📰 Adjust the card display depending on the screen width.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/DisplayStyleObserverAdapter.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/DisplayStyleObserverAdapter.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/DisplayStyleObserverAdapter.java
new file mode 100644
index 0000000000000000000000000000000000000000..4fb6e42549b34a7620e471c6c548b39a4263257e
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/DisplayStyleObserverAdapter.java
@@ -0,0 +1,66 @@
+// 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.view.View;
+
+import org.chromium.chrome.browser.ntp.DisplayStyleObserver;
+import org.chromium.chrome.browser.ntp.UiConfig;
+
+/**
+ * Implementation of {@link DisplayStyleObserver} designed to play nicely with
+ * {@link android.support.v7.widget.RecyclerView}. It will not notify of changes when the
+ * associated view is not attached to the window.
+ */
+public class DisplayStyleObserverAdapter
+        implements DisplayStyleObserver, View.OnAttachStateChangeListener {
+    private final UiConfig mConfig;
+    private final DisplayStyleObserver mListener;
+
+    private boolean mIsViewAttached;
+
+    /**
+     * @param view the view whose lifecycle is tracked to determine when to not fire the
+     *             observer.
+     * @param config the {@link UiConfig} object to subscribe to.
+     * @param listener the listener to adapt. It's {#onDisplayStyleChanged} will be called when
+     *                 the configuration changes, provided that {@code view} is attached to the
+     *                 window.
+     */
+    public DisplayStyleObserverAdapter(View view, UiConfig config, DisplayStyleObserver listener) {
+        mConfig = config;
+        mListener = listener;
+
+        // TODO(dgn): getParent() is not a good way to test that, but isAttachedToWindow()
+        // requires API 19.
+        mIsViewAttached = view.getParent() != null;
+
+        view.addOnAttachStateChangeListener(this);
+        mConfig.addObserver(this);
+
+        refreshDisplayStyle();
+    }
+
+    @Override
+    public void onDisplayStyleChanged(@UiConfig.DisplayStyle int newDisplayStyle) {
+        if (!mIsViewAttached) return;
+        mListener.onDisplayStyleChanged(newDisplayStyle);
+    }
+
+    @Override
+    public void onViewAttachedToWindow(View v) {
+        mIsViewAttached = true;
+        refreshDisplayStyle();
+    }
+
+    @Override
+    public void onViewDetachedFromWindow(View v) {
+        mIsViewAttached = false;
+    }
+
+    private void refreshDisplayStyle() {
+        onDisplayStyleChanged(mConfig.getDisplayStyle());
+    }
+}