Added OverscrollLinearLayoutManager to fix scrolling in AppDetails2

app/src/main/java/org/fdroid/fdroid/AppDetails2.java

@@ -13,6 +13,7 @@ import android.graphics.Bitmap;
 import android.graphics.Color;
 import android.net.Uri;
 import android.os.Bundle;
+import android.support.design.widget.AppBarLayout;
 import android.support.design.widget.CoordinatorLayout;
 import android.support.v4.content.LocalBroadcastManager;
 import android.support.v7.app.AlertDialog;
@@ -46,6 +47,7 @@ import org.fdroid.fdroid.installer.InstallerService;
 import org.fdroid.fdroid.net.Downloader;
 import org.fdroid.fdroid.net.DownloaderService;
 import org.fdroid.fdroid.views.AppDetailsRecyclerViewAdapter;
+import org.fdroid.fdroid.views.OverscrollLinearLayoutManager;
 import org.fdroid.fdroid.views.ShareChooserDialog;
 import org.fdroid.fdroid.views.apps.FeatureImage;
 
@@ -59,6 +61,8 @@ public class AppDetails2 extends AppCompatActivity implements ShareChooserDialog
 
     private FDroidApp fdroidApp;
     private App app;
+    private CoordinatorLayout coordinatorLayout;
+    private AppBarLayout appBarLayout;
     private RecyclerView recyclerView;
     private AppDetailsRecyclerViewAdapter adapter;
     private LocalBroadcastManager localBroadcastManager;
@@ -91,10 +95,42 @@ public class AppDetails2 extends AppCompatActivity implements ShareChooserDialog
 
         localBroadcastManager = LocalBroadcastManager.getInstance(this);
 
+        coordinatorLayout = (CoordinatorLayout) findViewById(R.id.rootCoordinator);
+        appBarLayout = (AppBarLayout) coordinatorLayout.findViewById(R.id.app_bar);
         recyclerView = (RecyclerView) findViewById(R.id.rvDetails);
         adapter = new AppDetailsRecyclerViewAdapter(this, app, this);
-        LinearLayoutManager lm = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
+        OverscrollLinearLayoutManager lm = new OverscrollLinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
         lm.setStackFromEnd(false);
+
+        /** The recyclerView/AppBarLayout combo has a bug that prevents a "fling" from the bottom
+         * to continue all the way to the top by expanding the AppBarLayout. It will instead stop
+         * with the app bar in a collapsed state. See here: https://code.google.com/p/android/issues/detail?id=177729
+         * Not sure this is the exact issue, but it is true that while in a fling the RecyclerView will
+         * consume the scroll events quietly, without calling the nested scrolling mechanism.
+         * We fix this behavior by using an OverscrollLinearLayoutManager that will give us information
+         * of overscroll, i.e. when we have not consumed all of a scroll event, and use this information
+         * to send the scroll to the app bar layout so that it will expand itself.
+         */
+        lm.setOnOverscrollListener(new OverscrollLinearLayoutManager.OnOverscrollListener() {
+            @Override
+            public int onOverscrollX(int overscroll) {
+                return 0;
+            }
+
+            @Override
+            public int onOverscrollY(int overscroll) {
+                int consumed = 0;
+                if (overscroll < 0) {
+                    CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) appBarLayout.getLayoutParams();
+                    CoordinatorLayout.Behavior behavior = lp.getBehavior();
+                    if (behavior != null && behavior instanceof AppBarLayout.Behavior) {
+                        ((AppBarLayout.Behavior) behavior).onNestedScroll(coordinatorLayout, appBarLayout, recyclerView, 0, 0, 0, overscroll);
+                        consumed = overscroll; // Consume all of it!
+                    }
+                }
+                return consumed;
+            }
+        });
         recyclerView.setLayoutManager(lm);
         recyclerView.setAdapter(adapter);
 

app/src/main/java/org/fdroid/fdroid/views/OverscrollLinearLayoutManager.java

@@ -0,0 +1,91 @@
+package org.fdroid.fdroid.views;
+
+import android.content.Context;
+import android.support.v7.widget.LinearLayoutManager;
+import android.support.v7.widget.RecyclerView;
+import android.util.AttributeSet;
+
+/**
+ * This class is like a standard LinearLayoutManager but with an option to add an
+ * overscroll listener. This can be used to consume overscrolls, e.g. to draw custom
+ * "glows".
+ */
+public class OverscrollLinearLayoutManager extends LinearLayoutManager {
+
+    /**
+     * A listener interface to get overscroll infromation.
+     */
+    public interface OnOverscrollListener {
+        /**
+         * Notifies the listener that an overscroll has happened in the x direction.
+         * @param overscroll If negative, the recycler view has been scrolled to the "start"
+         *                   position. If positive to the "end" position.
+         * @return Return the amount of overscroll consumed. Returning 0 will let the
+         * recycler view handle this in the default way. Return "overscroll" to consume the
+         * whole event.
+         */
+        int onOverscrollX(int overscroll);
+
+        /**
+         * Notifies the listener that an overscroll has happened in the y direction.
+         * @param overscroll If negative, the recycler view has been scrolled to the "top"
+         *                   position. If positive to the "bottom" position.
+         * @return Return the amount of overscroll consumed. Returning 0 will let the
+         * recycler view handle this in the default way. Return "overscroll" to consume the
+         * whole event.
+         */
+
+        int onOverscrollY(int overscroll);
+    }
+
+    private OnOverscrollListener overscrollListener = null;
+
+    public OverscrollLinearLayoutManager(Context context) {
+        super(context);
+    }
+
+    public OverscrollLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
+        super(context, orientation, reverseLayout);
+    }
+
+    public OverscrollLinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
+        super(context, attrs, defStyleAttr, defStyleRes);
+    }
+
+    /**
+     * Set the {@link OverscrollLinearLayoutManager.OnOverscrollListener} to get information about
+     * when the parent recyclerview is overscrolled.
+     *
+     * @param listener Listener to add
+     * @see OverscrollLinearLayoutManager.OnOverscrollListener
+     */
+    public void setOnOverscrollListener(OnOverscrollListener listener) {
+        overscrollListener = listener;
+    }
+
+    @Override
+    public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state) {
+        int consumed = super.scrollHorizontallyBy(dx, recycler, state);
+        int overscrollX = dx - consumed;
+        if (overscrollX != 0) {
+            if (overscrollListener != null) {
+                int consumedByListener = overscrollListener.onOverscrollX(overscrollX);
+                consumed += consumedByListener;
+            }
+        }
+        return consumed;
+    }
+
+    @Override
+    public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
+        int consumed = super.scrollVerticallyBy(dy, recycler, state);
+        int overscrollY = dy - consumed;
+        if (overscrollY != 0) {
+            if (overscrollListener != null) {
+                int consumedByListener = overscrollListener.onOverscrollY(overscrollY);
+                consumed += consumedByListener;
+            }
+        }
+        return consumed;
+    }
+}