objective-c - Xcode:如何访问子类中的方法？

当我尝试从SubView访问主ViewController中的方法时，我的应用程序崩溃。

请帮忙。

我的主ViewController中有一个UIButton，它可以更改UILabel中的文本，该UILabel也位于我的主View中。我在SubView中有一个UIButton，应该通过从主ViewController访问相同的方法来再次更改字符串。但是该应用程序崩溃了。

这是我的代码：

主ViewController

ViewController.h

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

@interface ViewController : UIViewController

@property (nonatomic, strong) UILabel *label;
@property (nonatomic, retain) UIButton *mainClassButton;

- (void) setLabelTo:(NSString *)copy;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

@synthesize label;
@synthesize mainClassButton;

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

    self.label = [[UILabel alloc] initWithFrame:CGRectMake(30.0, 30.0, 200.0, 30.0)];
    self.label.text = @"Let's Go Mets!";
    [self.view addSubview:label];

    mainClassButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    mainClassButton.frame = CGRectMake(30.0, 70.0, 200.0, 30.0);
    [mainClassButton setTitle:@"Main Class Button" forState:UIControlStateNormal];
    [mainClassButton addTarget:self action:@selector(touchAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:mainClassButton];

    SubViewController *subViewController = [[SubViewController alloc] init];
    subViewController.view.backgroundColor = [UIColor clearColor];
    [self.view addSubview:subViewController.view];

    [self.view bringSubviewToFront:self.mainClassButton];
}

- (IBAction)touchAction:(UIButton *) sender
{
    [self setLabelTo:@"Here we go Yankess!"];
}

- (void) setLabelTo:(NSString *)copy
{
    self.label.text = copy;
}

子ViewController

SubViewController.h

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

@interface SubViewController : UIViewController

@property (nonatomic, retain) UIButton *subClassButton;

@end

SubViewController.m

@implementation SubViewController

@synthesize subClassButton;

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

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.

    subClassButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    subClassButton.frame = CGRectMake(30.0, 115.0, 200.0, 30.0);
    [subClassButton setTitle:@"Sub Class Button" forState:UIControlStateNormal];
    [subClassButton addTarget:self action:@selector(touchAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:subClassButton];

}

- (IBAction)touchAction:(UIButton *) sender
{
    ViewController *vc = [[ViewController alloc] init];

    [vc setLabelTo:@"If you ask me, I prefer the White Sox."];
}

我还是Xcode和Objective-C的新手，希望您能提供任何帮助。

谢谢

最佳答案

您需要在-setLabelTo内的现有ViewController实例上调用-[SubViewController touchAction:]-目前，您正在创建ViewController的新实例，并在该新实例上调用-setLabelTo:。

为了在-setLabelTo上调用ViewController，我们需要对该ViewController的引用。

UIViewController提供一个属性parentViewController，在理想情况下，该属性将为您的SubViewController提供对您的ViewController的引用。但是，在这种情况下，它没有提供这样的参考。您将SubViewController的视图添加为ViewController的子视图，但是没有将SubViewController添加为ViewController的子视图控制器。 （另请参见this question和the accepted answer。）要解决此问题，请在-[ViewController viewDidLoad]中添加以下行

[self addChildViewController:subViewController];

后

SubViewController *subViewController = [[SubViewController alloc] init];

给你

SubViewController *subViewController = [[SubViewController alloc] init];
[self addChildViewController:subViewController];
subViewController.view.backgroundColor = [UIColor clearColor];
[self.view addSubview:subViewController.view];

此时，您的SubViewController是ViewController的子视图控制器，而SubViewController的视图是ViewController的视图的子视图。

此时，您可以将-[SubViewController touchAction:]的实现更改为

- (IBAction)touchAction:(UIButton *) sender
{
    ViewController *vc = self.parentViewController;

    [vc setLabelTo:@"If you ask me, I prefer the White Sox."];
}

它将在原始-setLabelTo:上调用ViewController，而不是创建新实例并导致崩溃。

关于objective-c - Xcode:如何访问子类中的方法？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/14205658/