带有WP8（MVVM）和异步Web服务的进度指示器

Question

I'm a newbie in async programming. I'm creating WP8 application.

What I would like to have

I would like to show list of eg news. When button is tapped:

1. there should appear proggress indicator,
2. data should be downloaded and displayed,
3. progress indicator should dissapear.

---

What I have so far:

Method in referenced webservice:

void GetNewsAsync() 
{
    //...
}

Two methods in viewModel:

public void GetNewsFromService()
{
    //call webservice
    //...
    client.GetNewsCompleted += client_GetNewsCompleted;
    client.GetNewsAsync(startDate);
}

void client_GetNewsCompleted(object sender, GetNewsCompletedEventArgs e)
{
//save result from webservice to db
//update viewmodel property
//...
}

OnClick method in view for button "sync":

void appBarSyncButton_Click(object sender, EventArgs e)
{
    TurnOnProgressBar();
    _viewModel.GetNewsFromService();
    //TurnOffProgressBar();
}

---

Everything is working (web service is called, result data is saved, list is updating, but...

How to redesign this code to inform view in order to hide progress indicator (when all work is completed)?

Answer 1

client_GetNewsCompleted should assign a public property like Completed to true. Following that, it would be more MVVM, if you had a property like IsInProgress that you manage completely in your ViewModel - set to true in GetNewsFromService and false in client_GetNewsCompleted . Then simply bind ProgressIndicator.Visibility to that property (using converter).