NSData返回0个字节

Question

我试图以下列方式加载图像.但是当我调用我的loadImageFromURL:(NSURL*)inURL函数时[self loadImagesFromURL:url],我tableView的显示0字节.如何获得(delta)NSData我的tableview？的价值,被宣布为全球...

NSURLConnection* connection;
NSMutableData* delta;

- (void)loadImageFromURL:(NSURL*)inURL {
    NSURLRequest *request = [NSURLRequest requestWithURL:inURL];
    NSURLConnection *conn = [NSURLConnection connectionWithRequest:request delegate:self];

    if (conn) {
        delta = [[NSMutableData data] retain];
    }    
}

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

    }

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {     
    NSURL *urlink=[NSURL URLWithString:[[objectsForImages objectForKey:[arrayOfCharacters objectAtIndex:indexPath.section]] objectAtIndex:indexPath.row]];
    [self loadImageFromURL:urlink];
    UIImage *imageForAz=[UIImage imageWithData:delta];
    cell.imageView.image=imageForAz; 

}

Answer 1

你对异步性感到困惑.如果loadImageFromURL:是同步的,例如包装sendSynchronousRequest:returningResponse:error:,您的代码将按预期工作; loadImageFromURL:在获取时会阻塞,并在delta填充时返回.

但是,这都是异步的,所以你真正需要做的是connectionDidFinishLoading:在你的委托中实现(在本例中是self)并在那里设置cell.imageView.image它.

相应地重写一些代码(我假设你tableView:cellForRowAtIndexPath:为了这个例子的目的删除了无关的代码):

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {     
    NSURL *urlink=[NSURL URLWithString:[[objectsForImages objectForKey:[arrayOfCharacters objectAtIndex:indexPath.section]] objectAtIndex:indexPath.row]];
    [self loadImageFromURL:urlink];
}

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

有关更多详细信息/示例,请查看NSURLConnection上的URL加载系统编程指南.