如果表单已经打开，如何重新打开它

问题描述：

你好朋友
我想知道如何检测表格是否已打开.如果窗体已打开，则将其关闭并重新打开它.

在我的应用程序中，我使用单一"表单查看客户信息并创建新的客户信息.
如果用户已经打开了客户表单，然后再次尝试打开IT，那么我想这样做，那么以前打开的表单应该关闭，并且新的表单实例将被打开.
请帮我.

硼酸丁酯
Equilux Technologies

Hello Frnds
I want to know how to detect is form already opened. If form is opened then close it and Reopen IT.

In my application I am using Single form to view customer information and create new customer Information.
I want to do if user has already opened a customer form and again tries to open IT then Previously opened form should be close and new instance of form will be opened .
Plz Help Me.

Nitin bhoyate
Equilux Technologies

答

请看下面的代码.

基本上我有一个带有2个按钮的表单，一个运行测试，另一个打开另一个表单的实例.

使用OpenForms集合，我们可以检查表单是否已打开；

Look at this code.

Basically i have a form with 2 buttons on it, one runs a test, the other opens an instance of an other form.

Using the OpenForms collection we can check if the form already is open;

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void buttonOpenOtherForm_Click(object sender, EventArgs e)
        {
            Form theOtherOne = new FormTheOtherForm();
            theOtherOne.Name = "SomeFormName";
            theOtherOne.Show();

        }

        private void buttonTest_Click(object sender, EventArgs e)
        {
            foreach (Form aForm in Application.OpenForms)
            {
                if (aForm.Name.Equals("SomeFormName"))
                {
                    MessageBox.Show("SomeFormName Already Open, closing and repopening next");

                    aForm.Close();

                    buttonOpenOtherForm.PerformClick();
                    break;
                }
            }
        }
    }

首先，即使可以关闭窗体，也不存在打开"操作(因此无法知道是否可以打开)表单已经打开" :-). Form的实例通过其构造函数实例化，然后显示，然后关闭.

一切都取决于您如何关闭表单.我认为最好的关闭方法是隐藏表格.为此，请覆盖:

First of all, even though a form can be closed, there is not such thing as "Open" operation (and, hence, it is not possible to know if a form is "already opened" :-). An instance of a Form is instantiated via its constructor, then shown, then closed.

Everything depends on how you close the form. I think the best way of closing is hiding the form; to do this, override :

protected override void OnFormClosing(FormClosingEventArgs e) {
    if (e.CloseReason == CloseReason.UserClosing) {
        e.Cancel = true;
        Hide();
    } else
        base.OnFormClosing(e);
}

您可以通过处理事件FormClosing来获得相同的效果，但是实现覆盖更容易.

有关关闭表单的详细信息，请参见 http://msdn.microsoft.com/en-us/library/system.windows.forms.form.close.aspx [

You can get the same effect by handling the event FormClosing, but override is implemented easier.

For more detail on what happens on closing the form, please see http://msdn.microsoft.com/en-us/library/system.windows.forms.form.close.aspx[^]. As you can see, hiding the form is the recommended way of handling this situation. Note, that a closed form is disposed (see below).

In this way, only one operation is needed: Form.Show.

If you need the form to be really closed, you can test the predicate Form.IsDisposed. To show the form again, you will need to instantiate an instance of the form again and then show new instance, as a disposed cannot be shown. Another way is checking Application.OpenForms and trying to find a form in question in the collection.

I do not recommend closing of the form by the user; hiding is much better. When a form is hidden, it preserved its status and status of all the controls, when a form is shown again. Don''t think you save memory on closing the form. You don''t.

Don''t forget the ownership relationship between forms. It is better to make non-main forms owned by main forms:

Form MyOwnedForm = new CustomerInformationForm();
MyOwnedForm.Owner = MyMainForm;
MyOwnedForm.ShowInTaskbar = false; //also very useful: only one task bar icon per application
MyOwnedForm.Show(MyMainForm);

这将保证同一应用程序形式的一致性激活，应与ShowInTaskbar = false一起使用以保持一致性.

最终建议:最好将每个应用程序的表单数量保持在最低限度，而更复杂的表单则是最佳选择.使用选项卡式UI，停靠UI或类似的方法.

—SA

This will guarantee coherent activation of the forms of the same application, should be used with ShowInTaskbar = false for consistency.

A final recommendation: it''s the best to keep number of forms per application to bare minimum, with one more complex form being the best option. Use tabbed UI, docking UI or something like that.

—SA

如果表单已经打开，如何重新打开它

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