Makes main activity FAB scroll aware

Hides the FAB when the user scrolls down and shows it when they scroll back up. Reuses the same animation that FloatingActionButton.Behavior uses for hiding/showing the FAB in reaction to the AppBarLayout exiting/entering.

Author: ianhanniballake

app/src/main/java/com/support/android/designlibdemo/ScrollAwareFABBehavior.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2015 The Android Open Source Project
+ *
+ * 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.
+ */
+package com.support.android.designlibdemo;
+
+import android.content.Context;
+import android.os.Build;
+import android.support.design.widget.CoordinatorLayout;
+import android.support.design.widget.FloatingActionButton;
+import android.support.v4.view.ViewCompat;
+import android.support.v4.view.ViewPropertyAnimatorListener;
+import android.support.v4.view.animation.FastOutSlowInInterpolator;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.animation.Animation;
+import android.view.animation.AnimationUtils;
+import android.view.animation.Interpolator;
+
+public class ScrollAwareFABBehavior extends FloatingActionButton.Behavior {
+    private static final Interpolator INTERPOLATOR = new FastOutSlowInInterpolator();
+    private boolean mIsAnimatingOut = false;
+
+    public ScrollAwareFABBehavior(Context context, AttributeSet attrs) {
+        super();
+    }
+
+    @Override
+    public boolean onStartNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child,
+                                       final View directTargetChild, final View target, final int nestedScrollAxes) {
+        // Ensure we react to vertical scrolling
+        return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL
+                || super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, nestedScrollAxes);
+    }
+
+    @Override
+    public void onNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child,
+                               final View target, final int dxConsumed, final int dyConsumed,
+                               final int dxUnconsumed, final int dyUnconsumed) {
+        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
+        if (dyConsumed > 0 && !this.mIsAnimatingOut && child.getVisibility() == View.VISIBLE) {
+            // User scrolled down and the FAB is currently visible -> hide the FAB
+            animateOut(child);
+        } else if (dyConsumed < 0 && child.getVisibility() != View.VISIBLE) {
+            // User scrolled up and the FAB is currently not visible -> show the FAB
+            animateIn(child);
+        }
+    }
+
+    // Same animation that FloatingActionButton.Behavior uses to hide the FAB when the AppBarLayout exits
+    private void animateOut(final FloatingActionButton button) {
+        if (Build.VERSION.SDK_INT >= 14) {
+            ViewCompat.animate(button).scaleX(0.0F).scaleY(0.0F).alpha(0.0F).setInterpolator(INTERPOLATOR).withLayer()
+                    .setListener(new ViewPropertyAnimatorListener() {
+                        public void onAnimationStart(View view) {
+                            ScrollAwareFABBehavior.this.mIsAnimatingOut = true;
+                        }
+
+                        public void onAnimationCancel(View view) {
+                            ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
+                        }
+
+                        public void onAnimationEnd(View view) {
+                            ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
+                            view.setVisibility(View.GONE);
+                        }
+                    }).start();
+        } else {
+            Animation anim = AnimationUtils.loadAnimation(button.getContext(), R.anim.fab_out);
+            anim.setInterpolator(INTERPOLATOR);
+            anim.setDuration(200L);
+            anim.setAnimationListener(new Animation.AnimationListener() {
+                public void onAnimationStart(Animation animation) {
+                    ScrollAwareFABBehavior.this.mIsAnimatingOut = true;
+                }
+
+                public void onAnimationEnd(Animation animation) {
+                    ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
+                    button.setVisibility(View.GONE);
+                }
+
+                @Override
+                public void onAnimationRepeat(final Animation animation) {
+                }
+            });
+            button.startAnimation(anim);
+        }
+    }
+
+    // Same animation that FloatingActionButton.Behavior uses to show the FAB when the AppBarLayout enters
+    private void animateIn(FloatingActionButton button) {
+        button.setVisibility(View.VISIBLE);
+        if (Build.VERSION.SDK_INT >= 14) {
+            ViewCompat.animate(button).scaleX(1.0F).scaleY(1.0F).alpha(1.0F)
+                    .setInterpolator(INTERPOLATOR).withLayer().setListener(null)
+                    .start();
+        } else {
+            Animation anim = AnimationUtils.loadAnimation(button.getContext(), R.anim.fab_in);
+            anim.setDuration(200L);
+            anim.setInterpolator(INTERPOLATOR);
+            button.startAnimation(anim);
+        }
+    }
+}

app/src/main/res/layout/include_list_viewpager.xml

@@ -54,6 +54,7 @@
         android:layout_height="wrap_content"
         android:layout_gravity="end|bottom"
         android:layout_margin="@dimen/fab_margin"
-        android:src="@drawable/ic_done" />
+        android:src="@drawable/ic_done"
+        app:layout_behavior="com.support.android.designlibdemo.ScrollAwareFABBehavior" />
 
 </android.support.design.widget.CoordinatorLayout>