Winforms 控件占位符

发布于 2024-10-14 14:02:43 字数 612 浏览 0 评论 0原文

我正在尝试将 System.Windows.Forms.Control 添加到给定的表单控件集合中。我通过创建类型控制的私有字段，然后在构造函数中将该字段实例化为 System.Windows.Forms.Control 的新实例来实现此目的。

在运行时，我尝试通过执行以下代码示例中的操作，将 _placeholder 变量的类型更改为 TextBox。所以基本上我试图拥有一个 Control 类型的占位符，并在运行时将其更改为另一个控件，例如 TextBox 或 Label。我的问题是我的表格上没有显示任何内容？任何见解将不胜感激。

public class MyForm : Form
{
  System.Windows.Forms.Control _placeholder = null;

  public MyForm()
  {
    _placeholder = new System.Windows.Forms.Control();
    this.Controls.Add(_placeholder);

    ChangeToTextBox();
  }

  public void ChangeToTextBox()
  {
    _placeholder = new TextBox();
  }
}

原文

I am trying to add a System.Windows.Forms.Control to a given forms control collection. I do this by creating a private field of type control and then instantiating this field to a new instance of System.Windows.Forms.Control in the constructor.

At runtime I am trying to change the type of the _placeholder variable to a TextBox, by doing something like in the following code example. So basically I am trying to have a placeholder of type Control and change it to another control like a TextBox or Label at runtime. My issue is that nothing shows up on my form? Any insight would be appreciated.

public class MyForm : Form
{
  System.Windows.Forms.Control _placeholder = null;

  public MyForm()
  {
    _placeholder = new System.Windows.Forms.Control();
    this.Controls.Add(_placeholder);

    ChangeToTextBox();
  }

  public void ChangeToTextBox()
  {
    _placeholder = new TextBox();
  }
}

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伪装你 2024-10-21 14:02:43

正如所写的，这是行不通的，因为原始占位符仍然是添加到控件的引用。您可以通过执行以下操作来修复它：

public void ChangeToTextBox()
{
  this.Controls.Remove(_placeholder); // Remove old
  _placeholder = new TextBox();
  this.Controls.Add(_placeholder); // Add new
}

也就是说，如果这要进入表单上的同一位置，您可能需要考虑放置 Panel 那里，只需将文本框添加到面板即可。这将避免删除现有控件的需要，因为它只是添加一个控件。

This won't work, as written, because the original placeholder is still the reference added to the controls. You could fix it by doing:

public void ChangeToTextBox()
{
  this.Controls.Remove(_placeholder); // Remove old
  _placeholder = new TextBox();
  this.Controls.Add(_placeholder); // Add new
}

That being said, if this is going to go into the same location on your form, you might want to consider putting a Panel there instead, and just adding the TextBox to the Panel. This will prevent the need to remove existing controls since it's just adding one in.

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