A cross-platform settings storage for .NET
C#
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Readme.md

Overview

Lager is an attempt to create a cross-platform settings storage for .NET that uses Akavache as a storage backend.

.NET 4.5, WP8, WinRT, Xamarin.Android and Xamarin.iOS is supported

Currently Lager can write and read every type of object that can be stored by Akavache. Later versions will also include some type of migration system, for renaming and deleting settings.

Installation

Lager is available on NuGet

Usage

public class UserSettings : SettingsStorage
{
    public UserSettings() : base("D5702B73-854F-4E92-93DD-99DB026918B4", BlobCache.UserAccount)
    { }
}

So, what have we done here?

First, we've inherited from the SettingsStorage class. This class will provide us with our necessary methods for storing and receiving values.

Next, we've provided the SettingsStorage constructor with a unique string that Lager uses to avoid key-collisions. The second parameter specifies the IBlobCache implementation of Akavache where our settings are stored.

Defining our settings is pretty easy too, just define properties that have the following structure:

public string MyCoolString
{
    get { return this.GetOrCreate("Some default value"); }
    set { this.SetOrCreate(value); }
}

or

public int MyCoolNumber
{
    get { return this.GetOrCreate(42); }
    set { this.SetOrCreate(value); }
}

But wait, what is this magic? How does Lager know which setting it should retrieve when I call GetOrCreate?

That's simple, both GetOrCreate and SetOrCreate have a second optional parameter that is marked with the CallerMemberName attribute. This means a property called MyCoolString is stored with the key MyCoolString

Dont forget to shutdown Akavache properly!

NET45, WP8, WinRT

SettingsStorage implements the INotifyPropertyChanged interface, just use normal XAML-Bindings to bind the settings to your UI

Xamarin.Android

Since the Android preferences API is a nightmare to use, Lager has a useful function called BindToSetting. BindToSetting is an extension method for the Preference class and creates a two-way binding between the Preference and a property in a SettingsStorage. Changes to the Preference are automatically propagated to the SettingsStorage and vice-versa.

An example:

Define you settings layout like normal, but without default values or any other nonsense

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
  <EditTextPreference
      android:key="pref_text"
      android:summary="Save text here"
      android:title="Text" />
</PreferenceScreen>

And in your settings activity you simply write:

protected override void OnCreate(Bundle bundle)
{
    // Layout setup and stuff

    var textPreference = (EditTextPreference)this.FindPreference("pref_text");
    textPreference.BindToSetting(UserSettings.Instance, x => x.MySettingsString, x => x.Text, x => x.ToString());
}

So what have we done here?

As said before, BindToSetting is an extension method for the Preference class, so we pulled an instance of our EditTextPreference from our PreferenceActivity.

The first parameter is an instance of our settings storage. For simplification, we just assume a singleton instance here.

The second parameter is an expression that describes what property in our settings storage we want to bind.

The third parameter is an expression that describes on which property of or Preference we want our setting to be bound on. Here we have an EditTextPreference, so we bind it the its Text property. If you have a CheckBoxPreference for example, you most likely want to bind on its Checked property.

The fourth parameter is a function that converts a value from the Preference class to our SettingsStorage. This is a necessary step, because we have no type info when the Preference notifies us that the user entered a value.

There is also an optional fifth and sixth parameter. The fifth parameter allows for a conversion from the setting in your SettingsStorage to the Preferences property. This is useful if you want to bind non-string types to the Text property of an EditTextPreference or an enum to a ListPreference.

With the sixth parameter you can validate user input. It takes a function that returns a bool and provides the value that the user has entered. Return true, and the value will be saved, return false and the value will be discarded.

Xamarin.iOS

Lager supports Xamarin.iOS, but there are no special bindings like the Android version has. This is simply because I have no Xamarin.iOS license.

You may be able to leverage ReactiveUI bindings to bind a setting to an iOS setting, but I don't know how settings work in iOS. Anybody that submits a PR with support for this is welcome!