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/// <summary>
        /// Set tree node checkbox state
        /// </summary>
        /// <param name="treeNode">tree node</param>
        /// <param name="checkboxState">checkbox state</param>
        private void SetTreeNodeState(TreeNode treeNode, CheckBoxState checkboxState)
        {
            IntPtr hWnd;
            TVITEM tvi;
            hWnd = this.Handle;

            // Send a TVM_SETIMAGELIST with TVSIL_STATE.
            if (!_ImageListSent)
            {

                SendMessage(hWnd, (UInt32)TVM_SETIMAGELIST, (UInt32)TVSIL_STATE,

(UInt32)CheckBoxStateImageList.Handle);


                _ImageListSent = true;
            }

            // The following uses the TVM_SETITEM message to set the State
            // of a given item. It uses the TVITEM structure.

            //  tvi.mask: include TVIF_HANDLE and TVIF_STATE
            tvi.mask = TVIF_HANDLE | TVIF_STATE;

            // To use the State image, tvi.State cannot be 0. 
            //Setting it to 1 means to use the second image in the image list.
            tvi.state = (uint)checkboxState;
            // Left shift 12 to put info in bits 12 to 15
            tvi.state = tvi.state << 12;
            // Set StateMask. -This is required to isolate State above.
            tvi.stateMask = TVIS_STATEIMAGEMASK;

            // Define the item we want to set the State in.
            tvi.hItem = treeNode.Handle;  //For example, try the root.

            //  Initialize the rest to zero.
            tvi.pszText = (IntPtr)0;
            tvi.cchTextMax = 0;
            tvi.iImage = 0;
            tvi.iSelectedImage = 0;
            tvi.cChildren = 0;
            tvi.lParam = (IntPtr)0;

            // Send the TVM_SETITEM message.
            //  TVM_SETITEM = 4365
            SendMessage(hWnd, (UInt32)TVM_SETITEM, (UInt32)0, ref tvi);

            //Set Node State
            SetNodeState(treeNode, checkboxState);
        }