topic Re: Updating a Graphic in GraphicsLayer / thread safeness in Qt Maps SDK Questions

Updating a Graphic in GraphicsLayer / thread safeness

ChristianEhrlicher — Mon, 15 Feb 2016 08:20:05 GMT

Hi,

we add a EsriRuntimeQt::Graphic to a EsriRuntimeQt::GraphicsLayer with GraphicsLayer::addGraphic(m_graphicPtr). Now we want to change the graphic (e.g. the line color). What's the recommended way to do this? The documentation does not say anything about this:

simply modify m_graphicPtr (and hope the GraphicsLayer notices the change and updates it's graphical representation)
- this would mean that all Functions for EsriRuntimeQt::Graphic must be thread-safe
- or is there another synchronization mechanism
- using updateGraphic with the same pointer used by addGraphic will lead to a crash (afaics addGraphic() moves ownership and updateGraphic() will delete the old graphic - at least this is what I'm seeing, the documentation only express this indirect with)
create a new Graphic and replace the current one with EsriRuntimeQt::GraphicsLayer::updateGraphic()
other ways I'm not aware of

Thx,

Christian

Re: Updating a Graphic in GraphicsLayer / thread safeness

ChristianEhrlicher — Tue, 16 Feb 2016 12:40:56 GMT

Ok, it looks like my assumption about ownership is wrong. I moved the code into a small testcase and calling updateGraphic() in a loop (via timer every 10ms) it's crashing now and then but everytime with a similar backtrace. If you're interested in this backtrace or the testcase, please let me know.

Re: Updating a Graphic in GraphicsLayer / thread safeness

LucasDanzinger — Tue, 16 Feb 2016 18:59:21 GMT

Christian-

If you are wanting to update the symbol of a particular graphic, can you just use updateGraphic that takes in the graphic's ID and the new symbol? ArcGIS Runtime SDK for Qt C++ API: EsriRuntimeQt::GraphicsLayer Class Reference

Otherwise, you can create a new Graphic, and update the existing one with updateGraphic ArcGIS Runtime SDK for Qt C++ API: EsriRuntimeQt::GraphicsLayer Class Reference

That would be the recommended approach. I would need to see your code to get a hint at why it might be crashing.

-Luke

Re: Updating a Graphic in GraphicsLayer / thread safeness

ChristianEhrlicher — Wed, 17 Feb 2016 06:56:16 GMT

What we're doing is more or less something like

qid = GraphicsLayer::addGraphic(m_graphicPtr);

...

modify m_graphicPtr (change geometry or smth. else)

...

GraphicsLayer::updateGraphic(gid, m_graphicPtr);

...

do more modifications

...

GraphicsLayer::updateGraphic(gid, m_graphicPtr);

...

This does lead to race conditions because the render thread is accessing attributes of m_grpahicPtr while we're modifying those attributes.

Our solution is exactly what you're proposed - using addGraphic(), working on a new (cloned) graphic for hte changes and then call updateGraphic() with new graphic.

Thx,

Christian