Added Preferences implementation for Android

Also added placeholders for other platform implementations that need to be completed.

F50/F50.csproj

@@ -22,7 +22,7 @@
     <Copyright>Copyright 2018</Copyright>
     <RepositoryUrl>https://github.com/xamarin/f50</RepositoryUrl>
     <PackageReleaseNotes>See: https://github.com/xamarin/f50 </PackageReleaseNotes>
-    <LangVersion>default</LangVersion>
+    <LangVersion>7.1</LangVersion>
     <DefineConstants>$(DefineConstants);</DefineConstants>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <GenerateDocumentationFile Condition=" '$(Configuration)' == 'Release' ">true</GenerateDocumentationFile>

F50/Preferences/Preferences.android.cs

@@ -1,14 +1,130 @@
 using System;
-using System.Collections.Generic;
-using System.Text;
+using System.Globalization;
+using Android.App;
+using Android.Content;
+using Android.Preferences;
 
 namespace Xamarin.F50
 {
 	public partial class Preferences
 	{
-		public void Set(string key, string val)
-		{
+		public bool ContainsKey(string key)
+		{
+			using (var sharedPreferences = GetSharedPreferences())
+			{
+				if (sharedPreferences == null)
+					return false;
+
+				return sharedPreferences.Contains(key);
+			}
+		}
 
+		public bool Remove(string key)
+		{
+			using (var sharedPreferences = GetSharedPreferences())
+			{
+				if (sharedPreferences == null)
+					return false;
+
+				return sharedPreferences.Edit().Remove(key).Commit();
+			}
+		}
+
+		public bool Clear()
+		{
+			using (var sharedPreferences = GetSharedPreferences())
+			{
+				if (sharedPreferences == null)
+					return false;
+
+				using (var editor = sharedPreferences.Edit())
+				{
+					return editor.Clear().Commit();
+				}
+			}
+		}
+
+		bool Set<T>(string key, T value)
+		{
+			using (var sharedPreferences = GetSharedPreferences())
+			{
+				if (sharedPreferences == null)
+					return false;
+
+				using (var editor = sharedPreferences.Edit())
+				{
+					switch (value)
+					{
+						case string s:
+							editor.PutString(key, s);
+							break;
+						case int i:
+							editor.PutInt(key, i);
+							break;
+						case bool b:
+							editor.PutBoolean(key, b);
+							break;
+						case long l:
+							editor.PutLong(key, l);
+							break;
+						case double d:
+							var strDbl = Convert.ToString(d, CultureInfo.InvariantCulture);
+							editor.PutString(key, strDbl);
+							break;
+						case float f:
+							editor.PutFloat(key, f);
+							break;
+					}
+					return editor.Commit();
+				}
+			}
+		}
+
+		T Get<T> (string key, T defaultValue)
+		{
+			object value = null;
+			using (var sharedPreferences = GetSharedPreferences())
+			{
+				if (sharedPreferences == null)
+					return default;
+
+				switch (defaultValue)
+				{
+					case string s:
+						value = sharedPreferences.GetString(key, s);
+						break;
+					case int i:
+						value = sharedPreferences.GetInt(key, i);
+						break;
+					case bool b:
+						value = sharedPreferences.GetBoolean(key, b);
+						break;
+					case long l:
+						value = sharedPreferences.GetLong(key, l);
+						break;
+					case double d:
+						double dbl;
+						if (double.TryParse(sharedPreferences.GetString(key, null), out dbl))
+							value = dbl;
+						break;
+					case float f:
+						value = sharedPreferences.GetFloat(key, f);
+						break;
+				}
+			}
+
+			return (T)value;
+		}
+
+		ISharedPreferences GetSharedPreferences ()
+		{
+			var context = Platform.CurrentContext;
+			if (context == null)
+				return null;
+
+			return string.IsNullOrWhiteSpace(SharedName) ?
+				PreferenceManager.GetDefaultSharedPreferences(Application.Context) :
+					Application.Context.GetSharedPreferences(SharedName, FileCreationMode.Private);
 		}
 	}
 }

F50/Preferences/Preferences.ios.cs

@@ -6,9 +6,19 @@ namespace Xamarin.F50
 {
     public partial class Preferences
     {
-        public void Set(string key, string val)
-        {
+		public bool ContainsKey(string key) =>
+			throw new NotImplentedInReferenceAssembly();
 
-        }
-    }
+		public bool Remove(string key) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		public bool Clear() =>
+			throw new NotImplentedInReferenceAssembly();
+
+		bool Set<T>(string key, T value) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		T Get<T>(string key, T defaultValue) =>
+			throw new NotImplentedInReferenceAssembly();
+	}
 }

F50/Preferences/Preferences.netstandard.cs

@@ -6,7 +6,19 @@ namespace Xamarin.F50
 {
     public partial class Preferences
     {
-        public void Set(string key, string val) =>
-            throw new NotImplentedInReferenceAssembly();
+		public bool ContainsKey(string key) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		public bool Remove(string key) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		public bool Clear() =>
+			throw new NotImplentedInReferenceAssembly();
+
+		bool Set<T>(string key, T value) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		T Get<T>(string key, T defaultValue) =>
+			throw new NotImplentedInReferenceAssembly();
     }
 }

F50/Preferences/Preferences.shared.cs

@@ -10,10 +10,29 @@ namespace Xamarin.F50
     /// </summary>
     public partial class Preferences
     {
-        public static void DoStuff()
-        {
+		public Preferences()
+		{
+		}
 
-        }
-    }
+		public Preferences(string sharedName)
+		{
+			SharedName = sharedName;
+		}
+
+		public string SharedName { get; private set; }
+
+		public string Get(string key, string defaultValue)
+			=> Get<string>(key, defaultValue);
+		public bool Get(string key, bool defaultValue)
+			=> Get<bool>(key, defaultValue);
+		public int Get(string key, int defaultValue)
+			=> Get<int>(key, defaultValue);
+		public double Get(string key, double defaultValue)
+			=> Get<double>(key, defaultValue);
+		public float Get(string key, float defaultValue)
+			=> Get<float>(key, defaultValue);
+		public long Get(string key, long defaultValue)
+			=> Get<long>(key, defaultValue);
+	}
 
 }

F50/Preferences/Preferences.uwp.cs

@@ -6,9 +6,19 @@ namespace Xamarin.F50
 {
     public partial class Preferences
     {
-        public void Set(string key, string val)
-		{
+		public bool ContainsKey(string key) =>
+			throw new NotImplentedInReferenceAssembly();
 
-        }
-    }
+		public bool Remove(string key) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		public bool Clear() =>
+			throw new NotImplentedInReferenceAssembly();
+
+		bool Set<T>(string key, T value) =>
+			throw new NotImplentedInReferenceAssembly();
+
+		T Get<T>(string key, T defaultValue) =>
+			throw new NotImplentedInReferenceAssembly();
+	}
 }