How to hide/show the UIimageview?

问题

- (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;
        }
}

The test results YES but the imageView doesn't listen the command .hidden or update every time when the viewDidAppear.If it is not when I restart the app and it disappear after I turn it to yes I show perfectly but after than I never goes always there I can't make it hidden. any idea why it is not reacting?

回答1:

The problem is you create new UIImageView every time when your view appears. You have to create UIImageView as once:

- (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];
}

and then show/hide it in -viewDidAppear method:

- (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;
    }
}

来源：https://stackoverflow.com/questions/7189082/how-to-hide-show-the-uiimageview