objective-c - 无法为 UIImageView 设置图像

Question

我有一个 UIImageView，但我无法获取图像并设置它显示。

在 viewDidLoad

albumContainer = [[UIImageView alloc]initWithFrame:CGRectMake(112, 7, 97, 97)];
[self.view addSubview:albumContainer];

不同类调用的方法

NSLog(@"URL:%@",url);
//URL is defined by different class
//URL is http://www.....882546328.jpg (I abbreviated it, but it is a valid url)
NSData *imageData = [NSData dataWithContentsOfURL:url];
NSLog(@"URL LENGTH:%d",[imageData length]);
// URL LENGTH:90158

UIImage *tempImage = [UIImage imageWithData:imageData];
[albumContainer setImage:tempImage];

完整代码

播放器 View Controller

-(void)viewDidLoad{
    [super viewDidLoad];
    playerView = [[AlbumViewController alloc]initWithNibName:@"AlbumViewController" bundle:nil];
}
-(void)playMusic{

    playerView.url = [NSURL URLWithString:imagePathForm];
    playerView.songData = receivedData;
    [loadingSong stopAnimating];
    [playerView play]; 

}

相册 View Controller

- (void)viewDidLoad
{
    [super viewDidLoad];
    albumContainer = [[UIImageView alloc]initWithFrame:CGRectMake(112, 7, 97, 97)];
    [self.view addSubview:albumContainer];
    url = [NSURL URLWithString:@""];
}

-(void)play{
    NSLog(@"SONGDATA:%d",[songData length]);
    player = [[AVAudioPlayer alloc] initWithData:songData error: nil];
    [player stop];

    player.delegate = self;
    player.numberOfLoops = 0;
    player.volume = 0.5; 
    [player prepareToPlay];
    [player play];
    NSLog(@"URL:%@",url);
    NSData *imageData = [NSData dataWithContentsOfURL:url];
    NSLog(@"URL LENGTH:%d",[imageData length]);

    UIImage *tempImage = [UIImage imageWithData:imageData];

    [albumContainer setImage:tempImage];

}

我检查了一下，albumContainer 记录为 NULL

Answer 1

在设置图像之前，您是否检查过 Controller 的 View 是否已加载？ UIViewControllers 在显示之前不会加载它们的 View ，有时它们会在屏幕外卸载它，因此在您调用您的 viewDidLoad 时可能尚未调用

[albumContainer setImage:tempImage];

从 Controller 外部。在设置图像之前尝试记录 albumContainer 以查看它是否为 nil，如下所示:

NSLog(@"albumContainer: %@", albumContainer); //might log as null
[albumContainer setImage:tempImage];

要强制加载 Controller 的 View ，您可以说:

[controller view]; // this will load the view and call viewDidLoad
[albumContainer setImage:tempImage];

但您最好在 View Controller 的 initWithNibName:bundle: 方法中创建 albumContainer，而不是在 viewDidLoad 中，如下所示:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)bundleOrNil
{
    if ((self = [super initWithNibName:nibNameOrNil bundle:bundleOrNil]))
    {
         albumContainer = [[UIImageView alloc]initWithFrame:CGRectMake(112, 7, 97, 97)];
[self.view addSubview:albumContainer];
    }
    return self;
}

这样，即使 View 尚未加载，它也会与 Controller 同时创建。