From 6a197ad3ca8e0e32f8d3e844e9a5bde998c3746b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=BDeljan=20Rikalo?= <zeljko@lazarus-ide.org>
Date: Sun, 13 Nov 2022 18:13:09 +0100
Subject: [PATCH] Qt5: fixed behaviour of TMemo.Lines.Add(), still slower than
 gtk or win32, but have correct behaviour when last line of memo is line
 break. For faster inserts remove last line break. issue #39444

---
 lcl/interfaces/qt5/qtprivate.pp | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/lcl/interfaces/qt5/qtprivate.pp b/lcl/interfaces/qt5/qtprivate.pp
index 751de2d8f0..ff7f395cad 100644
--- a/lcl/interfaces/qt5/qtprivate.pp
+++ b/lcl/interfaces/qt5/qtprivate.pp
@@ -437,11 +437,22 @@ begin
   // simplified because of issue #29670
   // allow insert invalid index like others do
   if Index >= FStringList.Count then
-    Index := FStringList.Add(S)
-  else
+  begin
+    Index := FStringList.Add(S);
+    if FHasTrailingLineBreak then
+      W := GetUTF8String(S + LineBreak)
+    else
+      W := GetUTF8String(S);
+    if FHasTrailingLineBreak then
+      TQtTextEdit(FOwner.Handle).setLineText(Index, W)
+    else
+      TQtTextEdit(FOwner.Handle).Append(W);
+  end else
+  begin
     FStringList.Insert(Index, S);
-  W := GetUTF8String(S);
-  TQtTextEdit(FOwner.Handle).insertLine(Index, W);
+    W := GetUTF8String(S);
+    TQtTextEdit(FOwner.Handle).insertLine(Index, W);
+  end;
   FTextChanged := False; // FStringList is already updated, no need to update from WS.
 end;