Question

我正在尝试使用此代码同时从我自己的服务器下载几个文件：

- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // create
    [[NSFileManager defaultManager] createFileAtPath:strFilePath contents:nil attributes:nil];
    _file = [NSFileHandle fileHandleForUpdatingAtPath:strFilePath];// read more about file handle
    if (_file)   {
        [_file seekToEndOfFile];
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)receivedata
{
    //write each data received
    if( receivedata != nil){
        if (_file)  {
            [_file seekToEndOfFile];
        }
        [_file writeData:receivedata];
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection*)theConnection {
    //close file after finish getting data;
    [_file closeFile];
}

- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    //do something when downloading failed
}
- (IBAction)downloadFromServer:(id)sender {

        NSLog(@"File now being downloaded");
    while (i<=3) {

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    NSURL *strFileURL =[NSURL URLWithString:[NSString stringWithFormat:@"SomePath/pic%d.png", i]];

    [request setURL:strFileURL]; 
    NSURLConnection *conection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
    [conection start];
    strFilePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:[NSString stringWithFormat:@"pic%d.png", i]];

    }

}

我有3张照片，pic1.png，pic2.png和pic3.png。现在，如果我运行此代码，应用程序将只保存一个名为pic3.png的损坏文件并自动崩溃。我需要下载所有三个文件，我出错的任何指针？

Answer 1

很明显，这不起作用。您启动三个异步操作。每次启动异步操作后，您都会将文件名存储在未知位置，但可能位于相同位置。那么当第一个异步操作完成时将使用什么文件名？提示：不是您认为会使用的那个。

Answer 2

不要使用简单的while循环来迭代REQUEST操作的数量。实际上Apple本身就有这么多内置库。所以我最好建议您尝试＆＃34; NSOPERATION QUEUE＆＃34; 。因此，您可以更好地查看Apple开发人员网站Notes，然后您就会明白：[1] https://developer.apple.com/library/IOs/documentation/Cocoa/Reference/NSOperationQueue_class/index.html

如何使用NSOperation处理不同的请求 - 如AddOperation或RemoveOperation，WaitUntilItFinishTheThread ..

Answer 3

最好的方法是将所有图片放在一个zip文件中，下载并使用以下代码在真实设备上解压缩：

    dispatch_queue_t queue = dispatch_get_global_queue(
                                                       DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{
        NSURL *url = [NSURL URLWithString:@"someDirectory/newPics.zip"];
        NSError *error = nil;
        // 2
        NSData *data = [NSData dataWithContentsOfURL:url options:0 error:&error];

        if(!error)
        {
            // 3
            NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
            NSString *path = [paths objectAtIndex:0];
            NSString *zipPath = [path stringByAppendingPathComponent:@"newPics.zip"];

            [data writeToFile:zipPath options:0 error:&error];

            if(!error)
            {

                ZipArchive *za = [[ZipArchive alloc] init];
                // 1
                if ([za UnzipOpenFile: zipPath]) {
                    // 2
                    BOOL ret = [za UnzipFileTo: path overWrite: YES];
                    if (NO == ret){} [za UnzipCloseFile];

                    // 3
                    NSString *imageFilePath = [path stringByAppendingPathComponent:@"newPics/pic1.png"];
                    //[self removeImage:zipPath];


                    [[NSFileManager defaultManager] removeItemAtPath:zipPath error: &error];

                    dispatch_async(dispatch_get_main_queue(), ^{

                            NSURL *fileURL = [NSURL fileURLWithPath:imageFilePath];
                            [_webV loadRequest:[NSURLRequest requestWithURL:fileURL]];



                    });

                }

            }
            else
            {
                NSLog(@"Error saving file %@",error);
            }
        }
        else
        {
            NSLog(@"Error downloading zip file: %@", error);
        }

    });

这是最好的方法，快速可靠。

未捕获的异常'NSFileHandleOperationException'

3 个答案: