[Android] Implement empty view for download manager ui

chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
index 3c9edc29be30306eb710207e6a68f626b7f7d64d..f4a70c04982b9c404bf21c75ef7b886195306d2d 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
@@ -13,6 +13,7 @@ import android.support.v4.widget.DrawerLayout;
 import android.support.v4.widget.DrawerLayout.DrawerListener;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
+import android.support.v7.widget.RecyclerView.AdapterDataObserver;
 import android.support.v7.widget.Toolbar.OnMenuItemClickListener;
 import android.text.TextUtils;
 import android.view.Gravity;
@@ -21,6 +22,7 @@ import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.ListView;
+import android.widget.TextView;
 
 import org.chromium.base.ApiCompatibilityUtils;
 import org.chromium.base.Callback;
@@ -83,12 +85,26 @@ public class DownloadManagerUi implements OnMenuItemClickListener, BackendProvid
     private final SpaceDisplay mSpaceDisplay;
     private final ListView mFilterView;
     private final RecyclerView mRecyclerView;
+    private final TextView mEmptyView;
 
     private BasicNativePage mNativePage;
     private OfflinePageDownloadBridge mOfflinePageBridge;
     private SelectionDelegate<DownloadHistoryItemWrapper> mSelectionDelegate;
     private final AtomicInteger mNumberOfFilesBeingDeleted = new AtomicInteger();
 
+    private final AdapterDataObserver mAdapterObserver = new AdapterDataObserver() {
+        @Override
+        public void onChanged() {
+            if (mHistoryAdapter.getItemCount() == 0) {
+                mEmptyView.setVisibility(View.VISIBLE);
+                mRecyclerView.setVisibility(View.GONE);
+            } else {
+                mEmptyView.setVisibility(View.GONE);
+                mRecyclerView.setVisibility(View.VISIBLE);
+            }
+        }
+    };
+
     public DownloadManagerUi(
             Activity activity, boolean isOffTheRecord, ComponentName parentComponent) {
         mActivity = activity;
@@ -103,6 +119,10 @@ public class DownloadManagerUi implements OnMenuItemClickListener, BackendProvid
         mHistoryAdapter = new DownloadHistoryAdapter(isOffTheRecord, parentComponent);
         mHistoryAdapter.initialize(this);
         addObserver(mHistoryAdapter);
+        mHistoryAdapter.registerAdapterDataObserver(mAdapterObserver);
+
+        mEmptyView = (TextView) mMainView.findViewById(R.id.empty_view);
+        mEmptyView.setCompoundDrawablesWithIntrinsicBounds(0, R.drawable.downloads_big, 0, 0);
 
         mSpaceDisplay = new SpaceDisplay(mMainView, mHistoryAdapter);
         mHistoryAdapter.registerAdapterDataObserver(mSpaceDisplay);
@@ -165,6 +185,7 @@ public class DownloadManagerUi implements OnMenuItemClickListener, BackendProvid
             mOfflinePageBridge = null;
         }
 
+        mHistoryAdapter.unregisterAdapterDataObserver(mAdapterObserver);
         mHistoryAdapter.unregisterAdapterDataObserver(mSpaceDisplay);
     }