I have created a custom UserControl with some Dependency properties.
This custom control is hosted on a Window.
When I try to get a value from a DependecyProperty in code behind it doesn't work.
public static readonly DependencyProperty ValueDp = DependencyProperty.Register("Value", typeof(string), typeof(MyCustomUserControl), new FrameworkPropertyMetadata(string.Empty, OutputHandler));
public string Value
{
get { return (string)GetValue(ValueDp); }
set { SetValue(ValueDp, value); }
}
private static void OutputHandler(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
var temp= dependencyObject as MyCustomUserControl;
if (temp!= null)
{
dependencyObject.SetValue(ValueDp,temp._conversionValue);
}
}
On the host I have put a button and when I click on it, I want to read the value stored in the DP, but I will always get the default value set in DP.
Any ideas what I`m doing wrong here?
Regards
I think that in the OutputHandler method you are always discarding the new value assigned to the property (dependencyPropertyChangedEventArgs.NewValue)
As #Alberto has said the OldValue and NewValue are the properties which hold the value of the DependencyProperty. The above properties are found in dependencyPropertyChangedEventArgs. In your Handler the member dependencyObject and temp refer to the same object.
Related
I created a user control and wanted to get the value of the DependencyProperty "ListBoxReadOnly" in the code. I set the value in the XAML:
<control:AutoCompleteTextBox x:Name="actbFullName" ListBoxReadOnly="True"/>
When I tried to read the value in the constructor, it only shows the default value which is false.
I tried to get the value via a callback back but probably I am lacking some understanding of the whole framework. Since the callback is a static method, I cannot apply it to the instance of my user control.
public static readonly DependencyProperty ListBoxReadOnlyDependency =
DependencyProperty.Register("ListBoxReadOnly", typeof(bool),
typeof(AutoCompleteTextBox), FrameworkPropertyMetadata
(false, FrameworkPropertyMetadataOptions.AffectsRender));
public bool ListBoxReadOnly
{
get
{
return (bool) GetValue(ListBoxReadOnlyDependency);
}
set
{
SetValue(ListBoxReadOnlyDependency, value);
}
}
// constructor of user control
public AutoCompleteTextBox()
{
InitializeComponent();
// *** shows "false" (default value) even though set to true in XAML
// *** see XAML above ***
var test = ListBoxReadOnly;
}
Any help is appreciated :-)
I would expect your code (as is) to show false. The DP is initialized to false. In the constructor of your control, neither the default control style, nor the properties set in xaml have been applied yet.
The style is only applied after OnApplyTemplate() is called (unless you force it).
If you want to track DP changes, you need a DP change handler.
When I tried to read the value in the constructor, it only shows the default value which is false.
The property can't be set before the control has been initialized.
Since the callback is a static method, I cannot apply it to the instance of my user control.
You could cast the DependencyObject to the type of your control in the callback:
public static readonly DependencyProperty ListBoxReadOnlyDependency =
DependencyProperty.Register("ListBoxReadOnly", typeof(bool),
typeof(AutoCompleteTextBox), new FrameworkPropertyMetadata
(false, FrameworkPropertyMetadataOptions.AffectsRender, new PropertyChangedCallback(OnChanged)));
private static void OnChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
AutoCompleteTextBox ctrl = (AutoCompleteTextBox)d;
var x = ctrl.ListBoxReadOnly;
//...
}
I have a WPF control that is based on the TextBox control:
public class DecimalTextBox : TextBox
I have a dependency property that is bound to, which manages the numeric value, and is responsible for setting the Text property:
public decimal NumericValue
{
get { return (decimal)GetValue(NumericValueProperty); }
set
{
if (NumericValue != value)
{
SetValue(NumericValueProperty, value);
SetValue(TextProperty, NumericValue.ToString());
System.Diagnostics.Debug.WriteLine($"NumericValue Set to: {value}, formatted: {Text}");
}
}
}
protected override void OnTextChanged(TextChangedEventArgs e)
{
base.OnTextChanged(e);
if (decimal.TryParse(Text, out decimal num))
{
SetValue(NumericValueProperty, num);
}
}
This works well when entering a value into the textbox itself (it updates the underlying values, etc...). However, when the bound property of NumericValue is changed, despite updating the NumericValue DP, the Text property is not updated. In the tests that I've done, it would appear that the reason for this is that the set method above is not called when the bound value is updated. The binding in question looks like this:
<myControls:DecimalTextBox NumericValue="{Binding Path=MyValue, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
Can anyone point me in the right direction as to why this property setter is not firing, or is there a better way to approach this?
As explained in Custom Dependency Properties and XAML Loading and Dependency Properties, you should not call anything else than GetValue and SetValue in the CLR wrapper of a dependency property:
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.
In order to get notified about value changes, you'll have to register a PropertyChangedCallback with the dependency property metadata.
public static readonly DependencyProperty NumericValueProperty =
DependencyProperty.Register(
"NumericValue", typeof(decimal), typeof(DecimalTextBox),
new PropertyMetadata(NumericValuePropertyChanged));
public decimal NumericValue
{
get { return (decimal)GetValue(NumericValueProperty); }
set { SetValue(NumericValueProperty, value); }
}
private static void NumericValuePropertyChanged(
DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
var textBox = (DecimalTextBox)obj;
textBox.Text = e.NewValue.ToString();
}
The WPF binding is not actually using your getter and setter, but instead directly interacts with the dependency property NumericValueProperty. In order to update the text, subscribe to the PropertyChanged event of the NumericValueProperty instead of trying to do anything special in the setter.
Subscribe to the change in your DependencyProperty definition, similar to the following:
// Using a DependencyProperty as the backing store for NumericValue. This enables animation, styling, binding, etc...
public static readonly DependencyProperty NumericValueProperty =
DependencyProperty.Register("NumericValue", typeof(decimal), typeof(DecimalTextBox), new FrameworkPropertyMetadata(0.0m, new PropertyChangedCallback(OnNumericValueChanged)));
private static void OnNumericValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var self = d as DecimalTextBox;
// if the new numeric value is different from the text value, update the text
}
Ok, so I'm trying to run some code that modifies a UI when a user changes a custom control's dependency property value in design mode; but only when in design mode.
I've tried these approaches:
1.
public static DependencyProperty x = ...Register(..., new PropertyMetadata(null, changeMethod));
2.
set { SetValue(XProp, value); changeMethod(value); }
3.
var observable = x as INotifyPropertyChanged;
observable.PropertyChanged += ObservablePropertyChanged;
But all of them seem to have their own issues in that they either trigger errors or don't work at all.
So does anyone know what the correct way to listen to a dependency property change in design mode is, and if so can you give an example?
The right way to handle DependencyProperty changes is to:
. Declare the DependencyProperty:
public static DependencyProperty MyXProperty;
. Create the public get/set Property:
public string MyX
{
get { return (string)GetValue(MyXProperty); } //Supposing that the property type is string
set { SetValue(MyXProperty, value); }
}
. Register the DependencyProperty in your static constructor:
static MyClass()
{
MyXProperty= DependencyProperty.Register("MyX", typeof(string), typeof(MyClass), new FrameworkPropertyMetadata("", OnMyXPropertyChanged));
}
. Declare the Property Changed Method:
private static void OnMyXPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MyClass thisClass = d as MyClass ;
//Do Something
}
Please provide more information if you still can't find your solution.
I have a custom Dependency Property defined like so:
public static readonly DependencyProperty MyDependencyProperty =
DependencyProperty.Register(
"MyCustomProperty", typeof(string), typeof(MyClass));
private string _myProperty;
public string MyCustomProperty
{
get { return (string)GetValue(MyDependencyProperty); }
set
{
SetValue(MyDependencyProperty, value);
}
}
Now I try set that property in XAML
<controls:TargetCatalogControl MyCustomProperty="Boo" />
But the setter in DependencyObject never gets hit! Although it does when I change the property to be a regular property and not a Dep Prop
Try this..
public string MyCustomProperty
{
get
{
return (string)GetValue(MyCustomPropertyProperty);
}
set
{
SetValue(MyCustomPropertyProperty, value);
}
}
// Using a DependencyProperty as the backing store for MyCustomProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MyCustomPropertyProperty =
DependencyProperty.Register("MyCustomProperty", typeof(string), typeof(TargetCatalogControl), new UIPropertyMetadata(MyPropertyChangedHandler));
public static void MyPropertyChangedHandler(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
// Get instance of current control from sender
// and property value from e.NewValue
// Set public property on TaregtCatalogControl, e.g.
((TargetCatalogControl)sender).LabelText = e.NewValue.ToString();
}
// Example public property of control
public string LabelText
{
get { return label1.Content.ToString(); }
set { label1.Content = value; }
}
It doesn't, unless you call it manually. There's a property-changed handler you can add to the DependancyProperty constructor call to be notified of when the property changes.
Call this constructor:
http://msdn.microsoft.com/en-us/library/ms597502.aspx
With a PropertyMetadata instance created by this constructor:
http://msdn.microsoft.com/en-us/library/ms557327.aspx
EDIT: Also, you are not implementing the dependancy property correctly. Your get and set should use GetValue and SetValue respectively, and you should not have a class member to store the value. The member name of the DP should also be {PropertyName}Property, e.g. MyCustomPropertyProperty if the get/set and property name as registered is MyCustomProperty. See http://msdn.microsoft.com/en-us/library/ms753358.aspx for more information.
Hope that helps.
Maybe you are using MVVM, and overriding the DataContext of your View ?
If you do, then the event for changing MyCustomProperty will be raised on the original DataContext and not on the new ViewModel.
I have a highly customized Edit control which inherits RichTextBox. I needed a way to bind a Value to this control, so I registered a new DependencyProperty, but I have trouble to code it like I need.
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value", typeof(string), typeof(XliffRichCellEditor),
new PropertyMetadata(new PropertyChangedCallback(XliffRichCellEditor.OnValuePropertyChanged)));
public String Value
{
get { return (String)this.GetValue(ValueProperty); }
set { this.SetValue(ValueProperty, value); }
}
private static void OnValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
// Need to change Document in RichTextBox when Binding Source is changed
// But also ignore if the change comes from RichTextBox which is only updating
// the DependencyProperty. In this case Binding Source should be updated.
}
Please help.
use can use UpdateSourceTrigger=Explicit in your Binding statement and get the control of property updation in your hand.
Check this Thread