[OpenLayers-Dev] multipleSelectFeature on one layer

Alexandre Dube adube at mapgears.com
Fri Jan 23 15:10:58 EST 2009

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

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 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

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