[NTP Snippets] Fill space below the last snippet if necessary

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java
index f09d1c43398b0dfd220e95c5b0166a01496f2bd5..06401edbc9b0524b26953e38ae543c09c5f175b5 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java
@@ -5,6 +5,7 @@
 package org.chromium.chrome.browser.ntp.cards;
 
 import android.content.Context;
+import android.content.res.Resources;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.util.AttributeSet;
@@ -14,13 +15,27 @@
 import android.view.inputmethod.EditorInfo;
 import android.view.inputmethod.InputConnection;
 
+import org.chromium.chrome.R;
+
 /**
  * Simple wrapper on top of a RecyclerView that will acquire focus when tapped.  Ensures the
  * New Tab page receives focus when clicked.
  */
 public class NewTabPageRecyclerView extends RecyclerView {
+    /**
+     * Minimum height of the bottom spacing item.
+     */

[mcwilliams, 2016/05/17 15:04:59]

I believe you can change these from /** to just //

+    private static final int MIN_BOTTOM_SPACING = 0;
+
+    /**
+     * Position in the adapter of the item we snap the scroll at, when switching between above and
+     * below the fold.
+     */
+    private static final int SNAP_ITEM_ADAPTER_POSITION = 1;
+
     private GestureDetector mGestureDetector;
     private LinearLayoutManager mLayoutManager;
+    private int mToolbarHeight;

[Bernhard Bauer, 2016/05/12 11:21:00]

This can be final.

[dgn, 2016/05/13 13:49:58]

Done.

 
     /**
      * Constructor needed to inflate from XML.
@@ -39,6 +54,10 @@ public boolean onSingleTapUp(MotionEvent e) {
                 });
         mLayoutManager = new LinearLayoutManager(getContext());
         setLayoutManager(mLayoutManager);
+
+        Resources res = context.getResources();
+        mToolbarHeight = res.getDimensionPixelSize(R.dimen.toolbar_height_no_shadow)
+                + res.getDimensionPixelSize(R.dimen.toolbar_progress_bar_height);
     }
 
     public boolean isFirstItemVisible() {
@@ -78,4 +97,60 @@ public InputConnection onCreateInputConnection(EditorInfo outAttrs) {
     public LinearLayoutManager getLinearLayoutManager() {
         return mLayoutManager;
     }
+
+    /**
+     * Returns the view associated to a given adapter position. This is to be used instead of
+     * {@link #getChildAt}, which takes indices in terms of visible items.

[Bernhard Bauer, 2016/05/12 11:21:00]

Couldn't you just use `findViewHolderForAdapterPosition().itemView`?

[dgn, 2016/05/13 13:49:58]

Ah thanks, I missed it. I was searching under "get*". Done.

+     */
+    private View getViewForAdapterPosition(int adapterPosition) {
+        int viewPosition = adapterPosition - mLayoutManager.findFirstVisibleItemPosition();
+        return mLayoutManager.getChildAt(viewPosition);
+    }
+
+    /**
+     * Calculates the height of the bottom spacing item, such that there is always enough content
+     * below the fold.

[gone, 2016/05/12 18:04:39]

Isn't the point of the bottom spacing item that there isn't enough content below
the fold?  Should this say that the spacing is large enough to push the header
to the top or something?

[dgn, 2016/05/13 13:49:58]

Hum, yes, there isn't enough content so we have this item grow to balance it and
make so that there is enough content. I updated to doc, please let me know if it
still needs to be clarified.

[gone, 2016/05/13 17:08:09]

Acknowledged.

+     */
+    int calculateBottomSpacing() {
+        int firstVisiblePos = mLayoutManager.findFirstVisibleItemPosition();
+
+        // We have enough items to fill the view, since the snap point item is not even visible.
+        if (firstVisiblePos > SNAP_ITEM_ADAPTER_POSITION) return MIN_BOTTOM_SPACING;
+
+        int fullHeight = getHeight() - mToolbarHeight;
+        if (getAdapter().getItemViewType(SNAP_ITEM_ADAPTER_POSITION)
+                == NewTabPageListItem.VIEW_TYPE_SPACING) {
+            // No snippets, the spacing item should occupy the full height.

[gone, 2016/05/12 18:04:39]

... full height because the header isn't being displayed?

(At least from the video)

[dgn, 2016/05/13 13:49:58]

Removed that code.

+            return fullHeight;

[gone, 2016/05/12 18:04:39]

Were there any concerns from UX about users accidentally swiping down and not
being able to tell how to get out of that state?  I saw that UX mocked a box for
"Check again soon"; is that coming?

[dgn, 2016/05/13 13:49:58]

Yes, it's going to be added for the MVP.

[gone, 2016/05/13 17:08:09]

Er, guessing that's a Most Visited Page or something.  Either way, acknowledged.

[dgn, 2016/05/16 09:44:09]

oh sorry, MVP here stands for Minimum Viable Product

+        }
+
+        int lastContentItemPosition = getAdapter().getItemCount() - 2;

[gone, 2016/05/12 18:04:39]

nit: Put a comment here about the spacing item being the last?

[dgn, 2016/05/13 13:49:58]

Done.

+        int contentHeight = getViewForAdapterPosition(lastContentItemPosition).getBottom()
+                - getViewForAdapterPosition(SNAP_ITEM_ADAPTER_POSITION).getTop();
+        int height = fullHeight - contentHeight;
+
+        return Math.max(MIN_BOTTOM_SPACING, height);
+    }
+
+    /**
+     * Updates the space added at the end of the list to make sure the above/below the fold
+     * distinction can be preserved.
+     *
+     * This method relies on the adapter and the layout being in sync, so the call sequence while
+     * removing items must be adjusted accordingly: either before the item is removed from both
+     * the adapter and the recyclerview
+     * ({@link android.support.v7.widget.helper.ItemTouchHelper.Callback#onSwiped}) or after it is
+     * removed from both
+     * ({@link android.support.v7.widget.helper.ItemTouchHelper.Callback#clearView})
+     */
+    public void refreshBottomSpacing() {
+        View bottomSpacing = getViewForAdapterPosition(getAdapter().getItemCount() - 1);
+
+        // It might not be in the layout yet if it's not visible or ready to be displayed.
+        if (bottomSpacing == null) return;
+
+        assert getChildViewHolder(bottomSpacing).getItemViewType()
+                == NewTabPageListItem.VIEW_TYPE_SPACING;
+        bottomSpacing.requestLayout();
+    }
 }