[OpenLayers-Dev] multipleSelectFeature on one layer

Amos Hayes ahayes at gcrc.carleton.ca
Mon Jan 26 11:08:11 EST 2009

I think the big questions for me are:

Where are you planning to store the states?

How will an app developer obtain a list of currently selected features  
and distinguish between the 'selections' that have been applied if  
more than one control has been set up?

Amos Hayes
Geomatics and Cartographic Research Centre
Carleton University
ahayes at gcrc.carleton.ca

On 26-Jan-09, at 10:13 AM, Alexandre Dube wrote:

> Hi devs,
>  My only problem remaining : should the layer keep its selectedFeature
> array ?  If so, on selection, it's easy to know if a feature is  
> already
> selected.  As soon as one control adds it to its own array, it  
> checks in
> the layer's one and add it if it's not there.
>  But for unselection, before removing it from the layer's array, we
> would need to check all select features control and all controls
> containing select features control.  Since we can easily say that one
> control does a specific task at a time, I don't really see the use of
> the selectedFeatures array in the layer.  I would just remove it and
> avoid the above problem.  What do you think ?
> Alexandre
> Alexandre Dube wrote:
>> Hi Eric,
>>  You're right.  So instead of removing the last renderIntent from the
>> stack, we need to remove the last renderIntent of the current  
>> SelectFeature.
>>  SFC = SelectFeature Control
>>  RIA = renderIntents array
>>  Let's say the mouse goes hover a feature and get selected by a 1st  
>> SFC :
>>  RIA : ["temporary"]
>>  Then the user click it to select it with an other SFC :
>>  RIA : ["temporary", "select"]
>>  Then the mouse goes out of the feature, unselecting it from the  
>> 1st SFC :
>>  RIA : ["select"]
>>  The feature is still drawn with the "select" renderIntent.  What do
>> you think ?  With this, you don't need to have 4 different
>> possibilities.  The user can define an infinite number of different
>> renderIntents, have a styleMap defining each one of them.
>> Alexandre
>> Eric Lemoine wrote:
>>> Hi Alex
>>> Consider this sequence: mouse goes over feature, feature is clicked
>>> (for selection), and clicked again (for unselection). With your  
>>> "stack
>>> of intents" logic, the feature isn't redrawn as a result of the  
>>> second
>>> click; instead it should be redrawn with the hover control's render
>>> intent, shouldn't it?
>>> Eric
>>> 2009/1/23, Alexandre Dube <adube at mapgears.com>:
>>>> Hi devs,
>>>>  Eric was right :
>>>> <<<
>>>> A first note. The current select feature implementation should
>>>> accomodate this use case: two controls on the same layer, one  
>>>> working
>>>> on click and the other on hover, only one of them actually changing
>>>> the feature style. This is achievable by registering a
>>>> beforefeatureselected listener, and have this listener return  
>>>> false.
>>>> Adding beforefeatureunselected might help fully accomodate that use
>>>> case.
>>>> Now if we want the two controls to do feature styling, we need the
>>>> stuff I mentioned previously - per-control selectedFeatures  
>>>> arrays and
>>>> events. But this is unfortunately not sufficient. Use case: two
>>>> controls, one working on click and the other on hover, both doing
>>>> feature styling but with different render intents. If we have this
>>>> sequence "mouse goes over feature, mouse clicks feature, mouse goes
>>>> out of feature", then the feature ends up being rendered with the
>>>> "default" render intent, while it's still selected from the click
>>>> control's perspective. In most cases, this isn't desirable I think.
>>>> At this point I don't have a solution to the above issue.
>>>> An idea that could resolve this issue : features could have a  
>>>> stack of
>>>> renderIntent instead of a normal string value.  Instead of  
>>>> assigning new
>>>> renderIntent value, it would stack in renderIntents array.   
>>>> Instead of
>>>> reseting to "default", it would remove the last renderIntent in the
>>>> stack.  When the stack is empty, the "default" renderIntent is  
>>>> applied.
>>>>  That could work.  I'll try this and come back with more details.
>>>> Alexandre
>>>> Alexandre Dube wrote:
>>>>> Hi devs,
>>>>>  I would like to propose some changes about the SelectFeature  
>>>>> control.
>>>>>  First, I'll introduce what I want to do : I want to change the  
>>>>> color
>>>>> of a feature while the mouse is over it without selecting it.  I  
>>>>> managed
>>>>> to do this by building a customized control similar to the  
>>>>> SelectFeature
>>>>> control named HighlightFeature.  I shared the code and some people
>>>>> showed interest in this feature.  In fact, it was a good enough  
>>>>> to be
>>>>> added to trunk but there was a problem : it's too similar to the
>>>>> SelectFeature control.
>>>>>  My first new option was to modify the SelectFeature control to  
>>>>> be able
>>>>> to select and highlight.  That's what I did, but I hit a wall :  
>>>>> I needed
>>>>> to add more new events "beforefeaturehighlighted",  
>>>>> "featurehighlighted",
>>>>> etc.  a new array of highlightedFeatures, etc...  That also  
>>>>> became a
>>>>> pain because it was yet an other duplication of something already
>>>>> existant ( similair "select" feature events, an array of selected
>>>>> features, etc....)
>>>>>  SO, that brings me to this solution, the first one Eric Lemoine
>>>>> proposed : an array of selectedFeatures and select events for the
>>>>> control ( without removing the ones of the layer ).  Doing that,  
>>>>> one
>>>>> vector layer could have multiple select feature controls that  
>>>>> would know
>>>>> which feature it has selected, they could all have a different
>>>>> renderIntent value ( this is already possible ) or their own  
>>>>> style.
>>>>> Then, the user could interact directly with the desired control's
>>>>> selectedFeatures.
>>>>>  My example : One SelectFeature that select on click, has the  
>>>>> default
>>>>> render intent "select", on which I register a "featureselected" to
>>>>> display a form to fill.  And one other SelectFeature that select  
>>>>> on
>>>>> hover, has a custom render intent "temporary" to have a  
>>>>> different color
>>>>> and an event registered to "featureselected" to display a quick  
>>>>> popup of
>>>>> the infos of the hovered feature.
>>>>>  Even my DeleteFeature control I created a couple of weeks ago  
>>>>> could
>>>>> work by using an other SelectFeature control and using its own
>>>>> featureSelected array.
>>>>>  I'll make thoses small changes, an example and propose this as an
>>>>> enhancement.  What do you think ?
>>>>>  Regards,
>>>> --
>>>> Alexandre Dubé
>>>> Mapgears
>>>> www.mapgears.com
>>>> _______________________________________________
>>>> Dev mailing list
>>>> Dev at openlayers.org
>>>> http://openlayers.org/mailman/listinfo/dev
> -- 
> Alexandre Dubé
> Mapgears
> www.mapgears.com
> _______________________________________________
> Dev mailing list
> Dev at openlayers.org
> http://openlayers.org/mailman/listinfo/dev

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