UITabBarController中的坑

Posted 2020-08-27 俊华的博客

当你创建一个继承与UITabBarController的子类 并想给其自定义构造方法 传一些值的时候这时候问题出现了：

 在创建的时候里面的init方法回调用了 viewdidload，导致每次传值的时候都会在viewdidload加载完了之后传的值才能传过去

如下代码

- (instancetype)initWithURLStrings:(NSArray *)urls{
    self = [super init];//在调用init的时候回调用viewDidLoad 导致参数传入进来时已经加载完了
    if (self) {

        self.urls = urls;
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
     [self setUpChild];
    self.tabBar.backgroundColor = [UIColor whiteColor];

}

- (void)setUpChild{
    // 1.初始化子控制器
    KHHomeVC *home = [[KHHomeVC alloc] initWithURL:self.urls[0]];
    [self addChildVc:home title:@"首页" image:@"tab_home_n" selectedImage:@"tab_home_s"];
    
    KHVipVC *vipVC = [[KHVipVC alloc] initWithURL:self.urls[1]];
    [self addChildVc:vipVC title:@"会员" image:@"tab_user_n" selectedImage:@"tab_user_s"];
    
    KHMineDetailVC *settingVC = [[KHMineDetailVC alloc] initWithURL:self.urls[2]];
    [self addChildVc:settingVC title:@"设置" image:@"tab_setting_n" selectedImage:@"tab_setting_s"];
}

- (void)addChildVc:(UIViewController *)childVc title:(NSString *)title image:(NSString *)image selectedImage:(NSString *)selectedImage
{
    // 设置子控制器的文字
    childVc.title = title; // 同时设置tabbar和navigationBar的文字
    
    // 设置子控制器的图片
    childVc.tabBarItem.image = [UIImage imageNamed:image];

    if (ios7) {
        childVc.tabBarItem.selectedImage = [[UIImage imageNamed:selectedImage] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    } else {
        childVc.tabBarItem.selectedImage = [UIImage imageNamed:selectedImage];
    }
    
    // 设置文字的样式
    NSMutableDictionary *textAttrs = [NSMutableDictionary dictionary];
    textAttrs[NSForegroundColorAttributeName] = [UIColor colorWithRed:136/255.0 green:136/255.0 blue:136/255.0 alpha:1];
    NSMutableDictionary *selectTextAttrs = [NSMutableDictionary dictionary];
    selectTextAttrs[NSForegroundColorAttributeName] = [UIColor colorWithRed:0 green:183/255.0 blue:283/255.0 alpha:1];
    [childVc.tabBarItem setTitleTextAttributes:textAttrs forState:UIControlStateNormal];
    [childVc.tabBarItem setTitleTextAttributes:selectTextAttrs forState:UIControlStateSelected];
    
    // 先给外面传进来的小控制器 包装 一个导航控制器
    KHNavigationController *nav = [[KHNavigationController alloc] initWithRootViewController:childVc];
    nav.navigationBarHidden = YES;
    // 添加为子控制器
    [self addChildViewController:nav];
}

 

这是怎么回事的 我们知道在一般控制器中我们想要自定义构造方法 会先走完初始化方法然后再走 viewDidLoad 但是这个UITabBarController怎么这么特殊呢呢？

经过一番查找终于知道了原来这是UITabBarController的一个特性

其实UITabBarController在init的时候，会增UITabbar到self.view，这时候必须加载self.view出来，从而就调用了loadview，进而调用viewdidload、viewwillappear等。这个是UITabBarController的特性

UITabBarController在调用【super init】的时候，系统调用了self.view的东西，但是此时view还没加载出来，于是系统强制先调用viewdidload去加载self.view，最后加载完了，再接着走init方法中的 if(self)条件语句。

 

解决方案：

就是不要在viewdidload 方法里写加载界面的代码，可以单独再写个方法，直接在init结束的时候调用。所以我的建议就是直接把viewdidload和viewwillappear方法删了，加载界面全都在init里写，如下：

- (instancetype)initWithURLStrings:(NSArray *)urls{
    self = [super init];//在调用init的时候回调用viewDidLoad 导致参数传入进来时已经加载完了
    if (self) {

        self.urls = urls; //初始化数据
         [self setUpChild]; //这是解决的重点

    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.tabBar.backgroundColor = [UIColor whiteColor];

}


- (void)setUpChild{
    // 1.初始化子控制器
    KHHomeVC *home = [[KHHomeVC alloc] initWithURL:self.urls[0]];
    [self addChildVc:home title:@"首页" image:@"tab_home_n" selectedImage:@"tab_home_s"];
    
    KHVipVC *vipVC = [[KHVipVC alloc] initWithURL:self.urls[1]];
    [self addChildVc:vipVC title:@"会员" image:@"tab_user_n" selectedImage:@"tab_user_s"];
    
    KHMineDetailVC *settingVC = [[KHMineDetailVC alloc] initWithURL:self.urls[2]];
    [self addChildVc:settingVC title:@"设置" image:@"tab_setting_n" selectedImage:@"tab_setting_s"];
}

- (void)addChildVc:(UIViewController *)childVc title:(NSString *)title image:(NSString *)image selectedImage:(NSString *)selectedImage
{
    // 设置子控制器的文字
    childVc.title = title; // 同时设置tabbar和navigationBar的文字
    
    // 设置子控制器的图片
    childVc.tabBarItem.image = [UIImage imageNamed:image];

    if (iOS7) {
        childVc.tabBarItem.selectedImage = [[UIImage imageNamed:selectedImage] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    } else {
        childVc.tabBarItem.selectedImage = [UIImage imageNamed:selectedImage];
    }
    
    // 设置文字的样式
    NSMutableDictionary *textAttrs = [NSMutableDictionary dictionary];
    textAttrs[NSForegroundColorAttributeName] = [UIColor colorWithRed:136/255.0 green:136/255.0 blue:136/255.0 alpha:1];
    NSMutableDictionary *selectTextAttrs = [NSMutableDictionary dictionary];
    selectTextAttrs[NSForegroundColorAttributeName] = [UIColor colorWithRed:0 green:183/255.0 blue:283/255.0 alpha:1];
    [childVc.tabBarItem setTitleTextAttributes:textAttrs forState:UIControlStateNormal];
    [childVc.tabBarItem setTitleTextAttributes:selectTextAttrs forState:UIControlStateSelected];
    
    // 先给外面传进来的小控制器 包装 一个导航控制器
    KHNavigationController *nav = [[KHNavigationController alloc] initWithRootViewController:childVc];
    nav.navigationBarHidden = YES;
    // 添加为子控制器
    [self addChildViewController:nav];
}

 

 

我发现只有继承自UINavigationController和UITabBarController的类的init函数会产生loadView、viewDidLoad函数在初始化［super init］函数调用后就执行，一般UIViewController没有这个问题

@implementation UIViewControllerSubclass

- (id)init {
        NSLog(@"0");
    if (self = [super init]) {
        NSLog(@"1");
    }
    return self;
}

- (void)loadView {
    [super loadView];
    NSLog(@"2");
}

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"3");
}

@end

console output

0
2
3
1

d