我有蓝牙连接附件的输入流和输出流

我要实现以下目标:

将数据写入outputStream
等待，直到在inputStream上接收到数据，或者直到10秒钟过去
如果inputStream数据到达，则返回数据
否则返回nil

我试图这样实现:

- (APDUResponse *)sendCommandAndWaitForResponse:(NSData *)request {
  APDUResponse * result;
  if (!deviceIsBusy && request != Nil) {
    deviceIsBusy = YES;
    timedOut = NO;
    responseReceived = NO;
    if ([[mySes outputStream] hasSpaceAvailable]) {
      [NSThread detachNewThreadSelector:@selector(startTimeout) toTarget:self withObject:nil];
      [[mySes outputStream] write:[request bytes] maxLength:[request length]];
      while (!timedOut && !responseReceived) {
        sleep(2);
        NSLog(@"tick");
      }
      if (responseReceived && response !=nil) {
        result = response;
        response = nil;
      }
      [myTimer invalidate];
      myTimer = nil;
    }
  }
  deviceIsBusy = NO;
  return result;
}

- (void) startTimeout {
  NSLog(@"start Timeout");
  myTimer = [NSTimer timerWithTimeInterval:10.0 target:self selector:@selector(timerFireMethod:) userInfo:nil repeats:YES];
  [[NSRunLoop currentRunLoop] addTimer:myTimer forMode:NSRunLoopCommonModes];
}

- (void)timerFireMethod:(NSTimer *)timer {
  NSLog(@"fired");
  timedOut = YES;
}

- (void)stream:(NSStream*)stream handleEvent:(NSStreamEvent)streamEvent
{
  switch (streamEvent)
  {
    case NSStreamEventHasBytesAvailable:
      // Process the incoming stream data.
      if(stream == [mySes inputStream])
      {
        uint8_t buf[1024];
        unsigned int len = 0;
        len = [[mySes inputStream] read:buf maxLength:1024];
        if(len) {
          _data = [[NSMutableData alloc] init];
          [_data appendBytes:(const void *)buf length:len];
          NSLog(@"Response: %@", [_data description]);
          response = [[APDUResponse alloc] initWithData:_data];
          responseReceived = YES;
        } else {
          NSLog(@"no buffer!");
        }
      }
      break;
     ... //code not relevant 
  }
}

最佳答案

而是对固有的异步问题强加不合适的同步方法，而应使方法sendCommandAndWaitForResponse异步。

可以将“流写入”任务包装到异步操作/任务/方法中。例如，您可以使用以下接口(interface)以NSOperation的并发子类结尾:

typedef void (^DataToStreamCopier_completion_t)(id result);

@interface DataToStreamCopier : NSOperation

- (id) initWithData:(NSData*)sourceData
  destinationStream:(NSOutputStream*)destinationStream
         completion:(DataToStreamCopier_completion_t)completionHandler;

@property (nonatomic) NSThread* workerThread;
@property (nonatomic, copy) NSString* runLoopMode;
@property (atomic, readonly) long long totalBytesCopied;


// NSOperation
- (void) start;
- (void) cancel;
@property (nonatomic, readonly) BOOL isCancelled;
@property (nonatomic, readonly) BOOL isExecuting;
@property (nonatomic, readonly) BOOL isFinished;

@end

- (void)sendCommand:(NSData *)request 
         completion:(DataToStreamCopier_completion_t)completionHandler
{
    DataToStreamCopier* op = [DataToStreamCopier initWithData:request 
                                            destinationStream:self.outputStream 
                                                   completion:completionHandler];
   [op start];

   // setup timeout with block:  ^{ [op cancel]; }
   ...
}

[self sendCommand:request completion:^(id result) {
    if ([result isKindOfClass[NSError error]]) {
        NSLog(@"Error: %@", error);
    }
    else {
        // execute on a certain execution context (main thread) if required:
        dispatch_async(dispatch_get_main_queue(), ^{
            APDUResponse* response = result;
            ...    
        });
    }
}];

@interface WriteDataToStreamOperation : AsyncOperation

- (void) start;
- (void) cancel;

@property (nonatomic, readonly) BOOL isCancelled;
@property (nonatomic, readonly) BOOL isExecuting;
@property (nonatomic, readonly) BOOL isFinished;
@property (nonatomic, readonly) Promise* promise;

@end

- (Promise*) sendCommand:(NSData *)command {
    WriteDataToStreamOperation* op = 
     [[WriteDataToStreamOperation alloc] initWithData:command 
                                         outputStream:self.outputStream];
    [op start];
    Promise* promise = op.promise;
    [promise setTimeout:100]; // time out after 100 seconds
    return promise;
}

[self sendCommand:request].then(^id(APDUResponse* response) {
    // do something with the response
    ...
    return  ...;  // returns the result of the handler
}, 
^id(NSError*error) {
    // A Stream error or a timeout error
    NSLog(@"Error: %@", error);
    return nil;  // returns nothing
});

Promise* promise = [self sendCommand:request];
[promise setTimeout:100];
promise.then(^id(APDUResponse* response) {
    // do something with the response
    ...
    return  ...;  // returns the result of the handler
}, 
^id(NSError*error) {
    // A Stream error or a timeout error
    NSLog(@"Error: %@", error);
    return nil;  // returns nothing
});

-(void) testSendingCommandShouldReturnResponseBeforeTimeout10 {
    Promise* promise = [self sendCommand:request];
    [promise setTimeout:10];
    [promise.then(^id(APDUResponse* response) {
        // do something with the response
        XCTAssertNotNil(response);            
        return  ...;  // returns the result of the handler
    }, 
    ^id(NSError*error) {
         // A Stream error or a timeout error
        XCTestFail(@"failed with error: %@", error);
        return nil;  // returns nothing

    }) runLoopWait];  // "wait" on the run loop
}

关于ios - 如何实现超时/等待NSStream有效地使方法同步，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20700326/