绑定到 ObservableCollection 的列表框不会更新

Question

I am using a ObservableCollection to store the Environment Variables of Windows.

class VariableVieWModel
{
    ObservableCollection<VariableModel> vars;

    public ObservableCollection<VariableModel> Variables
    {
        get
        {
            return vars;
        }
        set
        {
            vars = value;
        }
    }

    public VariableViewModel() 
    {
        Reload();
    }

    public void Reload()
    {
    // Code to retrieve vars
    }
}

This ObservableCollection is bound to a ListBox.

I have added a button in the GUI to reload the Variables whichi, on click, it calls the Reload() procedure.

ListBox content, however, does not change and I cannot add anymore items to the list afer calling Reload().

Under the constructor everything is working fine.

ListBox XAML:

<ListBox x:Name="lbVariables" Grid.Column="0" Margin="0,0,5,0" ItemsSource="{Binding Source={StaticResource variablesViewModel}, Path=Variables}" IsSynchronizedWithCurrentItem="True"> 

I tried using also PropertyChanged as UpdateSource trigger and set most of the Modes.

public void Reload()
    {
        vars = new ObservableCollection<VariableModel>();

        RegistryKey systemVarKey = Registry.LocalMachine.OpenSubKey(@"SYSTEM\CurrentControlSet\Control\Session Manager\Environment");

        string[] systemVars = systemVarKey.GetValueNames();

        foreach (string var in systemVars)
        {
            vars.Add(new VariableModel()
            {
                Name = var,
                Values = (systemVarKey.GetValue(var, null, RegistryValueOptions.DoNotExpandEnvironmentNames) as string).Split(';').ToList<string>(),
                Target = EnvironmentVariableTarget.Machine
            });
        } 
        systemVarKey.Close();

        RegistryKey userVarKey = Registry.CurrentUser.OpenSubKey(@"Environment");

        string[] userVars = userVarKey.GetValueNames();

        foreach (string var in userVars)
        {
            vars.Add(new VariableModel()
            {
                Name = var,
                Values = (userVarKey.GetValue(var, null, RegistryValueOptions.DoNotExpandEnvironmentNames) as string).Split(';').ToList<string>(),
                Target = EnvironmentVariableTarget.User
            });
        }
        userVarKey.Close();
    }

Answer 1

You haven't modified the ObservableCollection, only replaced it. You should implement INotifyPropertyChanged and call PropertyChanged in the Variables property setter.

BTW it's common in MVVM implementations to have a base class for your ViewModel:

class VariableViewModel : ViewModelBase

and implement common functionality such as INotifyPropertyChanged in the base class to avoid duplication of code.

Answer 2

You need to implement INotifyPropertyChanged for your VariableVieWModel to refresh your target object bindings. You just have to do this way -

class VariableVieWModel : INotifyPropertyChanged
    { .
      .
            public ObservableCollection<VariableModel> Variables
            {
               get
               {
                  return vars;
               }
               set
               {
                  if(vars!=value)
                  {
                      vars = value;
                      OnPropertyChanged("Variables");
                  }
               }
            }

            public event PropertyChangedEventHandler PropertyChanged;      
            protected void OnPropertyChanged(string name)
            {
                PropertyChangedEventHandler handler = PropertyChanged;
                if (handler != null)
                {
                    handler(this, new PropertyChangedEventArgs(name));
                }
            } 
    }

Answer 3

The problem is, that probably your VariableModel does not implement INotifyPropertyChanged . Through ObservableCollection, only changes to the collection are reported, not changes of the contained objects.

Here you will find some implementation possibilities.