Doc: Added a note to Code Editor example docs

    Task-number: QTBUG-9004
    Reviewed-by: David Boddie

1 files changed, 26 insertions, 0 deletions

diff --git a/doc/src/examples/codeeditor.qdoc b/doc/src/examples/codeeditor.qdoc
index 435f650..1718d52 100644
--- a/doc/src/examples/codeeditor.qdoc
+++ b/doc/src/examples/codeeditor.qdoc
@@ -194,4 +194,30 @@
     with QSyntaxHighlighter" article in Qt Quarterly 31 implements
     this. You find it here: \l{http://doc.qt.nokia.com/qq/}.
 
+    The line number area is now painted every time the cursor blinks
+    (because we connect \l{QPlainTextEdit::}{updateRequest()} to
+    \c updateLineNumberArea()). We can avoid this by introducing a new
+    member variable to CodeEditor that keeps track of when the update
+    request comes from a cursor blink (in which case we do not
+    repaint). The code below requires the \c m_countCache variable,
+    which is a QPair<int, int> initialized with \c -1 for both
+    \l{QPair::}{first} and \l{QPair::}{second}.
+
+    \code
+        void CodeEditor::updateLineNumberArea(const QRect &rect, int dy) 
+        {
+            if (dy) {
+                lineNumberArea->scroll(0, dy);
+            } else if (m_countCache.first != blockCount()
+                       || m_countCache.second != textCursor().block().lineCount()) {
+                lineNumberArea->update(0, rect.y(), lineNumberArea->width(), rect.height());
+                m_countCache.first = blockCount();
+                m_countCache.second = textCursor().block().lineCount();
+            }   
+
+            if (rect.contains(viewport()->rect()))
+                updateLineNumberAreaWidth(0);
+        }
+    \endcode
 */
+