可是，实际上 如果你调用 API 得话，从 API浏览器复制下来得代码却是 强制使用 ByVal 传参得
这就给了我们优化得机会。
我又重新使用该代码 分别测试了一下 ByRef ,ByVal 得区别，结果很振奋： ByRef 比 ByVal 提高了16倍
代码如下，插入ComboBox 得字符串越长，越能显示 ByRef 得威力
Option Explicit
Private Declare Function SendMessageByRef Lib "user32" Alias "SendMessageA" (ByRef hWnd As Long, ByRef wMsg As Long, ByRef wParam As Long, ByRef lParam As Any) As Long
Private Declare Function SendMessageByVal Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Any) As Long
Private Declare Function GetTickCount Lib "kernel32" () As Long
Private Const CB_ADDSTRING = &H143
Private Sub Command1_Click()
Dim II As Long
Dim t As Long
Dim s As String
Combo1.Clear
t = GetTickCount()
'使用API ByRef
For II = 1 To 10000
s = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
'重新赋值以改变地址
SendMessageByRef Combo1.hWnd, CB_ADDSTRING, 0, s
Next
MsgBox "ByRef " & GetTickCount - t
Combo1.Clear
t = GetTickCount()
'使用API ByVal
For II = 1 To 10000
s = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
SendMessageByVal Combo1.hWnd, CB_ADDSTRING, 0, s
Next
MsgBox "ByVal " & GetTickCount - t
Combo1.Clear
t = GetTickCount()
'使用普通 ComboBox Add
For II = 1 To 10000
s = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
Combo1.AddItem s
Next
MsgBox "ComboBox Add " & GetTickCount - t
End Sub
将 API 传参方式改为 ByRef ，可以提升速度，当然不是所有得API 得参数都能这么改，具体得看 API 函数内是否会对传入得参数进行修改，或者你是否还要继续使用 被传入得参数。
否则会引起一些错误，而有些API 是不允许使用 ByRef 传参得 .具体情况还得具体分析。当然上面得列子完全可以使用 Byref
