我怎样才能让表格1上的标签从表格2上说“你好”?

您将需要对Form1实例的引用—例如,如果是Form1正在构造Form2,您可能会通过 this 在中作为构造函数参数。

然后,您需要通过属性(或-ick!-非私有字段)公开Form1的标签,或者编写一个方法/属性来设置标签的文本。例如:

public class Form1 : Form 
{
    private Label label;

    // Construction etc as normal

    public string LabelText
    {
         get { return label.Text; }
         set { label.Text = value; }
    }

    public Form2 CreateForm2()
    {
        return new Form2(this);
    }
}

public class Form2 : Form
{
    private Form1 form1;

    public Form2(Form1 form1)
    {
        this.form1 = form1;
        // Normal construction
    }

    public void SayHello()
    {
        form1.LabelText = "Hello";
    }
}

Public Class Form1
    Inherits Form


    Friend label1 As New Label


    Public Sub openForm2()
        Dim f As New Form2(Me)
        f.Show()
    End Sub


End Class


Public Class Form2
    Inherits Form


    Private _ref As Form1


    Public Sub New()
        _ref = Nothing
    End Sub


    Public Sub New(ByVal formRef As Form1)
        _ref = formRef
    End Sub


    Public Sub accessLabel(ByVal setText As String)
        If (_ref IsNot Nothing) Then
            _ref.label1.Text = setText
        Else
            Throw New NullReferenceException("_ref is NULL")
        End If
    End Sub


End Class

http://www.c-sharpcorner.com/UploadFile/mosessaur/winformsdelegates09042006094826AM/winformsdelegates.aspx

在第二种形式中,我定义:

public delegate void AddItemDelegate(string item);
public AddItemDelegate AddItemCallback;

从打开它的表格中我写道:

private void btnScenario2_Click(object sender, EventArgs e)
{

    FrmDialog dlg = new FrmDialog();
    //Subscribe this form for callback
    dlg.AddItemCallback = new AddItemDelegate(this.AddItemCallbackFn);
    dlg.ShowDialog();

}
private void AddItemCallbackFn(string item)
{

    lstBx.Items.Add(item);

}