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发表评论(0)作者:不详, 平台:VB6.0+Win98, 阅读:12805, 日期:2000-11-20
A better way to gather multi-selected Visual Basic ListBox items

Conventional Visual Basic wisdom states that in order to gather the selected items from a multi-select ListBox, you should loop through all the items and test the Selected property. As with all loops, however, this can potentially bog down slower CPU注释:s. As a much faster and more elegant alternative, you can use the SendMessage() API function instead.

As you probably know, this function lets you send a message to one or more windows. The declaration statement conforms to the following syntax:

Private Declare Function SendMessage Lib "user32" _
   Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg _
   As Long, ByVal wParam As Long, lParam As Any) As Long

Since we want to gather the listbox注释:s selected items, we注释:ll send the LB_GETSELITEMS constant in the wMsg argument, which you declare like so:

Private Const LB_GETSELITEMS = &H191

In essence, the LB_GETSELITEMS message fills an array with the index numbers of all the selected items. As a result, you must pass two additional arguments with SendMessage(). The first argument should contain the maximum number of selected items. To retrieve this value, you can simply use the listbox注释:s SelCount property. The second argument should hold the array variable you want to fill with index values. The following example shows how you might use this function:

Dim ItemIndexes() As Long, x As Integer, iNumItems As Integer
iNumItems = ThisBox.SelCount
If iNumItems Then
   ReDim ItemIndexes(iNumItems - 1)
   SendMessage ListBox1.hwnd, LB_GETSELITEMS, iNumItems, _
End If
For x = 0 To iNumItems - 1
   MsgBox ListBox1.List(ItemIndexes(x))
Next x

After being passed to the SendMessage function, iNumItems holds the total number of selected items, and the ItemIndexes array holds the selected item index values. Notice, that you must pass a pointer to the ItemIndexes array, and not the array itself. Thus, we passed ItemIndexes(0) into the SendMessage function, not ItemIndexes().