UIImage returns 第一次为 null，直到重新加载？

Question

我从 url 中检索 NSData，然后尝试将其设置为图像。在控制台中它 returns 为空，但是当我请求数据并再次设置图像时，图像会加载吗？

为什么必须执行两次才能加载？

这是我用来获取图片的两种方法。

-(void)getUserPicture {
//Grab and upload user profile picture
imageData = [[NSMutableData alloc] init]; // the image will be loaded in here
NSString *urlString = [NSString stringWithFormat:@"http://graph.facebook.com/%@/picture?type=large", userId];
NSMutableURLRequest *urlRequest =
[NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]
                        cachePolicy:NSURLRequestUseProtocolCachePolicy
                    timeoutInterval:3];

NSURLConnection *urlConnection = [[NSURLConnection alloc] initWithRequest:urlRequest
                                                                 delegate:self];
if (!urlConnection) NSLog(@"Failed to download picture");
}



-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    userPicture = [UIImage imageWithData:data];
    NSLog(@"%@",userPicture); //returns null in console first time, until reloaded???
}

Answer 1

随着数据的递增加载，connection:didReceiveData: 方法被重复调用。您可能需要 connectionDidFinishLoading: 方法。

顺便说一句，您可能仍然需要 connection:didReceiveData:，但您无需尝试创建图像，只需将新数据附加到缓冲区即可。然后在 connectionDidFinishLoading: 方法中，获取缓冲区并创建图像。

示例代码，但请根据需要添加错误处理：

@property (strong, nonatomic) NSMutableData *data;

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    self.data = [NSMutableData data];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.data appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    self.userPicture = [UIImage imageWithData:self.data];
}

UIImage returns 第一次为 null，直到重新加载？

UIImage returns null first time, until reloaded?

objective-c

nsurl

uiimage

ios