如何从FormB打开FormC作为FormA的MDI_Child [英] How to open FormC as an MDI_Child of FormA, from FormB

问题描述

我是C＃.NET的初学者，尝试编写代码。我有三个Windows.Form：
 
 1. MainForm（MDI_FORM）
 2. Child1 
 3. Child2 
 
在MainForm上，我命令Child1。显示（）
然后从Child1，我打算通过以下代码分配并打开Child2作为孩子到MainForm：
 
在MainForm上，我声明：
 
 public static Child2 child2; 
 
 
然后在来自Child1的btnOpen上，我编码：
 
 private void btnOpen_Click（object sender，EventArgs e）
 {
 MainForm mainForm = new MainForm（）; 
 mainForm.child2 = new Child2（）; 
 mainForm.child2.MdiParent = fMainForm; 
 mainForm.child2.Show（）; 
} 
 
有人帮我做点什么。 
这不起作用。 
非常感谢!!! 

解决方案

嗨Salisu Shaibu，



您的代码无效，因为您正在创建MainForm的新实例。诀窍是使用对MainForm的引用并将其设置为MdiParent到您的第二个Form。看看这个（可运行的）示例：

 使用系统; 
 使用 System.Windows.Forms; 
 
 命名空间 MdiOhMy 
 {
 静态  class 程序
 {
 [STAThread] 
  static   void  Main（）
 {
 Form formMain =  new  Form {IsMdiContainer =  true }; 
 
表格formChild1 =  new 表格{Text =   Child1，MdiParent = formMain，Visible =  true }; 
 Button buttonShowChild2 =  new 按钮{Text =  打开Child2，Parent = formChild1}; 
 buttonShowChild2.Click + =（ object  sender，EventArgs e）= >  
 {
 Form formChild2 =  new 表格{Text =   Child2，MdiParent = formMain，Visible =  true }; 
}; 
 
 Application.Run（formMain）; 
} 
} 
} 

在这个例子中，我可以引用formMain实例，因为它在捕获的范围。在更现实的场景中，您可以通过Child1的 MdiParent 属性获取引用。



因此您的处理程序可能看起来像这个：



<前lang =cs> 私人 void btnOpen_Click（ object sender，EventArgs e）
{
MainForm mainForm = 这个 .MdiParent as MainForm; // this是Child1，它引用它的MdiParent
MainForm.child2 = new Child2（）;
MainForm.child2.MdiParent = fMainForm;
MainForm.child2.Show（）;
}

还要考虑是否要创建一个新的Child2实例你点击按钮的时间，或者只是隐藏/重新显示同一个实例...



快乐编码



Johannes

I am a beginner on C# .NET, trying to code out something. I have three Windows.Form:

1.	MainForm (MDI_FORM)
2.	Child1
3.	Child2

On MainForm, I commanded Child1.Show()
Then from Child1, I intend to assign and open Child2 as a child to MainForm via the codes below:

    On MainForm, I declared:

         public static Child2 child2;


    Then on btnOpen from Child1, I coded:

         private void btnOpen_Click(object sender, EventArgs e)
            {
                MainForm mainForm = new MainForm();
                mainForm.child2 = new Child2 ();
                mainForm.child2.MdiParent = fMainForm;
                mainForm.child2.Show();
            }

Someone help me on what to do please.
It's not working.
Thanks a lot!!!

解决方案

Hi Salisu Shaibu,

Your code doesn't work because you are creating a new instance of your MainForm. The trick is to use a reference to the MainForm and set it as MdiParent to your second Form. Have a look at this (runnable) example:

using System;
using System.Windows.Forms;

namespace MdiOhMy
{
    static class Program
    {
        [STAThread]
        static void Main()
        {
            Form formMain = new Form { IsMdiContainer = true };

            Form formChild1 = new Form { Text = "Child1", MdiParent = formMain, Visible = true };
            Button buttonShowChild2 = new Button { Text = "Open Child2", Parent = formChild1 };
            buttonShowChild2.Click += (object sender, EventArgs e) =>
                {
                    Form formChild2 = new Form { Text = "Child2", MdiParent = formMain, Visible = true };
                };

            Application.Run(formMain);
        }
    }
}

In this example I can reference the formMain instance because it's in the captured scope. In a more realistic Scenario you can obtain a reference via Child1's MdiParent property.

So your handler could look like this:

private void btnOpen_Click(object sender, EventArgs e)
 {
     MainForm mainForm = this.MdiParent as MainForm; // "this" is Child1 which refernces it's MdiParent
     MainForm.child2 = new Child2();
     MainForm.child2.MdiParent = fMainForm;
     MainForm.child2.Show();
 }

Also think about if you want to create a new instance of Child2 every time you click your button, or just hide/reshow the same instance...

Happy coding

Johannes

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