[OpenLayers-Dev] multipleSelectFeature on one layer

Alexandre Dube adube at mapgears.com
Mon Jan 26 13:52:06 EST 2009


  Here's an other possibility :

  SFA : selectedFeature Array
  RI : renderIntent
  RIA : renderIntent Array

  Let's say we forget about the controls to have their own SFA.  Only 
the layer has its own SFA.

  on featureselect
      if feature is not in SFA
          add feature to SFA
          trigger featureselected
      add RI of the control to the feature's RIA
      drawFeature(feature, RI)

  on featureunselect
      find RI of the control unselecting and remove it from RIA
      drawFeature(feature, LastRI)
      if LastRI == "default", meaning no more controls have this feature 
          remove feature from SFS
          trigger featureunselected
  Issues :
    - The wierd concept here is that the events "select" are only 
triggered once.
      solution ? : They could be triggered every time the feature gets 
drawn instead of added to the array.
    - If the user define a selectStyle in the SelectFeature control, 
then the renderIntent is not added to the stack.
      solution ? : When the user define a selectStyle, it could add the 
control's renderIntent to the feature stack without using it to draw the 
feature.  The only problem is that on unselection, the feature could 
sometime be drawn with the wrong color, but at least the problem of "is 
the feature still selected" would be resolved.  Using renderIntent would 
be preferable that way.

  What do you think ?

  On featureselect, add the feature to the SFA, add the RI of the 
control selecting it to the feature's RIA and drawFeature.

  On featureselect by an other control, do not add the feature in the 
SFA since it's already there but add the RI to the

  The SelectFeature controls does 2 things : select features ( adding 
them to the layer.sf array ) and changing the color.


Amos Hayes wrote:
> 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
> +1.613.520.2600x8179
> 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

Alexandre Dubé

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