C# 将表单设置为父级抛出异常“无法将顶级控件添加到控件中”
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原文地址: http://stackoverflow.com/questions/10746053/
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Set form as Parent throw exception "Top-level control cannot be added to a control"
提问by CaTx
I want to access variables of a form from another form. On clicking a button inside my Main form, I want to set my Main form as Parent, then bring up another form (child form) wherein I will access variables of the Main form. My click handler is as follow:
我想从另一个表单访问一个表单的变量。单击主窗体中的按钮时，我想将主窗体设置为父窗体，然后调出另一个窗体（子窗体），我将在其中访问主窗体的变量。我的点击处理程序如下：
private void btnSystem_Click(object sender, EventArgs e)
{
Form_EnterPassword EP = new Form_EnterPassword();
EP.Parent = this; //error: Top-level control cannot be added to a control
EP.ShowDialog();
}
It compiles fine without any error. However, when I run the Main form and click on the System button, it throws me an exception. I do something similar in another code (not mine) with the same button click, and encounter no error (just with setting Main form as Parent).
它编译得很好，没有任何错误。但是，当我运行主窗体并单击系统按钮时，它会引发异常。我在另一个代码（不是我的）中用相同的按钮单击做了类似的事情，并且没有遇到任何错误（只是将主窗体设置为父级）。
What am I doing wrong? Is there something in my Main code that cause this?
我究竟做错了什么？我的主要代码中是否有导致此问题的内容？
采纳答案by Grzegorz W
Best way would be to use EP.ShowDialog(this)and later use Ownerproperty.
最好的方法是使用EP.ShowDialog(this)和以后使用Owner财产。
回答by Matzi
You need the EP.TopLevelproperty to be set to false. It will let you to set a parent to it.
您需要将该EP.TopLevel属性设置为 false。它会让你为它设置一个父级。
In case you only want to access variables and controls of another form, then maybe you can reach it in other ways, not trough a Parent relationship.
如果您只想访问另一种形式的变量和控件，那么也许您可以通过其他方式访问它，而不是通过 Parent 关系。
回答by CaTx
OK, apparently the way to do it is to call
好的，显然这样做的方法是打电话
Form_Child.ShowDialog(this)
and then I can call
然后我可以打电话
FromParent_aVariable = ((Form_Parent)this.Owner).aVariable;
or if I define aVariable in the namespace Properties then
或者如果我在命名空间属性中定义了一个变量，那么
FromParent_aVariable = NameSpace.Properties.Settings.Default.aVariable;
there are two ways.
有两种方法。
回答by bharath
Writing this way, made the dialog display on the center of the parent form.
以这种方式编写，使对话框显示在父窗体的中心。
Form_Child.StartPosition = FormStartPosition.CenterParent;
Form_Child.ShowDialog(this);
回答by Wady Nicudemos
Form_EnterPassword EP = new Form_EnterPassword();
EP.MdiParent = this;
EP.Show();
try this way, it helps for me. you need to set principalform as isMdicontainer = true at the form properties
试试这种方式，它对我有帮助。您需要在表单属性中将 principalform 设置为 isMdicontainer = true
回答by Switch
I had a similar situation recently. I was attempting something similar but by controlling the Child Forms from a different class.
我最近也有类似的情况。我正在尝试类似的事情，但通过控制来自不同类的子表单。
Note(s):You're trying to set the Child Form(s) "TopMost" to something that does not allow it.
In this case the "MdiContainer".
注意：您试图将子表单“TopMost”设置为不允许的内容。
在本例中为“MdiContainer”。
To accomplish this:
要实现这一点：
? Disable MainForm "isMdiContainer" property (its use is kind of obsolete anyway).
? 禁用 MainForm "isMdiContainer" 属性（无论如何它的使用已经过时了）。
? Set the Form(s) TopMost properties to true.
? 将 Form(s) TopMost 属性设置为 true。
? You should now be able to accomplish your feature.
? 您现在应该能够完成您的功能。
Code Example:
代码示例：
/* On your Main Form Class */
private void btnSystem_Click(object sender, EventArgs e)
{
// Instantiate the Form_EnterPassword by passing the MainForm
Form_EnterPassword EP = new Form_EnterPassword(this);
EP.Show(); // No longer as modal Form to display in front.
}
/* Under your EnterPassword Form Class */
// Do not create a new Instance of MyMainForm.
// You want to use the same thread as your MainForm
private MyMainForm mainForm;
/* Constructor */
public Form_EnterPassword(MyMainForm form)
{
mainForm = form;
this.Owner = mainForm; // "this" refers to the: EnterPassword Form.
}
Remarks:The only additional thing that you (may) have to do is to to achieve perfection is to check the MainForm WindowState; and create a block to minimize or bring the Forms to their specific state.
备注：您（可能）需要做的唯一额外的事情就是检查 MainForm WindowState；并创建一个块以最小化表单或将表单置于其特定状态。
i.e:
IE：
if (WindowState == FormWindowState.Minimized)
{ /* Code to Minimize all the Child Forms. */ }
else { /* Code to bring all Forms to their "Normal" State */ }
