imageIO 实现渐进加载图片的效果

话不多说，直接上代码

- (void)viewDidLoad {

    [super viewDidLoad];

    

//    _imageURL = [imageURLS retain];

    

    _request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://avatar.youkuaiyun.com/2/C/D/1_totogo2010.jpg"]];

    _conn    = [[NSURLConnection alloc] initWithRequest:_request delegate:self];

    

    _incrementallyimgSource = CGImageSourceCreateIncremental(NULL);

    

    _recieveData = [[NSMutableData alloc] init];

    _isLoadFinished = false;

    view = [[UIImageView alloc] initWithFrame:CGRectMake(10,10, 300, 300)];

    

    view.image = self.image;

    [self.view addSubview:view];

    

}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{

    _expectedLeght = response.expectedContentLength;

    NSLog(@"expected Length: %lld", _expectedLeght);

    NSString *mimeType = response.MIMEType;

    NSLog(@"MIME TYPE %@", mimeType);

    

    NSArray * arr = [mimeType componentsSeparatedByString:@"/"];

    if (arr.count < 1 || ![[arr objectAtIndex:0] isEqual:@"image"]) {

        NSLog(@"not a image url");

        [connection cancel];

        [_conn release]; _conn = nil;

    }

    

}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{

     [_recieveData appendData:data];

    _isLoadFinished = false;

    if (_expectedLeght == _recieveData.length) {

        _isLoadFinished = true;

    }

    CGImageSourceUpdateData(_incrementallyimgSource, (CFDataRef)_recieveData, _isLoadFinished);

    CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyimgSource, 0, NULL);

    view.image = [UIImage imageWithCGImage:imageRef];

//    [self.view addSubview:view];

    CGImageRelease(imageRef);

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{

    if (!_isLoadFinished) {

        CGImageSourceUpdateData(_incrementallyimgSource, (CFDataRef)_recieveData, _isLoadFinished);

        CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyimgSource, 0, NULL);

        view.image = [UIImage imageWithCGImage:imageRef];

        CGImageRelease(imageRef);

        [view setNeedsLayout];

    }

}

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

}