C# async object initialization

Question

I'm writing Windows Phone 8.1 application and one of its part is LocalStorage access. I wrote code as presented below, but it has some serious issue. I need to initialize service using asynchronous methods and a while after, I'm using one of it's method (which is also asynchronous).

Service : IService
{
    private XmlFormatter xmlFormatter;

    public Service()
    {
        Initialize();
    }

    public async IList<Model> GetModelsAsync()
    {
        return xmlFormatter.GetModels();
    }

    private async void Initialize()
    {
        try
        {                
            StorageFile item = (StorageFile)await ApplicationData.Current.LocalFolder.GetItemAsync(this.settings.Get<string>(SettingNames.DataFilename));

            using (Stream readStream = await item.OpenStreamForReadAsync())
            {
                xmlFormatter = new XmlFormatter(XDocument.Load(readStream));
            }
        }
        catch (FileNotFoundException)
        {
            CreateFile();
            xmlFormatter = new XmlFormatter(null);
        }
        catch (Exception)
        {
            throw;
        }
    }
}

The problem is that GetModelsAsync methods runs before end of Initialize method, so xmlFormatter is null and I recieve NullReferenceException. How can I synchronize these methods?

Cybrosys · Accepted Answer · 2014-11-10 10:48:36Z

2

There are multiple solutions to this. I would suggest saving the Task that is returned from the Initialize method. I would then in GetModelsAsync call: await _initializeTask; before trying to use the xml formatter.

Another solution is to throw an exception saying that your service is not yet initialized, but since the user is not the one calling Initialize, that would just be bad design.

The third is to make the Initialize method public and place the responsibility on the user to invoke it and make sure that it has finished before invoking the other methods in your class.

answered Nov 10, 2014 at 10:48

Cybrosys

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2 Comments

Fka Over a year ago

So, you are suggesting me (option 1) to write await _initializeTask; just after opening bracket?

Cybrosys Over a year ago

I'm giving you three different solutions, it is up to you to pick one. If you want to use the first solution then I would place the await call right before trying to access the xml formatter.

Moti Azu · Accepted Answer · 2014-11-10 10:43:14Z

2

Never do long running processes in ctor, call initialize separately.

answered Nov 10, 2014 at 10:43

Moti Azu

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