单例---视图间数据的传递：标签显示输入的内容【多个视图中】

RootViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor greenColor];

    //创建显示文字的label
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(50, 100, 200, 40)];
    label.tag = 102;
    label.backgroundColor = [UIColor grayColor];
    [self.view addSubview:label];
    [label release];

    //加入按钮
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(20, 20, 90, 60);
    [button setTitle:@"打开模态" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];

}

- (void)viewWillAppear:(BOOL)animated {

     UILabel *label = (UILabel *)[self.view viewWithTag:102];

    //创建单例对象
    BackData *backData = [BackData shareData];

    label.text = backData.text;

    [super viewWillAppear:animated];
}

- (void)buttonAction {

    ModalViewController *modalCtrl = [[[ModalViewController alloc] init] autorelease];

    modalCtrl.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;

    [self presentViewController:modalCtrl animated:YES completion:NULL];

}

ModalViewController.m

#import "BackData.h"

@interface ModalViewController ()

@end

@implementation ModalViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor redColor];

    //加入按钮
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(20, 20, 90, 60);
    [button setTitle:@"关闭模态" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];

    //创建输入框
    UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(50, 100, 200, 40)];
    textField.tag = 101;
    textField.borderStyle = UITextBorderStyleRoundedRect;
    [self.view addSubview:textField];
    [textField release];

}

- (void)buttonAction {

    UITextField *field = (UITextField *)[self.view viewWithTag:101];

    //创建单例对象
    BackData *data = [BackData shareData];
    data.text = field.text;

    [self dismissViewControllerAnimated:YES completion:NULL];

}

BackData.h

@interface BackData : NSObject

@property (nonatomic, copy) NSString *text;

+ (BackData *)shareData;

BackData.m

static BackData *data = nil;

@implementation BackData

+ (BackData *)shareData {

    if (data == nil) {
        data = [[BackData alloc] init];
    }

    return data;
}