Question

我使用以下代码在几秒钟后隐藏UILabel。不幸的是，如果用户在NSInvocation期间关闭视图，则应用程序崩溃

- (void)showStatusBarwithText:(NSString*)text{
    lblNotification.hidden=NO;
    NSInvocation* invoc = [NSInvocation invocationWithMethodSignature:[lblNotification methodSignatureForSelector:@selector(setHidden:)]];
    [invoc setTarget:lblNotification];
    [invoc setSelector:@selector(setHidden:)];
    lblNotification.text=text;
    BOOL yes = YES;
    [invoc setArgument:&yes atIndex:2];
    [invoc performSelector:@selector(invoke) withObject:nil afterDelay:1];

}

那就是错误

 *** -[UILabel setHidden:]: message sent to deallocated instance 0x1a8106d0

我该如何解决？我尝试过使用

[NSObject cancelPreviousPerformRequestsWithTarget:lblNotification]

在- (void)viewDidDisappear:(BOOL)animated但它不起作用。

Answer 1

以下是使用performSelector

的方法

- (void)showStatusBarwithText:(NSString*)text{
   lblNotification.hidden=NO;
   [self performSelector:@selector(hideLabel) withObject:nil afterDelay:1];//1sec
}


-(void)hideLabel{
  lblNotification.hidden= YES;
}

或使用计时器

[NSTimer scheduledTimerWithTimeInterval:1//1sec
                                 target:self
                               selector:@selector(hideLabel)
                               userInfo:nil
                                repeats:NO];

Answer 2

为什么不使用dispatch_afer？语法更清晰：

- (void)showStatusBarwithText:(NSString*)text{
    lblNotification.hidden=NO;
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        lblNotification.hidden = YES;
    });
}

Answer 3

这是因为您在此处传递了lblNotification而不是infoc对象：
[NSObject cancelPreviousPerformRequestsWithTarget:lblNotification]

这样做会更好：

- (void)showStatusBarwithText:(NSString*)text{
    lblNotification.hidden=NO;
    lblNotification.text=text;
    [lblNotification performSelector:@selector(setHidden:) withObject:@(1) afterDelay:2];     
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated]
    [NSObject cancelPreviousPerformRequestsWithTarget:lblNotification];
}

几秒钟后隐藏UIlabel

3 个答案: