I have a WPF control that is supposed to be simple to (re)use. For that I have a custom type containing all the settings the control is supposed to represent and bind it over a DependencyProperty.
However, whenever I change one of the members in the control, the parent control gets the changes in the member (when evaluated through other means), but the PropertyChanged-Callback never gets triggered in the parent control.
public class Setting
{
public int Prop {get;set;}
//Other Properties, Constructor & Copy Constructor, etc.
public override bool Equals(object obj)
{
if (!(obj is Setting other)) return false;
return Prop == other.Prop;
}
}
public class SettingControl : UserControl, INotifyPropertyChanged
{
public static readonly DependencyProperty SettingProperty = DependencyProperty.Register
(nameof(Settings), typeof(Setting), typeof(SettingControl),
new PropertyMetadata(default(Setting), OnValuePropertyChanged));
public Setting Settings
{
get => (Setting)GetValue(SettingProperty);
set
{
SetValue(SettingProperty, value);
OnPropertyChanged(nameof(Settings));
}
}
public int Prop
{
get => ((Setting)GetValue(SettingProperty))?.Prop ?? 0;
set
{
//Does not work:
var temp = (Setting)GetValue(SettingProperty);
temp.Prop = value;
Settings = temp;
OnPropertyChanged(nameof(Prop));
//Does not work:
Settings.Prop = value;
OnPropertyChanged(nameof(Prop));
OnPropertyChanged(nameof(Settings));
//**Does work**, and triggers the OnSettingChanged in the parent control,
//but is simply not great memory usage
Settings = new Setting(Settings){ Prop = value };
OnPropertyChanged(nameof(Prop));
}
}
}
//Relevant snippet from parent Control ViewModel:
public static readonly DependencyProperty SettingProperty =
DependencyProperty.Register(nameof(Settings), typeof(Setting), typeof(ControlViewModel),
new PropertyMetadata(default(Setting), (d, e) => ((ControlViewModel)d).OnSettingChanged()));
//OnSettingChanged() is never called
public Setting Settings
{
get => (Setting)GetValue(SettingProperty);
set //Set is never called when the member properties are changed
{
SetValue(SettingProperty, value);
OnPropertyChanged(nameof(Settings));
}
}
//Relevant snippet from parent xaml:
<local:SettingControl Width="300"
Settings="{Binding Path=Settings, Mode=TwoWay}"/>
// UpdateSourceTrigger=PropertyChanged doesn't help here either
An obvious solution of course would be to either wrap the Setting class into a SettingViewModel, or implement it as a ViewModel itself (small testing didn't show results anyway). This however would make the usage of the control a lot harder, and to some degree break MVVM (more than this already). There are also some XML things in the Setting class for serialization that I don't want to mess with.
One thing I noticed is that if the Equals function in Setting is coded to always return true the two ways of setting the member property that normally don't work, suddenly work and trigger the desired behavior.
Thanks in Advance.
I have a property on my ViewModel that I need bound to a BindableProperty in my behaviour but I cant seem to get it to bind.
private int _test;
public int Test {
get {
return _test;
}
set {
if (SetProperty (ref _test, value)) {
_profileIsDirty = true;
NotifyPropertyChanged ("AllowUpdate");
}
}
}
Here is the property in the behaviour
public static readonly BindableProperty MinLengthProperty = BindableProperty.Create("MinLength", typeof(int), typeof(MinLengthValidator), 0);
public int MinLength
{
get { return (int)GetValue(MinLengthProperty); }
set { SetValue(MinLengthProperty, value); }
}
This is the property on the ViewModel and this is how I am trying to bind to it in XAML
<behave:TelephoneNumberValidatorBehaviour x:Name="phoneValidator" MinLength="{Binding Test, Mode=OneWay}"/>
But it never binds. Am I doing something wrong here?
Have you tried to change the value of your NotifyPropertyChanged to "Test" instead of "AllowUpdate"? Otherwise the UI is never notified that the value has changed of Test. Instead it raises that the value the AllowUpdate property has changed, which does not exist in your ViewModel.
The third parameter of BindableProperty.Create should be type of the class where the BindableProperty is defined. Based on your sample, I guess it should be typeof(TelephoneNumberValidatorBehaviour) and not typeof(MinLengthValidator)
I have this simple example in the ViewModel of a WPF application:
class VM_DiskPartition : DependencyObject
{
// (...) Other properties
public bool IsLowOnSpace
{
get { return (bool)GetValue(IsLowOnSpaceProperty); }
set { SetValue(IsLowOnSpaceProperty, value); }
}
public static readonly DependencyProperty IsLowOnSpaceProperty = DependencyProperty.Register("IsLowOnSpace", typeof(bool), typeof(VM_DiskPartition), new PropertyMetadata(false, OnLowOnSpaceChanged));
private static void OnLowOnSpaceChanged(DependencyObject d, DependencyPropertyChangedEventArgs args)
{
((VM_DiskPartition)d).CoerceValue(BgColorProperty);
}
public Brush BgColor
{
get { return (Brush)GetValue(BgColorProperty); }
set { SetValue(BgColorProperty, value); }
}
public static readonly DependencyProperty BgColorProperty = DependencyProperty.Register("BgColor", typeof(Brush), typeof(VM_DiskPartition), new PropertyMetadata(Brushes.Red, null, Coerce_BgColor));
private static object Coerce_BgColor(DependencyObject d, object baseValue)
{
return UIUtils.GetBgColor(((VM_DiskPartition)d).IsLowOnSpace);
}
}
I want the BgColor property to have its default value automatically set by its coercion function.
Is there a more elegant way to achieve this instead of calling CoerceValue(BgColorProperty) from the constructor?
The reason is that I may have many properties like this in the future and it doesn't look very clean to use a lot of CoerceValue() calls in the constructor.
Maybe it's better to use Converters in this scenario? I was trying to go without them and create new ViewModel properties instead.
You seem to be somewhat confused... the DependencyObject and DependencyProperty classes are UI classes. They don't belong in a view model. In view models, we use normal CLR properties and the INotifyPropertyChanged interface to handle property change notification. Therefore, there's no need to use them in a view model at all.
If you want to set a default value in a view model, you simply do this:
private int number = 5; // <-- default value
public int Number
{
get { return number; }
set { number = value; NotifyPropertyChanged("Number"); }
}
If you want property value coercion in a view model, you just do this:
public int Number
{
get { return number; }
set { number = Math.Max(0, value); NotifyPropertyChanged("Number"); }
}
UPDATE >>>
Looking again at your code, it occurs to me that it shouldn't be in a view model at all. It looks like it should be in the code behind of some UserControl. We put data in view models, not UI elements like Brushes. If you want to set a default value for a DependencyProperty, the correct way to do it is how you have shown us:
public static readonly DependencyProperty BgColorProperty =
DependencyProperty.Register("BgColor", typeof(Brush), typeof(VM_DiskPartition),
new PropertyMetadata(Brushes.Red/* <-- default value */, null, Coerce_BgColor));
Property coercion is for ensuring that a value stays within certain bounds like the example I gave above that ensures that the value will never be negative.
Consider this scenario, using MVVM:
On my ModelView, I have one property, of type "string", it does notify the change of properties through INotifyPropertyChanged.
In the view, there is (or not) one control, with a DependencyProperty "Notification" of a type which is not a string. That control may or may not change that property depending on facts that only the control knows (neither the ModelView or the View knows about those). That control might even be on other View which may or may not be on the current visual tree.
In the View, I need a bridge between that control's DependencyProperty and the ViewModel's property, so that changing the view property makes the control change its property, and changing the control's DependencyProperty makes the viewmodel's property change its value.
I've got it to work, but I don't think it's an elegant solution. I might be thinking fuzzy these days so I'm asking if there's something obvious that I might have missed.
The obvious way would be either having the ViewModel Property be a DependencyProperty (so it could be bound two ways), however that is not possible right now (plus, it'd break the MVVM pattern, adding view-specific implementations to the viewmodel).
The other obvious way would be binding the Control's DependencyProperty to the ViewModel's property: this works, but just for one view... several properties cannot (or, I don't know how to do it) be bound to the same DependencyProperty: when I set one binding, I lose the other.
Currently this is what I do:
public class BaseViewUserControl : UserControl
{
// Dependency property, bound to the view's property
public string AudioNotification
{
get { return (string)GetValue(AudioNotificationProperty); }
set { SetValue(AudioNotificationProperty, value); }
}
public static readonly DependencyProperty AudioNotificationProperty = DependencyProperty.Register("AudioNotification", typeof(string), typeof(BaseViewUserControl), new FrameworkPropertyMetadata("None", FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnAudioNotificationPropertyChanged));
// Dependency property, bound to the control's dependency property
public AudioNotificationType AudioNotificationToControl
{
get { return (AudioNotificationType)GetValue(AudioNotificationToControlProperty); }
set { SetValue(AudioNotificationToControlProperty, value); }
}
public static readonly DependencyProperty AudioNotificationToControlProperty = DependencyProperty.Register("AudioNotificationToControl", typeof(AudioNotificationType), typeof(BaseViewUserControl), new FrameworkPropertyMetadata(AudioNotificationType.None, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, null, OnAudioNotificationToControlCoerceValue));
// Converter
private static IValueConverter _audioNotificationTypeConverter;
private static IValueConverter AudioNotificationTypeConverter
{
get { return _audioNotificationTypeConverter ?? (_audioNotificationTypeConverter = new AudioNotificationConverter()); }
}
private Binding _audioNotificationBinding;
private bool PrepareAudioNotificationControlBinding()
{
if (_audioNotificationBinding != null) return true;
var b = this.FindVisualTreeRoot().TryFindChild<AudioNotification>();
if (b == null) return false;
_audioNotificationBinding = new Binding { Source = b, Mode = BindingMode.TwoWay, Path = new PropertyPath("Notification") };
SetBinding(AudioNotificationToControlProperty, _audioNotificationBinding);
return true;
}
private static void OnAudioNotificationPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
if (!(source is BaseViewUserControl)) return;
var src = (BaseViewUserControl)source;
if(src.PrepareAudioNotificationControlBinding())
{
var val = AudioNotificationTypeConverter.ConvertValue<AudioNotificationType>(e.NewValue);
src.AudioNotificationToControl = val;
}
}
private static object OnAudioNotificationToControlCoerceValue(DependencyObject source, object basevalue)
{
if (!(source is BaseViewUserControl)) return basevalue;
var src = (BaseViewUserControl)source;
var val = AudioNotificationTypeConverter.ConvertBackValue<string>(basevalue);
src.AudioNotification = val;
return basevalue;
}
public BaseViewUserControl()
{
var ab = new Binding { Path = new PropertyPath("AudibleNotification"), Mode = BindingMode.TwoWay };
SetBinding(AudibleNotificationProperty, ab);
}
}
NOTE: I'm using this for several things, not just for audio notification (that's an example only). Do not rely on the names to give a solution (if any), this needs to be quite generic. Also, any typos come from simplifying the code to the problem (I've removed much code and changed some property names for clarification).
As I said, it works... I just find it quite not-elegant and I'm sure there should be a better solution than this.
Any suggestions will be more than welcome.
Update
Based on Julien's code, I made this Behavior, which does exactly what I wanted. I implemented it using Converter, but for clarity's sake, I ended up doing the conversion on the control itself and using strings to pass variables along (with an undocumented property in the control's if I still want to use the native data type)
public class BridgePropertyBinderBehavior : Behavior<DependencyObject>
{
public static BridgePropertyBinderBehavior PrepareBindingToControl(FrameworkElement sourceView, string viewModelPropertyPath, FrameworkElement targetControl, string controlPropertyPath)
{
var b = new BridgePropertyBinderBehavior();
BindingOperations.SetBinding(b, AProperty, new Binding(viewModelPropertyPath) { Source = sourceView.DataContext, Mode = BindingMode.TwoWay, BindsDirectlyToSource = true, UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged });
BindingOperations.SetBinding(b, BProperty, new Binding(controlPropertyPath) { Source = targetControl, Mode = BindingMode.TwoWay });
Interaction.GetBehaviors(sourceView).Add(b);
return b;
}
public object A { get { return GetValue(AProperty); } set { SetValue(AProperty, value); } }
public static readonly DependencyProperty AProperty = DependencyProperty.Register("A", typeof(object), typeof(BridgePropertyBinderBehavior), new FrameworkPropertyMetadata(null, (d, e) => ((BridgePropertyBinderBehavior)d).OnAChanged(e.NewValue)));
public object B { get { return GetValue(BProperty); } set { SetValue(BProperty, value); } }
public static readonly DependencyProperty BProperty = DependencyProperty.Register("B", typeof(object), typeof(BridgePropertyBinderBehavior), new FrameworkPropertyMetadata(null, (d, e) => ((BridgePropertyBinderBehavior)d).OnBChanged(e.NewValue)));
private void OnAChanged(object value) { B = value; }
private void OnBChanged(object value) { A = value; }
protected override Freezable CreateInstanceCore()
{
return new BridgePropertyBinderBehavior();
}
}
Which I use like this on my view:
var audioNotificationControl = this.FindVisualTreeRoot().TryFindChild<AudioNotification>();
BridgePropertyBinderBehavior.PrepareBindingToControl(this, "AudioNotification", audioNotificationControl, "Notification");
or
<AudioNotification x:Name="Control">
<ia:Interaction.Behaviors>
<BridgePropertyBinderBehavior
A="{Binding Path=Notification, ElementName=Control, Mode=TwoWay}"
B="{Binding Path=AudioNotification, Mode=TwoWay}" />
</ia:Interaction.Behaviors>
</AudioNotification>
I've accepted his answer since it's what got me on the right track, thanks
If I understand you correctly, you need to bind one DP to two sources, one as a source and the other as a target. I actually have a behavior to do that.
The principle of this behavior is quite simple: it uses two dependency properties and makes the data of one (In) flows into the other (Out). Bind In with a one way binding and Out with a one way to source binding and you're done.
public class BindingBehavior : Behavior<DependencyObject> {
public static readonly DependencyProperty InProperty = DependencyProperty.Register(
"In",
typeof(object),
typeof(BindingBehavior),
new FrameworkPropertyMetadata(null, (d, e) => ((BindingBehavior) d).OnInPropertyChanged(e.NewValue)));
public static readonly DependencyProperty OutProperty = DependencyProperty.Register(
"Out",
typeof(object),
typeof(BindingBehavior),
new FrameworkPropertyMetadata(null));
// Bind OneWay
public object In {
get { return GetValue(InProperty); }
set { SetValue(InProperty, value); }
}
// Bind OneWayToSource
public object Out {
get { return GetValue(OutProperty); }
set { SetValue(OutProperty, value); }
}
private void OnInPropertyChanged(object value) {
Out = value;
}
protected override Freezable CreateInstanceCore() {
return new BindingBehavior();
}
}
This behavior needs a reference to System.Windows.Interactivity from Blend SDK, which you might be familiar with.
Assuming you remove your string property and only keep a AudioNotificationType one named AudtioNotification, the usage should be similar to:
<YourView x:Name="View">
<YourControl x:Name="Control" AudioNotification="{Binding Notification, ElementName=View}>
<i:Interaction.Behaviors>
<BindingBehavior
In="{Binding AudioNotification, ElementName=Control, Mode=OneWay}"
Out="{Binding YourVmProperty, Mode=OneWayToSource, Converter=YourConverter}" />
</i:Interaction.Behaviors>
</YourControl>
</YourView>
You can place the behavior on any element being on the correct name scope for resolving element names and having the view model as the data context.
This looks like it might be a useful time to add a layer of abstraction. I know. Ick. But bear with me.
What if you had a bridge object that an abitrary number of things can bind to that handles the notifications on change. It doesn't even need to be that complex. Just something that implements INotifyPropertyChanged and then has a property (or properties) that release a notification on change. That way, your ViewModel, your View and your control can all bind to the same property on this bridge object and when one of those changes the bridge object's property, all the others will know that it's time to change as well. As long as all the objects are bound two-way, everything should synch just fine.
That's essentially what you've done on your BaseViewUserControl, but encapsulating the behavior in a separate object might provide you flexibility benefits.
This is the part where is not working. My dependency property has a default value which is Entradas.Entero, and that value must be run this line:
Grid.SetColumnSpan(button0, 3);
And it should refresh it in my user control design, however there's no changes in it.
public partial class TableroUserControl : UserControl
{
public enum Entradas
{
Entero, Decimal
}
public Entradas Entrada
{
get { return (Entradas)GetValue(EntradaProperty); }
set { SetValue(EntradaProperty, value); }
}
static void textChangedCallBack(DependencyObject property, DependencyPropertyChangedEventArgs args)
{
Button button0 = ((TableroUserControl)property).button0;
switch ((Entradas)args.NewValue)
{
case Entradas.Entero:
Grid.SetColumnSpan(button0, 3);
break;
case Entradas.Decimal:
Grid.SetColumnSpan(button0, 2);
break;
}
}
public static readonly DependencyProperty EntradaProperty =
DependencyProperty.Register("Entrada", typeof(Entradas), typeof(TableroUserControl), new PropertyMetadata(Entradas.Entero, new PropertyChangedCallback(textChangedCallBack)));
public TableroUserControl()
{
InitializeComponent();
}
}
You might also consider doing this with a value converter. You should be able to bind the Grid.ColumnSpan attached property of button0 to the Entrada property of your user control. Then use a value converter to convert it to an integer. This way you don't have to deal with callbacks and state/timing issues.
Your dependency property is initialized to Entero. So unless the value is changed to Decimal and then again changed back to Entero you wont hit the property changed callback code.
Make sure that the colspan setter code is hit.