Question

我有2个视图控制器。 viewController1有一个名为nameLabel的UILabel，我希望在另一个类viewController2中设置。

我尝试从viewController2调用此代码。

Content1ViewController *viewController1 = [Content1ViewController new];
    viewController1.nameLabel.text = @"HELLO";

    NSLog(@"%@",viewController1.nameLabel);

但是，当我调用代码时，viewController1 nameLabel不会改变？ NSLog还返回“null”??有人能告诉我为什么会发生这种情况，以及我如何从另一个类中更改nameLabel？谢谢！

Answer 1

手动创建实例时，不会初始化控件。这是在视图控制器生命周期的后期阶段完成的。

如果我没有弄错的话，您将看到初始化控件的第一个事件是viewDidLoad

您可以做的是添加一个NSString属性名称（让我们说）nameLabelText并在nameLabel.text = nameLabelText;上执行viewDidLoad

Answer 2

您需要使用窗口上的viewController的相同实例。如果要将viewController2推入导航控制器堆栈，则从导航堆栈中获取viewController1的实例，然后尝试设置标签。

如果您使用的是现有模式，请使用presentingViewController viewController2实例来访问viewController1的实例

viewController1 *controller = [viewController2 presentingViewController];
[controller.nameLabel setText:@"WhatEver"];

Answer 3

您在哪里为namelabel设置了属性？您是否使用Interface Builder（XIB或Storyboard）或者您是否已在代码中完成所有操作？如果你在InterfaceBuilder中做到了

 [Content1ViewController new]

是错误的做法。对于XIB-Files，您应该使用

initWithNibName:(NSString *)nibName
                     bundle:(NSBundle *)nibBundle

如果您的ViewController已在故事板中定义，则应使用

instantiateViewControllerWithIdentifier:(NSString *)identifier

来自UIStoryboard。

但是，正如Claudio Redi已经说过，你能够访问UILabel的最早点将在viewDidLoad

如果代码中的所有内容都应该放

[self setNameLabel:[[UILabel alloc] initWithFrame:CGRectMake(50.0f,50.0f,100.0f,100.0f)];

在init - ViewController的方法。

Answer 4

//
//  ViewController.m
//  UIPageViewControllerDemo
//
//  Created by YunYi1118 on 15/5/20.
//  Copyright (c) 2015年 Xiaoyi. All rights reserved.
//

#import "ViewController.h"
#import "MoreViewController.h"

@interface ViewController () <UIPageViewControllerDataSource, UIPageViewControllerDelegate>

@property (strong, nonatomic) UIPageViewController *pageController;

@property (strong, nonatomic) NSArray *pageContent;

@end

@implementation ViewController

@synthesize pageContent = _pageContent;
@synthesize pageController = _pageController;

- (void)viewDidLoad {
    [super viewDidLoad];
    [self createContentPages];
    NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithInteger:UIPageViewControllerSpineLocationMin] forKey:UIPageViewControllerOptionSpineLocationKey];

    self.pageController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:options];

    _pageController.dataSource = self;
    _pageController.view.frame = self.view.bounds;

    MoreViewController *initialViewController = [self viewControllerAtIndex:0];
    NSArray *viewControllers = [NSArray arrayWithObject:initialViewController];
    [self.pageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
    [self addChildViewController:_pageController];
    [self.view addSubview:_pageController.view];


}

- (MoreViewController *)viewControllerAtIndex:(NSUInteger)index
{
    if (self.pageContent.count == 0 || index >= self.pageContent.count) {
        return nil;
    }
    MoreViewController *dataViewController = [[MoreViewController alloc] init];
    dataViewController.dataObject = [self.pageContent objectAtIndex:index];
    return dataViewController;
}

- (void)createContentPages
{
    NSMutableArray *pageStrings = [NSMutableArray array];
    for (int i = 1; i < 11; i++) {
        NSString *contentString = [[NSString alloc] initWithFormat:@"Chapter%d, This is the page %d of content displayed using UIPageViewController ",i,i];
        [pageStrings addObject:contentString];
    }
    self.pageContent = [NSArray arrayWithArray:pageStrings];
}

#pragma mark - delegate

- (NSUInteger)indexOfViewController:(MoreViewController *)viewController
{
    return [self.pageContent indexOfObject:viewController.dataObject];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    NSUInteger index = [self indexOfViewController:(MoreViewController *)viewController];
    if (index == 0 || index == NSNotFound) {
        return nil;
    }
    index--;
    return [self viewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
    NSUInteger index = [self indexOfViewController:(MoreViewController *)viewController];
    if (index == NSNotFound) {
        return nil;
    }
    index++;
    if (index == self.pageContent.count) {
        return nil;
    }
    return [self viewControllerAtIndex:index];
}

@end

为什么我的UILabel没有被设置？

4 个答案: