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Plb-0252.cfm v1.0


ANSI Standard PL/B Language and Visual PL/B


A DATALIST is one of box containing lines of data and a scroll bar on the right side. You can scroll to any line and click or double click on the line to work with the data.



LIST SIZE: In the designer you set the size of the box itself. That simply defines the size on the screen.

The list will hold just about as much data as you want. A ListView, on the other hand, starts to perform poorly when too much data is inserted. DATALIST PROPERTIES

Several properties are of interest and deserve comment here:
We've pre-defined several datalist work areas in the COMMONWK.PLS include file for MMCC:
DATALIST_CURR_ITEM       FORM      6       modifier 0
DATALIST_TOTAL_ITEMS     FORM      6       modifier 1
DATALIST_ITEMS_SELECTED  FORM      6       modifier 2
DATALIST_NEXT_ITEM       FORM      6       modifier 3

LOADING THE LIST You can pre-load the list from the designer by double clicking on the LISTDATA property. That will give you a dialog box in which you enter the data items and then add them to the list.

This loading window works intuitively in that you can just type in a value and tap enter. The item will be added to the initial list. When you have all the items that you want you press SAVE to save this list.

In the program you LOAD the initial values of the DATALIST like this:
     DELETEITEM    {datalist}, 0            ; Clear entire list

     INSERTITEM    {datalist},99999,{data}  ; Insert at END of the list

     INSERTITEM    {datalist},nnn,  {data}  ; Insert at a specific line

You can do a loop with a specific index value ("nnn") to fill the list. That is,
        MOVE          ZERO,IX1               ; Initialize the index
          ADD         ONE, IX1               ; increment index
          INSERTITEM  {datalist},IX1,{data}  ; Put {data} in line IX1
        REPEAT UNTIL {condition}
You can also loop and use the 99999 to tack onto the end of the list.
          INSERTITEM  {datalist},99999,{data}  ; Put {data} in LAST line
        REPEAT UNTIL {condition}

Use the specific index technique if you want to remember where a specific item is stored. For example: Say that you load a list with salesmen. When done you want to position to a particular person. To do this you load the list to specific locations looking for "your" salesman. When you find that person, you remember the index number.
        MOVE          ZERO,IX1               ; Initialize the index
        MOVE          ZERO,OURGUY            ; Don't know which line
          ADD         ONE, IX1               ; increment index
          INSERTITEM  {datalist},IX1,{data}  ; Put {data} in line IX1
          IF ({data} = {our salesman})       ; Is this our guy?
              MOVE    IX1, OURGUY            ; When true, remember IX1
        REPEAT UNTIL {condition}
        SETITEM       {datalist},0,OURGUY    ; Point to our salesman

REPLACING DATA IN A LINE You can replace the data in any line using the SETITEM command:
          SETITEM  {datalist},IX1,{data}  ; replace {data} in line IX1
Be sure to note that the index in this command is ONE BASED. Methods use ZERO BASED indexes. This is important because there is no method (as of PL/B Version 8.7) to replace text in a data list. There is a .GetText method for getting data OUT, but no corresponding .SetText to put it back.

So, if you're using a method based loop to access data, be sure to add one to the index before you try to use a Setitem to replace the value!

POINTING TO AN ENTRY: As mentioned above, you may want to pre-set the list to point to a specific line. Do that with the SETITEM as follows:
  SETITEM {datalist},0,{index}    ; Point to line at {index}
The above won't work properly with a MULTI-SELECT datalist.
You can instead use the better SetSel method:
  {datalist}.SetSel USING *Select={0|1}, *Index={index}  
  ... *Select = 1 for selected
  ...           0 for NOT selected
  ... *Index is ZERO BASED               

To set or reset a range of line use SetSel method. You may need to do this to clear the entire datalist first then SEL the one line you want.
  {datalist}.SelItemRange USING *Select={0|1}:
  ... *Select = 1 for selected
  ...           0 for NOT selected
  ... *Index is ZERO BASED               


You retreive data from the datalist with a standard GETITEM instruction or with METHODS. Both work well.

METHOD Technique:

There are a batch of methods in Sunbelt's manual. The most useful are:
  • DataListName.GetCount GIVING {numeric variable}
    Returns the number of lines in the list.

  • DataListName.GetSelCount GIVING {numeric variable}
    Returns the number of lines selected.

  • DataListName.GetFirstSel GIVING {numeric variable}
    Returns the zero based index to the first line the user has selected. This will be -1 if no items are selected.

  • DataListName.GetText GIVING {data string} USING {numeric variable}
    Returns the data from the line pointed to in the ZERO BASED using variable. (That variable is the *Index= variable).

  • DataListName.GetNextSel GIVING {numeric variable}
    Returns the zero based index of the next line after the one you just retreived using GetText. It's not clear what happens if you never do a GetText. Should test that.

    Getting data from a multi-select list using methods

    DLMAX        FORM   3    ;number of items in the data list
    DLSEL        FORM   3    ;number of items selected
    DLIX         FORM   3    ;Zero based line index
    DATA_STRING  DIM  250    ;Data from list
            F1_DL_Accounts.GetCount    GIVING DLMAX  ;information only
            F1_DL_Accounts.GetSelCount GIVING DLSEL  ;information only
            F1_DL_Accounts.GetFirstSel GIVING DLIX   ;first line we want
              IF (DLIX < 0)        ;is -1 if no more lines
              F1_DL_Accounts.GetText    GIVING DATA_STRING USING DLIX
    		  --- process the data ---
              F1_DL_Accounts.GetNextSel GIVING DLIX

    Getting data from DataList: GETITEM Technique:

    This works as well as well as the Method technique. Some people are move comfortable with it since it's a one based technique where the methods are zero based.

  • The first parameter to the GETITEM names the datalist object that you're working with.

  • The SECOND parameter is the number of the list item that you want. (This is a ONE based number. Methods are ZERO based.) The value will be zero if either it doesn't matter (example 1 below) or when you're asking for the value of the top entry (example 3).

  • The third parameter's type determines how the instruction works. If the third item is a CHARACTER STRING you'll get data from the list. If the third item is a NUMBER you'll get the index to the line that was clicked. Getting POINTERS for the datalist is done with GETITEM where the 3rd parameter is a number. A data value will be returned in that field as follows:
        GETITEM {datalist}, 0,   {numeric}   Gets the index of CURRENTLY
                                             active item in the list
        GETITEM {datalist}, 1,   {numeric}   Gets the TOTAL NUMBER of
                                             items that are in the list.
        GETITEM {datalist}, 2,   {numeric}   Gets the number of items
                                             which are SELECTED in a
                                             multi-select list.
        GETITEM {datalist}, 3,   {numeric}   Gets the index of the NEXT
                                             selected from a multi-select

    Note that there are pre-defined variables for these pointers in the COMMONWK.PLS include unit for MMCC. Those are defined at the top of this page.

    Getting DATA from the datalist is done with GETITEM where the 3rd parameter is a STRING. The second parameter is the index to the item you want.

    For an EDIT style list (where the user can key anything into the datalist's top line), you can use index ZERO to get the top line as it appears to the user.
        GETITEM {datalist}, nnn, {string}    Gets the contents of the
                                             entry number "nnn".
        GETITEM {datalist}, 0,   {string}    Get the actual value keyed
                                             but only if this is a style
                                             EDIT where they can put
                                             anything in the field.

    RETREIVING MULTI-SELECT DATA: Getting data out of a multi-select datalist is not as obvious at it seems.

    The trick is to use the CURRENT ITEM and the NEXT ITEM pointers properly. CURRENT ITEM points to the currently selected item. That part is obvious. What seems to be the confusion is the next item is the one after the first item in the list OR the next one after the last item you retrieved. Here's a loop that works:
          GETITEM      DataList, 0, CURR_ITEM
            COMPARE    ZERO,        CURR_ITEM
            BREAK IF EQUAL		
            GETITEM    Datalist,    CURR_ITEM, TEXT_STRING
            GETITEM    Datalist, 3, CURR_ITEM
    That seems a bit less than elegant, but it works. The point is that before starting the loop you have to learn the current item. That's the first one that the user selected. If that pointer is ZERO then no data was selected. If not zero then you can retreive that first item.

    After getting the first item, you need to use the "3" value to get the NEXT item after the one you just retreived. Note that in the sample code I used the CURR_ITEM variable. Although that's what I'm calling it, the "3" says to get the next item after the last one selected or retreived.

    With the NEXT item in hand we loop back to see if it's a valid item. If we got a ZERO then we're all done.

    NOTE: A useful method is DataList.GetSelCount GIVING WK_Counter.
    This will tell you how many lines are selected at any given time.

    FORMATTING THE DATALIST: Datalist contents are simple strings. You can load a list with data like this.
              PACK        WORK_STRING,ID, NAME, ADDRESS ; build string
              INSERTITEM  {datalist},999999,WORK_STRING ; put in list
            REPEAT UNTIL {condition}
    The above list will not produce nice columns of data as you might expect. If you use a proportional font the data will appear like this: 101 John Jones 600 Lakeshore Drive
    101 Larry Lewis 1420 Mountain
    103 Susie Sunshine 980 Summer Circle You can control the column spacing to some degree by insertting the TAB character (0x09) into your string. But tabs just skip to the next system defined tab, which you can't control. Sometimes things will come out right, sometimes they won't.

    To produce formatted columns, you must use a fixed width font such as Courier, or FIXEDSYS. (You can select the font when building the form in the forms designer, or you can set it by hand.)

    Using a fixed font you'll get this:
             101   John Jones         600 Lakeshore Drive
             101   Larry Lewis        1420 Mountain
             103   Susie Sunshine     980 Summer Circle
    Starting with Windows 95 users have become accoustomed to a structure that looks much like a DATALIST but is, in fact, something else. This is the LISTVIEW (aka DATAGRID).

    The LISTVIEW is typified by several features: There's a header bar across the top with dividers between columns.

    The data lines up under the columns regardless of the font.

    You can change the width of the columns with the mouse by grabbing a divider and sliding it left and right.

    You can sort the entire grid on any column by clicking in the column heading. Multiple clicks sort ascending then descending. A small arrow in the right corner of the heading shows which column was sorted last and the direction of the sort. PL/B provides this function with the LISTVIEW object described in this link.

    Multi-Select Notes

    Clearing Multi-Selections: If you have a multi-select data list, you may need to just clear ALL of the selections that a user may have made. There is no METHOD for doing that. You can loop over all of the selected lines and deselect them one at a time. But it's easier to use SETITEM {datalistname},0,0.

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