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copied!<p>After checking QWidget::update() source code I've found it calls this method in <code>src/gui/kernel/qwidget.cpp:9544</code> :</p> <pre><code>void QWidget::update(const QRect &rect) { if (!isVisible() || !updatesEnabled() || rect.isEmpty()) return; if (testAttribute(Qt::WA_WState_InPaintEvent)) { QApplication::postEvent(this, new QUpdateLaterEvent(rect)); return; } if (hasBackingStoreSupport()) { QTLWExtra *tlwExtra = window()->d_func()->maybeTopData(); if (tlwExtra && !tlwExtra->inTopLevelResize && tlwExtra->backingStore) tlwExtra->backingStore->markDirty(rect, this); } else { d_func()->repaint_sys(rect); } } </code></pre> <p>As you can see the <code>QUpdateLaterEvent</code> is only posted if the update() is already called from inside a paintEvent() method.</p> <p>You can also check <code>QWidget::repaint(const QRect &rect)</code> source on line 9456 - it lacks <code>testAttribute(Qt::WA_WState_InPaintEvent)</code> check.</p> <p><strong>EDIT</strong></p> <p>The <code>QUpdateLaterEvent</code> is posted as a <code>Qt::NormalEventPriority</code> event, so it gets processed after all other normal priority events (see <code>src/corelib/kernel/qcoreapplication.cpp:971</code> and <code>:1003</code>). You might also want to look into compressEvent code, I haven't checked that.</p> <p>So to finally answer the question: the QUpdateLaterEvent is processed after other high and normal priority events that were in queue before it was posted.</p>

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