<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="Generator" content="Microsoft Word 14 (filtered medium)">
<!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.MsoAcetate, li.MsoAcetate, div.MsoAcetate
{mso-style-priority:99;
mso-style-link:"Markeringsbobletekst Tegn";
margin:0cm;
margin-bottom:.0001pt;
font-size:8.0pt;
font-family:"Tahoma","sans-serif";
mso-fareast-language:EN-US;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Arial","sans-serif";
color:windowtext;
font-weight:normal;
font-style:normal;
text-decoration:none none;}
span.MarkeringsbobletekstTegn
{mso-style-name:"Markeringsbobletekst Tegn";
mso-style-priority:99;
mso-style-link:Markeringsbobletekst;
font-family:"Tahoma","sans-serif";}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:3.0cm 2.0cm 3.0cm 2.0cm;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="DA" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">Hi bold developers of QGIS.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">I’ve recently begun digging into utilizing the event (signal) model of QGIS (3.4).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">And I’ve encountered a number of frustrations, as the events don’t work the way they’re supposed to, at least according to the available documentation (<a href="https://qgis.org/pyqgis/master/core/index.html">https://qgis.org/pyqgis/master/core/index.html</a>).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">E.g., the event “layerLoaded” on the project instance with the description “<i>Emitted when a layer from a projects (sic) was read</i>”, which to me indicates,
that the loading is done (due to the use of “loaded” and “was”).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">But the event is emitted before the loading of the layer is done, and you are therefore unable to find the layer it concerns.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">Another example is the event “metadataChanged” on a loaded layer, which again to me indicates a past/done action (due to the use of “changed”). But again, it’s
emitted before the change actually takes place, and the changed metadata isn’t available.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">If the two events are indeed preload events, their names should instead be something like “layerLoading” and “metadataChanging”, or even “layerPreLoad” and “metadataPreChange”.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">Is there a guide somewhere to tell how the event system is envisioned, and which events are emitted pre-action and which are emitted post-action ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">Or must I (hopefully not) take a deep look into the QGIS source code itself for this kind of information ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">In general, pre-action events are of limited use, except when it comes to deletions and destructions. For loading and changing stuff, post-action events are almost
always what you need.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Med venlig hilsen</span><br>
<br>
<span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Lars I. Nielsen, LIFA A/S</span><br>
<span lang="EN-US" style="font-size:10.0pt;font-family:"Arial","sans-serif"">GIS-konsulent, FME Certified Professional</span><br>
<span style="font-size:10.0pt;font-family:"Arial","sans-serif"">Geoinformatik</span><br>
<span style="font-size:8.0pt;font-family:"Arial","sans-serif";color:black;mso-fareast-language:DA"><img border="0" width="284" height="82" id="_x0000_i1026" src="cid:image001.gif@01D5582A.0C09FEB0" alt="Beskrivelse: C:\Users\lin\AppData\Roaming\Microsoft\signatures\284x82-3741133837051347070"></span><o:p></o:p></p>
<table class="MsoNormalTable" border="0" cellspacing="0" cellpadding="0" width="300" style="width:225.0pt">
<tbody>
<tr>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:red">T</span></b><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">6313 6800</span><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:red">@</span></b><span style="font-size:10.0pt;font-family:"Arial","sans-serif""> </span><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">lin@lifa.dk</span><o:p></o:p></p>
</td>
</tr>
<tr>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:red">D</span></b><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">6313 6849</span><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:red">W</span></b><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><a href="http://www.lifa.dk"><span style="color:blue">www.lifa.dk</span></a></span><o:p></o:p></p>
</td>
</tr>
<tr>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:red">M</span></b><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">2492 4866</span><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:red">CVR</span></b><o:p></o:p></p>
</td>
<td style="padding:0cm 0cm 0cm 0cm">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">20937289</span><o:p></o:p></p>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><br>
<a href="https://www.linkedin.com/company/lifa-a-s/"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:blue;mso-fareast-language:DA;text-decoration:none"><img border="0" width="21" height="21" id="_x0000_i1025" src="cid:image002.png@01D5582A.0C09FEB0" alt="Beskrivelse: C:\Users\lin\AppData\Roaming\Microsoft\signatures\21x21-3019966288736195652"></span></a><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><br>
Følg os på LinkedIn og læs de seneste nyheder fra LIFA A/S </span><o:p></o:p></p>
</div>
</body>
</html>