Question

我从网址中检索NSData，然后尝试将其设置为图片。在控制台中它返回null，但是当我请求数据并再次设置图像时，图像比加载？

为什么要加载它必须完成两次？

这是我用来拍照的两种方法。

-(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

随着数据以递增方式加载，将重复调用connection:didReceiveData:方法。您可能需要使用connectionDidFinishLoading:方法。

顺便说一下，你仍然可能需要一个connection:didReceiveData:，但不是试图创建图像，而是将新数据附加到缓冲区。然后在connectionDidFinishLoading:方法中，您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第一次返回null，直到重新加载？

1 个答案: