用VB實現XMLHttp Pool

昨天看了鳥食軒的文章構建一個pool來管理無重新整理頁面的xmlhttp對象 ，自己用VB6實現了一下，結果出現了一點小問題，總結一下。

代碼：

Form：Form1

Option Explicit

Private Pools As HttpPool

Private Sub Command1_Click()
    Dim o As MSXML2.XMLHTTP
    Set o = Pools.GetObject()
    Dim Handler  As MyReadyStateHandler
    Set Handler = New MyReadyStateHandler
    Handler.ini o
    o.OnReadyStateChange = Handler
    o.open "GET", "Http://localhost/js/message.htm", True
    o.send
    Set Handler = Nothing
End Sub

Private Sub Form_Load()
    Set Pools = New HttpPool
End Sub

Private Sub Form_Unload(Cancel As Integer)
    Set Pools = Nothing
End Sub

Class：HttpPool

Option Explicit

Dim Pool As Collection

'沒有考慮池容量
Public Function GetObject() As MSXML2.XMLHTTP
    Dim i As Integer
    Dim o As MSXML2.XMLHTTP
    For i = 1 To Pool.Count
        Set o = Pool(i)
        If o.readyState = 4 Or o.readyState = 0 Then
        o.abort
        GoTo ExitLabel
        End If
    Next
    Set o = New MSXML2.XMLHTTP
    Pool.Add o
ExitLabel:
    Set GetObject = o
    Debug.Print Pool.Count
End Function

Private Sub Class_Initialize()
    Set Pool = New Collection
End Sub

Private Sub Class_Terminate()
    Dim i As Integer
    For i = 1 To Pool.Count
        Pool(i).abort
    Next
    Set Pool = Nothing
End Sub

Option Explicit

Dim p As XMLHTTP

Sub OnReadyStateChange()
    If p.readyState = 4 Then
        Debug.Print p.responseText
    End If
End Sub

Class：MyReadyStateHandler

Public Sub ini(o As XMLHTTP)
    Set p = o
End Sub

在原先的JavaScript的代碼中沒有黃色代碼對應的語句，因此在VB6的調試過程中一點一個XMlHttp對象被用過後readyState狀態一直是4，所以就不在觸發OnReadyStateChange事件了，因此responseText只能顯示一次，以後就無法工作了，最後加上o.abort一切搞定。