Question

在我的iphone应用程序中，我正在从网上下载一些图像。如果它阻止UI线程并不重要，事实上它需要阻止UI线程直到完全下载。完成后，我会通知用户界面唤醒并显示它们。

我的（简化）代码如下：

for (int i=0; i<10; i++)
{
    //call saveImageFromURL (params)
}
//Call to Notify UI to wake up and show the images

+(void) saveImageFromURL:(NSString *)fileURL :(NSString *)destPath :(NSString *)fileName
{
    NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:fileURL]];

    NSFileManager * fileManager = [NSFileManager defaultManager];

    BOOL bExists, isDir;
    bExists = [fileManager fileExistsAtPath:destPath isDirectory:&isDir];

    if (!bExists)
    {
        NSError *error = nil;
        [fileManager createDirectoryAtPath:destPath withIntermediateDirectories:YES attributes:nil error:&error];
        if (error)
        {
            NSLog(@"%@",[error description]);
            return;
        }
    }

    NSString *filePath = [destPath stringByAppendingPathComponent:fileName];
    [data writeToFile:filePath options:NSAtomicWrite error:nil];
}

当我完成for循环后，我非常确定所有图像都存储在本地。它在模拟器中工作正常。

然而，它在我的设备上无效。 UI在存储图像之前唤醒。几乎所有图像都显得空洞。

我做错了什么？

Answer 1

检查您的设备是否可以下载这些图片，请访问Mobile Safari中的图片网址进行测试。 dataWithContentsOfURL:将返回nil或者它不是正确的图像数据，例如404找不到
记录[data writeToFile:filePath]的错误，以查看保存的详细信息。

Answer 2

经过一些研究，我使用AFHttpClient enqueueBatchOfHTTPRequestOperations来完成多个文件下载。

这是怎么回事：

//Consider I get destFilesArray filled with Dicts already with URLs and local paths

NSMutableArray * opArray = [NSMutableArray array];
AFHTTPClient *httpClient = nil;

for (id item in destFilesArray)
{
    NSDictionary * fileDetailDict = (NSDictionary *)item;
    NSString * url = [fileDetailDict objectForKey:@"fileURL"];
    if (!httpClient)
            httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:url]];

    NSString * filePath = [photoDetailDict objectForKey:@"filePath"];
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];

    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];          

    operation.outputStream = [NSOutputStream outputStreamToFileAtPath:filePath append:NO];
    [opArray addObject:operation];
}    

[httpClient enqueueBatchOfHTTPRequestOperations:opArray progressBlock:nil completionBlock:^(NSArray *operations)
{
    //gets called JUST ONCE when all operations complete with success or failure
    for (AFJSONRequestOperation *operation in operations)
    {

        if (operation.response.statusCode != 200)
        {                
            NSLog(@"operation: %@", operation.request.URL);
        }

    }

}];

NSData writeToFile适用于模拟器，但不适用于设备

2 个答案: