通过数据源找到控件 再通过控件找到模板数据

 private void GetCheckBoxVal()
        {
            if (treeView != null)
            {
                ContentPresenter myContentPresenter = null;
                DataTemplate myDataTemplate = null;
                CheckBox ck = null;
                TextBlock tb = null;
                foreach (var item in treeView.Items)
                {
                    DependencyObject obj = treeView.ItemContainerGenerator.ContainerFromItem(item); ;
                    myContentPresenter = FindVisualChild<ContentPresenter>(obj);
                    myDataTemplate = myContentPresenter.ContentTemplate;
                    ck = (CheckBox)myDataTemplate.FindName("ck", myContentPresenter) as CheckBox;
                    tb = (TextBlock)myDataTemplate.FindName("txt", myContentPresenter) as TextBlock;
                }
            }
        } 


 private childItem FindVisualChild<childItem>(DependencyObject obj) where childItem : DependencyObject
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
            {
                DependencyObject child = VisualTreeHelper.GetChild(obj, i);
                if (child != null && child is childItem)
                    return (childItem)child;
                else
                {
                    childItem childOfChild = FindVisualChild<childItem>(child);
                    if (childOfChild != null)
                        return childOfChild;
                }
            }
            return null;
        }