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List:       pykde
Subject:    Re: [PyQt] How to have QML interpret a property as null (instead of undefined)?
From:       oliver <oliver.schoenborn () gmail ! com>
Date:       2017-10-12 16:27:49
Message-ID: CAMb+DaVkkQT7AMjpU-ZGEkyUXFK4TqkrFjTRqCAUvMWfA2jRTg () mail ! gmail ! com
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Is this a documented technique? If not, I would avoid it. Use only the
documented way of doing this, and if none is documented, there is likely a
reason that the feature is not available. In that case, find and understand
the reason, and fix your design accordingly.

On Thu, 12 Oct 2017 at 11:25 Russell Warren <russ@perspexis.com> wrote:

> Solution found: Returning a freshly instantiated QObject() does the
> trick.  QML interprets this as a null.  ie:
>
> @pyqtProperty(QVariant, notify = publicPropertyChanged)#'QDateTime')
> def my_date(self):
>     if self._my_date is None:
>         return QObject()  # QML interprets this as null
>     return QDateTime(self._my_date) # no PyQt autoconvert for
> datetime->QVariant
> _______________________________________________
> PyQt mailing list    PyQt@riverbankcomputing.com
> https://www.riverbankcomputing.com/mailman/listinfo/pyqt

-- 
Oliver
My StackOverflow contributions
My CodeProject articles
My Github projects
My SourceForget.net projects

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<div dir="ltr">Is this a documented technique? If not, I would avoid it. Use only the \
documented way of doing this, and if none is documented, there is likely a reason \
that the feature is not available. In that case, find and understand the reason, and \
fix your design accordingly.</div><br><div class="gmail_quote"><div dir="ltr">On Thu, \
12 Oct 2017 at 11:25 Russell Warren &lt;<a \
href="mailto:russ@perspexis.com">russ@perspexis.com</a>&gt; \
wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 \
.8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Solution found: \
Returning a freshly instantiated QObject() does the trick.   QML interprets this as a \
null.   ie:<div><br></div><div></div></div><div dir="ltr"><div><div \
style="font-size:9.6px"><font face="monospace, monospace" \
color="#351c75">@pyqtProperty(QVariant, notify = \
publicPropertyChanged)#&#39;QDateTime&#39;)</font></div><div \
style="font-size:9.6px"><font face="monospace, monospace" color="#351c75">def \
my_date(self):</font></div><div style="font-size:9.6px"><font face="monospace, \
monospace" color="#351c75">      if self._my_date is \
None:<br></font></div></div></div><div dir="ltr"><div><div \
style="font-size:9.6px"><font face="monospace, monospace" color="#351c75">            \
return QObject()   # QML interprets this as null</font></div></div></div><div \
dir="ltr"><div><div style="font-size:9.6px"><font face="monospace, monospace" \
color="#351c75">      return QDateTime(self._my_date) # no PyQt autoconvert for \
datetime-&gt;QVariant</font></div></div></div> \
_______________________________________________<br> PyQt mailing list      <a \
href="mailto:PyQt@riverbankcomputing.com" \
target="_blank">PyQt@riverbankcomputing.com</a><br> <a \
href="https://www.riverbankcomputing.com/mailman/listinfo/pyqt" rel="noreferrer" \
target="_blank">https://www.riverbankcomputing.com/mailman/listinfo/pyqt</a></blockquote></div><div \
dir="ltr">-- <br></div><div class="gmail_signature" \
data-smartmail="gmail_signature"><div dir="ltr">Oliver<div>My StackOverflow \
contributions<br><div>My CodeProject articles</div></div><div>My Github \
projects</div><div>My SourceForget.net projects</div></div></div>


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