ios - 从 url 获取图像作为空值

Question

嗨，我在从 url 获取图像时遇到问题。我从 Web 服务获取这些 url，然后逐个加载图像，这些图像附加在每个 url 中。

-(void)downloadMyfriendReqImage:(NSIndexPath *)path
{
    if (path.row<[arrayPendingRequests count]) {
        NSString *str=[[arrayPendingRequests objectAtIndex:path.row]valueForKey:@"USERIMAGE"];
        UIImage *img = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:str]]];

        if (img==nil) {
            img=[UIImage imageNamed:@"placeholder.png"];
        }

        [dicPendingReqImages setObject:img forKey:str];
        [tblFriendRequests performSelectorOnMainThread:@selector(reloadData) withObject:@"TAG_29" waitUntilDone:NO];
    }
}

这是我用来加载图像的方式。但问题是一些图像没有得到。img变成空值。但我在android中有相同的应用程序。它完美地加载了所有这些图像。这是什么问题..任何人都可以帮助我。

Answer 1

尝试这个：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSString *str=[[arrayPendingRequests objectAtIndex:path.row]valueForKey:@"USERIMAGE"];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:str]];
NSURLResponse *response;
NSError *error;
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
if (error) {
    // handle error
    return;
}
dispatch_async(dispatch_get_main_queue(), ^{
    // do something with the data
 UIImage *img = [[UIImage alloc] initWithData:data];
});
});

Answer 2

-(void)downloadMyfriendReqImage:(NSIndexPath *)path
{
    if (path.row<[arrayPendingRequests count]) {
        NSString *str=[[arrayPendingRequests objectAtIndex:path.row]valueForKey:@"USERIMAGE"];
        //ADDED LINE
        str=[str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

        UIImage *img = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:str]]];

        if (img==nil) {
            img=[UIImage imageNamed:@"placeholder.png"];
        }

        [dicPendingReqImages setObject:img forKey:str];
        [tblFriendRequests performSelectorOnMainThread:@selector(reloadData) withObject:@"TAG_29" waitUntilDone:NO];
    }
}

我认为您的网址包含一些NSURL无法读取的字符（例如空格），要使其正常工作，您需要为字符串添加编码，我认为它应该以这种方式工作.. 检查//ADDED LINE.

Answer 3

在将其转换为图像之前检查 NSData 请求的结果。可能是您从服务器获得超时。