Android Question ViewPager not firing settled state fast enough

[wimpie3]

This is a very annoying problem. When flicking through a ViewPager, the "settled" state fires a second AFTER the page has settled. In other words: the animation is already finished a while before the correct state is fired...

#Region Module Attributes
    #FullScreen: False
    #IncludeTitle: True
    #ApplicationLabel: Hello World
    #VersionCode: 1
    #VersionName:
    #SupportedOrientations: unspecified
    #CanInstallToExternalStorage: False
#End Region

Sub Process_Globals
End Sub

Sub Globals
    Private VP As ViewPager: ' https://www.b4x.com/android/forum/threads/viewpager-cleaned-up-viewpager.75342/
    Private PC As PageContainer
End Sub

Sub Activity_Create(FirstTime As Boolean)
    VP.Initialize("VP")
    Activity.AddView(VP,0,0,100%x,100%y)
    PC.Initialize
    For i = 0 To 10
        PC.AddPage("Page " & i)
    Next
    VP.PageContainer = PC
End Sub

Sub Activity_Resume
End Sub

Sub Activity_Pause (UserClosed As Boolean)
End Sub

Sub VP_PageCreated (Position As Int, Page As VPage)
    If Page.AlreadyCreated = False Then
        Page.Panel.Color = Colors.RGB(Rnd(0,256), Rnd(0,256), Rnd(0,256))
    End If
End Sub

Sub VP_PageScrollStateChanged (State As Int)
    If State=0 Then
        Msgbox ("Now settled, but should have already fired a second earlier","Demo")
    End If
End Sub

 

[wimpie3]

It seems the original ViewPager even exposes an Animation object to change the transitions...

https://developer.android.com/training/animation/screen-slide.html

Is changing the animation the clue to get a faster viewpager?

 

[Erel]

Why aren't you using TabStripViewPager?

 

[wimpie3]

Why aren't you using TabStripViewPager?

TabStripViewPager is based on ViewPager as well and has the same problem.

 

[Erel]

I've just tested it now with TabStrip and the PageSelected event. I don't see any delay.

 

[wimpie3]

The delay is caused by the animation type that is used by the viewpager. By default it's AccelerateDecelerateInterpolator. This means the animation slows down at the end, giving the impression there is a delay before PageScrollStateChanged is fired. It's fired at the end of the animation, but since the animation goes slow at the end, it gives the impression the event is fired too late.

The solution I've found on the internet is to use a LinearInterpolator for the viewpager:

private void setScroller() {
     try {
        Field mScroller;
        mScroller = ViewPager.class.getDeclaredField("mScroller");
        mScroller.setAccessible(true);
        FixedSpeedScroller scroller =
           new FixedSpeedScroller(this.getContext(), new LinearInterpolator());
        mScroller.set(this, scroller);
     } catch (NoSuchFieldException e) {
     } catch (IllegalArgumentException e) {
     } catch (IllegalAccessException e) {
     }
  }

private class FixedSpeedScroller extends Scroller {

    private int mDuration = 500;

    public FixedSpeedScroller(Context context) {
        super(context);
    }

    public FixedSpeedScroller(Context context, Interpolator interpolator) {
        super(context, interpolator);
    }

    public FixedSpeedScroller(Context context, Interpolator interpolator, boolean flywheel) {
        super(context, interpolator, flywheel);
    }

    @Override
    public void startScroll(int startX, int startY, int dx, int dy, int duration) {
        // Ignore received duration, use fixed one instead
        super.startScroll(startX, startY, dx, dy, mDuration);
    }

    @Override
    public void startScroll(int startX, int startY, int dx, int dy) {
        // Ignore received duration, use fixed one instead
        super.startScroll(startX, startY, dx, dy, mDuration);
    }

    public void setScrollDuration(int duration) {
        mDuration = duration;
    }
}

However, I've got no idea on how to implement this.

BTW, tabstrib does not seem to have an event called PageScrollStateChanged. Only PageSelected (which is fired BEFORE the animation ends!). Plus you can't remove the tabs.

 

[Erel]

I will repeat my previous post. I've tested TabStripViewPager and the PageSelected appears to be raised at the correct time.

 

[wimpie3]

I will repeat my previous post. I've tested TabStripViewPager and the PageSelected appears to be raised at the correct time.

But that is not true! PageSelected is fired a few milliseconds BEFORE THE ANIMATION ENDS.

 

[Erel]

So?

Who said that a few milliseconds before the animation ends is not the correct time?

I tested the UI feeling again with this code:

Sub TabStrip1_PageSelected (Position As Int)
   Activity.Title = Position
End Sub

It looks and feels perfect.

 

[wimpie3]

The problem is that I need to do some intensive calculations when PageSelected is fired. Doing so prevents the animation from finishing (there is a small hickup at the end).

 

[Erel]

Add Sleep(50) and then do the calculations. Which calculations are you doing? Maybe they should be optimized.

 

[wimpie3]

If I add sleep(200) it works, but that is kind of guesswork, that value will be different from phone to phone (and no, those calculations cannot be optimized).

My original question still remains:
- PageSelected is fired TOO SOON
- PageScrollStateChanged with the IDLE value is called a few milliseconds TOO LATE

I'm afraid the only solution that works is the one given in Java code. But I cannot implement it...

 

[Erel]

Sounds to me that you are looking for the solution in the wrong place. The simple solution of adding a short delay will work on all devices.

Anyway, to answer your question, you will need to write a Java library to implement this code.