如何隐藏/显示UIimageview？

Question

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    CGRect viewRect = CGRectMake(250, 100, 30, 30);
    as = [[UIImageView alloc] initWithFrame:viewRect];
    as.backgroundColor=[UIColor clearColor];
    UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"check" ofType:@"png"]];
    [as setImage:img];
    [self.view addSubview:as];
    BOOL test= [[NSUserDefaults standardUserDefaults] boolForKey:@"switch"];
    NSLog(@"%@", (test ? @"YES" : @"NO"));
    if(test == YES)
        {
            as.hidden=NO;
        }
    else
        {
            as.hidden=YES;
        }
}

该test结果YES ,但imageView不听指挥.hidden或更新每一次当viewDidAppear.如果它不是,当我重新启动应用程序,它消失,我把它变成是我完美的展示之后,但比之后,我从来没有总是去那里,我不能让它隐藏起来.知道为什么没有反应吗？

Answer 1

问题是UIImageView每次出现视图时都会创建新的.你必须创建UIImageView一次:

- (void)loadView {
    [super loadView];
    CGRect viewRect = CGRectMake(250, 100, 30, 30);
    as = [[UIImageView alloc] initWithFrame:viewRect];
    as.backgroundColor = [UIColor clearColor];
    UIImage *img = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"check" ofType:@"png"]];
    as.image = img;
    [self.view addSubview:as];
    [as release];
}

然后在 - viewDidAppear方法中显示/隐藏它:

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    BOOL test = [[NSUserDefaults standardUserDefaults] boolForKey:@"switch"];
    NSLog(@"%@", (test ? @"YES" : @"NO"));
    if(test == YES) {
        as.hidden = NO;
    }
    else {
        as.hidden = YES;
    }
}