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Stop redrawing the whole page on minor visual change like text content

BenMagistrisBenMagistris Member ✭✭
in Xamarin.Forms

I have an app with a digital clock in the corner of the page in the format HH:mm:ss
e.g. 10:35:23
This this done with a label that has its text property updated every second.

It all works fine but, using the Android GPU profiler and 'show view update' settings, I can see that the whole page is being redrawn every second!
Playing around further the whole page even gets redrawn with a seemingly harmless colour change!!

I have tried taking the Label out into a AbsoluteLayout in the hopes that the measure/layout phase didn't spill out into all the other parent views - but it does :(

Does anyone know of a nice way to stop this?

The only alternative I have found is drawing the text in a SKCanvas and having it update that way - only the canvas is redrawn in this instance.

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Answers

  • robbitrobbit CNMember Xamurai

    Hi @BenMagistris

    On Android, if you update the TextView in the Activity, TextView will request it's parent to Measure/Layout/Draw,and it's parent will call the TextView's grandparent to Measure/Layout/Draw, we know that there is a view tree in the activity. So, if you update the label, the whole page will be updated. So you can't stop it.

  • BenMagistrisBenMagistris Member ✭✭

    Hi @robbit,

    Thank you for your answer.
    Do you know of any alternatives to stop the whole page redrawing? If the view hierarchy is complex a Measure/Layout/Draw cycle has a performance impact if it is called every second. Do you know of any structures I could draw text in and the update not spill out into the rest of the view?
    I have only found one alternative which is drawing the text in a SKCanvas view.

  • JohnHardmanJohnHardman GBUniversity admin
    edited July 2018

    @robbit said:
    Hi @BenMagistris

    On Android, if you update the TextView in the Activity, TextView will request it's parent to Measure/Layout/Draw,and it's parent will call the TextView's grandparent to Measure/Layout/Draw, we know that there is a view tree in the activity. So, if you update the label, the whole page will be updated. So you can't stop it.

    I've never had to do it (although might in future when I get to optimising pages), but I recall this being discussed either in a Xamarin University class, Lightning Lecture, Guest Lecture or Evolve session (sorry, cannot recall which). In that discussion, it was said that it's possible to override part of the Measure/Layout cycle to prevent it from iterating all the way up the UI hierarchy. By doing that, unnecessary measurement/layout/draw can be avoided. I wonder if it was Jason Smith's session on performance (see this ), but I don't have time to check now.

  • BenMagistrisBenMagistris Member ✭✭

    @JohnHardman
    Funnily enough I have watched that video by Jason Smith, but unfortunately nothing is said about overriding the Measure/Layout cycle. The only thing mentioned that could provide a solution is creating a custom view. I'd imagine it would allow you to control how the view handled updates, but it seems a little over-kill for my example, which is just for a bit of text.

  • JohnHardmanJohnHardman GBUniversity admin

    @BenMagistris said:
    @JohnHardman
    Funnily enough I have watched that video by Jason Smith, but unfortunately nothing is said about overriding the Measure/Layout cycle. The only thing mentioned that could provide a solution is creating a custom view. I'd imagine it would allow you to control how the view handled updates, but it seems a little over-kill for my example, which is just for a bit of text.

    I wonder where I saw it - it might have been Xamarin University, but I had a sneaking suspicion it was Jason Smith. Will update if I remember where it was.

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