Invalid target position when scrolling

[youfacepalm]

Hi, Thanks for the great library. I encountered an app crash with the following stacktrace when using the latest (1.3.0) version. I simply fetch a list from an api and update the RV adapter with notifyDatasetChanged() after setting the new list. It works fine if there are more than 2 items in the list. But it crashes if there are 2 or fewer items in the list. The crash occurs soon after I scroll the first item.

java.lang.IllegalArgumentException: Invalid target position
    at android.support.v7.widget.RecyclerView$SmoothScroller.start(RecyclerView.java:11132)
    at android.support.v7.widget.RecyclerView$LayoutManager.startSmoothScroll(RecyclerView.java:7871)
    at com.yarolegovich.discretescrollview.DiscreteScrollLayoutManager.startSmoothPendingScroll(DiscreteScrollLayoutManager.java:463)
    at com.yarolegovich.discretescrollview.DiscreteScrollLayoutManager.onScrollEnd(DiscreteScrollLayoutManager.java:390)
    at com.yarolegovich.discretescrollview.DiscreteScrollLayoutManager.onScrollStateChanged(DiscreteScrollLayoutManager.java:351)
    at android.support.v7.widget.RecyclerView.dispatchOnScrollStateChanged(RecyclerView.java:4746)
    at android.support.v7.widget.RecyclerView.setScrollState(RecyclerView.java:1434)
    at android.support.v7.widget.RecyclerView.cancelTouch(RecyclerView.java:3023)
    at android.support.v7.widget.RecyclerView.onTouchEvent(RecyclerView.java:3001)
    at android.view.View.dispatchTouchEvent(View.java:11721)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2929)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2636)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2931)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2931)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2931)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2931)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2961)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2650)
    at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:445)
    at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1828)
    at android.app.Activity.dispatchTouchEvent(Activity.java:3292)
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:68)
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:68)
    at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:407)
    at android.view.View.dispatchPointerEvent(View.java:11960)
    at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4776)
    at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4590)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4128)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4181)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4147)
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4274)
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4155)

[youfacepalm]

The currentPosition was -1 before the crash in DiscreteScrollLayoutManager startSmoothPendingScroll method

[yarolegovich]

Thanks for the report, unfortunately I won't be able to look into it until weekends.

[youfacepalm]

Hey no problem at all. I traced down the issue and found out it is caused by how the DiscreteScrollView is placed in the layout. I have created a sample project that can reproduce the crash. I hope it saves you some time.

https://drive.google.com/open?id=0B4VSgmZteixRX002ZDVYR1c0RnM

Thanks again for all the effort!

[yarolegovich]

Yeah, the issue exists, I've checked the project. Can't yet say why it happens.
You started getting it after upgrading to 1.3?

[youfacepalm]

It happened even before 1.3

[bearprada]

I found the root cause might come from DiscreteScrollLayoutManager.onScrollEnd()

        Direction scrollDirection = Direction.fromDelta(scrolled);
        if (Math.abs(scrolled) == scrollToChangeCurrent) {
            currentPosition += scrollDirection.applyTo(1); <- it will return -1 if the recyclerview has zero items
            scrolled = 0;
        }

[yarolegovich]

@youfacepalm thanks a lot for the project you created, it saved me a lot of time. The issue is resolved.