fab: make fab respond to recyclerview scroll events

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java

@@ -26,6 +26,8 @@ import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
+import android.view.animation.AccelerateInterpolator;
+import android.view.animation.DecelerateInterpolator;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.R;
@@ -35,6 +37,7 @@ import com.wireguard.android.databinding.TunnelListFragmentBinding;
 import com.wireguard.android.databinding.TunnelListItemBinding;
 import com.wireguard.android.model.Tunnel;
 import com.wireguard.android.util.ExceptionLoggers;
+import com.wireguard.android.widget.CustomRecyclerViewScrollListener;
 import com.wireguard.config.Config;
 
 import java.io.BufferedReader;
@@ -189,6 +192,23 @@ public class TunnelListFragment extends BaseFragment {
             }
             return false;
         });
+        binding.tunnelList.setOnScrollListener(new CustomRecyclerViewScrollListener() {
+            @Override
+            public void show() {
+                binding.createMenu.animate()
+                        .translationY(0)
+                        .setInterpolator(new DecelerateInterpolator(2))
+                        .start();
+            }
+
+            @Override
+            public void hide() {
+                binding.createMenu.animate()
+                        .translationY(binding.createMenu.getHeight() + getResources().getDimension(R.dimen.fab_margin))
+                        .setInterpolator(new AccelerateInterpolator(2))
+                        .start();
+            }
+        });
         binding.executePendingBindings();
         return binding.getRoot();
     }

app/src/main/java/com/wireguard/android/widget/CustomRecyclerViewScrollListener.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright © 2018 Harsh Shandilya <msfjarvis@gmail.com>
+ * Copyright © 2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.widget;
+
+import android.support.v7.widget.RecyclerView;
+
+public abstract class CustomRecyclerViewScrollListener extends RecyclerView.OnScrollListener {
+
+    private int scrollDist;
+    private boolean isVisible = true;
+    private static final float FLING_THRESHOLD = 25;
+
+    @Override
+    public void onScrolled(final RecyclerView recyclerView, final int dx, final int dy) {
+        super.onScrolled(recyclerView, dx, dy);
+
+        if (isVisible && scrollDist > FLING_THRESHOLD) {
+            hide();
+            scrollDist = 0;
+            isVisible = false;
+        } else if (!isVisible && scrollDist < -FLING_THRESHOLD) {
+            show();
+            scrollDist = 0;
+            isVisible = true;
+        }
+
+        if (isVisible ? dy > 0 : dy < 0) {
+            scrollDist += dy;
+        }
+    }
+
+    public abstract void show();
+    public abstract void hide();
+}

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

@@ -40,7 +40,7 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="bottom|end"
-            android:layout_margin="16dp"
+            android:layout_margin="@dimen/fab_margin"
             app:fab_labelStyle="@style/fab_label"
             android:clipChildren="false"
             app:fab_labelsPosition="left"

app/src/main/res/values/dimens.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <dimen name="fab_margin">16dp</dimen>
+</resources>