View source for Qt3ToQt4 How to convert custom tool tip to an event filter

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[[Category:HowTo]]

= How to convert Qt 3 custom tool tip to Qt 4 event filter =

QToolTip no longer supports inheritance. To customize tooltip behavior on widgets, intercept QHelpEvents in the widget's event() function. Here is how to use an event filter rather than a class formerly deriving from QToolTip.

== Derive from QObject instead QToolTip ==

Change
<code>
class MyToolTipper : public QToolTip
</code>
to
<code>
class MyToolTipper : public QObject
</code>

== Declare the eventFilter rather than maybeTip. ==

Change maybeTip
<code>
 void maybeTip( const QPoint &pos );
</code>
to
<code>
protected:
 bool eventFilter( QObject *obj, QEvent *event );
</code>

== Convert the maybeTip() implementation to eventFilter() ==

<code>
bool MyToolTipper::eventFilter( QObject *obj, QEvent *event )
{
 if (event->type() == QEvent::ToolTip) { // Only process tool tip events
 QHelpEvent '''helpEvent = static_cast<QHelpEvent'''>(event); // Tool tip events come as the type QHelpEvent
 QPoint pos = helpEvent->pos(); // Get pos from event (instead of what was passed to maybeTip)

// Code from maybeTip function. Modified for Qt 4.
 // Rather than tip() use QToolTip::showText() and QToolTip::hideText()
 //
 // For example, convert
 // tip(r, text);
 // to
 // QToolTip::showText(helpEvent->globalPos(), text, widget, r);

return true; // Return true to filter event
 }
 return false; // Return false to allow other event processing
}
</code>

== Install event filter where custom tool tip class was used. ==

Change creation of custom tool tip
<code>
 _toolTipper = new MyToolTipper(viewport(), this);
</code>
to installing the event filter.
<code>
 viewport()->installEventFilter(new MyToolTipper(viewport(), this));
</code>