objective-c - 异步加载和更改图像

Question

我从网站异步加载 4 张图像，加载后我用计时器更改它们，但看起来图像数组总是第一张图像，当我更改到数组的另一个位置时，它包含相同的图像，根本不要改变...

- (void)viewDidLoad 
{
    [super viewDidLoad];

    [self getImages];
}

-(void)getImages
{
    receivedData = [[NSMutableData alloc]init];
    myImages = [[NSMutableArray alloc]init];
    myImagesAdresses = [[NSMutableArray alloc]initWithCapacity:5];

    [myImagesAdresses addObject:@"adress/Images/3.png"];
    [myImagesAdresses addObject:@"adress/Images/2.png"];
    [myImagesAdresses addObject:@"adress/Images/1.png"];
    [myImagesAdresses addObject:@"adress/Images/0.png"];

    [self loadNextImage];
}

-(void)loadNextImage
{
    if([myImagesAdresses count])
    {
        NSURL * imageURL = [NSURL URLWithString:[myImagesAdresses lastObject]];
        NSURLRequest * myRequest = [NSURLRequest requestWithURL:imageURL];
        [[NSURLConnection alloc]initWithRequest:myRequest delegate:self];
        NSLog(@"Start load URL %@",imageURL);
    }
    else {
        [self.theImage setImage:[myImages objectAtIndex:2]];
        [self changeImage];
        NSLog(@"No More Images to Load");
    }
}

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

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [myImages addObject:[UIImage imageWithData:[NSData dataWithData:receivedData]]];
    [connection release];
    connection = nil;
    NSLog(@"Image from %@ loaded",[myImagesAdresses lastObject]);
    [myImagesAdresses removeLastObject];
    [self loadNextImage];
}

-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    [connection release];
    connection =nil;
    NSLog(@"Image from %@ not loaded", [myImagesAdresses lastObject]);
    [myImagesAdresses removeLastObject];
    [self loadNextImage];
}

以及更改图像的代码:

-(void)changeImage
{
    SEL selectorToCall = @selector(change: );

    NSMethodSignature *methodSignature = [[self class] instanceMethodSignatureForSelector:selectorToCall];

    NSInvocation * invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
    [invocation setTarget:self];
    [invocation setSelector:selectorToCall];

    NSTimer * newTimer = [NSTimer scheduledTimerWithTimeInterval:5.0 invocation:invocation repeats:YES];

    self.paintingTimer = newTimer;
}

- (void) change:(NSTimer *)paramTimer
{
    static NSInteger currentElement = 0;
    if(++currentElement == [myImages count]) currentElement = 0;
    [self.theImage setImage:[myImages objectAtIndex:currentElement]];
}

- (void) stopPainting
{
    if (self.paintingTimer != nil){
        [self.paintingTimer invalidate];
    }
}

我没有收到任何错误，但图像根本没有改变...

Answer 1

看起来 receivedData 是一个重复追加的 ivar，但它永远不会被清除。所以在收到第一张图片后，第二张图片被附加到它上面，依此类推。

在这一行之后，你应该清空receivedData:

[myImages addObject:[UIImage imageWithData:[NSData dataWithData:receivedData]]];