Create a gist now

Instantly share code, notes, and snippets.

What would you like to do?
FAB behavior that lets FAB scroll out towards the bottom in sync with AppBarLayout scrolling out towards the top
/**
* Behavior for FABs that does not support anchoring to AppBarLayout, but instead translates the FAB
* out of the bottom in sync with the AppBarLayout collapsing towards the top.
* <p>
* Extends FloatingActionButton.Behavior to keep using the pre-Lollipop shadow padding offset.
*/
public class AppBarBoundFabBehavior extends FloatingActionButton.Behavior {
public AppBarBoundFabBehavior(Context context, AttributeSet attrs) {
super();
}
@Override
public boolean layoutDependsOn(CoordinatorLayout parent, FloatingActionButton child, View dependency) {
if (dependency instanceof AppBarLayout) {
((AppBarLayout) dependency).addOnOffsetChangedListener(new FabOffsetter(parent, child));
}
return dependency instanceof AppBarLayout || super.layoutDependsOn(parent, child, dependency);
}
@Override
public boolean onDependentViewChanged(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {
//noinspection SimplifiableIfStatement
if (dependency instanceof AppBarLayout) {
// if the dependency is an AppBarLayout, do not allow super to react on that
// we don't want that behavior
return true;
}
return super.onDependentViewChanged(parent, fab, dependency);
}
}
public class FabOffsetter implements AppBarLayout.OnOffsetChangedListener {
private final CoordinatorLayout parent;
private final FloatingActionButton fab;
public FabOffsetter(@NonNull CoordinatorLayout parent, @NonNull FloatingActionButton child) {
this.parent = parent;
this.fab = child;
}
@Override
public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
// fab should scroll out down in sync with the appBarLayout scrolling out up.
// let's see how far along the way the appBarLayout is
// (if displacementFraction == 0.0f then no displacement, appBar is fully expanded;
// if displacementFraction == 1.0f then full displacement, appBar is totally collapsed)
float displacementFraction = -verticalOffset / (float) appBarLayout.getHeight();
// need to separate translationY on the fab that comes from this behavior
// and one that comes from other sources
// translationY from this behavior is stored in a tag on the fab
float translationYFromThis = coalesce((Float) fab.getTag(R.id.fab_translationY_from_AppBarBoundFabBehavior), 0f);
// top position, accounting for translation not coming from this behavior
float topUntranslatedFromThis = fab.getTop() + fab.getTranslationY() - translationYFromThis;
// total length to displace by (from position uninfluenced by this behavior) for a full appBar collapse
float fullDisplacement = parent.getBottom() - topUntranslatedFromThis;
// calculate and store new value for displacement coming from this behavior
float newTranslationYFromThis = fullDisplacement * displacementFraction;
fab.setTag(R.id.fab_translationY_from_AppBarBoundFabBehavior, newTranslationYFromThis);
// update translation value by difference found in this step
fab.setTranslationY(newTranslationYFromThis - translationYFromThis + fab.getTranslationY());
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
OnOffsetChangedListener that = (OnOffsetChangedListener) o;
return parent.equals(that.parent) && fab.equals(that.fab);
}
@Override
public int hashCode() {
int result = parent.hashCode();
result = 31 * result + fab.hashCode();
return result;
}
}
<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:tools="http://schemas.android.com/tools" tools:ignore="MissingTranslation">
<item type="id" name="fab_translationY_from_AppBarBoundFabBehavior"/>
</resources>

In FabOffsetter#equals, I think you're not casting the correct class. OnOffsetChangedListener should be FabOffsetter to be able to access parent and fab fields.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment