vb.net 检查表单是否已打开
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Check if form is Opened
提问by Mohammed Khaled
I give this question for more knowledge. How can I know if the form is Opened in my application or not, in order not to open it again I mean not to create an instance of the same form while it's running
我给这个问题更多的知识。我怎么知道表单是否在我的应用程序中打开，为了不再打开它，我的意思是不要在运行时创建相同表单的实例
Dim frmCollection As New FormCollection()
frmCollection = Application.OpenForms()
If frmCollection.Item("Form2").IsHandleCreated Then
MsgBox("Yes Opened")
Else
Dim f As New Form2()
With f
.Text = "form2"
.Show()
End With
End If
if I executes this code many times it will create more instances of the form Form2 How can I check if this form is not already opened
如果我多次执行此代码，它将创建表单 Form2 的更多实例 如何检查此表单是否尚未打开
回答by LarsTech
You can try it like this:
你可以这样试试：
Imports System.Linq ' need to add
If Application.OpenForms().OfType(Of Form2).Any Then
MessageBox.Show("Opened")
Else
Dim f2 As New Form2
f2.Text = "form2"
f2.Show()
End If
回答by user3124064
You can use the following code:
您可以使用以下代码：
If myForm.IsHandleCreated then
myForm is open
End If
回答by Muhammad Zubair ALi
For more simplicity you may create a public static bool variable which will tell whether the form is opened or not. On form load event assign 'true' and on closed event assign 'false' value.
为更简单起见，您可以创建一个公共静态 bool 变量，该变量将告知表单是否已打开。在表单加载事件上分配“真”，在关闭事件上分配“假”值。
回答by Fobbert
Hate to be a kill joy but some day some one is going to try and understand your code.
讨厌成为一种杀戮的乐趣，但总有一天有人会尝试理解你的代码。
Dim frm as New frmDontknow
Dim frmCollection = System.Windows.Forms.Application.OpenForms
For i As Int16 = 0I To frmCollection.Count - 1I
If frmCollection.Item(i).Name = frm.Name Then
frmCollection.Item(i).Activate()
Exit Sub
End If
Next i
Then do the show etc as required?
然后根据需要进行表演等吗？
回答by Dave
ANOTHER refactoring way from the one initiated by HumbleBeginnings:
从 HumbleBeginnings 发起的另一种重构方式：
Dim xChildWindows = Application.OpenForms.OfType(Of frmForm2)
If xChildWindows.Any Then
xChildWindows.First().Focus() 'Focus if exists
Else
Dim xfrmNew As New frmForm2() 'Open window if doeasn't exists
xfrmNew.MdiParent = Me
xfrmNew.Show()
End If
回答by HumbleBeginnings
As an extension of the answers given (thank you, all), here's a simple way to activate or show:
作为给出的答案的扩展（谢谢大家），这里有一个简单的激活或显示方法：
Dim frmCollection = System.Windows.Forms.Application.OpenForms
If frmCollection.OfType(Of Form2).Any Then
frmCollection.Item("Form2").Activate()
Else
Dim newForm2 = New Form2
newForm2.Show()
End If
回答by FERIOS
Check if form is Opened, To validate if a form is open we use this method and function to be able to invoke from any form and use less code.
检查表单是否已打开，为了验证表单是否已打开，我们使用此方法和函数能够从任何表单调用并使用更少的代码。
Example : This will use it in a form with mdiContainer and a panel object with 3 buttons that shows the 3 windows form.
示例：这将在一个带有 mdiContainer 的表单和一个带有 3 个按钮的面板对象中使用它，该对象显示 3 个窗口表单。
Imports System Imports System.Reflection
导入系统导入 System.Reflection
Private Sub OpenWindowsForm(ByVal FormName As String)
Dim instForm As Form = Application.OpenForms.OfType(Of Form)().Where(Function(frm) frm.Name = FormName).SingleOrDefault()
If instForm Is Nothing Then
Dim frm As New Form
frm = DirectCast(CreateObjectInstance(FormName), Form)
frm.MdiParent = Me
Me.Panel1.Controls.Add(frm)
Me.Panel1.Tag = frm
frm.Show()
Else
instForm.Select()
instForm.WindowState = FormWindowState.Maximized
instForm.BringToFront()
End If
End Sub
Public Function CreateObjectInstance(ByVal objectName As String) As Object
Dim obj As Object
Try
If objectName.LastIndexOf(".") = -1 Then
objectName = [Assembly].GetEntryAssembly.GetName.Name & "." & objectName
End If
obj = [Assembly].GetEntryAssembly.CreateInstance(objectName)
Catch ex As Exception
obj = Nothing
End Try
Return obj
End Function
How to use in click eventsPrivate Sub btnRegistro_Click(sender As Object, e As EventArgs) Handles btnRegistro.Click OpenWindowsForm("Registro") End Sub
如何在点击事件中使用Private Sub btnRegistro_Click(sender As Object, e As EventArgs) 处理 btnRegistro.Click OpenWindowsForm("Registro") End Sub
Private Sub btnBusqueda_Click(sender As Object, e As EventArgs) Handles btnBusqueda.Click
OpenWindowsForm("Busqueda")
End Sub
Private Sub btnCalendario_Click_1(sender As Object, e As EventArgs) Handles btnCalendario.Click
OpenWindowsForm("Calendario")
End Sub
回答by Jun Gie Cas
you can try this
你可以试试这个
Dim formText As String
Dim prevText As String
Private Sub OpenForm(ByVal frm As Windows.Forms.Form)
formText = frm.Text
If formText = prevText Then Exit Sub
CloseForms()
' Make it a child of this MDI form before showing it.
frm.MdiParent = Me
frm.Show()
frm.Location = New Point(0, 0)
prevText = formText
End Sub
Private Sub CloseForms()
For Each ChildForm As Form In Me.MdiChildren
ChildForm.Close()
Next
End Sub
Private Sub NewToolStripButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PayablesToolStripMenuItem.Click
OpenForm(frmPayables)
End Sub
