grid 绑定会重复附加数据

grid 绑定会重复叠加数据

     <ScrollViewer Height="633" HorizontalAlignment="Left"  Name="scrollViewer1" VerticalAlignment="Top" Width="441">

                    <!--show score-->

                    <Canvas x:Name="CanvasScores">

                        <TextBlock Text="{Binding Path=LocalizedResources.productName, Source={StaticResource LocalizedStrings}}" Canvas.Top="50" Canvas.Left="0" />

                        <TextBlock Text="{Binding Path=LocalizedResources.barCode, Source={StaticResource LocalizedStrings}}" Canvas.Top="50" Canvas.Left="200" />


                        <TextBlock x:Name="TextBlockID" Canvas.Top="100" Canvas.Left="0" />

                        <TextBlock x:Name="TextBlockName" Canvas.Top="100" Canvas.Left="200" />

                       


                    </Canvas>


                </ScrollViewer>


            </Grid>

 protected override void OnNavigatedTo(NavigationEventArgs e)

        {

           

            loadData();

        }

        private void loadData()

        {

           if(belong==null||belong.Length==0)

           {

               belong = "product";

           }

            string strSelect = "SELECT * FROM aa";

            if (_invoiceEntries!=null)

            {

                _invoiceEntries.Clear();//为什么clear 不了

            }

            _invoiceEntries = (Application.Current as App).db.SelectObservableCollection<productType>(strSelect);

            int count = _invoiceEntries.Count;

            foreach (productType data in _invoiceEntries)

            {

                TextBlockID.Text += data.Id + Environment.NewLine;

               // string Typename = (Application.Current as App).db.GetSingle("select typename from producttype where id=" + data.Id);

                TextBlockName.Text += data.typeName + Environment.NewLine;

               

            }

                 //假如之前已经有10行，再添加一行返回该页面时就会绑定21行。。。有10行重复了



        }

------解决方案--------------------
返回页面时navigatedto也执行了，这个这么简单的问题，跟踪一下就知道了，你要判断navigatedto是第一次进入，还是从其他页面导航进入，还是从墓碑恢复来的。。。