iOS開發——block傳值

要實現界面之間值得傳遞，有兩種方法，一種是利用代理傳值，另一種是利用block傳值。
Apple 官方文檔中是這樣介紹block的，A block is an anonymous inline collection of code，and sometimes also called a “closure”.block是個代碼塊，但可以將他當做一個對象處理。下面就舉個利用block實現界面間的傳值。

本例說明：（firstView 的lablel文本初始值是first，當點擊按鈕進行頁面跳轉之後進入secondView的時候，此時block改變firstView中label的文本值爲second）

firstView.m

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor yellowColor];

    //創建一個Label，用於觀察block調用前後label.text的變化
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(50, 50, 300, 100)];
    label.text = @"first";
    self.label = label;
    [self.view addSubview:self.label];


    //創建一個button實現界面間的跳轉
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];

    button.frame = CGRectMake(50, 150, 150, 100);

    [button setTitle:@"To secondView" forState:UIControlStateNormal];

    [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:button];
}

-(void)buttonPressed
{
    SecondViewController *secondView = [[SecondViewController alloc] init];

    //block聲明的同時賦值
    secondView.myBlock = ^(NSString *color){
        self.label.text = color;
    };

    //跳轉到secondView的實現方法
    [self presentViewController:secondView animated:YES completion:nil];
}

secondView.h

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController

//block屬性
@property(nonatomic,strong)void(^myBlock)(NSString *color);

@end

secondView.m

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    self.view.backgroundColor = [UIColor greenColor];

    //創建一個按鈕，用於返回firstView
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];

    button.frame = CGRectMake(50, 150, 150, 100);

    [button setTitle:@"cancle" forState:UIControlStateNormal];

    [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:button];

    //調用myBlock，傳入second參數
    self.myBlock(@"second");
}


-(void)buttonPressed
{
    //返回之前的控制器
    [self dismissViewControllerAnimated:YES completion:nil];
}

運行代碼，結果如下：

開始的firstView界面

點擊按鈕後跳轉到secondView

點擊按鈕返回firstView，可看到label文本從first改變成了second