C# Winform child form accesses controls and properties of parent form

Today, when I was designing a contact management C#, I encountered this problem. I needed to pass the value in the textBox in the parent form to the child form and perform database query operations. I used new parent form().; to pass the value, but it was useless. After many experiments, I found a relatively simple solution:

1. The child form calls the parent form's static variable

Parent form: Logout

Subform: Affirm

Parent form text box: tB_Logout_Username

public partial class Logout : Form
{

  //Define a static variable to store the value of the text box in the parent form
  public static string tB_LogoutName;

  // Events that instantiate subform
  private void btt_Logout_Click(object sender, EventArgs e)
  {

    //Get the value of the text box in the parent form
    tB_LogoutName = tB_Logout_Username.Text;
    Affirm aff = new Affirm();
    ();

  }

}

Next, you need to call it in the child form directly: parent form. variable

That is: Logout.tB_LogoutName

This method seems to be more flawless. In theory, you should first find a way to get the parent form and then operate it.

2. Pass the parent form as a property to the child form

Define the parent form field of public in your child form, such as:

public class Affirm:Form
{
  public Logout MyLogout;
}

Then set its value in the parent form, such as:

public partial class Logout : Form
{
 
  //Define a static variable to store the value of the text box in the parent form 
  public static string tB_LogoutName;
 
  // Events that instantiate subform 
  private void btt_Logout_Click(object sender, EventArgs e)
  {
 
    //Get the value of the text box in the parent form 
    //tB_LogoutName = tB_Logout_Username.Text;
    Affirm aff = new Affirm();
    =this;
    ();
 
  }
 
}

In this way, you can access and use all the members exposed in the parent form in the child form.