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)];