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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
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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];}
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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
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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
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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)];
