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;
        }
}

测试结果为YES，但imageView没有响应.hidden命令或者在每次viewDidAppear后更新。如果我重启应用程序并将其转换为“yes”后它消失了，我可以完美地显示，但之后它永远不会再出现，我无法使其隐藏。有什么想法为什么它没有反应？

- john doe

Answer 1

问题在于每次视图出现时都创建了新的UIImageView。你需要只创建一次UIImageView：

- (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;
    }
}

- Narmo