Block传值 反向传值

反向传值可以用单例、代理和Block，当然SEL也可以，下面简单介绍一下Block传值，直接上代码

1.新建一个single view工程

2.在AppDelegate.m中

    self.viewController = [[[ViewController alloc] initWithNibName:@"ViewController" bundle:nil] autorelease];        self.viewController.title = @"Block传值";    UINavigationController *nc = [[UINavigationController alloc] initWithRootViewController:self.viewController];        self.window.rootViewController = nc;

3.ViewController.h

@interface ViewController : UIViewController {    UILabel *valueLabel;//用来接收SecondViewController传回的值}@end

4.实现ViewController.m

- (void)viewDidLoad{    [super viewDidLoad];    valueLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 100, 300, 50)];    [self.view addSubview:valueLabel];    [valueLabel release];        UIBarButtonItem *nextBtn = [[UIBarButtonItem alloc] initWithTitle:@"next" style:UIBarButtonItemStylePlain target:self action:@selector(nextClick)];    self.navigationItem.rightBarButtonItem = nextBtn;    [nextBtn release];}

- (void)nextClick{    SecondViewController *svc = [[SecondViewController alloc] init];    svc.backValue = ^(NSString *strValue) {//设置SecondViewController里边的block属性，这是本程序的关键        valueLabel.text = strValue;    };    [self.navigationController pushViewController:svc animated:YES];    [svc release];}

5.SecondViewController.h

@interface SecondViewController : UIViewController@property (nonatomic, copy) void (^backValue)(NSString *strValue);@property (nonatomic, retain) UITextField *text;@end

6.实现SecondViewController.m

@implementation SecondViewController@synthesize backValue;@synthesize text;- (void)viewDidLoad{    [super viewDidLoad];        self.view.backgroundColor = [UIColor whiteColor];        text = [[UITextField alloc] initWithFrame:CGRectMake(10, 50, 300, 40)];    text.borderStyle = UITextBorderStyleRoundedRect;    [self.view addSubview:text];    [text release];        UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];    btn.frame = CGRectMake(10, 110, 60, 30);    [btn setTitle:@"返回" forState:UIControlStateNormal];    [btn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:btn];}- (void)btnClick{    self.backValue(self.text.text);//调用block方法    [self.navigationController popViewControllerAnimated:YES];}@end

效果图                                

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