How to fix variable line height in data grid with SQLite database when using callbacks

Question

I'm working with the data grid with SQLite database using a feature called callbacks as described in this lesson: displaying-large-amounts-of-data

I'd like to make some changes to the sample stack included in that lesson (you can download the stack from the link on the top of that page).

I'd like to display the 'plot' text in the DG instead of the 'Title' of the movie and the plot text should have variable line heights as described in this lesson: how-do-i-create-a-form-with-variable-line-heights

In the sample stack I made these changes:

in the Row Template: renamed field "Title" to "plot", set the dontWrap to false and changed fixedLineHeight to false

renamed field "ReleaseDate" to "nr"

added: set the text of field "nr" of me to pDataArray["id"]

in the Row Behavior:

    ## changed the layoutControl to make space for wrapping of field "plot"

    on LayoutControl pControlRect
    local theFieldRect

   put the rect of me into theFieldRect
   set the right of button "Genre" of me to item 3 of theFieldRect
   set the right of field "LblGenre" of me to the left of button "Genre" of me

   set the right of field "nr" of me to item 3 of theFieldRect

   ## Expand field "plot"
   put the rect of field "plot" of me into theFieldRect
   put item 3 of pControlRect - 180 into item 3 of theFieldRect
   set the rect of field "plot" of me to theFieldRect

   ##Now resize field to fit content
   put item 2 of theFieldRect \
         + the formattedheight of field "plot" of me - \
         the bottommargin of field "plot" of me \
   into item 4 of theFieldRect
   set the rect of field "plot" of me to theFieldRect

   ## Now update the bounding rect to match total height you
   ## want this row to have
   put item 4 of theFieldRect into item 4 of pControlRect

   set the rect of graphic "Background" of me to pControlRect
end LayoutControl

In the lesson on setting variable line heights it says to turn off the "fixed control height" of the data grid. However when I do that nothing gets displayed and I'm getting a scrip error.

The stack with my changes is here: Databases-callbacks-variable-line-height.zip (just replace the original stack from the lesson with it; the SQLite database is the same and should be placed in the same folder as the stack).

How to fix this so that the variable line height will work?

Answer 1

I located the problem with fixed control height turned off. The data grid behavior isn't setting the GetDataForLine pLine parameter properly when caching the height for each row. I'll provide a modification you can make to the data grid behavior until a fix is included in LiveCode, but you should probably reconsider your approach. When fixed line height is turned off the data grid has to compute the height of every line prior to displaying the data grid. This takes a loooooong time for the 50,000 record example you are working with.

First, edit the script of the data grid behavior:

edit script of btn "data grid" of stack "revdatagridlibrary"

Next, go to line 3097. Below 3097 add the following line of code:

add 1 to theSequence

The code should now look like this:

repeat for each key theIndex in sDataArray     
            add 1 to theSequence

            ## Get height
            if sDataArray[theIndex] is NULL then

Save the script. This will save the change in your current version of LiveCode. Be aware that the next time you update LiveCode the change will be lost. I submitted the fix to RunRev, however, so it should be fixed in the next release.

Also, your code that sets the rect of graphic "Background" needs a small change. Right now it won't work if the bottom of the field is higher than the bottom of the "Genre" button. The code should probably be something like this:

put max(item 4 of theFieldRect, the bottom of button "Genre" of me + 4) into item 4 of pControlRect