这样的话你就不要直接把子窗口show出来，先在父窗口创建一个子窗口对象的变量，通过实例化该变量达到创建子窗口的目的，然后在下次又要打开子窗口时也可以通过该变量关闭原有的子窗口
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示例代码如下(假设Form1为父窗口，Form2为子窗口):
Form1的代码:
Public
Class
Form1
Dim
nform
As
Form2
=
Nothing
Private
Sub
Button1_Click(ByVal
sender
As
System.Object,
ByVal
e
As
System.EventArgs)
Handles
Button1.Click
If
nform
IsNot
Nothing
Then
nform.Close()
nform.Dispose()
End
If
nform
=
New
Form2
nform.Show()
Me.Hide()
End
Sub
End
Class
通过nform变量，你可以很轻易就处理掉原来已经打开但隐藏着的子窗口了
下面的代码示例说明了更改线程优先级的结果。创建两个线程，其中一个线程的优先级设置为 BelowNormal。两个线程在 while 循环中都增加一个变量，并运行一段设定的时间。
Option Explicit
Option Strict
Imports System
Imports System.Threading
Public Class Test
MTAThread _
Shared Sub Main()
Dim priorityTest As New PriorityTest()
Dim threadOne As Thread = _
New Thread(AddressOf priorityTest.ThreadMethod)
threadOne.Name = "ThreadOne"
Dim threadTwo As Thread = _
New Thread(AddressOf priorityTest.ThreadMethod)
threadTwo.Name = "ThreadTwo"
threadTwo.Priority = ThreadPriority.BelowNormal
threadOne.Start()
threadTwo.Start()
' Allow counting for 10 seconds.
Thread.Sleep(10000)
priorityTest.LoopSwitch = False
End Sub
End Class
Public Class PriorityTest
Dim loopSwitchValue As Boolean
Sub New()
loopSwitchValue = True
End Sub
WriteOnly Property LoopSwitch As Boolean
Set
loopSwitchValue = Value
End Set
End Property
Sub ThreadMethod()
Dim threadCount As Long = 0
While loopSwitchValue
threadCount += 1
End While
Console.WriteLine("{0} with {1,11} priority " _
"has a count = {2,13}", Thread.CurrentThread.Name, _
Thread.CurrentThread.Priority.ToString(), _
threadCount.ToString("N0"))
End Sub
End Class
VB点虐 （VS2008）里面比C#还好弄，不需要自己加manifest，直接在项目属性的“应用程序”里面点击“查看UAC设置”，在新打开的app.manifest里面把 requestedExecutionLevel level="asInvoker" uiAccess="false" / 替换成 requestedExecutionLevel level="requireAdministrator" uiAccess="false" / 再编译就行了。