iOS Objective-C塊回調問題

Question

我正在嘗試使用純代碼在viewController之間創建UI練習塊傳遞值。 但是回調塊不起作用。 NSLog方法未在調試區域上打印任何內容。 這是代碼。 給我一些提示，謝謝。

VC文件

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController
    @property (copy, nonatomic) void (^callBack)(NSString *text);
@end

VC

- (UITextField *)textField {
    if (!_textField) {
        _textField = [[UITextField alloc] init];
        _textField.backgroundColor = [UIColor whiteColor];
    }
    return _textField;
}

- (UIButton *)button {
    if (!_button) {
        _button = [[UIButton alloc] init];
        _button.backgroundColor = [UIColor blueColor];
        [_button addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];
    }
    return _button;
}

- (void)setupUI {
    [self.view addSubview:self.textField];
    [self.view addSubview:self.button];

    [self.textField mas_makeConstraints:^(MASConstraintMaker *make) {
        make.width.mas_equalTo(200);
        make.height.mas_equalTo(50);
        make.centerX.mas_equalTo(self.view.mas_centerX);
        make.centerY.mas_equalTo(self.view);
    }];

    [self.button mas_makeConstraints:^(MASConstraintMaker *make) {
        make.width.mas_equalTo(200);
        make.height.mas_equalTo(50);
        make.centerX.mas_equalTo(self.view);
        make.centerY.mas_equalTo(self.view).offset(100);
    }];
}

- (void)buttonAction {

    NSString *str = self.textField.text;
    if (self.callBack != nil) {
        self.callBack(str);
        NSLog(@"This statement didnt print in log");
    }
}

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

    self.view.backgroundColor = [UIColor redColor];
}

---

更新代碼

VC2.m

- (void)viewWillAppear:(BOOL)animated{

            self.callBack = ^(NSString *text){

            };
    }
- (void)buttonAction {

    if (self.callBack) {
        NSLog(@"It worked on debug area %@", self.textField.text);
        self.callBack(self.textField.text);
    }
    self.textField.text = @"";
}

VC1.m

- (void)viewDidLoad {
    [super viewDidLoad];
    _secondVc = [[SecondViewController alloc] init];
    _secondVc.callBack = ^(NSString *str){

    };
    [self setupUI];

    self.view.backgroundColor = [UIColor greenColor];
}

- (void)viewWillAppear:(BOOL)animated {

    if (_secondVc.callBack != nil) {
        NSLog(@"It wrked on debug screen");
        _secondVc.callBack = ^(NSString *str){
            NSLog(@"It didn't worked on debug screen");
            //I want set my label.text = str;
        };
};

}

Answer 1

唯一的辦法就是你財產

@property (copy, nonatomic) void (^callBack)(NSString *text);

是空的。 嘗試在buttonAction方法中放置斷點並查看屬性。

Answer 2

正如Sander和KrishnaCA提到的，您的callBack叫為零。 我建議您像這樣創建塊的定義：

typedef void(^TextBlock)(NSString *text);

然后將您的屬性更改為：

@property (copy, nonatomic) TextBlock callBack;

在第一個視圖控制器中創建塊的副本：

@interface FirstViewController()

@property (copy, nonatomic) TextBlock firstViewControllerCallBack;

@end

初始化回調副本（即在viewDidLoad中）

- (void)viewDidLoad {
    [super viewDidLoad];
    self.firstViewControllerCallBack = ^(NSString *text){
        NSLog(@"Second view controller's button tapped!");
    };
}

在呈現/推動回調之前，將回調分配給第二個視圖控制器：

SecondViewController *secondVC = [[SecondViewController alloc] init];
secondVC.callBack = self.firstViewControllerCallBack; // Assign the callback
// ... Presenting the view controller

完成后，清理完成塊（即在viewWillDisappear中）：

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    self.firstViewControllerCallBack = nil;
}