WPF - how not to update a slider's value on dragging

Question

you might say it's a duplicate of How to stop update value of slider while dragging it? but honestly the solution there is from 2011 and just not working for me (as even commented on the accepted answer by other users), and the other answers aren't relevant for me. So please be patient guys.

That's my problem: I have a slider that is binded to a value like that:

<Slider Name="AudioSlider" Value="{Binding AudioValue}" 
        Grid.Column="1"    Grid.Row="1"    Height="30" 
        SmallChange="1"    Maximum="100" 
        IsSnapToTickEnabled="True"                                      
        IsMoveToPointEnabled="True"/>

And this is the value:

        private double _audioValue;
        public double AudioValue
        {
            get { return _audioValue; }
            set
            {
                if (_audioValue == value)
                    return;
                _audioValue = value;
                SendPacket(cockpitType, (byte)Index.AudioSlider, (byte)_audioValue);
                OnPropertyChanged("AudioValue");
            }
        }

As you can see, every time the value changes I am sending a packet, when it updates the value on drag it's just spamming the value on the server and it's something that must be prevented.

I have tried to bind the slider to a function (mouseUp) but I couldn't get the value this way.

Any ideas what I can do?

Thanks a lot.

Edit:

The answer here WPF: Slider with an event that triggers after a user drags doesn't help me since it's a generated slider inside a data template, events aren't relevant for me.

Answer 1

If you are using WPF 4.5 you can just use

Value="{Binding AudioValue, Delay=500}"

which will throttle the change notifications. If the user drags the slider quickly this will "reset" an internal timer and will drop the pending notifications. When the user stops and the 500 ms delay is over, it will call your setter method once.

There are lots of ways of doing this, so this is just one suggestion. You could do this with Rx and its Throttle method in the VM. That would be essentially the same as the Binding's Delay property.

I have a problem with overriding only the OnThumbDragCompleted method as suggested in other answers. That means the change would only propagate if the Slider was manipulated by dragging the thumb. If you click next to the thumb for example, your property wouldn't get notified. Basically what I'm saying is that you have to be sure to synchronize the value of Value and FinalValue if you are going with a solution where you derive from Slider.

Answer 2

What I suggest is to create your own slider inheriting from the original one, which will clear the binding on drag start and restore it once the drag is completed. Here's an example:

public class CustomSlider : Slider
{
    private Binding SupressedBinding { get; set; }

    protected override void OnThumbDragStarted(DragStartedEventArgs e)
    {
        base.OnThumbDragStarted(e);
        var expression = BindingOperations.GetBindingExpression(this, ValueProperty);
        if (expression != null)
        {
            SupressedBinding = expression.ParentBinding;
            //clearing the binding will cause the Value to reset to default,
            //so we'll need to restore it
            var value = Value;
            BindingOperations.ClearBinding(this, ValueProperty);
            SetValue(ValueProperty, value);
        }
    }

    protected override void OnThumbDragCompleted(DragCompletedEventArgs e)
    {
        if (SupressedBinding != null)
        {
            //again, restoring the binding will cause the Value to update to source's
            //value (which is "out of date" by now), so we'll need to restore it
            var value = Value;
            BindingOperations.SetBinding(this, ValueProperty, SupressedBinding);
            SetCurrentValue(ValueProperty, value);
            SupressedBinding = null;
        }
        base.OnThumbDragCompleted(e);
    }
}

Answer 3

Create a boolean property that you set to false on mousedown and to true on mouseup, and in your property, send the packet only if that property is true ?

Answer 4

I completely agree with Noctis, in addition you can use behavior which get the Action<bool>, and using that action and mousedown/mouseup events can signalize if you can send the packet. Moreover you can handle the final value on mouseup, pass that value to the viewmodel, update the AudioValue indicator and send the packet you need (you need another action in behavior, something like Action<bool, double>, where boolean signalize if you can sent packet and double is for the AudioValue itself).

I'll glad to help, if will need help with the code. Regards.