在Xamarin.Android/Xamarin.iOS中使用Akavache

Question

I've successfully got Akavache working for a Windows desktop, .NET 4.5 WPF project, but when I try to build it for the Xamarin (iOS and Android) targets, the BlobCache singleton is not properly initialized. BlobCache.Secure is null. (I've tried both the SQLite and 'vanilla' builds)

I'll be honest, I find the examples/documentation for Akavache a bit thin. I'm not a user of the Reactive stuff, I find much of Paul's code very opaque.

I'm just trying to do some very simple, secure caching of app state for a cross-platform app.

// where we store the user's application state
BlobCache.ApplicationName = "myApp";
BlobCache.EnsureInitialized();

public AppState State
{
    get
    {
        return _appState;
    }
    set
    {
        _appState = value;
    }
}

public void Load()
{
    try
    {
        State = BlobCache.Secure.GetObjectAsync<AppState>.FirstOrDefault();
    }
    catch (Exception ex)
    {
        Debug.WriteLine(ex.ToString());
        State = new AppState();
    }           
}

public void Save()
{
    try
    {           
        BlobCache.Secure.InsertObject("AppState", State);
    }
    catch(Exception ex)
    {
        Debug.WriteLine(ex.ToString());
    }
}

Answer 1

So, there are some dumb tricks you have to do right now on Xamarin, that I've only very recently found out. I'm going to add these to the docs (or in the Android case, just fix the bug)

Xamarin.iOS

On iOS, Type.GetType() won't load assemblies, which isn't the same as any other platform. So, you have to run this silly goose code in your AppDelegate:

var r = new ModernDependencyResolver();
(new ReactiveUI.Registrations()).Register((f,t) => r.Register(f, t));
(new ReactiveUI.Cocoa.Registrations()).Register((f,t) => r.Register(f, t));
(new ReactiveUI.Mobile.Registrations()).Register((f,t) => r.Register(f, t));

RxApp.DependencyResolver = r;
(new Akavache.Registrations()).Register(r.Register);
(new Akavache.Mobile.Registrations()).Register(r.Register);
(new Akavache.Sqlite3.Registrations()).Register(r.Register);

Normally, this code runs AutoMagically™.

Xamarin.Android

Registration works fine on Xamarin.Android, but because of what I suspect is a bug in Akavache, you may have to register for AutoSuspend (even if you don't use it).

1. In all your activities, declare AutoSuspendActivityHelper autoSuspendHelper;

2. In the constructor, add:

    autoSuspendHelper = new AutoSuspendActivityHelper(this); autoSuspendHelper.OnCreate(bundle); 

3. Override OnPause , OnResume , and OnSaveInstanceState and call the appropriate autoSuspendHelper method ie:

    autoSuspendHelper.OnPause(); 

More trouble?

Please let me know, either by Emailing me at paul@github.com or filing issues at github/akavache . I've shipped a production application with Akavache that runs on both iOS and Android, and it definitely works, but I realize it might be a bit Tricky™ to get stuff to work.