简述

在上篇文章 Windows Mobile下GPS管理软件NavsGo之GPS监控功能的开发 概述了NavsGo项目以及讲述了GPS监控功能的开发，GPS.net控件的使用，这篇文章讲述侦测功能的开发。

关于

所谓GPS侦测功能就是扫描手机上所有可用的GPS设备(available GPS devices)，把各个设备运行状态展现给用户，如果发现问题，通过友善的方式提示用户如果解决设备连通性问题。这些建议包括启动GPS设备，修改GPS Intermediate Driver的配置，启动蓝牙GPS设备等等。

实现

这个模块是GPS.net 作者jperson的一个demo程序，原程序可以到 GPS Diagnostics for .NET 下载。我做了少量修改加到NavsGo里面来了。

发现/检测功能(Detection)

发现功能在上篇文章讲过，通过注册静态事件，然后回调相应的处理函数。

/* Hook into GPS device detection events.  These events are static, allowing them to * be easily sunk by any other class or form. */Devices.DeviceDetectionStarted += newEventHandler(Devices_DeviceDetectionStarted);Devices.DeviceDetectionCompleted += newEventHandler(Devices_DeviceDetectionCompleted);Devices.DeviceDetected += newEventHandler<DeviceEventArgs>(Devices_DeviceDetected);Devices.DeviceDetectionAttempted += newEventHandler<DeviceEventArgs>(Devices_DeviceDetectionAttempted);Devices.DeviceDetectionAttemptFailed += newEventHandler<DeviceDetectionExceptionEventArgs>(Devices_DeviceDetectionAttemptFailed);

由于GPS.net是开源的，我们这次钻到他的源代码看看Detection的实现逻辑。

启动发现功能是在 Devices.BeginDetection() 函数里面。

        public static voidBeginDetection()        {// Start detection on another thread.if(_IsDetectionInProgress)return;

// Signal that detection is in progress_IsDetectionInProgress = true;

// Start a thread for managing detection_DetectionThread = newThread(newThreadStart(DetectionThreadProc));            _DetectionThread.Name = "GPS.NET Device Detector (http://www.geoframeworks.com)";            _DetectionThread.IsBackground = true;

#if!PocketPC// Do detection in the background            _DetectionThread.Priority = ThreadPriority.Lowest;#endif_DetectionThread.Start();

#ifPocketPC// Signal that the thread is alive (no Thread.IsAlive on the CF :P)_IsDetectionThreadAlive = true;#endif}

启动发现过程，系统会启动一个线程调用DetectionThreadProc()进行发现。下面是DetectionThreadProc()函数。

        private static voidDetectionThreadProc()        {try{// Signal that it startedOnDeviceDetectionStarted();

// Monitor this thread up to the timeout, then quitThreadPool.QueueUserWorkItem(newWaitCallback(DetectionThreadProcWatcher));

#ifPocketPC                              // Are we using the GPS Intermediate Driver?GpsIntermediateDrivergpsid = GpsIntermediateDriver.Current;

// Is the GPSID supported?if(gpsid != null)                {// Yes.  Test it to be suregpsid.BeginDetection();

// Wait for one device to get detected.  Was it confirmed?if(gpsid.WaitForDetection())                    {// Yes.  If we only need one device, exitif(_IsOnlyFirstDeviceDetected)return;                    }                }

#endif/* If we get here, the GPS Intermediate Driver is not responding! */intcount;

#regionDetect Bluetooth devices

// Is Bluetooth supported and turned on?if(IsBluetoothSupported && IsBluetoothEnabled)                {// Start bluetooth detection for each devicecount = _BluetoothDevices.Count;for(intindex = 0; index < count; index++)                        _BluetoothDevices[index].BeginDetection();                }

#endregion

                #regionDetect serial GPS devices

if(AllowSerialConnections)                {                    count = SerialDevices.Count;for(intindex = 0; index < count; index++)                        _SerialDevices[index].BeginDetection();

/* If we're performing "exhaustive" detection, ports are scanned                     * even if there's no evidence they actually exist.  This can happen in rare                     * cases, such as when a PCMCIA GPS device is plugged in and fails to create                     * a registry entry.                     */if(_AllowExhaustiveSerialPortScanning)                    {// Try all ports from COM0: up to the maximum port numberfor(intindex = 0; index < _MaximumSerialPortNumber; index++)                        {// Is this port already being checked?boolalreadyBeingScanned = false;for(intexistingIndex = 0; existingIndex < _SerialDevices.Count; existingIndex++)                            {if(_SerialDevices[existingIndex].PortNumber.Equals(index))                                {// Yes.  Don't test it againalreadyBeingScanned = true;break;                                }

// If it's already being scanned, stopif(alreadyBeingScanned)break;                            }

// If it's already being scanned, skip to the next portif(alreadyBeingScanned)continue;

// This is a new device.  Scan itSerialDeviceexhaustivePort = newSerialDevice("COM"+ index.ToString() + ":");                            exhaustivePort.BeginDetection();                        }                    }                }

#endregion

                #regionDiscover new Bluetooth devices

// Is Bluetooth supported and turned on?if(IsBluetoothSupported && IsBluetoothEnabled)                {/* NOTE: For mobile devices, only one connection is allowed at a time.                     * As a result, we use a static SyncRoot to ensure that connections                     * and discovery happens in serial.  For this reason, we will not attempt                     * to discover devices until *after* trying to detect existing ones.                     */#ifPocketPC// Wait for existing devices to be testedcount = _BluetoothDevices.Count;for(intindex = 0; index < count; index++)                    {// Complete detection for this device_BluetoothDevices[index].WaitForDetection();                    }#endif// Begin searching for brand new devicesBluetoothDevice.DiscoverDevices(true);

// Block until that search completesBluetoothDevice.DeviceDiscoveryThread.Join();                }

#endregion

                #regionWait for all devices to finish detection

/* A list holds the wait handles of devices being detected.  When it is empty,                  * detection has finished on all threads.                 */while(_CurrentlyDetectingWaitHandles.Count != 0)                {try{ManualResetEventhandle = _CurrentlyDetectingWaitHandles[0];#if!PocketPCif (!handle.SafeWaitHandle.IsClosed)#endifhandle.WaitOne();                    }catch(ObjectDisposedException)                    {/* In some rare cases a device will get disposed of and nulled out.                         * So, regardless of what happens we can remove the item.                         */}finally{                        _CurrentlyDetectingWaitHandles.RemoveAt(0);                    }                }

#endregion

#ifPocketPC#regionReconfigure the GPS Intermediate Driver (if necessary)

/* The GPS Intermediate Driver may not have the right "Program Port" (actual GPS port/baud rate)                 * settings.  Now that detection has completed, let's see if the GPSID needs configuration.                 * If it is flagged as NOT being a GPS device, then it could not connect.  In this case, let's                 * find the most reliable serial device and use it.                 */if(// Is the GPSID supported?gpsid != null// Are we allowed to configure it?&& gpsid.IsAutomaticallyConfigured // Is it currently NOT identified as a GPS device?  (connections failed)&& !gpsid.IsGpsDevice)                {// Look through each confirmed GPS devicecount = _GpsDevices.Count;for(intindex = 0; index < count; index++)                    {// Is it a serial device?SerialDevicedevice = _GpsDevices[index] asSerialDevice;if(device == null)continue;

// Yes.  Use it!try{                            gpsid.HardwarePort = device;

// The GPSID is now workingAdd(gpsid);                        }catch(Exceptionex)                        {// Notify of the error gracefullyOnDeviceDetectionAttemptFailed(newDeviceDetectionException(gpsid, ex));                        }

// That's the best device, so quitbreak;                    }                }

#endregion#endif// Signal completionOnDeviceDetectionCompleted();            }catch(ThreadAbortException)            {#regionAbort detection for all devices#ifPocketPC// Stop detection for the GPSIDif(GpsIntermediateDriver.Current != null)GpsIntermediateDriver.Current.CancelDetection();#endif// Stop detection for each Bluetooth devicefor(intindex = 0; index < _BluetoothDevices.Count; index++)                    _BluetoothDevices[index].CancelDetection();

// Stop detection for each serial devicefor(intindex = 0; index < _SerialDevices.Count; index++)                    _SerialDevices[index].CancelDetection();

#endregion// Wait for all the threads to die.  Just... sit and watch.  And wait.while(_CurrentlyDetectingWaitHandles.Count != 0)                {try{ _CurrentlyDetectingWaitHandles[0].WaitOne(); }catch{ }finally{ _CurrentlyDetectingWaitHandles.RemoveAt(0); }                }

// Signal the cancellationif(DeviceDetectionCanceled != null)                    DeviceDetectionCanceled(null, EventArgs.Empty);            }finally{// Detection is no longer in progress_DetectionCompleteWaitHandle.Set();                _CurrentlyDetectingWaitHandles.Clear();    // <--  Already empty?_IsDetectionInProgress = false;

#ifPocketPC// Signal that the thread is alive (no Thread.IsAlive on the CF :P)_IsDetectionThreadAlive = false;#endif}        }

DetectionThreadProc()负责整个发现过程，是一个很长的函数，有必要重构一下，把它分离(split)成几个小函数。他的处理逻辑是，检测超时，一旦发现发现过程超时，就好中途停止所有的处理。然后按顺序检测设备。检测的设备包括GPS Intermediate Driver设备(GpsIntermediateDriver)，串口设备(SerialDevice)和蓝牙设备(BluetoothDevice)。支持的设备类图如下：

所有设备都是继承于父类Device，这样可以通过容器类Devices类统一管理所有设备的对象，通过多态的方式去调用各个具体设备的处理函数来实现发现过程。对于每个独立的设备，他们统一发现流程是启动一个线程，然后试图打开该设备，如果超时，认为设备不可用，如果在超时之前读取到数据就分析输出数据，如果数据是标准的NMEA就认为这个是GPS设备。NMEA相关的可以参考.NET Compact Framework下的GPS NMEA data数据分析。

GPS Intermediate Driver设备的发现

发现过程首先检查的是GPS Intermediate Driver设备。在Windows Mobile 5+和Wince 6+的系统下一般都内嵌GPS Intermediate Driver，关于GPS Intermediate Driver的开发可以参考30 Days of .NET [Windows Mobile Applications] - Day 03: GPS Compass(GPS指南针) 。我计划增加 GPS Intermediate Driver管理功能到NavsGo里面，后续会把GPS Intermediate Driver管理的开发写下来。

已经配对了的蓝牙设备的发现

检测完GPS Intermediate Driver设备，就开始检查已经配对了的蓝牙设备(Paired Bluetooth Devices)，这些已经配对了的蓝牙设备保存在注册表HKEY_LOCAL_MACHINE\SOFTWARE\GeoFrameworks\GPS.NET\3.0\Devices\Bluetooth\中。关于蓝牙配对也可以参考一下 .NET Compact Framework下的Bluetooth设备的配对。

软件意义上的串口设备的发现

检测完已经配对了的蓝牙设备后，就开始检查串口设备，这里的串口设备是指软件意义上的串口，不是仅仅只通过硬件串口线连接的设备。由于 NMEA 0183 的规范规定GPS设备的联通性通过波特率(Baud rate)为4800的串口设备。所以GPS设备厂商尽管使用其他联通方式，但是都可以转成软件上的串口设备。例如USB GPS设备可以通过驱动转成串口设备，蓝牙可以建立虚拟串口，关于虚拟串口可以参考 .NET Compact Framework下的Bluetooth开发 之 Bluetooth Virtual Serial Port。总的来说，这里软件意义上的串口，真实的设备可能是 真正的串口线，USB，PCMCIA，蓝牙，红外等。

新蓝牙设备的发现

做完GPS Intermediate Driver设备，已经配对了的蓝牙设备和软件意义上的串口的发现流程后，进入了对新蓝牙设备的发现过程，这些蓝牙设备是不在已经配对了的蓝牙设备的范畴里面的，是手机周边新的蓝牙设备。由于手机对蓝牙的通信只能是一对一，也就是一个时间内一台手机只能和一个蓝牙设备进行通信，所以在发现新蓝牙设备之前，需要先等待已经配对了的蓝牙设备的发现过程的结束。关于蓝牙设备的开发和发现可以参考一下 .NET Compact Framework下的Bluetooth开发 之 Windows Embedded Source Tools for Bluetooth 和 .NET Compact Framework下的Bluetooth开发 之 32feet.NET。

GPS Intermediate Driver设备配置

一般来说移动设备都是通过GPS Intermediate Driver设备来对外部GPS程序提供服务的，有时候尽管GPS Intermediate Driver设备存在，并在运行，但是由于配置不正确也会导致外部GPS程序未能正确连接和使用GPS设备。所以最后一步是检查GPS Intermediate Driver设备的配置情况。我计划也在NavsGo增加GPS Intermediate Driver设备的配置管理功能。

最后的最后是清理所有资源，一个好的程序的习惯。

建议功能

发现功能实现了整个GPS诊断模块的核心，建议功能也就是呈现发现功能缓存的信息。建议功能实现在SummaryForm和DeviceForm两个类里面，SummaryForm提示建议，而DeviceForm现实某个设备的检查情况。

建议功能的流程是，判断GPS Intermediate Driver设备是否可用，如果不可用可能是硬件端口配置错误，建议把可用的串口端口配置为GPS Intermediate Driver的硬件端口，如果没有可用的串口端口，建议使用蓝牙设备。

日志功能

GPS.net提供日志发送功能，把设备发现和检查信息发送到服务器，方便开发者改进。这个功能很简单。

源码请看 Windows Mobile下GPS管理软件NavsGo之GPS监控功能的开发