Don't create an instance of FontStylingSpan until any of the properties changed

Summary: Minor optimization/cleanup: instead of creating an instance of FontStylingSpan for every RCTVirtualText, start with a global immutable instance of use copy-on-write when any of the properties change.

Reviewed By: ahmedre

Differential Revision: D2817156

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

@@ -16,18 +16,28 @@ import android.text.TextPaint;
 import android.text.style.MetricAffectingSpan;
 
 /* package */ final class FontStylingSpan extends MetricAffectingSpan {
+
+  /* package */ static final FontStylingSpan INSTANCE = new FontStylingSpan(
+      Double.NaN /* mTextColor */,
+      0 /* mBackgroundColor */,
+      -1 /* mFontSize */,
+      -1 /* mFontStyle */,
+      -1 /* mFontWeight */,
+      null /* mFontFamily */,
+      true /* mFrozen */);
+
   // text property
-  private double mTextColor = Double.NaN;
+  private double mTextColor;
   private int mBackgroundColor;
 
   // font properties
-  private int mFontSize = -1;
-  private int mFontStyle = -1;
-  private int mFontWeight = -1;
+  private int mFontSize;
+  private int mFontStyle;
+  private int mFontWeight;
   private @Nullable String mFontFamily;
 
   // whether or not mutation is allowed.
-  private boolean mFrozen = false;
+  private boolean mFrozen;
 
   FontStylingSpan() {
   }
@@ -38,13 +48,15 @@ import android.text.style.MetricAffectingSpan;
       int fontSize,
       int fontStyle,
       int fontWeight,
-      @Nullable String fontFamily) {
+      @Nullable String fontFamily,
+      boolean frozen) {
     mTextColor = textColor;
     mBackgroundColor = backgroundColor;
     mFontSize = fontSize;
     mFontStyle = fontStyle;
     mFontWeight = fontWeight;
     mFontFamily = fontFamily;
+    mFrozen = frozen;
   }
 
   /* package */ FontStylingSpan mutableCopy() {
@@ -54,7 +66,8 @@ import android.text.style.MetricAffectingSpan;
         mFontSize,
         mFontStyle,
         mFontWeight,
-        mFontFamily);
+        mFontFamily,
+        false);
   }
 
   /* package */ boolean isFrozen() {

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

@@ -50,6 +50,7 @@ import com.facebook.react.uimanager.ViewProps;
 
   public RCTText() {
     setMeasureFunction(this);
+    getSpan().setFontSize(getDefaultFontSize());
   }
 
   @Override

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

@@ -29,11 +29,7 @@ import com.facebook.react.uimanager.ViewProps;
   private static final String ITALIC = "italic";
   private static final String NORMAL = "normal";
 
-  private FontStylingSpan mFontStylingSpan = new FontStylingSpan();
-
-  RCTVirtualText() {
-    mFontStylingSpan.setFontSize(getDefaultFontSize());
-  }
+  private FontStylingSpan mFontStylingSpan = FontStylingSpan.INSTANCE;
 
   @Override
   protected void performCollectText(SpannableStringBuilder builder) {
@@ -176,7 +172,7 @@ import com.facebook.react.uimanager.ViewProps;
     return (int) Math.ceil(PixelUtil.toPixelFromSP(sp));
   }
 
-  private FontStylingSpan getSpan() {
+  protected final FontStylingSpan getSpan() {
     if (mFontStylingSpan.isFrozen()) {
       mFontStylingSpan = mFontStylingSpan.mutableCopy();
     }