@synthesize delegate;

- (IBAction)backBtn:(id)sender {
    [delegate updateLabel];
}
@end

ParentViewController.h

#import <UIKit/UIKit.h>
#import "childViewController.h"

@interface ParentViewController : UIViewController<UserResizableViewDelegate,ViewControllerDelegate>

@end

ParentViewController.m

@implementation ParentViewController

- (void)viewDidLoad
{
   ChildViewController.delegate=self;   //here it show error that ChildViewController does not have property delegate
}
- (void)updateLabel
{
    alabel.textColor = [UIColor blueColor];
}

@end

UPDATE

this is how i am creating label

ParentViewController.m

- (void)viewDidLoad
{
CGRect imageFrame = CGRectMake(10, 10, 150, 80);
    labelResizableView = [[UserResizableView alloc] initWithFrame:imageFrame];
    alabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 100, 100)];

    alabel.text = @"Drag me!";
    //alabel.text = self.newsAsset.title;
    alabel.adjustsFontSizeToFitWidth = NO;
    alabel.autoresizingMask = UIViewAutoresizingFlexibleWidth;
    alabel.font = [UIFont boldSystemFontOfSize:18.0];
    //alabel.textColor = [UIColor blueColor];    
    // alabel.shadowColor = [UIColor whiteColor];
    // alabel.shadowOffset = CGSizeMake(0, 1);
    alabel.backgroundColor = [UIColor clearColor];
    alabel.lineBreakMode = UILineBreakModeWordWrap;
    alabel.numberOfLines = 10;
    alabel.minimumFontSize = 8.;
    alabel.adjustsFontSizeToFitWidth = YES;
    [alabel sizeToFit];
    labelResizableView.autoresizingMask = UIViewAutoresizingFlexibleWidth;



    // enable touch delivery
    alabel.userInteractionEnabled = YES;

    UITapGestureRecognizer *doubleTap =[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(labelTap:)]; 
    doubleTap.numberOfTapsRequired = 2; 
    [self.view addGestureRecognizer:doubleTap];

    //Calculate the expected size based on the font and linebreak mode of your label
    CGSize maximumLabelSize = CGSizeMake(296,9999);

    CGSize expectedLabelSize = [myString sizeWithFont:alabel.font 
                                    constrainedToSize:maximumLabelSize 
                                        lineBreakMode:alabel.lineBreakMode]; 


    //adjust the label the the new height.
    CGRect newFrame = alabel.frame;
    newFrame.size.height = expectedLabelSize.height+40;
    newFrame.size.width = expectedLabelSize.width+40;

    alabel.frame = newFrame;
    labelResizableView.frame = newFrame;

    labelResizableView.contentView = alabel;
    labelResizableView.delegate = self;
    [self.view addSubview:labelResizableView];

}

And when user tap label then

- (void)labelTap:(UITapGestureRecognizer *)tapGesture {
    ChildViewController *childViewController = [[ChildViewController alloc] initWithNibName:@"ChildViewController" bundle:[NSBundle mainBundle]];


    [self presentModalViewController:childViewController animated:NO];

}

and in ChildViewCoontroller when user click done button then

-(IBAction)doneBtn:(id)sender
{

    [adelegate updateLabel];

     [self dismissModalViewControllerAnimated:NO];

}

回答1:

#import <UIKit/UIKit.h>
#import "childViewController.h"

@interface ParentViewController : UIViewController<UserResizableViewDelegate,ViewControllerDelegate>

@property (strong, nonatomic) ChildViewController *childViewController;

@end

@implementation ParentViewController

- (void)viewDidLoad
{
    self.childViewController = [[ChildViewController alloc] init];
    childViewController.delegate=self;   //here it show error that ChildViewController does not have property delegate
}
@end

回答2:

You are not setting delegate property of ChildViewController. You are setting it as it is of ParentViewController. But ParentViewController don't have that property. Set delegate property of ChildViewController's object in ParentViewController

ChildViewController.delegate=self

来源：https://stackoverflow.com/questions/13454043/change-label-text-color-using-delegate