Question

如果表格已经打开，有没有办法阻止在MDI容器中打开某个表单？

Answer 1

您可以遍历OpenForms集合以检查是否已存在给定类型的表单：

foreach (Form form in Application.OpenForms)
{
    if (form.GetType() == typeof(MyFormType))
    {
        form.Activate();
        return;
    }
}

Form newForm = new MyFormType();
newForm.MdiParent = this;
newForm.Show();

Answer 2

AFAIK没有标准的方法。你必须自己实现它。我这样做：

class TheForm: Form
{
    private static TheForm Instance;

    private TheForm() // Constructor is private
    {
    }

    public static Show(Form mdiParent)
    {
        if ( Instance == null )
        {
            // Create new form, assign it to Instance
        }
        else
            Instance.Activate(); // Not sure about this line, find the appropriate equivalent yourself.
    }

    protected override OnFormClose(EventArgs e)
    {
        Instance = null;
        base.OnFormClose(e);
    }
}

如果需要考虑线程安全性，请添加相应的lock s。

Answer 3

请参阅http://gurucoders.blogspot.com/2009/08/avoid-duplicate-child-form-in-mdi.html

Answer 4

此代码正常工作

    private void openToolStripMenuItem_Click(object sender, EventArgs e)
    {
        foreach (Form form in Application.OpenForms)
        {


            if (form.GetType() == typeof(Form2))
            {
                form.Activate();
                return;
            }
        }

        Form2 newForm = new Form2();
        newForm.MdiParent = this;
        newForm.Show();
    }

Answer 5

虽然这篇文章很老，但我认为这会增加一些帮助。

如果表格也最小化，需要处理。这是完整的例子：

method(T anyClass)

Answer 6

此代码适用于vb.net

 

For Each f As Form In Application.OpenForms
            If TypeOf f Is form_name Then
                f.Activate()
                f.WindowState = FormWindowState.Normal
                f.StartPosition = FormStartPosition.WindowsDefaultLocation
                f.WindowState = FormWindowState.Maximized

            Return
        End If    
    Next 
    form_name .MdiParent = Me
    form_name .Show()

            Return
        End If    
    Next 
    form_name .MdiParent = Me
    form_name .Show()

Answer 7

可以使用Generics（在C＃和VB.net下面选项）实现一个方法，如果需要打开不同的MDI表单，这可能很有用。

C＃

private void OpenMDI<T>(bool multipleInstances)
    where T : Form, new()
{
    if (multipleInstances == false)
    {
        // Look if the form is open
        foreach (Form f in this.MdiChildren)
        {
            if (f.GetType() == typeof(T))
            {
                // Found an open instance. If minimized, maximize and activate
                if (f.WindowState == FormWindowState.Minimized)
                {
                    f.WindowState = FormWindowState.Maximized;
                }

                f.Activate();
                return;
            }
        }
    }

    T newForm = new T();
    newForm.MdiParent = this;
    newForm.Show();
}

按如下方式使用它（在false中指明multipleInstances以阻止它们）

OpenMDI<Form2>(false);

VB.NET

Public Sub Open_MDI(Of T As {New, Form})(bMultipleInstances As Boolean)
    If bMultipleInstances = False Then
        For Each f As Form In Me.MdiChildren
            If TypeOf f Is T Then
                If (f.WindowState = FormWindowState.Minimized) Then
                    f.WindowState = FormWindowState.Maximized;
                End If

                f.Activate()
                Exit Sub
            End If
        Next
    End If

    Dim myChild As New T()
    myChild.MdiParent = Me
    myChild.Show()
End Sub

按如下方式使用它（为False指示bMultipleInstances以防止它们）

Open_MDI(Of Form2)(False)

Answer 8

此代码在C＃中对我有用

<div class="book">
   <div class="book__form"></div>
</div>

防止重复的MDI子表单

8 个答案:

C＃

VB.NET