WinCE5.0移动平台开发笔记(OpenNETCF.Desktop.Communication连接和断开使用心得)

    当用PC机读取和操作PDA时候，需要用到RAPI,那么为了更好的使用RAPI，我们会使用到OpenNETCF.Desktop.Communication.dll文件，这个文件在Rapi.dll(win32 api)的基础上进行了NET封装。我们更能方便的使用它。对于连接和断开移动设备的方法，在使用过程中出现了一点问题，这里将记录下来，和朋友们分享：

     1、当我们首先实例化时：RAPI m_rapi = new RAPI();调用：m_rapi.Connect(false, 2).如果当PDA和PC没有连接成功时候，根据OpenNetCF.Desktop.Communication里面的方法，就会在子线程中抛出异常，主线程不能Catch获取子线程中异常，导致程序无法正常运行下去。相关代码如下：

    public void Connect(bool WaitForInit, int TimeoutSeconds)
        {
            int ret = 0;
            m_timeout = TimeoutSeconds;

            if(WaitForInit)
            {
                ret = CeRapiInit();
                if( ret != 0)
                {
                    int e = CeRapiGetError();

                    Marshal.ThrowExceptionForHR(ret);
                }

                lock(this)
                {
                    m_connected = true;
                }

                // throw the connected event
                if(RAPIConnected != null)
                {
                    RAPIConnected();
                }

                return;
            }

            // non-blocking init call
            m_ri = new RAPIINIT();

            m_ri.cbSize = Marshal.SizeOf(m_ri);
            m_ri.hrRapiInit = m_InitResult;

            m_hInitEvent = CreateEvent(IntPtr.Zero, 0, 0, "OpenNETCF.RAPI");

            if((uint)m_hInitEvent == uint.MaxValue)
            {
                throw new RAPIException("Failed to Initialize RAPI");
            }

            m_ri.heRapiInit = m_hInitEvent;

            ret = CeRapiInitEx(ref m_ri);
            if(ret != 0)
            {
                Marshal.ThrowExceptionForHR(ret);
            }

            // create a wait thread
            m_initThread = new Thread(new ThreadStart(InitThreadProc));

            // Start thread
            m_initThread.Start();
        }
        private void InitThreadProc()
        {
            int ret = 0;
            int timeout = m_timeout * 4;
            bool infinitetimeout = (timeout < 0);

            // check for Init event 4 times / sec
            do
            {
                // check for abort command from Dispose()
                if(m_killThread)
                {
                    return;
                }

                // see if the event is set
                ret = WaitForSingleObject(m_ri.heRapiInit, 250);

                if((ret == WAIT_FAILED) || (ret == WAIT_ABANDONED))
                {
                    throw new RAPIException("Failed to Initialize RAPI");
                }

                if(! infinitetimeout)
                {
                    if(timeout-- < 0)
                    {
                        throw new RAPIException("Timeout waiting for device connection");
                    }
                }
            } while(ret != WAIT_OBJECT_0);

            // check the hresult
            if(m_InitResult != 0)
            {
                Marshal.ThrowExceptionForHR(m_InitResult);
            }

            lock(this)
            {
                m_connected = true;
            }

            // throw the connected event
            if(RAPIConnected != null)
            {
                RAPIConnected();
            }

            // clean up
            CloseHandle(m_hInitEvent);
        }

 上面的代码当我们调用m_rapi.Connect(false,2)时候，最终在子线程中抛出异常:Timeout waiting for device connection

 为了在主线程中捕捉在子线程中出现的异常，我们对上面的代码做一些修改：

    public delegate void ExceptionEventHandler(RAPIException e);
    public event ExceptionEventHandler ThrowException;
    protected virtual void OnThrowException(RAPIException e)
        {
            if (ThrowException != null)
            {
                ThrowException(e);
            }
        }
    private void InitThreadProc()
        {
            int ret = 0;
            int timeout = m_timeout * 4;
            bool infinitetimeout = (timeout < 0);

            // check for Init event 4 times / sec
            do
            {
                // check for abort command from Dispose()
                if(m_killThread)
                {
                    return;
                }

                // see if the event is set
                ret = WaitForSingleObject(m_ri.heRapiInit, 250);

                if((ret == WAIT_FAILED) || (ret == WAIT_ABANDONED))
                {
                             CeRapiUninit();
                             OnThrowException(new RAPIException("Failed to Initialize RAPI"));
                             return;                           
               }
               if(! infinitetimeout)
                {
                    if(timeout-- < 0)
                    {
                             CeRapiUninit();
                             OnThrowException(new RAPIException("Timeout waiting for device connection"));
                             return;        
                    }                                                          
                }
            } while(ret != WAIT_OBJECT_0);

            // check the hresult
            if(m_InitResult != 0)
            {
                Marshal.ThrowExceptionForHR(m_InitResult);
            }

            lock(this)
            {
                m_connected = true;
            }

            // throw the connected event
            if(RAPIConnected != null)
            {
                RAPIConnected();
            }

            // clean up
            CloseHandle(m_hInitEvent);
        }

通过对上面代码的修改，我们定义了ExceptionEventHandler委托，那么当m_rapi初始化时:   获取连接失败的提示，给用户展示提示信息。

 m_rapi.ThrowException += new ExceptionEventHandler(m_rapi_ThrowException);
 void m_rapi_ThrowException(RAPIException e)
 {
        MessageBox.Show("连接超时！请确认把PDA和PC机连接好！");
 }

 上面的修改的代码中添加了CeRapiUninit()这个方法的调用，也就是说当PC和PDA没有连接时候，调用CeRapiInitEx方法，连接超时，但是资源仍然被占用，因此需要调用这个方法来释放资源。

  [DllImport("rapi.dll", CharSet = CharSet.Unicode)]
        internal static extern int CeRapiUninit();

曾经在项目中因没有调用这个CeRapiUninit时候，在pda和pc机没有连接:设备断开，抛出上面的异常情况给用户提示后，再将pda和pc连接，发现当pda和pc连接不成功,再一次断开，再一次连接，断开，始终都是连接不成功。最后发现问题是第一次连接设备抛出异常后没有释放资源引起的。

2、为了详细说明关于pda和pc连接状况监控，自己写了一个简单demo。做为学习的记录：

  public partial class MainForm : Form
    {
        internal class MyEventArgs : EventArgs
        {
            public Control Target;
            public string Text;
            public MyEventArgs(Control target, string text)
            {
                Target = target;
                Text = text;
            }
        }

        private RAPI m_rapi = new RAPI();
        private EventHandler statusUpdate;

        public MainForm()
        {
            InitializeComponent();
            m_rapi.RAPIConnected += new RAPIConnectedHandler(m_rapi_RAPIConnected);
            m_rapi.RAPIDisconnected += new RAPIConnectedHandler(m_rapi_RAPIDisconnected);
            m_rapi.ActiveSync.Listen += new ListenHandler(ActiveSync_Listen);
            m_rapi.ActiveSync.Answer += new AnswerHandler(ActiveSync_Answer);
            m_rapi.ThrowException += new ExceptionEventHandler(m_rapi_ThrowException);
            statusUpdate = new EventHandler(StatusUpdate);
             m_rapi.Connect(false, 2);
        }

        private void StatusUpdate(object sender, EventArgs args)
        {
            (sender as Label).Text = (args as MyEventArgs).Text;
        }

        void m_rapi_ThrowException(RAPIException e)
        {
            MessageBox.Show("连接超时！请确认把PDA和PC机连接好！");
        }

        void ActiveSync_Answer()
        {
            if (this.label1.InvokeRequired)
            {
                this.Invoke(statusUpdate, new object[] { this.label1, new MyEventArgs(this.label1, "连接状态:连接中...!") });
            }
            else
            {
                statusUpdate(this.label1, new MyEventArgs(this.label1, "连接状态:连接中...!"));
            }
        }

        void ActiveSync_Listen()
        {
            if (this.label1.InvokeRequired)
            {
                this.Invoke(statusUpdate, new object[] { this.label1, new MyEventArgs(this.label1, "连接状态:设备未连接!") });
            }
            else
            {
                statusUpdate(this.label1, new MyEventArgs(this.label1, "连接状态:设备未连接!"));
            }
        }

        void m_rapi_RAPIDisconnected()
        {
            if (this.label1.InvokeRequired)
            {
                this.Invoke(statusUpdate, new object[] { this.label1, new MyEventArgs(this.label1, "连接状态:连接关闭!") });
            }
            else
            {
                statusUpdate(this.label1, new MyEventArgs(this.label1, "连接状态:连接关闭!"));
            }
        }

        void m_rapi_RAPIConnected()
        {
            if (this.label1.InvokeRequired)
            {
                this.Invoke(statusUpdate, new object[] { this.label1, new MyEventArgs(this.label1, "连接状态:设备已连接!") });
            }
            else
            {
                statusUpdate(this.label1, new MyEventArgs(this.label1, "连接状态:设备已连接!"));
            }
        }

        private void MainForm_Load(object sender, EventArgs e)
        {
          
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (m_rapi.DeviceFileExists(@"\***\****.sdf"))
            {
                MessageBox.Show("文件存在！连接是成功的！");
            }
            else
            {
                MessageBox.Show("文件不存在！，连接不成功！");
            }
        }
    }

通过demo发现，连接状态的变化过程：

1.连接pda时候：设备未连接---->连接中...----->设备已连接

2.断开pda上：设备已连接----->连接关闭------->设备未连接

Best Regards,

Charles Chen