How to get runtime property in ClickEvent?

I write code like this:

    public class TestTextObject : TextObject
    {
        private String _TestProperty;
        public String TestProperty
        {
            get { return _TestProperty; }
            set { _TestProperty = value; }
        }
    }

And register it:

    FastReport.Utils.RegisteredObjects.Add(typeof(TestTextObject ), "ReportPage", new Bitmap(16,16), "TestTextObject", 0, false);

In a FastReport, I add a instance of TestTextObject and set ClickEvent, BeforePrintEvent, AfterPrintEvent

    DataBand _DataBand = FReport.FindObject("Data1") as DataBand;
    TestTextObject text3 = new TestTextObject ();
    text3.Bounds = new RectangleF(10, 10,
    Units.Centimeters * 10, Units.Centimeters * 0.5f);
    text3.Text = "中文字ddddddddd";
    text3.BeforePrintEvent = "text3_BeforePrint";
    text3.AfterPrintEvent = "text3_AfterPrint";
    text3.ClickEvent = "text3_Click";
    _DataBand.Objects.Add(text3);

The script like this:

    private void text3_BeforePrint(object sender, EventArgs e)
    {
      TestTextObject _PrintObject = sender as TestTextObject;
                  String[] _Expressions = (_PrintObject.OriginalComponent as FastReport.TextObject).GetExpressions();
                  foreach (String _Expression in _Expressions)
                  {
                      String[] _ElementList = _Expression.Split('.');
                      //it isn't from DataSource
               if (_ElementList.Length <= 1)
                          continue;
                      //TableName
               String TableName = _ElementList[_ElementList.Length - 2];
                      FastReport.Data.TableDataSource _DataSourceBase = _PrintObject.Report.Dictionary.FindByAlias(TableName) as FastReport.Data.TableDataSource;
                      if (_DataSourceBase == null)
                          _DataSourceBase = _PrintObject.Report.Dictionary.FindByName(TableName) as FastReport.Data.TableDataSource;
                       if (_DataSourceBase == null)
                            continue;
                      //Set the first value of DataRow   
                       _PrintObject.TestProperty = (_DataSourceBase.CurrentRow as System.Data.DataRow)[0].ToString();
                    }
    }
    private void text3_AfterPrint(object sender, EventArgs e)
    {
                     //the code is same to text3_BeforePrint
    }
    private void text3_Click(object sender, EventArgs e)
    {
      TestTextObject _PrintObject = sender as TestTextObject;  
      MessageBox.Show(_PrintObject.TestProperty.ToString());
    }

I expect the result of Message is: the first column's value of each datarow, But it is null! Why?! How can i do?
If use (PrintObject.OriginalComponent as TestTextObject).TestProperty, it get the value of last datarow