How to reset the Toolbar position controlled by the CoordinatorLayout?

Question

The app I'm working on consists of a Navigation Drawer which is implemented in an Activity. The activity layout is as follows:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

<android.support.v4.widget.DrawerLayout
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.CoordinatorLayout
        android:id="@+id/coordinator"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <include
            android:id="@+id/appbar"
            layout="@layout/appbar" />

    </android.support.design.widget.CoordinatorLayout>

    <android.support.design.widget.NavigationView
        android:id="@+id/navigation_drawer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/header_drawer"
        app:menu="@menu/menu_nav">
    </android.support.design.widget.NavigationView>

</android.support.v4.widget.DrawerLayout>

</FrameLayout>

This is a very common pattern, only thing that changes frequently is the Fragment inside the container layout.

If any of the Fragment has a scrolling element, upon scrolling, the CoordinatorLayout will happily make position translations, including the Toolbar/AppBarLayout.

The real problem here is, when the Fragment gets replaced, the position for the Toolbar remains the same, i.e., if the Toolbar is hidden, it will stay so which isn't intended.

Result is this:

This:

Gets stuck:

How can one reset the Toolbar position for this case?

EDIT: A bug is probable, the AppBarLayout offset change listener gets called only when relaunching the app (press back button and open the app), and stops getting called again after an intense fling.

Solution 1

To reset the scroll state, just get the AppBarLayout.Behavior object

CoordinatorLayout coordinator = (CoordinatorLayout) findViewById(R.id.coordinator);
AppBarLayout appbar = (AppBarLayout) findViewById(R.id.appbar);
CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) appbar.getLayoutParams();
AppBarLayout.Behavior behavior = (AppBarLayout.Behavior) params.getBehavior();       

and call onNestedPreScroll method manually:

int[] consumed = new int[2];
behavior.onNestedPreScroll(coordinator, appbar, null, 0, -1000, consumed);

If you would like to reset smoothly with an animation, you can try calling onNestedFling instead:

behavior.onNestedFling(coordinator, appbar, null, 0, -1000, true);

Solution 2

First get a AppBarLayout refrence in you MainActivity, then in the pause state of the fragment that is being replaced, use the method below to expand toolbar :

MainActivity.appbar.setExpanded(true,true);

And or to close the toolbar :

MainActivity.appbar.setExpanded(false,true);

The second parameter is used to scroll the toolbar smoothly.

Solution 3

Update your support lib to v23 then you can use:

appBarLayout.setExpanded(true/false);

public void setExpanded (boolean expanded)

Sets whether this AppBarLayout is expanded or not, animating if it has already been laid out.

As with AppBarLayout's scrolling, this method relies on this layout being a direct child of a CoordinatorLayout.

expanded true if the layout should be fully expanded, false if it should be fully collapsed

Solution 4

@razzledazzle The AppBarLayout stores onOffsetChangedListeners as WeakReferences, which means they are garbage collected when needed, for instance when you do a intense fling. See solution here:

https://code.google.com/p/android/issues/detail?id=176328

Solution 5

I'm using this codes before fragment changes.

scrollingElement.startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
scrollingElement.dispatchNestedPreScroll(0, -Integer.MAX_VALUE, null, null);
scrollingElement.stopNestedScroll();

View more solutions

Comments

[Peanut]

Can you add some explanations?

[theb1uro]

For me it only works for collapsing AppBarLayout by setting positive 'velocityY' value. Above code with negative 'velocityY' value has no effect. I'm calling it from NestedScrollView's onTouchListener after ACTION_UP action. I want to implement snap behavior - to always collapse or expand AppBarLayout.

[razzledazzle]

Thanks for the answer, this is a good solution, I used the onNestedFling() inside the drawer open callback and it works pretty nicely.

[razzledazzle]

Ah, this was definitely the case, I did see WeakReferences in the source but never thought how easily they could get GCed. This also explains why referencing the listeners as field under onResume() worked better as opposed to initializing anonymous classed during onCreate(). Implementing the listener as a class is a guaranteed solution as mentioned in the link. Thank you very much for your input!

[Tomas]

I have exactly the same experience like @theb1uro. Only work for collapse with positive 'velocityY' value. Expand with negative 'velocityY' value has no effect...

[Tomas]

I tested it also on cheesesquare and the same result, any idea why this work only when collapsing AppBarLayout?

[User31689]

params.getBehavior() is returning null. In xml, layout_behaviour tag is set on sibling NestedScrollView, not the AppBarLayout. Please help!

[Nati Dykstein]

Works nicely with ViewPager+TabLayout inside CoordinatorLayout

[Dan Dar3]

Idea appears to be coming from the doc for startNestedScroll(), see developer.android.com/reference/android/view/…

[razzledazzle]

This does not cover the use case when you would want to lock the AppBarLayout.

[razzledazzle]

This fails to lock the AppBarLayout in place. It however does work for regular cases.

[Michael]

According to that post is has been fixed.

[xiaoyee]

negative 'velocityY' value will have effect, when you set app:layout_scrollFlags="scroll|enterAlways" ,

[Muhammad Babar]

AppBarLayout has no such method setExpanded?

[Pkmmte]

@MuhammadBabar Update your dependencies, bro.