Dependency Properties in User Controls

Question

I have a simple Slider and Label user control that I load into my window and I want to change the following properties using databinding from the main window.

Slider Properties -> Value, SelectionStart, SelectionEnd (all doubles)

Label Properties -> Title (string)

I have created a dependency property for the Title property and that works fine for the Label but the slider properties have me stumped. I can change the value manually in the xaml code but not programmatically.

public static readonly DependencyProperty SelStart_Property =

DependencyProperty.Register("Set_SelStart", typeof(double), typeof(UserTest), new PropertyMetadata(0.0, OnSelStart_Changed));

// Set SELECTION START (double) property of Slider

// MODE = 1 Way (Set)

public double Set_SelStart

{

**get { return (double)GetValue(SelStart_Property); }**

**set { SetValue(SelStart_Property, value); }**

}

private static void OnSelStart_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)

{

**var User = d as UserTest;**

**User.Digit_Slider.SelectionStart = (double)e.NewValue;**

}

XAML

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I have a normal slider and label at the side of the user control and have no problem with that so the dependency properties are not right.

I have placed a breakpoint in the set / get properties and they do break but no change to the screen.

Any advice is grateful

Regards

Answer

Hi, @dmccric. Welcome to Microsoft Q&A.

You could refer to the following code to fix your problem.

UserTest.xaml

UserTest.xaml.cs

    public partial class UserTest : UserControl
    {
        public double Set_SelStart
        {
            get { return (double)GetValue(SelStart_Property); }
            set { SetValue(SelStart_Property, value); }
        }

        public static readonly DependencyProperty SelStart_Property = DependencyProperty.Register("Set_SelStart", typeof(double), typeof(UserTest), new PropertyMetadata(0.0, OnSelStart_Changed));

        private static void OnSelStart_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var User = d as UserTest;
            User.Digit_Slider.Minimum = (double)e.NewValue;
        }

        public double Set_SelEnd
        {
            get { return (double)GetValue(SelEnd_Property); }
            set { SetValue(SelEnd_Property, value); }
        }

        public static readonly DependencyProperty SelEnd_Property = DependencyProperty.Register("Set_SelEnd", typeof(double), typeof(UserTest), new PropertyMetadata(0.0, OnSelEnd_Changed));

        private static void OnSelEnd_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var User = d as UserTest;
            User.Digit_Slider.Maximum = (double)e.NewValue;
        }

        public double Position
        {
            get { return (double)GetValue(Position_Property); }
            set { SetValue(Position_Property, value); }
        }

        public static readonly DependencyProperty Position_Property = DependencyProperty.Register("Position", typeof(double), typeof(UserTest), new PropertyMetadata(0.0));
        public UserTest()
        {
            InitializeComponent();
        }
    }

MainWindow.xaml

MainWindow.xaml.cs

public partial class MainWindow : Window,INotifyPropertyChanged
{
    private double pos;
    public double Pos { get { return pos; } set { pos = value; OnPropertyChanged(nameof(Pos)); } }

    private double start;
    public double Start { get { return start; } set { start = value; OnPropertyChanged(nameof(Start)); } }

    private double end;

    public double End { get { return end;} set { end = value; OnPropertyChanged(nameof(End)); } }

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        Start = 1f;
        End = 100f;
    }

    public event PropertyChangedEventHandler? PropertyChanged;

    public void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    private void btn_Press_Click(object sender, RoutedEventArgs e)
    {
        Pos = 50f;
    }
}

Not sure if you want to set the minimum value of the Slider via Set_SelStart, so in the OnSelStart_Changed method I replaced User.Digit_Slider.SelectionStart = (double)e.NewValue; with User.Digit_Slider.Minimum = (double)e.NewValue;

In order to ensure that the Position could also sense the change when the Digit_Slider is dragged, I replaced the new PropertyMetadata(0.0, OnSelStart_Changed) method with Value="{Binding Position,Mode=TwoWay,RelativeSource={RelativeSource AncestorType=UserControl}}" to update Value

Finally, the normal data binding in MainWindow.

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Dependency Properties in User Controls

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