Question

我有两个viewControllers，其中一个包含UILabel和一个UIButton，另一个包含UITableView。当按下第一个视图中的UIButton时，将显示新的ViewController，当选择tableview中的一行时，将取消tableview，并且应更新第一个viewController中的UILabel，使其文本与在其中点击的单元格名称相同。实现代码如下。代码：

在第一个Viewcontroller中：

- (void)changeTitleWithString:(NSString *)title
{
    UILabel* selected_station = [[UILabel alloc ]initWithFrame:CGRectMake(45, 153+45, 231, 20)];
    [selected_station setFont:[UIFont systemFontOfSize:16.0]];
    selected_station.textAlignment = NSTextAlignmentCenter;
    selected_station.text = [NSString stringWithFormat:@"%@", title];
    [self.view addSubview:selected_station];
    NSLog(@"%@", selected_station);
    NSLog(@"%@", title);
}

在第二个viewController中

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    self.currentString = [NSString stringWithFormat:@"Cell %d", indexPath.row+1];

    NewViewController *viewCOntroller = [[NewViewController alloc] init];
    [viewController changeTitleWithString:self.currentString];

    [self.navigationController dismissViewControllerAnimated:YES completion:nil];    
}

调用changeTitleWithString函数并在函数中成功接收来自tableview的字符串，但UILabel不会显示。当我注销UILabel（selected_station）时，它不是零并且其文本是正确的。为什么字符串不显示在视图上？

Answer 1

这看起来并不像您正在引用回到之前分配的视图控制器（NewViewController）。而是分配一个新的NewViewController。

更好的方法可能是为第二个视图控制器创建一个委托协议，并使NewViewController成为委托 -

因此，使用委托属性创建第二个视图控制器。

类似这样的事情

@protocol SecondViewControllerDelegate;

@interface SecondViewController : UIViewController

@property (nonatomic, strong) NSString *currentString;
@property (nonatomic, assign) id<SecondViewControllerDelegate>delegate;
@end

//----------------------------------------------------------------------------------
@protocol SecondViewControllerDelegate <NSObject>

@optional
-(void) secondViewController:(SecondViewController*)secondViewController didChangeSelectionText:(NSString *)string;
@end

现在在SecondViewController的实现中做了类似这样的事情

@implementation SecondViewController

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    self.currentString = [NSString stringWithFormat:@"Cell %ld", indexPath.row+1];

    if ([self.delegate respondsToSelector:@selector(secondViewController:didChangeSelectionText:)]) {
        [self.delegate secondViewController:self didChangeSelectionText:self.currentString];
    }
    [self.navigationController dismissViewControllerAnimated:YES completion:nil];
}

@end

现在在FirstViewController（你的NewViewController）的实现中做了类似这样的事情

@implementation FirstViewController

-(void) showSecondController
{
    SecondViewController *viewController = [[SecondViewController alloc] init];
    [viewController setDelegate:self]; // set this controller as the delegate
    // add the rest of the display code here
}

#pragma mark - SecondViewControllerDelegate Methods
-(void) secondViewController:(SecondViewController*)secondViewController didChangeSelectionText:(NSString *)string
{
    //change your text here
}
@end

这足以让你指向正确的方向

Answer 2

在FirstViewController中

- (void)changeTitleWithString:(NSString *)title :(UIView *)labelView
{
    UILabel* selected_station = [[UILabel alloc ]initWithFrame:CGRectMake(45, 153+45, 231, 20)];
    [selected_station setFont:[UIFont systemFontOfSize:16.0]];
    selected_station.textAlignment = NSTextAlignmentCenter;
    selected_station.text = title;
    [labelView addSubview:selected_station];
    NSLog(@"%@", selected_station);
    NSLog(@"%@", title);
}

InSecondViewController

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    self.currentString = [NSString stringWithFormat:@"Cell %d", indexPath.row+1];

    NewViewController *viewCOntroller = [[NewViewController alloc] init];
    [viewController changeTitleWithString:self.currentString:self.view];

    [self.navigationController dismissViewControllerAnimated:YES completion:nil];    
}

我希望它有所帮助

UILabel没有添加到视图中

2 个答案: