BaseViewController和自定义返回键的小故事

2016-01-07

ViewController基类

应用开发的时候,总有一些ViewController是样式相同的,那么就可以给这些样式相同的ViewController创建一些基类,并且利用里面的viewDidLoad等函数完成一些重复的功能.出于自定义需求,我们还可以自定义一个LeftBarButtonItem.

//BaseViewController.m
#import "BaseViewController.h"

@implementation BaseViewController

- (void)popToPreview{
    [self.navigationController popViewControllerAnimated:YES];
}

- (void)setLeftBarButtonItemTarget:(id)target action:(SEL)action{
    //自定义一个返回键
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    UIImage *nImage = [UIImage resourceImageNamed:@"btn_back_white"];
    [button setFrame:CGRectMake(0, 0, nImage.size.width, nImage.size.height)];
    [button setBackgroundImage:nImage forState:UIControlStateNormal];
    //自定义返回键功能
    [button addTarget:target action:action forControlEvents:UIControlEventTouchUpInside];
    //添加到NavigationBar上
    UIBarButtonItem *barBtnItem = [[UIBarButtonItem alloc] initWithCustomView:button];
    barBtnItem.style = UIBarButtonItemStylePlain;
    [self.navigationItem setLeftBarButtonItem:barBtnItem];
}

#pragma mark - View Life Cycle

- (void)viewDidLoad{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    //自定义基类返回按键
    [self setLeftBarButtonItemTarget:self action:@selector(popToPreview)];
    //设置个背景色
    self.view.backgroundColor = [UIColor whiteColor];
}

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

子ViewController里换掉LeftBarButtonItem

如果我在自ViewController里换掉了LeftBarButtonItem,那我push进入一个新的同样基类的ViewController,返回键是那种情况呢

@interface ViewControllerOne : BaseViewController
@end
@interface ViewControllerTwo : BaseViewController
@end


//ViewControllerOne.m

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    [self setLeftBarButtonItemAsDismissBtn];
}

- (void)setLeftBarButtonItemAsDismissBtn {
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    UIImage *nImage = [UIImage resourceImageNamed:@"btn_dismiss"];
    [button setFrame:CGRectMake(0, 0, nImage.size.width, nImage.size.height)];
    [button setBackgroundImage:nImage forState:UIControlStateNormal];
    //
    [button addTarget:self action:@selector(touchUpInsideDismissBtn:) forControlEvents:UIControlEventTouchUpInside];
    //
    UIBarButtonItem *barBtnItem = [[UIBarButtonItem alloc] initWithCustomView:button];
    barBtnItem.style = UIBarButtonItemStylePlain;
    [self.navigationItem setLeftBarButtonItem:barBtnItem];
}

- (void)pushToViewControllerTwo {
ViewControllerTwo *vc = [[ViewControllerTwo alloc]init];
[self.navigationController pushViewController:vc animated:YES];
}

答案是,返回键仍然保持基类的样式,第一次我遇见的时候有个疑问既然navigationItem是共享的,为什么我换掉后ViewControllerTwo没有保持我替换后的LeftBarButtonItem呢

没有被替换的原因

因为ViewControllerTwo进行init的时候,又从新调用了基类的ViewDidLoad把LeftBarButtonItem换回来了.

//伪代码
//堆栈调用顺序
[ViewControllerOne viewDidLoad];
[ViewControllerOne setLeftBarButtonItemAsDismissBtn];
[ViewControllerOne pushToViewControllerTwo];
[[ViewControllerTwo alloc]init]
[ViewControllerOne viewDidLoad];
[BaseViewController viewDidLoad];
[BaseViewController setLeftBarButtonItemTarget:self action:@selector(popToPreview)];