gps.vb

清华大学出版社出版的 移动应用开发宝典 张大威（2008）的附书源代码

Imports System.Threading
Imports System.Runtime.InteropServices

Namespace Microsoft.WindowsMobile.Samples.Location


    Public Class Gps

        Private deviceStateChangedHandle As EventWaitHandle
        Private gpsEventThread As Thread = Nothing
        Private gpsHandle As IntPtr = IntPtr.Zero
        Private newLocationHandle As EventWaitHandle
        Private stopHandle As EventWaitHandle

        Private Event m_deviceStateChanged As DeviceStateChangedEventHandler

        Public Custom Event DeviceStateChanged As DeviceStateChangedEventHandler
            AddHandler(ByVal value As DeviceStateChangedEventHandler)
                AddHandler m_deviceStateChanged, value
                Me.CreateGpsEventThread()
            End AddHandler
            RemoveHandler(ByVal value As DeviceStateChangedEventHandler)
                RemoveHandler m_deviceStateChanged, value
            End RemoveHandler
            RaiseEvent(ByVal sender As Object, ByVal args As DeviceStateChangedEventArgs)
                RaiseEvent m_deviceStateChanged(sender, args)
            End RaiseEvent
        End Event

        Private Event m_locationChanged As LocationChangedEventHandler

        Public Custom Event LocationChanged As LocationChangedEventHandler
            AddHandler(ByVal value As LocationChangedEventHandler)
                AddHandler m_locationChanged, value
                Me.CreateGpsEventThread()
            End AddHandler
            RemoveHandler(ByVal value As LocationChangedEventHandler)
                RemoveHandler m_locationChanged, value
            End RemoveHandler
            RaiseEvent(ByVal sender As Object, ByVal args As LocationChangedEventArgs)
                RaiseEvent m_locationChanged(sender, args)
            End RaiseEvent
        End Event

        Public Sub Close()
            If (Me.gpsHandle <> IntPtr.Zero) Then
                Gps.GPSCloseDevice(Me.gpsHandle)
                Me.gpsHandle = IntPtr.Zero
            End If
            Me.stopHandle.Set()
            SyncLock Me
                Me.newLocationHandle.Close()
                Me.deviceStateChangedHandle.Close()
                Me.stopHandle.Close()
            End SyncLock
        End Sub

        Private Sub CreateGpsEventThread()
            If ((Me.gpsEventThread Is Nothing) AndAlso (Me.gpsHandle <> IntPtr.Zero)) Then
                Me.gpsEventThread = New Thread(New ThreadStart(AddressOf Me.WaitForGpsEvents))
                Me.gpsEventThread.Start()
            End If
        End Sub

        Protected Overrides Sub Finalize()
            Try
                Me.Close()
            Finally
                MyBase.Finalize()
            End Try
        End Sub

        Public Function GetDeviceState() As GpsDeviceState
            Dim device As New GPS_DEVICE
            device.dwVersion = 1
            device.dwSize = Marshal.SizeOf(GetType(GPS_DEVICE))
            If (Gps.GPSGetDeviceState(device) = 0) Then
                Return New GpsDeviceState(device)
            End If
            Return Nothing
        End Function

        Public Function GetPosition() As GpsPosition
            Return Me.GetPosition(TimeSpan.Zero)
        End Function

        Public Function GetPosition(ByVal maxAge As TimeSpan) As GpsPosition
            If Me.Opened Then
                Dim position As New GPS_POSITION
                position.dwVersion = 1
                position.dwSize = Marshal.SizeOf(GetType(GPS_POSITION))
                If (Gps.GPSGetPosition(Me.gpsHandle, position, &H7A120, 0) = 0) Then
                    Dim gp As New GpsPosition(position)
                    If ((maxAge <> TimeSpan.Zero) AndAlso Not (gp.TimeValid AndAlso ((DateTime.Now - maxAge) <= gp.Time))) Then
                        Return Nothing
                    End If
                    Return gp
                End If
            End If
            Return Nothing
        End Function

        <DllImport("gpsapi.dll")> _
        Private Shared Function GPSCloseDevice(ByVal hGPSDevice As IntPtr) As Integer
        End Function

        <DllImport("gpsapi.dll")> _
        Private Shared Function GPSGetDeviceState(ByRef pGPSDevice As GPS_DEVICE) As Integer
        End Function

        <DllImport("gpsapi.dll")> _
        Private Shared Function GPSGetPosition(ByVal hGPSDevice As IntPtr, ByRef pGPSPosition As GPS_POSITION, ByVal dwMaximumAge As Integer, ByVal dwFlags As Integer) As Integer
        End Function

        <DllImport("gpsapi.dll")> _
        Private Shared Function GPSOpenDevice(ByVal hNewLocationData As IntPtr, ByVal hDeviceStateChange As IntPtr, ByVal szDeviceName As String, ByVal dwFlags As Integer) As IntPtr
        End Function

        Public Sub Open()
            If Not Me.Opened Then
                Me.newLocationHandle = New EventWaitHandle(False, EventResetMode.AutoReset, Nothing)
                Me.deviceStateChangedHandle = New EventWaitHandle(False, EventResetMode.AutoReset, Nothing)
                Me.stopHandle = New EventWaitHandle(False, EventResetMode.AutoReset, Nothing)
                Me.gpsHandle = Gps.GPSOpenDevice(Me.newLocationHandle.Handle, Me.deviceStateChangedHandle.Handle, Nothing, 0)
                'If ((Not Me.locationChanged Is Nothing) OrElse (Not Me.deviceStateChanged Is Nothing)) Then
                Me.CreateGpsEventThread()
                'End If
            End If
        End Sub

        Private Sub WaitForGpsEvents()
            SyncLock Me
                Dim listening As Boolean = True
                Dim m_handles As WaitHandle() = New WaitHandle() {Me.stopHandle, Me.deviceStateChangedHandle, Me.newLocationHandle}
                Do While listening
                    Select Case EventWaitHandle.WaitAny(m_handles)
                        Case 0
                            listening = False
                            Exit Select
                        Case 1
                            RaiseEvent DeviceStateChanged(Me, New DeviceStateChangedEventArgs(Me.GetDeviceState))
                            Exit Select
                        Case 2
                            RaiseEvent LocationChanged(Me, New LocationChangedEventArgs(Me.GetPosition))
                            Exit Select
                    End Select
                Loop
                Me.gpsEventThread = Nothing
            End SyncLock
        End Sub

        Public ReadOnly Property Opened() As Boolean
            Get
                Return (Me.gpsHandle <> IntPtr.Zero)
            End Get
        End Property


    End Class

End Namespace