using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Text; 
using System.Windows.Forms; 
namespace TestMouseMove 
{ 
  public delegate void SetVisiableHandler(); 
  public partial class Form2 : Form 
  { 
    public Form2() 
    { 
      InitializeComponent(); 
    } 
    private void button1_Click(object sender, EventArgs e) 
    { 
      Form3 frm = new Form3(new SetVisiableHandler(SetVisiable)); 
      frm.Show(); 
    } 
    private void SetVisiable() 
    { 
      SetVisiable(this.label1, !this.label1.Visible); 
    } 
    private void SetVisiable(Control control, bool visiable) 
    { 
      if (this.Controls.Contains(control)) 
      { 
        control.Visible = visiable; 
      } 
    } 
  } 
} 

using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Text; 
using System.Windows.Forms; 
namespace TestMouseMove 
{ 
  public partial class Form3 : Form 
  { 
    private SetVisiableHandler m_setVisible; 
    public Form3(SetVisiableHandler setvisible) 
    { 
      InitializeComponent(); 
      this.m_setVisible = setvisible; 
    } 
    private void btnVisible_Click(object sender, EventArgs e) 
    { 
      if (this.m_setVisible != null) 
      { 
        this.m_setVisible(); 
      } 
    } 
  } 
} 

using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Text; 
using System.Windows.Forms; 
namespace TestMouseMove 
{ 
  public partial class Form4 : Form 
  { 
    public Form4() 
    { 
      InitializeComponent(); 
    } 
    #region 子窗口刷新父窗口的值 
    private string strLabel1 = ""; 
    public string StrLabel1 
    { 
      get 
      { 
        return strLabel1; 
      } 
      set 
      { 
        strLabel1 = value; 
        this.label1.Text = strLabel1; 
      } 
    } 
    #endregion 
    private void button1_Click(object sender, EventArgs e) 
    { 
      Form5 form5 = new Form5(this);//这里注意传个this 
      form5.Show(); 
    } 
  } 
} 

using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Text; 
using System.Windows.Forms; 
namespace TestMouseMove 
{ 
  public partial class Form5 : Form 
  { 
    Form4 form4 = new Form4(); 
    public Form5(Form4 formFrm)//这个构造方法里有参数 
    { 
      form4 = formFrm; //这个必须要有 
      InitializeComponent(); 
    } 
    private void button1_Click(object sender, EventArgs e) 
    { 
      form4.StrLabel1 = this.textBox1.Text; 
    } 
  } 
}