[OpenLayers-Users] Permalink doesn't update
on addlayer/removelayer
Slawomir Messner
slawomir.messner at staff.uni-marburg.de
Wed Aug 25 04:23:26 EDT 2010
Hi,
if I read the code of Permalink and ArgParser right it's a pretty
confusing behaviour at all, especially if you have an application with
dynamic loading of layers.
While I'm working with these controls I noticed some other things:
1. If A sends his link, then changes the visibility of the third layer
during his work than A has the same url like B. I think for a normal
user pretty confusing to have to different links for one view.
2. If we change Andreas's example a little and B has "&layers=BFT" in
the url. At the beginning the views of A and B are equal(if we assume
the default config is all layers visible) because ArgParser configures
the layer only if there are the same number of layers in url and map:
"if (this.layers.length == this.map.layers.length) {"
If a user now adds a layer then she/he wonders why his first overlay
layer is not visible. This can also happen when he forgets why she/he's
on the site because removes the second adds a new one, removes the
"second", adds a new one... all is as expected till he adds the third
then the second is not visible. This happens because the addlayer
listener of ArgParser is unregistered after the line above. That's why
standard Permalink and ArgParser combination is only useful to change
the initial configuration, this should be mentioned in the documentation.
3. One thing, i would separate visibility and base/overlay-layer. When
you have two baselayers in your map ArgParser doesn't parse the "0" for
baselayers which are not visible(or not THE baselayer of the map) and
the unvisible baselayer becomes an overlay. So something like
"&layers=BTBFOTOF" would be better for two baselayers(first the
baselayer) and two overlay layer (first visible, second not)... or just
make ArgParser parse "0".
configureLayers: function() {
if (this.layers.length == this.map.layers.length) {
this.map.events.unregister('addlayer', this, this.configureLayers);
for(var i=0, len=this.layers.length; i<len; i++) {
var layer = this.map.layers[i];
var c = this.layers.charAt(i);
if (c == "B") {
this.map.setBaseLayer(layer);
} else if (c == "0") {
layer.isBaseLayer = true; //trigger change-event?
} else if ( (c == "T") || (c == "F") ) {
layer.setVisibility(c == "T");
}
}
}
},
Regards,
Slawomir
Am 24.08.2010 15:38, schrieb Andreas Hocevar:
> On Aug 24, 2010, at 15:15 , Marc Jansen wrote:
>
>> Hi Andreas,
>>
>> first of all, sorry for cross-posting in the past. I thought it was
>> useful in this case.
>>
>> I'd disagree about the not handling of the layeradd/layerremove event
>> for the Permalink-control -- but can easily live without this addition
>> to OpenLayers :-)
>>
>> Your suggestions of alternative ways of handling application "state" are
>> valid and often better suited, yet I think the addition of two
>> additional listeners to the control would be very intuitive.
> This is where I have to disagree. Let's say you have a map with two pre-configured layers. Now user A, who uses the Permalink control as is, adds a layer, resulting in a permalink with "&layers=BT".
>
> User B has the same map, adds a completely different layer, but uses your add/removelayer aware Permalink control, resulting in a permalink with "&layers=BTT".
>
> Now the interesting part comes when both users send this permalink to someone who opens the permalink. That person will see exactly the same layers with both permalinks - because the map will load only the two pre-configured layers.
>
> This is why I wouldn't consider adding add/removelayer handlers to the Permalink control useful or intuitive at all.
>
> Regards,
> Andreas.
>
>> Best regards,
>>
>> Marc
>>
>>
>>
>> On 24.08.2010 14:49, Andreas Hocevar wrote:
>>> Hi,
>>>
>>> first of all, please don't cross-post dev and users.
>>>
>>> I am not sure if a permalink as provided by OpenLayers is what you really want for applications where the user can add or remove layers. The permalink only stores the visible/invisible state of the available layers in their order. It does not know anything about what these layers are. So a permalink will look exactly the same for any map with the same extent with let's say 3 layers that are all visible.
>>>
>>> If you want to store information on what layers are actually configured, you should look into Format.WMC, Format.OWS or solutions like the OpenGeo Suite's GeoExplorer (http://suite.opengeo.org/geoexplorer), which stores layer configurations in a database and provides a permalink with a map id.
>>>
>>> Regards,
>>> Andreas.
>>>
>>> On Aug 24, 2010, at 14:31 , Marc Jansen wrote:
>>>
>>>
>>>> Hi Slawomir,
>>>>
>>>> I'd consider this a bug with a (on first sight) reasonable easy fix:
>>>>
>>>> In the Permalinks draw-method:
>>>>
>>>> this.map.events.on({
>>>> 'moveend': this.updateLink,
>>>> 'changelayer': this.updateLink,
>>>> 'changebaselayer': this.updateLink,
>>>> 'addlayer': this.updateLink,
>>>> 'removelayer': this.updateLink,
>>>> scope: this
>>>> });
>>>>
>>>> Or one could think of triggering a changelayer event when a layer has
>>>> been added/removed in Map.js.
>>>>
>>>> I am unsure which design is better, so I'd suggest opening up a ticket
>>>> (I cc'ed the developer list so the core developers notice this discussion).
>>>>
>>>> Regards,
>>>> Marc
>>>>
>>>>
>>>>
>>>>
>>>> On 24.08.2010 13:53, Slawomir Messner wrote:
>>>>
>>>>> Hello,
>>>>> Does anyone know why Permalink doesn't listen to addlayer/removelayer?
>>>>> Every time I add a new layer I have to change a property(i.e.
>>>>> visibility) to refresh the link. It's a bug or a feature?
>>>>> Regards,
>>>>> Slawomir
>>>>>
>>>>>
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>>>>
>>
>> --
>>
>> .................................................................
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>>
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>>
>> ISBN: 978-3-937514-92-5
>> URL: http://openlayers-buch.de
>> .................................................................
>>
>>
>> Dipl.-Geogr. Marc Jansen
>> - Anwendungsentwickler -
>>
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--
-----------------------------------------------
Slawomir Messner
Forschungszentrum "Deutscher Sprachatlas"
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