Question

我正在尝试使用纯代码在viewController之间创建UI练习块传递值。但回调块无法正常工作。 NSLog方法没有在调试区域上打印任何内容。这是代码。给我一些提示，谢谢。

VC.h

#import <UIKit/UIKit.h>

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

VC.m

- (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];
}

更新代码

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

唯一的方法是你的财产

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

是空的。尝试在buttonAction方法中放置断点并查看属性。

Answer 2

Sander和KrishnaCA提到你的callBack是零。我建议你像这样创建一个块的定义：

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

然后将您的财产更改为：

@property (copy, nonatomic) TextBlock callBack;

在第一个视图控制器中创建块的副本：

@interface FirstViewController()

@property (copy, nonatomic) TextBlock firstViewControllerCallBack;

@end

初始化回调副本（即在viewDidLoad中）

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

在呈现/推送之前将回调分配给第二个视图控制器：

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

完成后清理完成块（即在viewWillDisappear中）：

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

iOS Objective-C阻止回调问题

2 个答案: