Unable to read from a Bluetooth socket

I am trying to communicate with a Bluetooth device. I have succeeded in outStream.Write(outBuf, 0, outBuf.Length); but int readLen = inStream.Read(inBuf, 0, inBuf.Length); never returns.

I am sure that the device has successfully received the bytes I sent and returned some bytes. I have written a Java version of this program and it works well, but now get problem on C# Xamarin.

Here is my code, please anybody help me:

        BluetoothSocket btSocket = null;
        BluetoothAdapter mBluetoothAdapter = null;
        try{
            mBluetoothAdapter = BluetoothAdapter.DefaultAdapter;
        }
        catch (Exception e){

        }
        if (mBluetoothAdapter == null){
            return null;
        }


        ICollection<BluetoothDevice> boundSet = mBluetoothAdapter.BondedDevices;
        BluetoothDevice btDevice1 = boundSet.ElementAt(0);
        btSocket = btDevice1.CreateRfcommSocketToServiceRecord(UUID.FromString("00001101-0000-1000-8000-00805F9B34FB"));
        mBluetoothAdapter.CancelDiscovery();
        try{
            btSocket.Connect();
        }
        catch (Exception e)
        {
            return e.Message;
        }

        Stream outStream = btSocket.OutputStream;
        Stream inStream = btSocket.InputStream;
        //inStream.ReadTimeout = 5000;
        byte[] outBuf = new byte[5] { 0xAC, 0x00, 0x00, 0x74, 0xAA };
        byte[] inBuf = new byte[1];
        outStream.Write(outBuf, 0, outBuf.Length);

        int readLen = inStream.Read(inBuf, 0, inBuf.Length);   //This line NEVER returns.
        return string.Format("readLen{0} {1} readRet!", readLen, inBuf[0]);

Thank you very much.