UIImage完成加载时是否有事件

Question

我正在使用以下代码显示UIImage视图：

NSURL *imageUrl = [[NSURL alloc]initWithString:@"http://..."];
NSData *imageData = [[NSData alloc] initWithContentsOfURL:imageUrl];
UIImage *audioArt =[[UIImage alloc] initWithData:imageData];
UIImageView *artView =[[UIImageView alloc] initWithImage:audioArt];

artView.contentMode = UIViewContentModeScaleAspectFit;
artView.autoresizesSubviews = NO;
artView.frame = viewRef.bounds;
[artView setAutoresizingMask:UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight];
[artView setBackgroundColor:[UIColor blackColor]];

[viewRef setBackgroundColor:[UIColor blackColor]];
[viewRef addSubview:artView];

在Objective C中是否有一个事件可以告诉您该UIImage完成加载的时间或UIImageView完成显示图像的时间？

非常感谢。

Answer 1

在你的.h

@interface YourClass : YourSuperclass<NSURLConnectionDataDelegate>

@property (nonatomic) NSMutableData *imageData;
@property (nonatomic) NSUInteger totalBytes;
@property (nonatomic) NSUInteger receivedBytes;

和某处打电话

NSURL *imageUrl = [[NSURL alloc]initWithString:@"http://..."];
NSURLRequest *request = [NSURLRequest requestWithURL: imageUrl];
NSURLConnection *connection = [NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];

并实现委托方法

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *) urlResponse;
    NSDictionary *dict = httpResponse.allHeaderFields;
    NSString *lengthString = [dict valueForKey:@"Content-Length"];
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    NSNumber *length = [formatter numberFromString:lengthString];
    self.totalBytes = length.unsignedIntegerValue;

    [self.imageData = [[NSMutableData alloc] initWithLength:self.totalBytes];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.imageData appendData:data];
    self.receivedBytes += data.length;

    // Actual progress is self.receivedBytes / self.totalBytes
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    imageView.image = [UIImage imageWithData:self.imageData];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    //handle error
}

更新：

由于NSMutableData initWithLength:创建一个数据对象，其原始数据用零填充，因此将initWithLength:替换为init 。

Answer 2

UIImage没有任何委托或回调来告诉您其成功加载。

如果要从任何URL获取图像，则可以使用NSURL的委托和通知来跟踪是否收到图像。

您也可以通过以下方式实现它：

- (void)loadImage:(NSString *)filePath {
    [self performSelectorInBackground:@selector(loadImageInBackground:) withObject:filePath];
}

- (void)loadImageInBackground:(NSString *)filePath {
   @autoreleasepool{
        UIImage *image = [[UIImage alloc] initWithContentsOfFile:filePath];
        [self performSelectorOnMainThread:@selector(didLoadImageInBackground:) withObject:image waitUntilDone:YES];
    }
}

- (void)didLoadImageInBackground:(UIImage *)image {
    self.imageView.image = image;
}