我如何打开表单并通过一个按钮将其关闭[关闭]

Question

我打开了一个表单，但我无法使用 same 按钮关闭它。我怎么能做到这一点？ 我尝试这样做：

...
{
    var openform = new Form2();

    if (openform != null) openform.Show(); 
    else openform.Hide();
}

Answer 1

看来你必须实现以下逻辑：

1. 如果有一个打开 Form2 实例，关闭它
2. 否则创建并显示新的Form2实例。

如果是您的情况，我们应该首先寻找打开的Form2 实例；然后才使用new 创建它（如果需要）

  using System.Linq;

  ... 

  // Search: do we have opened Form2 instances?
  Form2 openform = Application
    .OpenForms        // among all opened forms 
    .OfType<Form2>()  // of type Form2
    .LastOrDefault(); // in case we have several instances, let's choose the last one

  if (null == openform) {   // no Form2 instance has been found
    openform = new Form2(); 

    openform.Show();
  }   
  else {                    // Instance (openform) has been found 
    openform.Close(); // Or openform.Hide();   
  }

Answer 2

也许这样的事情会帮助你：

Form2 openform = new Form2();
if (Application.OpenForms.OfType<Form2>().Count() > 0)
    openform.Hide();

openform.Show();

虽然我没有完全理解您的问题的上下文 - 您可能需要调整代码。您也可以查看How to check if a windows form is already open, and close it if it is?。

Answer 3

private Form2 form2;

private void button1_Click(object sender, EventArgs e)
{
    if (form2 == null || form2.IsDisposed)
    {
        // Either no form has been created or the last one created has been closed.
        form2 = new Form2();
        form2.Show();
    }
    else
    {
        form2.Close();
    }
}

如果你喜欢空传播：

if (form2?.IsDisposed == false)
{
    form2.Close();
}
else
{
    // Either no form has been created or the last one created has been closed.
    form2 = new Form2();
    form2.Show();
}

Answer 4

使用 bool 变量作为打开按钮，就像下面一样，并使 openform 全局化。

var openform = new Form2();      // it must be defined out 

方法和类内作为全局变量。

private static bool isOpen = true; 

在按钮内点击方法

if (isOpen) openform.Show();
else openform.Hide();

isOpen = !isOpen;

测试代码

public partial class Form2 : Form
{
    public Form2() => InitializeComponent();

    Form1 openForm = new Form1();
    private static bool isOpen = true;

    private void button1_Click(object sender, EventArgs e)
    {
        if (isOpen) openForm.Show(); 
        else openForm.Hide(); 

        isOpen = !isOpen;
    }
}

检查这个测试。 https://youtu.be/o9I77dhEvYg

Answer 5

我认为如果其他表单像 windows 中的所有其他表单一样关闭，操作员会更直观：按关闭按钮，单击右上角的十字，选择 ALT-F4 等。

但是，如果你真的想从你的主窗体中关闭另一个窗体，你不应该只是关闭它，而是应该很好地询问另一个窗体是否可以自行关闭。这样您就可以让其他表单向操作员询问一些问题，例如询问是否需要保存更改的项目。

private Form myForm = null;

public void OnButton1_Clicked(object sender, ...)
{
    if (this.myform == null)
    {   // not shown yet. Show it now:
        this.myForm = new Form2()
        this.myForm. properties = ...

        // make sure I get notified if the Form closes in any way:
        this.myForm.Closed += onMyFormClosed;
        // show the form
        this.myform.Show(this);
    }
    else
    {   // ask the form nicely to close itself
        this.CloseForm(); 
        // this might (or might not) lead to the event Form.Closed
    }
}

private void OnMyFormClosed(object sender, ...)
{
     if (!object.ReferenceEquals(sender, this.myForm))
     {    // someone else is closed. I have nothing to do with this
          return;
     }

     // if here, my Form is closed. Save to Dispose and assign Null
     this.myForm.Dispose();
     this.myForm = null;
}
}

public void ShowFo