从后台线程下载时未调用的可可下载文件回调，适用于主线程。

Question

我是可可编程新手，我正在尝试从url下载二进制文件到磁盘。不幸的是，由于某些原因，这些方法没有被调用。对downloadFile的调用是由后台线程通过self performSelectorOnBackground等启动的。有什么想法我做错了什么？

注意:当我从主UI线程调用downloadFile时，它似乎正常工作，后台线程是怎么回事?

-(BOOL) downloadFile
{
        BOOL downloadStarted = NO;
        // Create the request.
    NSURLRequest *theRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:versionLocation]
                cachePolicy:NSURLRequestUseProtocolCachePolicy
                timeoutInterval:60.0];

    // Create the connection with the request and start loading the data.
        NSURLDownload  *theDownload = [[NSURLDownload alloc] initWithRequest:theRequest
                                                                                                                                delegate:self];
    if (theDownload) {
        // Set the destination file.
        [theDownload setDestination:@"/tmp" allowOverwrite:YES];
                downloadStarted = YES;
    } else {
        // inform the user that the download failed.
                downloadStarted = NO;
    }

        return downloadStarted;

}


- (void)download:(NSURLDownload *)download didFailWithError:(NSError *)error
{
    // Release the connection.
    [download release];

    // Inform the user.
    NSLog(@"Download failed! Error - %@ %@",
          [error localizedDescription],
          [[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}

- (void)downloadDidFinish:(NSURLDownload *)download
{
    // Release the connection.
    [download release];

    // Do something with the data.
    NSLog(@"%@",@"downloadDidFinish");
}

Answer 1

我认为您应该启动连接NSURLDownload对象的run循环。默认情况下，它将使用当前线程的run循环，因此您可能应该在初始化NSURLDownload对象之后执行类似的操作：

NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
while (!self.downloaded && !self.error && [runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]])
        ;

属性self.downloaded和self.error应该在回调中设置。

在主线程中，运行循环可能是由NSApplication对象启动的。