在 WM 平台上开发 GPS 导航系统

核心提示：60 Dim Today As DateTime = System.DateTime.Now.ToUniversalTime61 Dim SatelliteTime As New System.DateTime(Today.Year, Today.Month, _62 Today.Day, UtcHours, UtcM

60 Dim Today As DateTime = System.DateTime.Now.ToUniversalTime

61 Dim SatelliteTime As New System.DateTime(Today.Year, Today.Month, _

62 Today.Day, UtcHours, UtcMinutes, UtcSeconds, UtcMilliseconds)

63 ' Notify of the new time, adjusted to the local time zone

64 RaiseEvent DateTimeChanged(SatelliteTime.ToLocalTime)

65 End If

66 ' Indicate that the sentence was recognized

67 Return True

68 End Function

69 ' Returns True if a sentence's checksum matches the calculated checksum

70 Public Function IsValid(ByVal sentence As String) As Boolean

71 ' Compare the characters after the asterisk to the calculation

72 Return sentence.Substring(sentence.IndexOf("*") + 1) = _

73 GetChecksum(sentence)

74 End Function

75 ' Calculates the checksum for a sentence

76 Public Function GetChecksum(ByVal sentence As String) As String

77 ' Loop through all chars to get a checksum

78 Dim Character As Char

79 Dim Checksum As Integer

80 For Each Character In sentence

81 Select Case Character

82 Case "$"c

83 ' Ignore the dollar sign

84 Case "*"c

85 ' Stop processing before the asterisk

86 Exit For

87 Case Else

88 ' Is this the first value for the checksum?

89 If Checksum = 0 Then

90 ' Yes. Set the checksum to the value

91 Checksum = Convert.ToByte(Character)

92 Else

93 ' No. XOR the checksum with this character's value

94 Checksum = Checksum Xor Convert.ToByte(Character)

95 End If

96 End Select

97 Next

98 ' Return the checksum formatted as a two-character hexadecimal

99 Return Checksum.ToString("X2")

100 End Function