How can I use combobox with wpf mvvm

Question

I have an employee table. and location field in employee table. I have to use combobox to filter that. If I choose "A location" in combobox only A location people should come in screen if I choose B location only B location people should come in screen. It's my xaml Entries and ComboBox.ParticularEntries is my all entries (A and B locations together)

Initialized ParticularEntries like that:

private IEnumerable<EntryReportParticular> _particularEntries;
public IEnumerable<EntryReportParticular> ParticularEntries
{
    get { return _particularEntries; }
    set { Set(ref _particularEntries, value); }
}

And EntryReportParticular Model Class:

public class EntryReportParticular : BindableItem
{
    private Employee _employee;
    public Employee Employee
    {
        get { return _employee; }
        set { Set(ref _employee, value); }
    }

    private DateTime _entry;
    public DateTime Entry
    {
        get { return _entry; }
        set { Set(ref _entry, value, () => OnPropertyChanged(nameof(Duration))); }
    }

    private DateTime _exit;
    public DateTime Exit
    {
        get { return _exit; }
        set { Set(ref _exit, value, () => OnPropertyChanged(nameof(Duration))); }
    }

    public TimeSpan Duration { get { return Exit - Entry; } }

    private Region _region;
    public Region Region
    {
        get { return _region; }
        set { Set(ref _region, value); }
    }
}

It's my xaml ParticularEntries

<DataGrid  
    ItemsSource="{Binding ParticularEntries}" 
    AutoGenerateColumns="False" 
    IsReadOnly="True" 
    RowHeaderWidth="0" 
    GridLinesVisibility="All"
    HorizontalGridLinesBrush="WhiteSmoke"
    VerticalGridLinesBrush="WhiteSmoke" 
    Margin="4">

And It's my combobox with command.

<ComboBox 
    ItemsSource="{Binding Locations}" 
    SelectedItem ="{Binding SelectedLocation}">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <i:InvokeCommandAction Command="{Binding LocationFilterCommand}"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</ComboBox>

And It's my related part of ViewModel: ComboBox:

private string _selectedLocation;
public string SelectedLocation
{
    get { return _selectedLocation; }
    set
    {
        _selectedLocation = value;
        OnPropertyChanged("SelectedLocation");
        Trace.WriteLine(SelectedLocation);
    }
}

private ObservableCollection<string> _locations;
public ObservableCollection<string> Locations
{
    get { return _locations; }
    set
    {
        _locations = value;
        OnPropertyChanged("Locations");
    }
}

public EntryReportViewModel()//Constructor
{
    Locations = new ObservableCollection<string>()
    {
        "A Location","B Location"
    };
}

LocationFilterCommand(to filtered according to location without button)

#region LocationFilterCommand

private DelegateCommand _locationFilterCommand;
public DelegateCommand LocationFilterCommand
{
    get { return _locationFilterCommand ?? (_locationFilterCommand = new DelegateCommand(CanLocationFilter, LocationFilter)); }
}

private bool CanLocationFilter()
{

    if (ParticularEntries == null || DailyEntries == null || MonthlyEntries == null)
        return false;

    return true;
}
private void LocationFilter()
{
   ParticularEntries.Select(pg => pg.Region.Location == _selectedLocation);
   MonthlyEntries.Select(pg => pg.Employee.CostCenter.Location == _selectedLocation);

}
#endregion

I did that. I have ComboBox with A and B locations but when I choose A or B location anything changed.How can I fix this and how can I filtered according to location? What should I change in UI or others to do that?

Answer 1

Your code in LocationFilter make no sense at all.

ParticularEntries.Select(pg => pg.Region.Location == _selectedLocation);

It returns an IEnumerable<bool> but it is never assigned.

If you want to filter, you have to use Where .

But even if you change your code to

ParticularEntries = ParticularEntries.Where(pg => pg.Region.Location == _selectedLocation);

you will see a change, but you will face the next problem next time when you select a different location.

Solution

You need a collection with all unfiltered items stored inside a private field and use that for filtering.

private IEnumerable<EntryReportParticular> _allEntries;

private IEnumerable<EntryReportParticular> _particularEntries;
public IEnumerable<EntryReportParticular> ParticularEntries
{
    get { return _particularEntries; }
    set { Set(ref _particularEntries, value); }
}

private void LocationFilter()
{
   ParticularEntries = _allEntries
       .Where(pg => pg.Region.Location == _selectedLocation)
       .ToList();
}