Consider the following toy example:
I have a "dynamical, interactive" graphics primitive like the following:
ClearAll[dynamicPoint];
dynamicPoint[point_List] := DynamicModule[{color = Red},
EventHandler[
Dynamic@{[email protected], color, Point@point},
{"MouseClicked" :> (
If[color === Red,
color = Green, color = Red
]
)}
]
]
If I use the above function instead of the regular primitive Point, I get a point that changes color when I click on it:
This is all well and fine, but now I want to be able to add more dynamical points like this by clicking on the graphics.
The naive way would be to wrap the whole Graphics into another EventHandler with an appropriately set event, like in the following:
DynamicModule[{
allData = <|"NumberOfPoints" -> 1,
"PointsCoordinates" -> {{-1, 0}}|>
},
EventHandler[
Graphics[{
Dynamic@Table[
dynamicPoint[allData["PointsCoordinates"][[pointIndex]]],
{pointIndex, Range@allData["NumberOfPoints"]}
]
},
Frame -> True, PlotRange -> {{-2, 2}, {-2, 2}}
],
{"MouseClicked" :> (
allData["NumberOfPoints"]++;
AppendTo[allData["PointsCoordinates"], MousePosition["Graphics"]]
)},
PassEventsDown -> True
]
]
As you can see, I can now add points, but I lost all the ability to change their colors.
As I understand it, this happens because when I click on an existing point the corresponding change-color event is triggered (it's easy to check), but immediately after the EventHandler associated with the whole Graphics is also triggered, causing a redraw of all the points, and therefore of all the DynamicModules associated with them, in which the local variables are initialized again.
I think the most obvious way to avoid this problem is to prevent the outer EventHandler to be triggered when I click on a point, but how can I accomplish that?
I can put a check inside the outer event handler to make it redraw only when the mouse click is not on an already occupied part of the graphics, but I don't want to do it in this way because that would require me to change the code in this check every time I change the actual things produced by dynamicPoint.
In my actual project I want these objects to be also dynamically resizable, which would make this solution hardly feasible.
Another method I thought was to add an element to allData marking whether the mouse is on a point or not.
I could easily set this flag to True with a MouseMoved event in the EventHandler of every point, and then checks whether the flag is true when the outer EventHandler is triggered.
The problem with this is that I cannot think of an easy way to set this flag back to False when the mouse exits the point, as there seems to be no MouseExited event.
EDIT:
As of Kuba's suggestion, to have the two EventHandler events not interfere with each other it is enough to add the option PassEventUp -> False to the inner EventHandlers.
Using this we get the following:
ClearAll[dynamicPoint];
dynamicPoint[point_List] := DynamicModule[{color = Red},
EventHandler[
Dynamic@{[email protected], color, Point@point},
{"MouseClicked" :> (
If[color === Red,
color = Green, color = Red
]
)},
PassEventsUp -> False
]
]
DynamicModule[{
allData = <|"NumberOfPoints" -> 1,
"PointsCoordinates" -> {{-1, 0}}|>
},
EventHandler[
Graphics[{
Dynamic@Table[
dynamicPoint[allData["PointsCoordinates"][[pointIndex]]],
{pointIndex, Range@allData["NumberOfPoints"]}
]
},
Frame -> True, PlotRange -> {{-2, 2}, {-2, 2}}
],
{"MouseClicked" :> (
allData["NumberOfPoints"]++;
AppendTo[allData["PointsCoordinates"], MousePosition["Graphics"]]
)},
PassEventsDown -> True
]
]
As you can see, we still have the problem that redrawing all the points when a new one is added, all the DynamicModules reinitialize their variables and so all the objects' states reinitialize.
How can we solve this?
PassEventsUp -> Falseput into the innerEventHandlers solved the problem, great! Did you mean this with your comment? Because withPassEventDown -> Falseput into the outer event handler it seems I just prevent the inner ones (of the points) to be triggered, and if I putPassEventDown -> Falseinto the inner event handlers it doesn't do anything $\endgroup$