c# - How to scroll to the bottom of a ScrollViewer automatically with Xaml and binding?

Question

I've got a TextBlock whose content is data bound to a string property of the ViewModel. This TextBlock has a ScrollViewer wrapped around it.

What I want to do is every time the logs change, the ScrollViewer will scroll to the bottom. Ideally I want something like this:

    <ScrollViewer ScrollViewer.HorizontalScrollBarVisibility="Auto"
                  ScrollPosition="{Binding Path=ScrollPosition}">
        <TextBlock Text="{Binding Path=Logs}"/>
    </ScrollViewer>

I don't want to use Code Behind! The solution I'm looking for should be using only binding and/or Xaml.

Answer 1

You can either create an attached property or a behavior to achieve what you want without using code behind. Either way you will still need to write some code.

Here is an example of using attached property.

Attached Property

public static class Helper
{
    public static bool GetAutoScroll(DependencyObject obj)
    {
        return (bool)obj.GetValue(AutoScrollProperty);
    }

    public static void SetAutoScroll(DependencyObject obj, bool value)
    {
        obj.SetValue(AutoScrollProperty, value);
    }

    public static readonly DependencyProperty AutoScrollProperty =
        DependencyProperty.RegisterAttached("AutoScroll", typeof(bool), typeof(Helper), new PropertyMetadata(false, AutoScrollPropertyChanged));

    private static void AutoScrollPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var scrollViewer = d as ScrollViewer;

        if (scrollViewer != null && (bool)e.NewValue)
        {
            scrollViewer.ScrollToBottom();
        }
    }
}

Xaml Binding

<ScrollViewer local:Helper.AutoScroll="{Binding IsLogsChangedPropertyInViewModel}" .../>

You will need to create a boolean property IsLogsChangedPropertyInViewModel and set it to true when the string property is changed.

Hope this helps! :)