I have the following custom control:
<abc:MyControl MyProperty="{Binding FieldInMyModel, Mode=TwoWay}">
And in my custom control I have
public static readonly DependencyProperty MyPropertyProperty =
DependencyProperty.Register("MyProperty", typeof(double), typeof(MyControl),
new PropertyMetadata(0.0, OnMyPropertyChanged));
public double MyProperty
{
get { return (double)GetValue(MyPropertyProperty ); }
set { SetValue(MyPropertyProperty , value); }
}
private static void OnMyPropertyChanged(DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
if (d is MyControl mc)
{
// here I check if the new value is valid for my scope.
// if it is not I update it here to be valid
var v = (double)e.NewValue;
if (!mc.IsValidValue(v))
{
v = mc.MakeValidValue(v);
mc.MyProperty = v;
}
}
}
In my model I change the value of FieldInMyModel to be not valid for my scope. OnMyPropertyChanged is called, and after making a valid value from received invalid value I expect that the FieldInMyModel will be updated to have the new value of MyProperty but actually nothing happens. Any thought?
Setting MyProperty from code will break your TwoWay Binding.
Instead you can use SetCurrentValue method.
Related
When I set the value of IsClosed during runtime, OnIsClosedChanged() is called fine.
However, the Designer sets the value of the property but does not call the OnIsClosedChanged().
public static DependencyProperty IsClosedProperty = DependencyProperty.Register("IsClosed", typeof(bool), typeof(GroupBox), new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender));
public bool IsClosed {
get {
return (bool)this.GetValue(IsClosedProperty);
}
set {
if ((bool)this.GetValue(IsClosedProperty) == value)
return;
this.SetValue(IsClosedProperty, value);
OnIsClosedChanged();
}
}
private void OnIsClosedChanged() {
_rowDefContent.Height = new GridLength((IsClosed ? 0 : 1), GridUnitType.Star);
}
Obviously IsClosed is not modified by the Designer and only IsClosedProperty receives the xaml change.
My question is: How can I run IsClosed after the value has been modified in the Designer. Or at least add some logic to the non-runtime changes.
You would have to register a PropertyChangedCallback with property metadata.
The reason is that dependency properties set in XAML or by bindings or some other source do not invoke the CLR wrapper (the setter method). The reason is explained in the XAML Loading and Dependency Properties article on MSDN:
For implementation reasons, it is computationally less expensive to
identify a property as a dependency property and access the property
system SetValue method to set it, rather than using the property
wrapper and its setter.
...
Because the current WPF implementation of the XAML processor behavior
for property setting bypasses the wrappers entirely, you should not
put any additional logic into the set definitions of the wrapper for
your custom dependency property. If you put such logic in the set
definition, then the logic will not be executed when the property is
set in XAML rather than in code.
Your code should look like this:
public static readonly DependencyProperty IsClosedProperty =
DependencyProperty.Register(
"IsClosed", typeof(bool), typeof(GroupBox),
new FrameworkPropertyMetadata(false,
FrameworkPropertyMetadataOptions.AffectsRender,
(o, e) => ((GroupBox)o).OnIsClosedChanged()));
public bool IsClosed
{
get { return (bool)GetValue(IsClosedProperty); }
set { SetValue(IsClosedProperty, value); }
}
private void OnIsClosedChanged()
{
_rowDefContent.Height = new GridLength((IsClosed ? 0 : 1), GridUnitType.Star);
}
Found the answer myself now. ValidateValueCallback comes really close! (as Alex K has pointed out) But it is a static method and I don't get any reference to the instance which has been changed. The key is to use a PropertyChangedCallback in FrameworkPropertyMetadata which is also an argument passed to the Property.Register method.
See:
public static DependencyProperty IsClosedProperty = DependencyProperty.Register("IsClosed", typeof(bool), typeof(GroupBox), new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender, new PropertyChangedCallback(OnIsClosedChangedPCC)));
public bool IsClosed {
get {
return (bool)this.GetValue(IsClosedProperty);
}
set {
this.SetValue(IsClosedProperty, value);
OnIsClosedChanged();
}
}
private static void OnIsClosedChangedPCC(DependencyObject d, DependencyPropertyChangedEventArgs e) {
GroupBox current = (GroupBox)d;
current.IsClosed = current.IsClosed;
}
private void OnIsClosedChanged() {
_rowDefContent.Height = new GridLength((IsClosed ? 0 : 1), GridUnitType.Star);
}
That does now re-set the IsClosedValue which triggers the OnIsClosedChanged to run.
Thank's for your help guys!
I have the following code in my sample.
public string MyProperty
{
get { return (string)GetValue(MyPropertyProperty); }
set { SetValue(MyPropertyProperty, value); }
}
public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register("MyProperty", typeof(string), typeof(MainWindow), new PropertyMetadata("Hello"));
private TestClass1 test;
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
Binding binding = new Binding
{
Path = new PropertyPath("MyProperty"),
Mode = BindingMode.TwoWay,
UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
};
test.SetValueBinding(binding);
test.DataContext = this;
Console.WriteLine(test.Value);
}
public class TestClass1 : FrameworkElement
{
public object Value
{
get { return (object)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(object), typeof(TestClass1), new PropertyMetadata(null));
public void SetValueBinding(Binding binding)
{
this.SetBinding(ValueProperty, binding);
}
}
After binding is set, if i access test.Value, it returns null for the first time. After that,if i access it (from another method) it returns correct value "Hello".
But i do not know first time why binding is not working and null value is returned? any suggestion?
Thanks in advance.
It's not that you can't get the value for the first time. It's that you can't get it so fast. When binding is set at the time the DataContext is NULL, the source is resolved in a deferred way, perhaps later by the UI thread. You ask for value just after the binding is set, too early to get valid results.
You should switch lines in your code to:
test.DataContext = this;
test.SetValueBinding(binding);
This way the binding gets the value immediately from DataContext in the first instruction.
I created a DependencyProperty for UserControl that should be in the range of -2 .. 2
When rotating the mouse scroll wheel in the properties window.
The property value changes by one. And I want to value changed by 0.1
How do I set a step change in DependencyProperty?
I work with properties in XAML editor.
public double Value
{
get { return (double)GetValue(BarValueProperty); }
set { SetValue(BarValueProperty, value); }
}
public static readonly DependencyProperty BarValueProperty =
DependencyProperty.Register("Value", typeof(double), typeof(MeterBar), new FrameworkPropertyMetadata(0.0, FrameworkPropertyMetadataOptions.AffectsRender));
When adding the FrameworkPropertyMetadata options into the definition of a DependencyProperty, there is an option to provide a CoerceValueCallback handler. You can change the incomming values in this handler. For complete details, please see the Dependency Property Callbacks and Validation page on MSDN. From the linked page:
public static readonly DependencyProperty CurrentReadingProperty =
DependencyProperty.Register(
"CurrentReading",
typeof(double),
typeof(Gauge),
new FrameworkPropertyMetadata(
Double.NaN,
FrameworkPropertyMetadataOptions.AffectsMeasure,
new PropertyChangedCallback(OnCurrentReadingChanged),
new CoerceValueCallback(CoerceCurrentReading)
),
new ValidateValueCallback(IsValidReading)
);
public double CurrentReading
{
get { return (double)GetValue(CurrentReadingProperty); }
set { SetValue(CurrentReadingProperty, value); }
}
...
private static object CoerceCurrentReading(DependencyObject d, object value)
{
// Do whatever calculation to update your value you need to here
Gauge g = (Gauge)d;
double current = (double)value;
if (current
<g.MinReading) current = g.MinReading;
if (current >g.MaxReading) current = g.MaxReading;
return current;
}
I'm working on a custom behavior for the visiblox chart. This custom behavior has a dependency property Value that identifies the position of a cursor that consists of vertical line draw in the chart. This cursor follows the mouse if I set the property FollowMouse to true.
If I bind the Value property the changedvaluecallback only gets 0 as the newValue, while if the value is not bound it works properly. But if i change the source property of the binding (property on ViewModel) it works too. So the problem is setting the value with SetCurrentValue on PointerMoved.
Here is the source code of the behavior:
public class TimeCursorBehavior : BehaviourWithAxesBase
{
private System.Windows.Shapes.Line _line;
public TimeCursorBehavior()
: base("TimeCursor")
{
_line = new System.Windows.Shapes.Line();
_line.Stroke = System.Windows.Media.Brushes.Black;
_line.StrokeThickness = 2;
}
public override void DeInit()
{
base.DeInit();
Chart.BehaviourCanvas.Children.Remove(_line);
}
protected override void Init()
{
base.Init();
Chart.BehaviourCanvas.Children.Add(_line);
}
public override void PointerMoved(IBehaviourEventSource sender, PointerEventContext context)
{
base.PointerMoved(sender, context);
if (!FollowMouse)
return;
IComparable xDataValue = XAxis.GetRenderPositionAsDataValueWithZoom(context.Point.X);
SetCurrentValue(ValueProperty, xDataValue);
}
public override void BehaviourCanvasSizeChanged(IBehaviourEventSource sender, SizeChangedEventArgs e)
{
base.BehaviourCanvasSizeChanged(sender, e);
_line.Y2 = e.NewSize.Height;
}
#region Value
public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(IComparable), typeof(TimeCursorBehavior), new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnValueChanged));
private static void OnValueChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
{
(sender as TimeCursorBehavior).OnValueChanged(args.OldValue as IComparable, args.NewValue as IComparable);
}
private void OnValueChanged(IComparable oldValue, IComparable newValue)
{
if (XAxis == null)
return;
double x = XAxis.GetDataValueAsRenderPositionWithZoom(newValue);
_line.X1 = x;
_line.X2 = x;
}
public IComparable Value
{
get
{
return GetValue(ValueProperty) as IComparable;
}
set
{
SetValue(ValueProperty, value);
}
}
#endregion
#region FollowMouse
public static readonly DependencyProperty FollowMouseProperty = DependencyProperty.Register("FollowMouse", typeof(bool), typeof(TimeCursorBehavior), new PropertyMetadata(false));
public bool FollowMouse
{
get
{
return (bool)GetValue(FollowMouseProperty);
}
set
{
SetValue(FollowMouseProperty, value);
}
}
#endregion
}
Does anyone know why setcurrentvalue is not updating the value accordingly?
Found the problem.
My property in the ViewModel is an decimal, and the property returned by the line below is a double.
IComparable xDataValue = XAxis.GetRenderPositionAsDataValueWithZoom(context.Point.X);
I added an converter to the binding it everything worked as expected.
In the code below you can see what I'm trying to do, but it doesn't work. I want an event that I can attach to outside of my user control and fires whenever the dependency property changes.
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value"
, typeof(Double)
, typeof(ucSlider)
, new PropertyMetadata(50d, new PropertyChangedCallback(OnValueChanged)));
public Double Value
{
get { return (Double)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
public event PropertyChangedCallback OnValueChanged;
Dependency properties are static, but your event is related with the instance of the class. So you need an intermediate method between the static property and the event of instance.
In this example I pass the static method OnValuePropertyChanged as a callback parameter and inside it I raise the event:
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value"
, typeof(Double)
, typeof(ucSlider)
, new PropertyMetadata(50d, new PropertyChangedCallback(OnValuePropertyChanged)));
public Double Value
{
get { return (Double)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
public static void OnValuePropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
var sl = sender as ucSlider;
if (sl != null)
sl.RaiseValueChangedEvent(e);
}
private void RaiseValueChangedEvent(DependencyPropertyChangedEventArgs e)
{
if(this.OnValueChanged != null)
this.OnValueChanged(this, e);
}
public event PropertyChangedCallback OnValueChanged;