How can I highlight a line in TMemo?
delphi, delphi-2007
Solution
`TMemo` doesn't support that feature natively, and attempting to add that feature will lead to no end of headaches.
Instead, consider using a different text-editing control. That's what the Delphi IDE does. SynEdit, for example, supports the feature: Set the `ActiveLineColor` property to something other than `clNone`.
Problem
I would like to highlight the line that contains the caret in a `TMemo` control, similar to the editor in the Delphi IDE. I tried the following code and it kind of works: (Sorry for the With-statement, this needs refactoring.) ``` procedure TMemo.WMPaint(var Message: TWMPaint); var PS: TPaintStruct; DC: Hdc; Canvas: TCanvas; LineIdx: Integer; X, Y: Integer; Max: Integer; s: string; h: Integer; begin DC := Message.DC; if DC = 0 then DC := BeginPaint(Handle, PS); Canvas := TCanvas.Create; try Canvas.Handle := DC; Canvas.Font.Name := Font.Name; Canvas.Font.Size := Font.Size; with Canvas do begin Max := TopLine + VisibleLines; if Max > Pred(Lines.Count) then Max := Pred(Lines.Count); Brush.Color := Self.Color; FillRect(Self.ClientRect); Brush.Color := clYellow; h := Canvas.TextHeight('Mg'); Y := (Line - TopLine) * h; Marker.Top := y + self.Top; FillRect(Rect(0, Y, ClientRect.Right, Y + h)); Brush.Color := Self.Color; Y := 1; for LineIdx := TopLine to Max do begin X := 2; s := Lines[LineIdx]; if LineIdx = Line then Brush.Color := clYellow else Brush.Color := Self.Color; TextOut(X, Y, s); Inc(Y, h); end; end; finally if Message.DC = 0 then EndPaint(Handle, PS); end; Canvas.Free; inherited; end; ``` (This code is added to the memo through an interposer class.) This works, but it isn't triggered often enough. E.g. when I scroll using the down arrow. I could, of course now start adding all kinds of events in order to call the memo's invalidate method and so forcing a repaint, but that doesn't seem right. Maybe there is already such a component, that I could just use? I already checked `TJvMemo` from the `Jvcl` which doesn't seem to have such a feature. Edit: I ended up using SynEdit.