ViewController基類

應(yīng)用開發(fā)的時候,總有一些ViewController是樣式相同的,那么就可以給這些樣式相同的ViewController創(chuàng)建一些基類,并且利用里面的viewDidLoad等函數(shù)完成一些重復(fù)的功能.出于自定義需求,我們還可以自定義一個LeftBarButtonItem.

//BaseViewController.m

import "BaseViewController.h"

@implementation BaseViewController

• (void)popToPreview{

  [self.navigationController popViewControllerAnimated:YES];

}

• (void)setLeftBarButtonItemTarget:(id)target action:(SEL)action{

  //自定義一個返回鍵

  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];

  //自定義返回鍵功能

  [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.

  //自定義基類返回按鍵

  [self setLeftBarButtonItemTarget:self action:@selector(popToPreview)];

  //設(shè)置個背景色

  self.view.backgroundColor = [UIColor whiteColor];

}

• (void)didReceiveMemoryWarning{

  [super didReceiveMemoryWarning];

  // Dispose of any resources that can be recreated.

}

@end

子ViewController里換掉LeftBarButtonItem

如果我在自ViewController里換掉了LeftBarButtonItem,那我push進(jìn)入一個新的同樣基類的ViewController,返回鍵是那種情況呢

@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,返回鍵仍然保持基類的樣式,第一次我遇見的時候有個疑問既然navigationItem是共享的,為什么我換掉后ViewControllerTwo沒有保持我替換后的LeftBarButtonItem呢

沒有被替換的原因

因為ViewControllerTwo進(jìn)行init的時候,又從新調(diào)用了基類的ViewDidLoad把LeftBarButtonItem換回來了.

//偽代碼

//堆棧調(diào)用順序

[ViewControllerOne viewDidLoad];

[ViewControllerOne setLeftBarButtonItemAsDismissBtn];

[ViewControllerOne pushToViewControllerTwo];

[[ViewControllerTwo alloc]init]

[ViewControllerOne viewDidLoad];

[BaseViewController viewDidLoad];

[BaseViewController setLeftBarButtonItemTarget:self action:@selector(popToPreview)];