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

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/PaddingListItem.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/PaddingListItem.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/PaddingListItem.java
new file mode 100644
index 0000000000000000000000000000000000000000..5485837a786f83632b3a6aad7847d2ac2df39eaf
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/PaddingListItem.java
@@ -0,0 +1,91 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.ntp.cards;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.support.v7.widget.LinearLayoutManager;
+import android.view.View;
+import android.view.ViewGroup;
+
+import org.chromium.base.Log;
+import org.chromium.chrome.R;
+
+/**
+ * Placeholder item to let the snippets flow to the top of the scroll list even when it does not
+ * contain enough of them. It is displayed as a dummy item with variable height that just occupies
+ * the remaining space between the last item in the RecyclerView and the bottom of the screen.
+ */
+public class PaddingListItem implements NewTabPageListItem {

[mcwilliams, 2016/05/10 12:42:52]

Possibly rename this to SpacingListItem. You might change to margins later on
for some reason

[dgn, 2016/05/10 14:26:12]

Done.

+    private static final String TAG = "Ntp";
+
+    private static class PaddingListItemView extends View {
+        private final int mMinHeight;
+        private final int mToolbarHeight;
+
+        public PaddingListItemView(Context context) {
+            super(context);
+            Resources res = context.getResources();
+            mMinHeight = res.getDimensionPixelSize(R.dimen.snippets_bottom_padding);

[mcwilliams, 2016/05/10 12:42:52]

Remove this

[dgn, 2016/05/10 14:26:12]

Done.

+            mToolbarHeight = res.getDimensionPixelSize(R.dimen.toolbar_height_no_shadow)
+                    + res.getDimensionPixelSize(R.dimen.toolbar_progress_bar_height);
+        }
+
+        @Override
+        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
+            Log.d(TAG, "onMeasure");

[May, 2016/05/10 10:31:51]

Remove

[dgn, 2016/05/10 14:26:12]

Done.

+            setMeasuredDimension(0, calculateHeight());
+        }
+
+        private int calculateHeight() {
+            // An item has been dismissed, ending up calling this method. But the PaddingListItem
+            // is currently not visible and not in the recycler view, so we don't care.
+            if (getParent() == null) return mMinHeight;
+
+            if (!(getParent() instanceof NewTabPageRecyclerView)) {
+                Log.wtf(TAG, "PaddingListItem not in recyclerview: parent=%s", getParent());
+                return mMinHeight;
+            }
+
+            NewTabPageRecyclerView rv = (NewTabPageRecyclerView) getParent();

[mcwilliams, 2016/05/10 12:42:52]

avoid using abbreviations like rv and lm - it makes the code really hard to read

[dgn, 2016/05/10 14:26:12]

Done.

+            LinearLayoutManager lm = ((LinearLayoutManager) rv.getLayoutManager());
+            int firstPos = lm.findFirstVisibleItemPosition();

[May, 2016/05/10 10:31:51]

As discussed, please clarify what's being done here with comments

[mcwilliams, 2016/05/10 12:42:52]

What is firstPos?

[dgn, 2016/05/10 14:26:12]

Is the current state enough or should I comment some more?

[dgn, 2016/05/10 14:26:12]

Done.

+            if (firstPos > 1) {
+                Log.d(TAG, "Too many items (first at %d), using min height (%d)", firstPos,
+                        mMinHeight);
+                return mMinHeight;
+            }
+
+            int fullHeight = rv.getHeight() - mToolbarHeight;
+            if (rv.getAdapter().getItemViewType(1) == NewTabPageListItem.VIEW_TYPE_PADDING) {

[May, 2016/05/10 10:31:51]

Ditto.

[dgn, 2016/05/10 14:26:12]

Done.

+                Log.d(TAG, "No item, we just use the full height (%d)", fullHeight);
+                return fullHeight;
+            }
+
+            // View position of the item that should be aligned with the top of the screen
+            // It's the item at position 1 since the above-the-fold one is at 0.
+            int snapItemPos = 1 - firstPos;
+            // Position of the last item before the padding item.
+            int prevViewPos = rv.getChildViewHolder(this).getAdapterPosition() - snapItemPos;
+
+            int contentHeight =
+                    rv.getChildAt(prevViewPos).getBottom() - rv.getChildAt(snapItemPos).getTop();
+            int height = fullHeight - contentHeight
+                    - getResources().getDimensionPixelSize(R.dimen.tab_strip_height);
+
+            return Math.max(mMinHeight, height);
+        }
+    }
+
+    /** Creates the View object for displaying the variable padding. */
+    public static View createView(ViewGroup parent) {
+        return new PaddingListItemView(parent.getContext());
+    }
+
+    @Override
+    public int getType() {
+        return NewTabPageListItem.VIEW_TYPE_PADDING;
+    }
+}