I need to display the size in label (textdim)

What's wrong with my code?

ISldWorks m_swApp;
        IDisplayDimension m_swDisplayDim;
        Dimension swDim;
        Annotation swAnn;
        IModelDoc2 swModel;

public void WorkDimension(IModelDoc2 swModel)
        {
            ISelectionMgr swSelMgr = swModel.ISelectionManager;
            if (swSelMgr.GetSelectedObjectCount() == 1)
            {
                int selType = swSelMgr.GetSelectedObjectType2(1);
                if (selType == (int)swSelectType_e.swSelDIMENSIONS)
                {
                    object DP;
                    object DimProp;
                    double DPValue;
                    m_swDisplayDim = (IDisplayDimension)swSelMgr.GetSelectedObject5(1);
                    DP = m_swDisplayDim.GetDimension();
                    DPValue = swDim.GetValue2("");
                    //swAnn = m_swDisplayDim.GetText((int)swDimensionTextParts_e.swDimensionTextAll);
                    textdim.Text = DPValue.ToString();
                }
                else
                {
                    textdim.Text = "Выберите размер";
                    m_swDisplayDim = null;
                }
            }
            else
            {
                textdim.Text = "Выберите один размер";
                m_swDisplayDim = null;
            }
        }