Cache Typefaces in shadow/flat/CustomStyleSpan

Summary: @public `Typeface` handling in `shadow/flat/CustomStyleSpan` wasn't very efficient. This diff introduces `TypefaceCache` to avoid allocating duplicated `Typeface`s.

Reviewed By: sriramramani

Differential Revision: D2564363

ReactAndroid/src/main/java/com/facebook/react/flat/FontStylingSpan.java

@@ -84,14 +84,10 @@ import android.text.style.MetricAffectingSpan;
       return;
     }
 
-    // TODO: optimize this part (implemented in a followup patch)
-
     if (mFontFamily != null) {
-      // efficient in API 21+
+      typeface = TypefaceCache.getTypeface(mFontFamily, newStyle);
-      typeface = Typeface.create(mFontFamily, newStyle);
     } else {
-      // efficient in API 16+
+      typeface = TypefaceCache.getTypeface(typeface, newStyle);
-      typeface = Typeface.create(typeface, newStyle);
     }
 
     ds.setTypeface(typeface);

ReactAndroid/src/main/java/com/facebook/react/flat/TypefaceCache.java

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.flat;
+
+import java.util.HashMap;
+
+import android.graphics.Typeface;
+
+/**
+ * TypefaceCache provides methods to resolve typeface from font family, or existing typeface
+ * with a different style.
+ */
+/* package */ final class TypefaceCache {
+
+  private static final int MAX_STYLES = 4; // NORMAL = 0, BOLD = 1, ITALIC = 2, BOLD_ITALIC = 3
+
+  private static final HashMap<String, Typeface[]> FONTFAMILY_CACHE = new HashMap<>();
+  private static final HashMap<Typeface, Typeface[]> TYPEFACE_CACHE = new HashMap<>();
+
+  /**
+   * Returns a Typeface for a given a FontFamily and style.
+   */
+  public static Typeface getTypeface(String fontFamily, int style) {
+    Typeface[] cache = FONTFAMILY_CACHE.get(fontFamily);
+    if (cache == null) {
+      // cache is empty, create one.
+      cache = new Typeface[MAX_STYLES];
+      FONTFAMILY_CACHE.put(fontFamily, cache);
+    } else if (cache[style] != null) {
+      // return cached value.
+      return cache[style];
+    }
+
+    Typeface typeface = Typeface.create(fontFamily, style);
+    cache[style] = typeface;
+    TYPEFACE_CACHE.put(typeface, cache);
+    return typeface;
+  }
+
+  /**
+   * Returns a derivative of a given Typeface with a different style.
+   */
+  public static Typeface getTypeface(Typeface typeface, int style) {
+    if (typeface == null) {
+      return Typeface.defaultFromStyle(style);
+    }
+
+    Typeface[] cache = TYPEFACE_CACHE.get(typeface);
+    if (cache == null) {
+      // This should not happen because all Typefaces are coming from TypefaceCache,
+      // and thus should be registered in TYPEFACE_CACHE.
+      // If we get here, it's a bug and one of the 2 scenarios happened:
+      // a) TypefaceCache created a Typeface and didn't put it into TYPEFACE_CACHE.
+      // b) someone else created a Typeface bypassing TypefaceCache so it's not registered here.
+      //
+      // If it's not registered, we can just register it manually for consistency, and so that
+      // next time someone requests a un unknown Typeface, it's already cached and we don't create
+      // extra copies.
+      cache = new Typeface[MAX_STYLES];
+      cache[typeface.getStyle()] = typeface;
+    } else if (cache[style] != null) {
+      // return cached value.
+      return cache[style];
+    }
+
+    typeface = Typeface.create(typeface, style);
+    cache[style] = typeface;
+    TYPEFACE_CACHE.put(typeface, cache);
+    return typeface;
+  }
+}