ios - 下载大文件时应用程序崩溃 - NSFileHandle seekToEndOfFile

Question

我有一个循环获取一堆文件的 URL(10 个小的 txt 文件和 1 个大约 700KB 的大图像文件)并运行“getFile”为每个文件创建一个 NSUrlConnection。

当应用程序到达 [file writeData:data] 之前的 [fileeekToEndOfFile] 时，它会崩溃:

*** 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(即慢慢地允许每个连接进行和返回)，那么所有文件都会正常下载。如果我只是让应用程序执行它的操作，它就会崩溃。

以下是连接代码:

-(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时是否存在问题？我假设 NSURLConnections 默认情况下是异步的，您不需要“跟踪”它们？

编辑我已对 NSURLConnection 进行子类化并实例化如下:

-(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(delegate)的文件属性。而且我认为您不需要 [file seekToEndOfFile];

编辑:示例子类 NSURLConnection

@interface FileURLConnection: NSURLConnection

@property (nonatomic, strong) NSFileHandle *file;

@end