I have a column in a DB table which stores pressure. The pressure is always stored as PSI and can be converted to BAR by diving by 14.5.
The user can toggle display of PSI/BAR with a Radio Group.
I was using a TStringGrid
and am converting to a TDbGrid
- which is quite new to me.
When the user toggles PSI/BAR, how to I update the display in my DB grid? (I imagine that I just execute it's query again? or Call query.Refresh()
?) But how do I do the conversion?
SELECT
statement of my query? But how would I do that? SELECT pressure / 14.5 FROM measurements
? Or how? OnBeforeXXX()
which I can code? Or OnGetDisplayText()
or some such?I am sure thta this is very basic, but until now I have just been displaying unmanipulated data and now I need a conversion function. Google didn'ty help, but I probably didn't know what to ask for.
I also want to change the text of the column title, toggling between "Presure (PSI)" and "pressure (BAR)". Thanks in advance for any help.
Code a OnGetText event handler for the pressure field like this:
type
TPressureMU = (pmuPSI, pmuBAR);
const
PSIToBarFactor = 1/14.5;
procedure TdmData.qMeasurementsPressureGetText(Sender: TField; var Text: string;
DisplayText: Boolean);
begin
case PressureMU of
pmuPSI: Text := FloatToStr(Sender.AsFloat); //Already PSI
pmuBAR: Text := FloatToStr(Sender.AsFloat * PSIToBarFactor); //ConvertingToBAR
end
end;
I'm using a property PressureMU of the declared enumeration to control if the pressure is shown in PSI or BAR measurement unit.
This way, when the user changes the selection, you just adjust the value of that property.
If you use persistent fields, you can link the event handler directly to you field using the object inspector, and if not, you can do it by code like this:
begin
qMeasurements.FieldByName('Pressure').OnGetText := qMeasurementsPressureGetText;
end;
where qMeasurementsPressureGetText
is the name of the method.