iphone - 使用当前时间以编程方式添加 UILabel

Question

我有一个问题。也许我在错误的地方弄错了什么，但该死的我就是想不通!任何帮助将不胜感激。

我试图简单地以编程方式制作一个只在我的 subview 中显示的时钟。

我已经设置了一个计时器和一个更新程序 -(void)，我想在我创建的 subview 中显示它。我正在以编程方式构建 subview ，这就是不添加 IBOutlet 并将其连接到我的 Storyboard 中的原因 - 我正在尝试只用代码完成这一切。

我在我的 updateTimer 标签上收到错误消息 - 使用未声明的标识符“rightLabel”，它对我来说不起作用。哈哈 - 任何帮助将不胜感激!

.h

@interface DemoRootViewController : UIViewController <PaperFoldViewDelegate> {
    NSTimer *timer;
}
@property (nonatomic, strong) UIView *rightView;
-(void)updateTimer;

.m

- (id)init
{
    self = [super init];
    if (self) {

        //Timer Setup
        timer = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(updateTimer) userInfo:nil repeats:YES];

        //PaperFold Setup
        _paperFoldView = [[PaperFoldView alloc] initWithFrame:CGRectMake(0,0,[self.view bounds].size.width,[self.view bounds].size.height)];
        [_paperFoldView setAutoresizingMask:UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth];
        [self.view addSubview:_paperFoldView];

        //Setup Subview
        _rightView = [[UIView alloc] initWithFrame:CGRectMake(0,0,240,[self.view bounds].size.height)];

        //Setup UILabel
        UILabel *rightLabel = [[UILabel alloc] initWithFrame:_rightView.frame];
        [_rightView addSubview:rightLabel];

        //Using PaperFold Framework to Add the Subview (this works fine)
        [_paperFoldView setRightFoldContentView:_rightView foldCount:2 pullFactor:1];

    }
    return self;
}


-(void)updateTimer {
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"hh:mm:ss"];
    //This is where I get my error "Use of Undeclared Identifier 'rightLabel' 
    rightLabel.text = [formatter stringFromDate:[NSDate date]];
}

@end

Answer 1

您没有将 rightLabel 声明为属性(或实例变量)。只需将您的 .m 更改为以下代码:

.m

@interface DemoRootViewController ()
@property (nonatomic, strong) UILabel *rightLabel;
@property (nonatomic, strong) NSDateFormatter *dateFormatter;
@end

@implementation DemoRootViewController
- (id)init
{
    self = [super init];
    if (self) {

        //Timer Setup
        timer = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(updateTimer) userInfo:nil repeats:YES];

        //PaperFold Setup
        _paperFoldView = [[PaperFoldView alloc] initWithFrame:CGRectMake(0,0,[self.view bounds].size.width,[self.view bounds].size.height)];
        [_paperFoldView setAutoresizingMask:UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth];
        [self.view addSubview:_paperFoldView];

        //Setup Subview
        _rightView = [[UIView alloc] initWithFrame:CGRectMake(0,0,240,[self.view bounds].size.height)];

        //Setup UILabel
        self.rightLabel = [[UILabel alloc] initWithFrame:_rightView.frame];
        [_rightView addSubview:self.rightLabel];

        //Using PaperFold Framework to Add the Subview (this works fine)
        [_paperFoldView setRightFoldContentView:_rightView foldCount:2 pullFactor:1];

        //Formatter setup
        self.formatter = [[NSDateFormatter alloc] init];
        [self.formatter setDateFormat:@"hh:mm:ss"];
    }
    return self;
}


-(void)updateTimer {
    self.rightLabel.text = [self.formatter stringFromDate:[NSDate date]];
}

@end

@interface DemoRootViewController () 部分称为类扩展。它本质上允许您使用“私有(private)”属性，因此它们不会通过头文件公开。如果您希望将它们公开，只需将这两个属性定义放入 .h 文件即可。