SAMPLE: How to Simulate Multiple-Selection TreeView Control

• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows NT version 3.51
      - Microsoft Windows 95 version 4.0
  

SUMMARY

The TVWSTATE sample demonstrates how to simulate a multiple-selection TreeView control. The Windows 95 TreeView control does not support multiple selection. If you want a multiple-selection TreeView, you can use state images to simulate it in your application.

The TVWSTATE sample accomplishes this by using a checkbox type of state image to indicate that the item is selected or cleared (de-selected). These checkboxes will retain their state even if the TreeView loses focus.

Download TVWSTATE.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download TVWSTATE.EXE (size: 49318 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the SOFTLIB\MSLFILES directory
        Get TVWSTATE.EXE (size: 49318 bytes) 
  

MORE INFORMATION

The multiple-selection TreeView control simulation is implemented by setting the state image list of the TreeView control to an image list that contains the checked and unchecked checkbox bitmaps. This image list is set by using the TVM_SETIMAGELIST message with lParam == TVSIL_STATE (see InitImageList in TVWSTATE.C). A TreeView control can have two image lists, a normal image list and a state image list. In the TreeView, the display order from left to right is: the expansion button, the state image (if present), the normal image (if present), and then the item text.

When processing the WM_NOTIFY message where (LPNMHDR)lParam->code == NM_CLICK (see MsgNotifyTreeView in TVWSTATE.C), the code checks to see if the user clicked the left mouse button in the checkbox. If this is the case, the state image index of the item is retrieved, the index is toggled between the checked and unchecked image list items, and then the new index is saved.

The state image index identifies which member of the state image list should be displayed. The state image index is stored in bits 12-16 of the item state value. Either TVIS_STATEIMAGEMASK or TVIS_USERMASK can be used to mask off the lower bits. To access just the state image index, use a statement similar to this:

   StateIndex = tvi.state & TVIS_STATEIMAGEMASK;

   tvi.state = INDEXTOSTATEIMAGEMASK(1);