Ios UIImage完成加载时是否存在事件

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中是否存在一个事件来告知此UIImage何时完成加载或UIImageView何时完成图像显示

---

非常感谢。

UIImage

没有任何委托或回调通知您其成功加载

如果您从任何url获取图像，您可以使用

NSURL

的委托和通知来跟踪您是否收到图像

您还可以通过以下方式实现：

- (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;
}

---

在您的

.h

@interface YourClass : YourSuperclass<NSURLConnectionDataDelegate>

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

并实现了委托方法

- (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:

创建了一个数据对象，该对象的原始数据用零填充，因此将

initWithLength:

替换为

initWithLength:

，它就会工作。

OP对“加载”的理解有点不清楚。但此“通知”不会安排在图像“加载”的时间点。其中“已加载”是指图像已加载其数据、对数据进行编码，并且UIKit已最终呈现该数据。UIImage惰性地“加载”图像

initWithContentsOfFile:

可能只在内部设置文件路径，就是这样。谢谢。我已经记录了整个过程，我肯定收到了数据。然而，在这一切的最后，

imageView.image=（null）

-你能想出任何原因吗？你分配了你的imageView吗？是的，图像视图被分配了，当I NSLog

self.imageData

当连接完成加载时，数据以零的加载开始（比如几kb的零）-我试过做一些类似于

if（data！=nil）{[self.imageData appendData:data]}

的事情，但这不起作用。你有什么想法吗？

NSMutableData initWithLength:

创建了一个数据对象，它的原始数据填充了zerosah，我用

initWithLength:

替换了

initWithLength:

，效果非常好！非常感谢！

- (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
}