Don't create FontExtensions Regex unless/until necessary (#676)

* Lazy load Regex for loading fonts from assets

* Allow Regex class to handle Regex initialization and caching

diff --git a/Xamarin.Forms.Platform.Android/Renderers/FontExtensions.cs b/Xamarin.Forms.Platform.Android/Renderers/FontExtensions.cs
index d7394a1..981065b 100644 (file)
--- a/Xamarin.Forms.Platform.Android/Renderers/FontExtensions.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/FontExtensions.cs
@@ -10,7 +10,10 @@ namespace Xamarin.Forms.Platform.Android
        {
                static readonly Dictionary<Tuple<string, FontAttributes>, Typeface> Typefaces = new Dictionary<Tuple<string, FontAttributes>, Typeface>();
 
-               static readonly Regex LoadFromAssets = new Regex(@"\w+\.((ttf)|(otf))\#\w*");
+               // We don't create and cache a Regex object here because we may not ever need it, and creating Regexes is surprisingly expensive (especially on older hardware)
+               // Instead, we'll use the static Regex.IsMatch below, which will create and cache the regex internally as needed. It's the equivalent of Lazy<Regex> with less code.
+               // See https://msdn.microsoft.com/en-us/library/sdx2bds0(v=vs.110).aspx#Anchor_2
+               const string LoadFromAssetsRegex = @"\w+\.((ttf)|(otf))\#\w*";
 
                static Typeface s_defaultTypeface;
 
@@ -56,7 +59,7 @@ namespace Xamarin.Forms.Platform.Android
                                var style = ToTypefaceStyle(self.FontAttributes);
                                result = Typeface.Create(Typeface.Default, style);
                        }
-                       else if (LoadFromAssets.IsMatch(self.FontFamily))
+                       else if (Regex.IsMatch(self.FontFamily, LoadFromAssetsRegex))
                        {
                                result = Typeface.CreateFromAsset(AApplication.Context.Assets, FontNameToFontFile(self.FontFamily));
                        }
@@ -88,7 +91,7 @@ namespace Xamarin.Forms.Platform.Android
                                var style = ToTypefaceStyle(self.FontAttributes);
                                result = Typeface.Create(Typeface.Default, style);
                        }
-                       else if (LoadFromAssets.IsMatch(self.FontFamily))
+                       else if (Regex.IsMatch(self.FontFamily, LoadFromAssetsRegex))
                        {
                                result = Typeface.CreateFromAsset(AApplication.Context.Assets, FontNameToFontFile(self.FontFamily));
                        }