用委托更新主窗体界面报未将对象引用设置到对象的实例

子窗体委托：

  public partial class Form_settings : Form
        {
            public delegate void DataChangeHandler(Object sender, EventArgs e);
            public event DataChangeHandler ReturnEvent;
            public Form_settings()
                {
                        InitializeComponent();
                }
         }

子窗体调用

  ReturnEvent(null,null);

主窗体：

  public MainFrom()
         {
             Form_settings CF = new Form_settings();
             CF.ReturnEvent += new Form_settings.DataChangeHandler(On_request);
            InitializeComponent();

        }
                 private void On_request(object sender,EventArgs e)
        {
            this.defaultLabel2.Text = AllVariable.XDBL.ToString() + "箱每跺";
        }

报错

参数能NULL吗，你ReturnEvent（NULL，NULL）当让报错了，

子窗体委托：
public partial class Form_settings : Form
{
public delegate void DataChangeHandler();
public DataChangeHandler ReturnEvent;
public Form_settings(DataChangeHandler fun)
{
this.ReturnEvent = fun;
InitializeComponent();
}
}

子窗体调用
this.ReturnEvent();

主窗体：

public MainFrom()
{
Form_settings CF = new Form_settings(On_request);
InitializeComponent();

    }
             private void On_request()
    {
        this.defaultLabel2.Text = AllVariable.XDBL.ToString() + "箱每跺";
    }



            先试试