如何使用NSOutputStream的write消息？

Question

我想通过套接字将UIImage发送到服务器。

A)我打开outputstream：

- (IBAction)send:(id)sender {
    NSURL *website = [NSURL URLWithString:str_IP];
    NSHost *host = [NSHost hostWithName:[website host]];
    [NSStream getStreamsToHost:host port:1100 inputStream:nil outputStream:&oStream];
    [oStream retain];
    [oStream setDelegate:self];
    [oStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [oStream open];
}

b)在打开完成后，我将NSData写入outputstream，并在发生错误时处理错误。

- (void) stream: (NSStream *) stream handleEvent: (NSStreamEvent) eventCode
{
    //printf("EVENT: Start.\n");

    switch(eventCode)
    {
            case NSStreamEventOpenCompleted:
            {
                //printf("EVENT: Open completed.\n");

                if(stream == oStream)
                    {
                        //printf("Sending...\n");
                        NSData *data = UIImageJPEGRepresentation(drawImage.image, 90);
                        NSInteger x = [oStream write:[data bytes] maxLength:[data length]];
                    }

                break;
            }
            case NSStreamEventEndEncountered:
            {
                //printf("EVENT: End encountered.\n");
                break;
            }
            case NSStreamEventHasSpaceAvailable:
            {
                //printf("EVENT: Has space available.\n");
                break;
            }
            case NSStreamEventHasBytesAvailable:
            {
                //printf("EVENT: Has bytes available.\n");
                break;
            }
            case NSStreamEventErrorOccurred:
            {
                UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error Occurred"       
                                                                message:nil 
                                                               delegate:nil             
                                                      cancelButtonTitle:@"OK"               
                                                      otherButtonTitles:nil];                   
                [alert show];
                [alert release];
                break;
            }
            case NSStreamEventNone:
            {
                //printf("EVENT: None.\n");
                break;
            }
    }

    //printf("EVENT: End.\n");
}

当我运行这段代码时，NSStreamEventOpenCompleted和NSStreamEventErrorOccurred是空的NSOutputStream的called.The方法被成功调用，并且所有数据都不是空的。但在将数据写入oStream之后，eventCode将更改为NSStreamEventErrorOccurred。

所以我认为这可能不是使用oStream write的正确方式。那么使用这条消息的正确方式是什么呢？我发现此消息返回的NSInteger为-1073748088，这可能是什么问题？

Answer 1

您应该仅在输出流中有可用空间后才写入数据。当流完成打开时，它并不总是立即有可用的空间，因此写入它将不起作用。如果将write调用移动到NSStreamEventHasSpaceAvailable处理程序，它应该会成功。

此外，套接字另一端的计算机无法知道您正在发送的数据的长度。除非您通过关闭套接字来发出数据结束的信号，否则您应该显式地将数据长度与数据一起发送：

case NSStreamEventHasSpaceAvailable:
{
    if(stream == oStream)
    {
        NSData *data = UIImageJPEGRepresentation(drawImage.image, 90);
        // Convert from host to network endianness
        uint32_t length = (uint32_t)htonl([data length]);
        // Don't forget to check the return value of 'write'
        [oStream write:(uint8_t *)&length maxLength:4];
        [oStream write:[data bytes] maxLength:length];
    }
    break;
}