WP8 - Bind ProgressBar visibility - binding

Question

I have a simple thing to code, i checked other questions but couldn't it yet.
I have an application which loads some data from an xml file retrieved from the web, and then displays it inside a longlistselector.
I did it, it works, now i would like to add an indeterminate progressbar which stays active until I finished the data loading.
I enclosed the progressbar in a stackpanel, before my longlistselector, and i bound its visibility to the function ProgressBarVisibility (see code below).
<phone:PivotItem Header="Status">
<StackPanel>
<ProgressBar Value ="0" IsIndeterminate="True" Visibility="{Binding ProgressBarVisibility}"/>
<phone:LongListSelector Margin="0,0,-12,0" ItemsSource="{Binding PivotOne}">
<phone:LongListSelector.ItemTemplate>
<!-- lots of code here -->
</phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>
</StackPanel>
</phone:PivotItem>
In the MainViewModel.cs , that's how i wrote the thing.
using System.Windows;
public class MainViewModel : INotifyPropertyChanged
{
public MainViewModel()
{
this.PivotOne = new ObservableCollection<ItemViewModel>();
this.PivotTwo = new ObservableCollection<ItemViewModel>();
this.PivotThree = new ObservableCollection<ItemViewModel>();
}
/// <summary>
/// A collection for ItemViewModel objects.
/// </summary>
public ObservableCollection<ItemViewModel> PivotOne { get; private set; }
public ObservableCollection<ItemViewModel> PivotTwo { get; private set; }
public ObservableCollection<ItemViewModel> PivotThree { get; private set; }
private string _detailPageTitle = "Default";
/// <summary>
/// DetailPageTitle ritorna il titolo della pagina di dettaglio. Viene settato nella funzione che carica la pagina secondaria
/// </summary>
/// <returns></returns>
public string DetailPageTitle
{
get
{
return _detailPageTitle;
}
set
{
if (value != _detailPageTitle)
{
_detailPageTitle = value;
NotifyPropertyChanged("DetailPageTitle");
}
}
}
public bool IsDataLoaded
{
get;
private set;
}
private Visibility _progressBarVisibility = Visibility.Collapsed;
public Visibility ProgressBarVisibility
{
get
{
return _progressBarVisibility;
}
set
{
if (value != _progressBarVisibility)
{
_progressBarVisibility = value;
NotifyPropertyChanged("ProgressBarVisibility");
}
}
}
private Visibility _progressBarVisibility = Visibility.Visible;
public Visibility ProgressBarVisibility
{
get
{
return _progressBarVisibility;
}
set
{
if (value != _progressBarVisibility)
{
_progressBarVisibility = value;
NotifyPropertyChanged("ProgressBarVisibility");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (null != handler)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
public void LoadData()
{
//progressbar is visible, data not loaded
this.IsDataLoaded = false;
ProgressBarVisibility = Visibility.Visible;
// Load Static and dynamic data -- populate the different pivots
LoadStaticData();
LoadXMLFile();
// data loaded, progressbar collapsed
this.IsDataLoaded = true;
ProgressBarVisibility = Visibility.Collapsed;
}
So i included system.windows library, and used the visibility class.
Anyway, i cannot get the progressbar to disappear when the loading is done, it keeps going.
Any suggestion? where am i doing it wrong?
Thanks in advance!
Solution: loaddata is executed on the app activation, so the content is not even rendered at that moment.

Answer 1

Your MainViewModel must implement INotifyPropertyChanged to signal to the View that one of the properties has changed. In addition, when you change the ProgressBarVisibility property, it should fire the PropertyChanged event.
There are a number of MVVM frameworks that come with some implementation of INotifyPropertyChanged, but you could easily implement something simple yourself.

Answer 2

You need to report the changed made to the view:
Change
public Visibility ProgressBarVisibility { get; set; }
by
private Visibility _progressBarVisibility;
public Visibility ProgressBarVisibility
{
get { return _progressBarVisibility;}
set { _progressBarVisibility = value; RaisePropertyChanged("ProgressBarVisibility");}
}
Make sure you implement INotifyPropertyChanged or a base ViewModel that implement it (MVVMLigth : ViewModelBase).