📰 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..90fffb675cabac9898ee341f257e41c39e886349
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/DisplayStyleObserverAdapter.java
@@ -0,0 +1,82 @@
+// 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 DisplayStyleObserver mObserver;
+
+    /** Current display style, gets updated as the UiConfig detects changes and notifies us. */
+    @UiConfig.DisplayStyle
+    private int mCurrentDisplayStyle;
+
+    /**
+     * Latest value that we transmitted to the adapted observer. If we didn't transfer any yet,
+     * the value is not a valid {@code DisplayStyle}
+     */
+    @UiConfig.DisplayStyle
+    private Integer mNotifiedDisplayStyle;
+
+    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 observer the observer 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 observer) {
+        mObserver = observer;
+
+        // TODO(dgn): getParent() is not a good way to test that, but isAttachedToWindow()
+        // requires API 19.
+        mIsViewAttached = view.getParent() != null;
+
+        view.addOnAttachStateChangeListener(this);
+
+        // This call will also assign the initial value to |mCurrentDisplayStyle|
+        config.addObserver(this);
+    }
+
+    @Override
+    public void onDisplayStyleChanged(@UiConfig.DisplayStyle int newDisplayStyle) {
+        mCurrentDisplayStyle = newDisplayStyle;
+
+        if (!mIsViewAttached) return;
+        if (mNotifiedDisplayStyle != null && mCurrentDisplayStyle == mNotifiedDisplayStyle) return;
+
+        mNotifiedDisplayStyle = mCurrentDisplayStyle;
+
+        mObserver.onDisplayStyleChanged(mCurrentDisplayStyle);
+    }
+
+    @Override
+    public void onViewAttachedToWindow(View v) {
+        mIsViewAttached = true;
+        onDisplayStyleChanged(mCurrentDisplayStyle);
+    }
+
+    @Override
+    public void onViewDetachedFromWindow(View v) {
+        mIsViewAttached = false;
+    }
+
+    @UiConfig.DisplayStyle
+    public int getDisplayStyle() {
+        return mCurrentDisplayStyle;
+    }
+}