Can't find fragment by tag

[vincentjames501]

When setting a OnSliderStateChangeListener and using a FragemtnPagerAdapter, getView() is puking because no fragment is being returned by id. Relying on internal API code such as "android:switcher:" + R.id.internal_pager_id + ":" + position is fragile and will break. Is the View object really necessary for the OnSliderStateChangeListener? It seems like position could suffice and maybe just make getPage public instead?

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.v4.app.Fragment.getView()' on a null object reference
                                                                 at com.telenav.expandablepager.ExpandablePager.getPage(ExpandablePager.java:241)
                                                                 at com.telenav.expandablepager.ExpandablePager.access$200(ExpandablePager.java:46)
                                                                 at com.telenav.expandablepager.ExpandablePager$1.onPageScrolled(ExpandablePager.java:92)
                                                                 at android.support.v4.view.ViewPager.dispatchOnPageScrolled(ViewPager.java:1845)
                                                                 at android.support.v4.view.ViewPager.onPageScrolled(ViewPager.java:1819)
                                                                 at android.support.v4.view.ViewPager.pageScrolled(ViewPager.java:1757)
                                                                 at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:633)
                                                                 at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1706)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1079)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1079)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1695)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
                                                                 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
                                                                 at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                                                                 at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
                                                                 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
                                                                 at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                                                                 at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
                                                                 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
                                                                 at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                                                                 at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                                                                 at com.android.internal.policy.PhoneWindow$DecorView.onLayout(PhoneWindow.java:2678)
                                                                 at android.view.View.layout(View.java:16636)
                                                                 at android.view.ViewGroup.layout(ViewGroup.java:5437)
                                                                 at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2171)
                                                                 at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1931)
                                                                 at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
                                                                 at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
                                                                 at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
                                                                 at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                                                                 at android.view.Choreographer.doFrame(Choreographer.java:606)
                                                                 at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                                                                 at android.os.Handler.handleCallback(Handler.java:739)
                                                                 at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                 at android.os.Looper.loop(Looper.java:148)
                                                                 at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:72

[vincentjames501]

Also, getPage can be called with an index that is out of bounds.

java.lang.IndexOutOfBoundsException: Invalid index 3, size is 3
                                                                         at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
                                                                         at java.util.ArrayList.get(ArrayList.java:308)
                                                                         at com.singlewire.cirrus.AreaOfInterestRecipientsFragment$1.getItem(AreaOfInterestRecipientsFragment.java:109)
                                                                         at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:105)
                                                                         at com.telenav.expandablepager.ExpandablePager.getPage(ExpandablePager.java:243)
                                                                         at com.telenav.expandablepager.ExpandablePager.access$200(ExpandablePager.java:46)
                                                                         at com.telenav.expandablepager.ExpandablePager$1.onPageScrolled(ExpandablePager.java:92)
                                                                         at android.support.v4.view.ViewPager.dispatchOnPageScrolled(ViewPager.java:1845)
                                                                         at android.support.v4.view.ViewPager.onPageScrolled(ViewPager.java:1819)
                                                                         at android.support.v4.view.ViewPager.pageScrolled(ViewPager.java:1757)
                                                                         at android.support.v4.view.ViewPager.performDrag(ViewPager.java:2261)
                                                                         at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2153)
                                                                         at android.view.View.dispatchTouchEvent(View.java:9300)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2547)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2240)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2575)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2553)
                                                                         at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2254)
                                                                         at com.android.internal.policy.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2403)
                                                                         at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1737)
                                                                         at android.app.Activity.dispatchTouchEvent(Activity.java:2771)
                                                                         at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
                                                                         at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
                                                                         at com.android.internal.policy.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2364)
                                                                         at android.view.View.dispatchPointerEvent(View.java:9520)
                                                                         at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4230)
                                                                         at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4096)
                                                                         at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642)
                                                                         at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695)
                                                                         at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3661)
                                                                         at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3787)
                                                                         at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3669)
                                                                         at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3844)
                                                                         at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642)
                                                                         at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695)
                                                                        at android.view.ViewRootImpl$InputStage.forward(ViewRootI

[dimatim]

• Since every fragment in a FragmentPagerAdapter is tagged by calling

private static String makeFragmentName(int viewId, long id) {
    return "android:switcher:" + viewId + ":" + id;
}

I don't see how it could break in the near future; unless there will be some drastic changes in the Android API...

Although, I guess it'll make more sense to get a fragment reference via
instantiateItem(container, position) since it's already used for FragmentStatePagerAdapter.

• The idea behind passing a View in OnSliderStateChangeListener is that you can easily change / animate its content on a state change (as shown in the demo app).
• getPage(index) is not intended to be a public method because it's main purpose is to return the current or neighboring page, in other words - pages that are most likely to be inflated by the ViewPager. I suppose I could add getCurrentPage() in the future, but i'm not sure whether it will be useful or not.