属性传值
顾名思义,属性传值是通过类的属性来进行值得传递.属性传值是最容易理解的一种传值方式.通常程序中页面的从前向后传值应用的都是属性传值.下面我们来看一下代码的实现:
AppDelegate.m
- (void)dealloc
{
[_window release];
[super dealloc];
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
ViewController *vc = [[ViewController alloc] init];
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:vc];
self.window.rootViewController = nav;
[vc release];
[nav release];
[_window release];
return YES;
}
ViewController.h
@interface ViewController : UIViewController
@property(nonatomic, copy) NSString *string;
@end
这里声明的字符串string就是我们要从第一页传到第二页的值.
ViewController.m
#import "ViewController.h"
#import "SecondViewController.h"
@interface ViewController ()
@property(nonatomic, retain) UITextField *textField;
@end
@implementation ViewController
- (void)dealloc
{
[_textField release];
[super dealloc];
}
- (void)loadView
{
[super loadView];
self.view.backgroundColor = [UIColor whiteColor];
self.navigationItem.title = @"首页";
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(didClickedRightBarButton:)];
self.textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 100, 175, 40)];
self.textField.placeholder = @"请输入文本";
self.textField.borderStyle = UITextBorderStyleRoundedRect;
[self.view addSubview:_textField];
}
- (void)didClickedRightBarButton:(UIBarButtonItem *)barButton
{
SecondViewController *vc2 = [[SecondViewController alloc] init];
vc2.secondString = self.textField.text;
//属性传值就在此执行,在我们push页面时需要在首页的按钮点击方法中建立一个新的SecondViewController的对象,在这里也就是vc2
//而我们在SecondViewController中已经声明了一个属性secondString用来接收传过去的值
//所以vc2现在要进行的操作我们可以理解为将要传的值存在vc2自己的属性secondString中
[self.navigationController pushViewController:vc2 animated:YES];
}
在ViewController中仅初始化一个textField用来输入字符串
直接使用navigationItem的rightBarButton创建一个执行push页面方法的按钮,点击后可以将页面推送到第二页.
SecondViewController.h
@interface SecondViewController : UIViewController
@property(nonatomic, copy) NSString *secondString;
@end
在SecondViewController中创建一个属性secondString用来接收第一页传过来的值.
@interface SecondViewController ()
@property(nonatomic, retain) UITextField *textField;
@end
@implementation SecondViewController
- (void)dealloc
{
[_textField release];
[super dealloc];
}
- (void)loadView
{
[super loadView];
self.view.backgroundColor = [UIColor whiteColor];
self.navigationItem.title = @"第二页";
self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(didClickedLeftBarButton:)];
self.textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 100, 175, 40)];
self.textField.placeholder = @"请输入文本";
self.textField.borderStyle = UITextBorderStyleRoundedRect;
self.textField.text = self.secondString;
//这里进行的就是将之前存在secondString中的值取出来放在textField中
[self.view addSubview:_textField];
}
- (void)didClickedLeftBarButton:(UIBarButtonItem *)leftButton
{
[self.navigationController popViewControllerAnimated:YES];
}
这里不再自定义button直接使用系统的按钮样式.
首页文本框中输入文本
会在第二页的文本框中进行显示
总结:属性传值通常用于从前向后的界面传值,当然从后向前通过属性传值也是可以实现的,不过不推荐使用.因为在界面过多的情况下,从后向前的属性传值过于繁琐(需要通过下标在栈中寻找要传值的ViewController)且不够灵活.在之后我写的文章中会介绍其他几种传值方式,更加灵活
