下载大文件时应用崩溃-NSFileHandle seekToEndOfFile

Question

我有一个循环，它获取一堆文件（10个小txt文件和1个大图像文件，大约700KB）的URL，然后运行“ getFile”，为每个文件创建一个NSUrlConnection。

当应用程序在[file writeData：data]之前到达[file seekToEndOfFile]时，它崩溃并显示：

*** Terminating app due to uncaught exception 'NSFileHandleOperationException', reason: '*** -[NSConcreteFileHandle seekToEndOfFile]: No such process'
*** First throw call stack:

奇怪的是，如果我单步执行代码（即慢慢允许每个连接前进并返回），那么所有文件都可以正常下载。 如果我只是让应用执行其操作，则它会崩溃。

这是连接的代码：

-(void)getFile {
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:fullURL]];
    NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
    [conn start];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    NSString *fileName = [[response URL] lastPathComponent];
    NSString *filePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]stringByAppendingPathComponent:fileName];
    [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
    file = [NSFileHandle fileHandleForUpdatingAtPath:filePath];
    [file seekToEndOfFile];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [file seekToEndOfFile]; // crashing here
    [file writeData:data]; 
}
- (NSCachedURLResponse *)connection:(NSURLConnection *)connection
              willCacheResponse:(NSCachedURLResponse*)cachedResponse {
    return nil;
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"Connection is %@", connection);
    [file closeFile];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"error - %@", error);
}

我的应用程序在保留对传出连接的引用方面是否有问题？ 我假设默认情况下，NSURLConnections是异步的，您不需要“跟踪”它们吗？

编辑我有子类化NSURLConnection并实例化如下：

-(void)getFile {
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:fullURL]];
    FileURLConnection *conn = [[FileURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES ];
    conn.fileName = [fullURL lastPathComponent];
    [conn start];
}

Answer 1

我认为您正在与一位代表同时下载多个文件。 尝试子类NSURLConnection连接，并在其中添加属性file ，而不是委托的file属性。 而且我认为您不需要[file seekToEndOfFile];

编辑：子类NSURLConnection的示例

@interface FileURLConnection: NSURLConnection

@property (nonatomic, strong) NSFileHandle *file;

@end