1.每一个实体都有一个首地址值
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2.堆内存中的每一个变量都有默认初始化值,根据类型的不同而不同.整数是0,小数0.0或者0.0f,boolean是false,char是'\u0000'
3.垃圾回收机制//自动回收垃圾
右击工具箱/部件/WindowsMediaPlayer
//类模块Mmedia
Option Explicit
'-----------------------------------------------------
' Name : MMedia.cls
' Author : Peter Wright, For BG2VB4 BG2VB5
'
' Notes : A multimedia class, which when turned
' : into an object lets you load and play
' : multimedia files, such as sound and
' : video.
'-----------------------------------------------------
' -=-=-=- PROPERTIES -=-=-=-
' Filename Determines the name of the current file
' Length The length of the file (Read Only)
' Position The current position through the file
' Status The current status of the object (Read Only)
' Wait True/False...tells VB to wait until play done
' -=-=-=- METHODS -=-=-=-=-
' mmOpen Filename Opens the requested filename
' mmClose Closes the current file
' mmPause Pauses playback of the current file
' mmStop Stops playback ready for closedown
' mmSeek Position Seeks to a position in the file
' mmPlay Plays the open file
'-------------------------------------------------------------
' NOTES
' -----
'
' Open a file, then play it. Pause it in response to a request
' from the user. Stop if you intend to seek to the start and
' play again. Close when you no longer want to play the file
'--------------------------------------------------------------
Private sAlias As String ' Used internally to give an alias name to
' the multimedia resource
Private sFilename As String ' Holds the filename internally
Private nLength As Single ' Holds the length of the filename
' internally
Private nPosition As Single ' Holds the current position internally
Private sStatus As String ' Holds the current status as a string
Private bWait As Boolean ' Determines if VB should wait until play
' is complete before returning.
'------------ API DECLARATIONS -------------
'note that this is all one code line:
Private Declare Function mciSendString Lib "winmm.dll" _
Alias "mciSendStringA" (ByVal lpstrCommand As String, _
ByVal lpstrReturnString As String, ByVal uReturnLength As Long, _
ByVal hwndCallback As Long) As Long
Public Sub mmOpen(ByVal sTheFile As String)
' Declare a variable to hold the value returned by mciSendString
Dim nReturn As Long
' Declare a string variable to hold the file type
Dim sType As String
' Opens the specified multimedia file, and closes any
' other that may be open
If sAlias "" Then
mmClose
End If
' Determine the type of file from the file extension
Select Case UCase$(Right$(sTheFile, 3))
Case "WAV"
sType = "Waveaudio"
Case "AVI"
sType = "AviVideo"
Case "MID"
sType = "Sequencer"
Case Else
' If the file extension is not known then exit the subroutine
Exit Sub
End Select
sAlias = Right$(sTheFile, 3) Minute(Now)
' At this point there is no file open, and we have determined the
' file type. Now would be a good time to open the new file.
' Note: if the name contains a space we have to enclose it in quotes
If InStr(sTheFile, " ") Then sTheFile = Chr(34) sTheFile Chr(34)
nReturn = mciSendString("Open " sTheFile " ALIAS " sAlias _
" TYPE " sType " wait", "", 0, 0)
End Sub
Public Sub mmClose()
' Closes the currently opened multimedia file
' Declare a variable to hold the return value from the mciSendString
' command
Dim nReturn As Long
' If there is no file currently open then exit the subroutine
If sAlias = "" Then Exit Sub
nReturn = mciSendString("Close " sAlias, "", 0, 0)
sAlias = ""
sFilename = ""
End Sub
Public Sub mmPause()
' Pause playback of the file
' Declare a variable to hold the return value from the mciSendString
' command
Dim nReturn As Long
' If there is no file currently open then exit the subroutine
If sAlias = "" Then Exit Sub
nReturn = mciSendString("Pause " sAlias, "", 0, 0)
End Sub
Public Sub mmPlay()
' Plays the currently open file, from the current position
' Declare a variable to hold the return value from the mciSendString
' command
Dim nReturn As Long
' If there is no file currently open, then exit the routine
If sAlias = "" Then Exit Sub
' Now play the file
If bWait Then
nReturn = mciSendString("Play " sAlias " wait", "", 0, 0)
Else
nReturn = mciSendString("Play " sAlias, "", 0, 0)
End If
End Sub
Public Sub mmStop()
' Stop using a file totally, be it playing or whatever
' Declare a variable to hold the return value from mciSendString
Dim nReturn As Long
' If there is no file currently open then exit the subroutine
If sAlias = "" Then Exit Sub
nReturn = mciSendString("Stop " sAlias, "", 0, 0)
End Sub
Public Sub mmSeek(ByVal nPosition As Single)
' Seeks to a specific position within the file
' Declare a variable to hold the return value from the mciSendString
' function
Dim nReturn As Long
nReturn = mciSendString("Seek " sAlias " to " nPosition, "", 0, 0)
End Sub
Property Get Filename() As String
' Routine to return a value when the programmer asks the
' object for the value of its Filename property
Filename = sFilename
End Property
Property Let Filename(ByVal sTheFile As String)
' Routine to set the value of the filename property, should the programmer
' wish to do so. This implies that the programmer actually wants to open
' a file as well so control is passed to the mmOpen routine
mmOpen sTheFile
End Property
Property Get Wait() As Boolean
' Routine to return the value of the object's wait property.
Wait = bWait
End Property
Property Let Wait(bWaitValue As Boolean)
' Routine to set the value of the object's wait property
bWait = bWaitValue
End Property
Property Get Length() As Single
' Routine to return the length of the currently opened multimedia file
' Declare a variable to hold the return value from the mciSendString
Dim nReturn As Long, nLength As Integer
' Declare a string to hold the returned length from the mci Status call
Dim sLength As String * 255
' If there is no file open then return 0
If sAlias = "" Then
Length = 0
Exit Property
End If
nReturn = mciSendString("Status " sAlias " length", sLength, 255, 0)
nLength = InStr(sLength, Chr$(0))
Length = Val(Left$(sLength, nLength - 1))
End Property
Property Let Position(ByVal nPosition As Single)
' Sets the Position property effectively by seeking
mmSeek nPosition
End Property
Property Get Position() As Single
' Returns the current position in the file
' Declare a variable to hold the return value from mciSendString
Dim nReturn As Integer, nLength As Integer
' Declare a variable to hold the position returned
' by the mci Status position command
Dim sPosition As String * 255
' If there is no file currently opened then exit the subroutine
If sAlias = "" Then Exit Property
' Get the position and return
nReturn = mciSendString("Status " sAlias " position", sPosition, 255, 0)
nLength = InStr(sPosition, Chr$(0))
Position = Val(Left$(sPosition, nLength - 1))
End Property
Property Get Status() As String
' Returns the playback/record status of the current file
' Declare a variable to hold the return value from mciSendString
Dim nReturn As Integer, nLength As Integer
' Declare a variable to hold the return string from mciSendString
Dim sStatus As String * 255
' If there is no file currently opened, then exit the subroutine
If sAlias = "" Then Exit Property
nReturn = mciSendString("Status " sAlias " mode", sStatus, 255, 0)
nLength = InStr(sStatus, Chr$(0))
Status = Left$(sStatus, nLength - 1)
End Property
//窗体fm
Dim m As New Mmedia
Dim fn
Private Sub Command1_Click()
On Error GoTo r
dlg.ShowOpen
fn = dlg.Filename
m.mmOpen fn
r:
If Err Then MsgBox Err.Description
End Sub
Private Sub Command2_Click()
On Error GoTo rp
m.mmPlay
rp:
If Err Then MsgBox Err.Description
End Sub
Private Sub Command3_Click()
On Error GoTo rap
m.mmPause
rap:
If Err Then MsgBox Err.Description
End Sub
Private Sub Command4_Click()
On Error GoTo racp
m.mmStop
racp:
If Err Then MsgBox Err.Description
End Sub
VB2008里的设置：
项目属性-应用程序-生成单个实例应用程序