# .NET MAUI ComboBox Filtering

The [Telerik UI for .NET MAUI ComboBox](https://www.telerik.com/maui-ui/documentation/controls/combobox/overview) provides filtering, which allows the users to refine their search results as they type into the input field. The default filtering is performed according to the `SearchMode` and `SearchTextPath` properties of the ComboBox.

For more details on the search functionality of the ComboBox, go to the [Edit Mode & Search](https://www.telerik.com/maui-ui/documentation/controls/combobox/editmode-and-search) topic.

This topic describes in detail the configuration options related to the filtering feature of the ComboBox:

* `IsFilteringEnabled`(`bool`)—Indicates whether the filtering is enabled. Its default value is `False`.
* `FilteredItems`(`IReadOnlyCollection<object>`)—Gets the filtered items collection.
* `NoResultsMessage`(`string`)—Defines the message visualized when no items match the applied filter.
* `NoResultsTemplate`(`DataTemplate`)—Defines the `DataTemplate` visualized when no items match the applied filter.

Here is a quick example of `RadComboBox` with enabled filtering:

**1.** First, add the ComboBox definition with `IsEditable`, `IsFilteringEnabled` and `SearchMode` applied:

```XAML
<telerik:RadComboBox ItemsSource="{Binding Items}"
                     DisplayMemberPath="Name"
                     IsEditable="True"
                     IsFilteringEnabled="True"
                     SearchTextPath="Name"
                     SearchMode="Contains"
                     NoResultsMessage="No items found." />
```

**2.** Add the `ViewModel` class:

```C#
public class ViewModel
{
    public ViewModel()
    {
        this.Items = new ObservableCollection<City>
        {
            new City { Name = "Tokyo", Population = 13929286 },
            new City { Name = "New York", Population = 8623000 },
            new City { Name = "London", Population = 8908081 },
            new City { Name = "Madrid", Population = 3223334 },
            new City { Name = "Los Angeles", Population = 4000000},
            new City { Name = "Paris", Population = 2141000 },
            new City { Name = "Beijing", Population = 21540000 },
            new City { Name = "Singapore", Population = 5612000 },
            new City { Name = "New Delhi", Population = 18980000 },
            new City { Name = "Bangkok", Population = 8305218 },
            new City { Name = "Berlin", Population = 3748000 },
        };
    }

    public ObservableCollection<City> Items { get; set; }
}
```

**3.** Add the `City` data item:

```C#
public class City
{
    public string Name { get; set; }
    public int Population { get; set; }
}
```

Here is the result:

![Telerik .NET MAUI ComboBox Filtering](https://www.telerik.com/maui-ui/documentation/assets/093c56a966cc6368bef97ea4ff482bee/combobox-filtering.gif)

## Custom Filtering Behavior

You can override the default item filtering logic by applying custom filtering in the ComboBox. When you override `FilterItems`, your custom logic fully replaces the built-in filtering for that operation (no second built-in search pass is applied). To implement a custom filter:

1. Create a custom class that inherits from `ComboBoxFilteringBehavior` and override its `FilterItems` method with a custom filtering condition.
2. Assign the `ComboBoxFilteringBehavior` to the `FilteringBehavior` property of the `ComboBox`.

* `FilteringBehavior`(`ComboBoxFilteringBehavior`)—Defines the filtering behavior used to filter items.

Here is a quick example which demonstrates the custom filtering behavior—the items are filtered not only by the entered search text, but also according to the `Population` property.

**1.** Create a custom filtering behavior class:

```C#
public class CustomFilteringBehavior : ComboBoxFilteringBehavior
{
    public override IList<object> FilterItems(string searchText, SearchMode searchMode, string path, IEnumerable source)
    {
        return source.OfType<City>().Where(city => city.Name.Contains(searchText, System.StringComparison.CurrentCultureIgnoreCase) &&
                                          (city.Population > 5000000)).ToList<object>();
    }
}
```

**2.** Assign it to the ComboBox instance:

```XAML
<telerik:RadComboBox ItemsSource="{Binding Items}"
                     DisplayMemberPath="Name"
                     IsEditable="True"
                     IsFilteringEnabled="True"
                     Placeholder="cities with > 5 million population">
    <telerik:RadComboBox.FilteringBehavior>
        <local:CustomFilteringBehavior />
    </telerik:RadComboBox.FilteringBehavior>
</telerik:RadComboBox>
```

For the purpose of the example, use the same `ViewModel` and `City` data item as in the previous filtering example.

Here is the result after applying the custom filtering behavior:

![Telerik .NET MAUI ComboBox Custom Filtering](https://www.telerik.com/maui-ui/documentation/assets/e0017451cd540a095c83f5e7270d9734/combobox-custom-filtering.gif)

## See Also

* [Edit Mode & Search](https://www.telerik.com/maui-ui/documentation/controls/combobox/editmode-and-search)
* [Configuration](https://www.telerik.com/maui-ui/documentation/controls/combobox/configuration)
* [Single and Multiple Selection](https://www.telerik.com/maui-ui/documentation/controls/combobox/selection)