This library encapsulates scrolling logic when implementing scrolling tabs (hot topic nowadays in Android development). It saves us from unpleasant routine aka addHeader, addFooter for every scrolling content which appears in tabs and synchronising it with our real headers. It also works good for a single scrolling widget, for e.g. RecyclerView which has it's own issues with headers (at least parallaxing them). Also check out the ScrollableDialog in sample application it mimics new Android Lollipop Intent chooser behavior.

compile 'ru.noties:scrollable:x.x.x'

• Improved interception of ghost touches when ScrollableLayout.getScrollY() > 0 && < max scroll y
• Added Close-up logic (turned off by default)

Simply wrap your views in ru.noties.scrollable.ScrollableLayout. The final xml might be looking something like that (don't copy, it's not valid):

<ru.noties.scrollable.ScrollableLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/scrollable_layout"
    app:scrollable_maxScroll="@dimen/header_height"> --!(1)

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="@dimen/header_height" --!(2)
            android:background="@color/header_background"
            android:textColor="@color/white"
            android:textSize="30sp"
            android:text="Header"
            android:id="@+id/header"
            android:gravity="center"/>

        <ru.noties.scrollable.sample.TabsLayout
            android:layout_width="match_parent"
            android:layout_height="@dimen/tabs_height" --!(3)
            android:background="@color/tabs_background"
            android:id="@+id/tabs" />

    </LinearLayout>

    <android.support.v4.view.ViewPager
        android:layout_width="match_parent"
        android:layout_height="match_parent" --!(4)
        android:layout_marginTop="@dimen/tabs_height" --!(5)
        android:id="@+id/view_pager" />

</ru.noties.scrollable.ScrollableLayout>

The most imprortant things here are:

1. app:scrollable_maxScroll="@dimen/header_height" - it's the value of header height aka the max scroll distance for a ScrollableLayout
2. It's what will be a header
3. It you wish to create sticky behavior to a certain View, you should indicate it's heigth here & in step 5
4. Out main content should have match_parent as it's layout_height attribute
5. Crucial for a sticky behavior

Then we should init out logic in code (copied from sample application):

final View header = findViewById(R.id.header);
final TabsLayout tabs = findView(this, R.id.tabs);

mScrollableLayout = findView(this, R.id.scrollable_layout);
mScrollableLayout.setDraggableView(tabs);
final ViewPager viewPager = findView(this, R.id.view_pager);
final ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager(), getResources(), getFragments());
viewPager.setAdapter(adapter);

tabs.setViewPager(viewPager);

// Note this bit, it's very important
mScrollableLayout.setCanScrollVerticallyDelegate(new CanScrollVerticallyDelegate() {
    @Override
    public boolean canScrollVertically(int direction) {
    	return adapter.canScrollVertically(viewPager.getCurrentItem(), direction);
    }
});

mScrollableLayout.setOnScrollChangedListener(new OnScrollChangedListener() {
  @Override
  public void onScrollChanged(int y, int oldY, int maxY) {

	// Sticky behavior
    final float tabsTranslationY;
    if (y < maxY) {
    	tabsTranslationY = .0F;
    } else {
    	tabsTranslationY = y - maxY;
    }

    tabs.setTranslationY(tabsTranslationY);

    header.setTranslationY(y / 2);
  }
});

In order to start rolling we should pass to our ScrollableLayout a ru.noties.scrollable.CanScrollVerticallyDelegate. For e.g. PagerAdapter implements it what way:

boolean canScrollVertically(int position, int direction) {
	return getItem(position).canScrollVertically(direction);
}

And fragments implements it that way:

@Override
public boolean canScrollVertically(int direction) {
	return mView != null && mView.canScrollVertically(direction);
}

Additionally you could provide a ScrollableLayout with a ru.noties.scrollable.OnScrollChangedListener and implement where your own logic. It's the place to implement parallax and all other possible stuff.

Since 1.1.0 it's possible to evaluate custom close-up logic. For a simple close-up (with only two states of ScrollableLayout - collapsed & expanded) use ru.noties.scrollable.DefaultCloseUpAlgorithm. For more fancy stuff create your own by implementing ru.noties.scrollable.CloseUpAlgorithm.

Might be set with ScrollableLayout.setCloseUpAlgorithm() or (if default implementation is desired) via xml definition app:scrollable_defaultCloseUp="true"

ru.noties.scrollable.CloseUpIdleAnimationTime is used to compute the duration of the close-up animation. For a simple case when duration for all close-ups is constant ru.noties.scrollable.SimpleCloseUpIdleAnimationTime might be used via ScrollableLayout.setCloseUpIdleAnimationTime() or via xml definition app:scrollable_closeUpAnimationMillis="200". Default value is 200 ms.

Value in milliseconds after which scroll state of a ScrollableLayout is considered idle and thus close-up logic is evaluated. Might be set via ScrollableLayout.setConsiderIdleMillis() or via xml definition app:scrollable_considerIdleMillis="100". Default value is 100 ms.

ru.noties.scrollable.CloseUpAnimatorConfigurator is used to configure an ObjectAnimator of a pending close-up animation. If the only configurable value is an Interpolator then ru.noties.scrollable.InterpolatorCloseUpAnimatorConfigurator might be used via ScrollableLayout.setCloseUpAnimatorConfigurator() or via xml definition app:scrollable_closeUpAnimatorInterpolator="@android:anim/bounce_interpolator". Default value is null

    app:scrollable_maxScroll="@dimen/header_height"
    app:scrollable_considerIdleMillis="100"
    app:scrollable_friction="0.075"
    app:scrollable_closeUpAnimationMillis="200"
    app:scrollable_defaultCloseUp="true"
    app:scrollable_scrollerFlywheel="false"
    app:scrollable_closeUpAnimatorInterpolator="@android:anim/bounce_interpolator"

  Copyright 2015 Dimitry Ivanov ([email protected])

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.