IPhone - 下载异步工作，但加载异步不要

我建立我的表格视图的自定义单元格。我试图从互联网加载图片，为此，我正在使用异步下载。图像正在下载，但它没有在我的手机中显示此图像。我已经尝试在正常的视图中显示，并且工作正常。如果图像已经下载，或者如果我滚动表格视图并再次显示单元格，它也可以工作。有人知道发生了什么事吗？IPhone - 下载异步工作，但加载异步不要

代码：

DownloadImageManager.m

-(id)initWithImageName:(NSString *)imageAddress{ 
    self = [super initWithFrame:CGRectMake(10, 5, 100, 100)]; 
    if (self){ 
     self.urlString = imageAddress; 
     av = [[[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge] autorelease]; 
     av.frame = self.frame; 
     [av setBackgroundColor:[UIColor greenColor]]; 
     [self addSubview:av]; 
     [av startAnimating]; 
     [self checkImage]; 
    } 
    return self; 
} 

-(void)checkImage{ 
    bool isImageOnSysten = [self isImageOnFileSystem]; 
    if (isImageOnSysten) { 
     //If image is on the system, loads the image, it's working fine here 
     NSLog(@"CSantos: isImageOnSysten %@ is on system", self.urlString); 
    } else { 
     //here is the problem: 
     [self downloadImage]; 
    } 
} 

-(void)downloadImage{ 
    NSURL *url = [NSURL URLWithString:self.urlString]; 
    ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url]; 
    [request setDelegate:self]; 
    [request setAllowCompressedResponse:YES]; 
    [request setQueuePriority:NSOperationQueuePriorityLow]; 
    [request setDidFinishSelector:@selector(requestFinished:)]; 
    [request setDidFailSelector:@selector(requestFailed:)]; 
    [request setTimeOutSeconds:25]; 
    [request setNumberOfTimesToRetryOnTimeout:3]; 

    [request startAsynchronous]; 
} 

- (void)requestFinished:(ASIHTTPRequest *)request 
{ 
    NSData *responseData = [request responseData]; 
    NSArray *words = [self.urlString componentsSeparatedByString:@"/"]; 
    NSString *fileName = [words lastObject]; 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    NSString *writablePath = [documentsDirectory stringByAppendingPathComponent:fileName]; 
    NSError *error = nil; 
    [responseData writeToFile:writablePath options:NSDataWritingAtomic error:&error]; 
    NSLog(@"Write returned error: %@", [error localizedDescription]); 
    [av stopAnimating]; 
    [av removeFromSuperview]; 
}

CellForProgram.m

- (id)initWithFrame:(CGRect)frame reuseIdentifier:(NSString *)reuseIdentifier { 
    if (self = [super initWithFrame:frame reuseIdentifier:reuseIdentifier]) { 

     textLabel = [[UILabel alloc]initWithFrame:CGRectMake(60, 31, 235, 40)] ; 
     [self.contentView addSubview:textLabel]; 

     photo = [[UIImageView alloc] initWithFrame:CGRectMake(5, 5, 70, 70)]; 
     [photo setBackgroundColor:[UIColor blueColor]]; 
     photo.image = imagePhoto.image; 
     [self.contentView addSubview:photo]; 
    } 
    return self

细胞来电

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

    static NSString *CellIdentifier = @"Cell"; 

    CellForProgram *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier] ; 
    if (cell == nil) { 
     cell = [[[CellForProgram alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease]; 
    } 

    cell.textLabel.text = [speaker objectAtIndex:indexPath.row]; 

    DownloadImageManager *imageManager = [[DownloadImageManager alloc] initWithImageName:[images objectAtIndex:indexPath.row]]; 
    [cell.photo setImage:imageManager.image]; 
    return cell; 
}

来源

2011-11-16 Claudio

我告诉我不需要在DownloadImageManager上做这种改变！但是，谢谢你的帮助，它帮助我完成了其他的事情！

CellForProgram.m

- (id)initWithFrame:(CGRect)frame reuseIdentifier:(NSString *)reuseIdentifier { 
    if (self = [super initWithFrame:frame reuseIdentifier:reuseIdentifier]) { 

     textLabel = [[UILabel alloc]initWithFrame:CGRectMake(60, 31, 235, 40)] ; 
     [self.contentView addSubview:textLabel]; 

     imagePhoto = [[DownloadImageManager alloc] initWithImageName:imageAdress.text]; 
     [self.contentView addSubview:imagePhoto]; 
    } 
    return self 
}

DownLoadImageManager.m：添加此方法

-(void)changeImage:(NSString *)newImage{ 
    self.urlString = newImage; 
    [self checkImage]; 
}

细胞来电

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

    static NSString *CellIdentifier = @"Cell"; 

    CellForProgram *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier] ; 
    if (cell == nil) { 
     cell = [[[CellForProgram alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease]; 
    } 

    cell.textLabel.text = [speaker objectAtIndex:indexPath.row]; 

    [cell.imagePhoto changeImage:[images objectAtIndex:indexPath.row]]; 
    return cell; 
}

来源

2011-11-18 11:41:34 Claudio

你不与指针正常工作。

当您致电[cell.photo setImage:imageManager.image];并且图像不存在时，您将它指向零或随机存储器空间。

您需要在DownloadImageManager类上创建一个指向您的单元格的指针，以便在图像完成下载时更新单元格。

下面是我建议：

创建指向您的自定义的UITableViewCell
类不要设置上的tableView的图像DownloadImageManager属性：的cellForRowAtIndexPath：选择。相反，请直接在DownloadImageManager上设置它。

这里有一个简单的修改代码：

细胞来电

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

    static NSString *CellIdentifier = @"Cell"; 

    CellForProgram *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier] ; 
    if (cell == nil) { 
     cell = [[[CellForProgram alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease]; 
    } 

    cell.textLabel.text = [speaker objectAtIndex:indexPath.row]; 

    DownloadImageManager *imageManager = [[DownloadImageManager alloc] initWithImageName:[images objectAtIndex:indexPath.row] andCell:cell]; 
    return cell; 
}

DownloadImageManager.m

-(id)initWithImageName:(NSString *)imageAddress andCell:(CellForProgram*)cell{ 
    self = [super initWithFrame:CGRectMake(10, 5, 100, 100)]; 
    if (self){ 
     self.urlString = imageAddress; 
     self.cell = cell; 
     av = [[[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge] autorelease]; 
     av.frame = self.frame; 
     [av setBackgroundColor:[UIColor greenColor]]; 
     [self addSubview:av]; 
     [av startAnimating]; 
     [self checkImage]; 
    } 
    return self; 
} 

-(void)checkImage{ 
    bool isImageOnSysten = [self isImageOnFileSystem]; 
    if (isImageOnSysten) { 
     //If image is on the system, loads the image, it's working fine here 
     NSLog(@"CSantos: isImageOnSysten %@ is on system", self.urlString); 
     cell.photo = self.image; 
    } else { 
     //here is the problem: 
     [self downloadImage]; 
    } 
} 

-(void)downloadImage{ 
    NSURL *url = [NSURL URLWithString:self.urlString]; 
    ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url]; 
    [request setDelegate:self]; 
    [request setAllowCompressedResponse:YES]; 
    [request setQueuePriority:NSOperationQueuePriorityLow]; 
    [request setDidFinishSelector:@selector(requestFinished:)]; 
    [request setDidFailSelector:@selector(requestFailed:)]; 
    [request setTimeOutSeconds:25]; 
    [request setNumberOfTimesToRetryOnTimeout:3]; 

    [request startAsynchronous]; 
} 

- (void)requestFinished:(ASIHTTPRequest *)request 
{ 
    NSData *responseData = [request responseData]; 
    NSArray *words = [self.urlString componentsSeparatedByString:@"/"]; 
    NSString *fileName = [words lastObject]; 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    NSString *writablePath = [documentsDirectory stringByAppendingPathComponent:fileName]; 
    NSError *error = nil; 
    [responseData writeToFile:writablePath options:NSDataWritingAtomic error:&error]; 
    NSLog(@"Write returned error: %@", [error localizedDescription]); 
    [av stopAnimating]; 
    [av removeFromSuperview]; 

    cell.photo = self.image; 
}

这应该让你去。如果您需要澄清，请务必留言，我会尽快回复。

编辑：作为替代方案，实现对DownloadImageManager的委托方法...

一下添加到DownloadImageManager。H：

@protocol DownloadImageManagerDelegate <NSObject> 
@optional 
- (void)DownloadFinished:(DownloadImageManager*)manager; 
@end

取而代之的是CellForProgram的，使用DownloadImageManager协议，与此构造为例：

，改变你的requestFinished的实现：像这样：

- (void)requestFinished:(ASIHTTPRequest *)request 
{ 
    NSData *responseData = [request responseData]; 
    NSArray *words = [self.urlString componentsSeparatedByString:@"/"]; 
    NSString *fileName = [words lastObject]; 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    NSString *writablePath = [documentsDirectory stringByAppendingPathComponent:fileName]; 
    NSError *error = nil; 
    [responseData writeToFile:writablePath options:NSDataWritingAtomic error:&error]; 
    NSLog(@"Write returned error: %@", [error localizedDescription]); 
    [av stopAnimating]; 
    [av removeFromSuperview]; 

    if ([delegate respondsToSelector:@selector(DownloadFinished:)]) { 
     [delegate DownloadFinished:self]; 
    } 
}

然后，使您的细胞达到给定的协议，如下所示：

- (void)DownloadFinished:(DownloadImageManager*)manager { 
    this.photo = manager.image; 
}

这样您就可以随意地将您的功能保留在DownloadImageManager上。

来源

2011-11-16 14:14:25

伴侣，这是不是一个真正的好主意。这正在改变DownloadImageManager，我可以在这个单元格中使用它。如果我尝试在其他地方使用，我会收到很多错误消息。 – Claudio

@Claudio我向协议/委托理念添加了答案，您可以使用它来保持您的下载类的功能，并且仍然可以解决您的问题。 –

我刚刚说过：DownloadImageManager在所有其他接口中工作，但那一个（cell/tableview）。这不是课堂上的问题，而是我在这里使用的方式。 – Claudio

IPhone - 下载异步工作，但加载异步不要

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