ios - 阻塞 for 循环，直到委托(delegate)方法被触发

Question

我目前正在使用 CBPeripheralDelegate 在 iOS 设备和低功耗蓝牙 USB 加密狗之间交换消息。我必须实现使用串行仿真服务写入数据字节的 sendMessage: 方法。此方法必须同时发送一个 15 字节(或更少)的帧，在发送下一个之前等待来自加密狗的确认。

下面是我的代码:

- (void)sendMessage:(NSData *)message {
    NSArray *chuncks = [self splitMessage:message];
    for (NSUInteger i = 0; i < chunks.count; i++) {
        NSData *chunk = [chunks objectAtIndex:i];
        [self sendChunk:chunk withId:i ofChunks:chances.count];
        // Wait for the ack to be received
    }
}

- (void)sendChunk:(NSData *)chunk withId:(NSInteger)id ofChunks:(NSInteger)count {
    NSMutableData *frame = [NSMutableData new];
    // Here I build my frame, adding header, current chunk ID and total number of chunks, then I call...
    [serialEmulationService writeValue:frame forCharacteristic:serialEmulationServiceCharacteristic type:CBCharacteristicWriteWithResponse];
}

现在的问题是:必须阻止 sendMessage: 方法中的 for 循环，直到外围设备不会收到 ack，可能会超时。这个ack是在委托(delegate)方法- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(nonnull CBCharacteristic *)characteristic error:(nullable NSError *)error里面收到的，所以这里我要重启for 循环先前被阻止。

针对这种特定情况的最佳做法是什么？我想使用 GCD 的信号量，但我不知道如何实现同步调用，也无法理解解释该技术的许多在线示例中的任何一个。

有人可以帮我一下吗？

Answer 1

如何完全跳过 for 循环……

@property (nonatomic) NSMutableArray *chunks;
@property (nonatomic) NSInteger chunkId;

- (void)sendMessage:(NSData *)message {
    self.chunks = [[self splitMessage:message] mutableCopy];
    self.chunkId = 0;

    [self sendNextChunk];
}

- (void sendNextChunk {

   NSData * chunk = self.chunks.firstObject;

   if chunk == nil  {
      return 
   }

   [self.chunks removeObjectAtIndex: 0];
   [self sendChunk:chunk withId:chunkId++ ofChunks:chances.count];
}    


- (void)sendChunk:(NSData *)chunk withId:(NSInteger)id ofChunks:(NSInteger)count {
    NSMutableData *frame = [NSMutableData new];
    // Here I build my frame, adding header, current chunk ID and total number of chunks, then I call...
    [serialEmulationService writeValue:frame forCharacteristic:serialEmulationServiceCharacteristic type:CBCharacteristicWriteWithResponse];
}

- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(nonnull CBCharacteristic *)characteristic error:(nullable NSError *)error {
    [self sendNextChunk];
}