Question

下面的代码显示我（我认为）“for each”循环比“i to n”循环快10％，但“for each”循环在新内存中创建567k？这是正确的吗？哪种方式在速度和内存使用方面通常最有效？

如果您想在VB中运行此代码，只需在表单中添加一个按钮和2个标签。

Public Class StateObject
    Public WorkSocket As String = "FFFFFFFFFFFF"
    Public BufferSize As Integer = 32767
    Public Buffer(32767) As Byte
End Class

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    For cnt As Integer = 1 To 250
        Dim StateObjecter As New StateObject
        ClientNetList.Add(cnt.ToString, StateObjecter)
    Next
End Sub


Private ClientNetList As New SortedList(Of String, StateObject)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim stop1 As New Stopwatch
    Dim stop2 As New Stopwatch

    Dim TotalMemory1 As Integer = GC.GetTotalMemory(False)
    stop1.Start()
    For cnt As Integer = 1 To 1000000
        For i = 0 To ClientNetList.Count - 1
            ClientNetList.Values(i).WorkSocket = "FFF"
        Next

    Next
    stop1.Stop()
    Dim TotalMemory2 As Integer = GC.GetTotalMemory(False)
    MsgBox(TotalMemory2 - TotalMemory1)

    TotalMemory1 = GC.GetTotalMemory(False)
    Dim fff As Integer = GC.GetGeneration(ClientNetList)
    stop2.Start()
    For cnt As Integer = 1 To 1000000
        For Each ValueType As StateObject In ClientNetList.Values
            ValueType.WorkSocket = "FFF"
        Next
    Next
    stop2.Stop()

    Dim ffff As Integer = GC.GetGeneration(ClientNetList)
    TotalMemory2 = GC.GetTotalMemory(False)
    MsgBox(TotalMemory2 - TotalMemory1)

    Label1.Text = "i: " & stop1.ElapsedMilliseconds
    Label2.Text = "e: " & stop2.ElapsedMilliseconds
End Sub

Answer 1

在我的系统上，第一次测试（第一次点击程序运行按钮）的“for i = 1”循环速度提高了约20％。但是“for each”循环在随后的测试中更快。 “for each”循环占用了更多的内存，但这是暂时的，最终将被垃圾收集。

“for each”和“for i =”的利弊在这里一直争论不休。对于每个都很好，因为它适用于除数组之外的结构，并使对象可用。 “For i =”具有在循环中指定数组项的边界和顺序的优点，并避免了数组中可能遇到的错误：

Dim a(50) As Integer
Dim i As Integer
For Each i In a
  i = 22
  Next i

在这个例子中，数组永远不会初始化为22.变量i只是数组元素的副本，当i被赋值为22时，原始数组元素不会改变。

在VB 2008中循环使用SortedList的最有效方法是什么？

1 个答案: