Develop Reference

Updating a secondary property from a DependencyProperty

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
}

Binding Command lost

I have a control (a) that needs to show / hide another control (b) in it
(a) Has:
1- A reference to (b)
2- A dependency property for (b) viewmodel
(b) Has a Dependency property for its viewmodel Named ViewModel.
Here is the code:
For (a)
If I create that way All mi binds works pretty well, my problem is if I have many instances of (a), each one works as b is the same instance for all of them because it is a static property.
public partial class a : UserControl
{
public a()
{
}
public bVM b
{
get { return (bVM)GetValue(bProperty); }
set { SetValue(bProperty, value); }
}
public static readonly DependencyProperty bProperty =
DependencyProperty.Register("b", typeof(bVM), typeof(a)), new PropertyMetadata(new bVM()));
}
now if I create a bVM instance into (a) constructor, all my binds work fine except for command bindings.
public partial class a : UserControl
{
public a()
{
b = new bVM();
}
public bVM b
{
get { return (bVM)GetValue(bProperty); }
set { SetValue(bProperty, value); }
}
public static readonly DependencyProperty bProperty =
DependencyProperty.Register("b", typeof(bVM), typeof(a));
}
And here is my bind for (b) at (a) xaml:
<local:b
x:Name="bName"
ViewModel="{Binding ElementName=ThisAControl,Path=b}"/>
And this is my bind for command lost
<Button Content="Test"
Command="{BindingElementName=ThisBControl,Path=ViewModel.ExitCommand }" />
Why my command binds are lost second way?
What I'm doing wrong?

I agree with #dymanoid comment, that normally you should not have a dependency property for VM. Aside of this strange implementation, technically the reason why binding is lost is because in constructor you are breaking it with:
b = new bVM();
To set value for a dependency property inside dependency object you should you SetCurrentValue method, that will not break any binding.
SetCurrentValue(a.bProperty, new bVM());
MSDN:
The SetCurrentValue method changes the effective value of the property, but existing triggers, data bindings, and styles will continue to work.

nested property propertychanged event only fired once in usercontrol in silverlight

There are two Viewmodels, both of them had implemented the INotifyPropertyChanged interface (I have called the OnpropertyChanged("propertyname") in my actual code).
Public Class A{
public B BProperty
{
get
{
return _BProperty;
}
set
{
if (_BProperty != null)
_BProperty.PropertyChanged -= _BProperty_PropertyChanged;
_BProperty = value;
OnPropertyChanged("BProperty");
if (_BProperty != null)
_BProperty.PropertyChanged += _BProperty_PropertyChanged;
}
}
void _BProperty_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
if (e.PropertyName == "status")
{
OnPropertyChanged("BProperty");
}
}
B _BProperty;
}
Public Class B
{
public int status{get;set;}
}
I also had a userControl:
<MyUserControl ...
... >
<Grid>
</Grid>
</MyUserControl>
And I had a dependencyProperty:
/// <summary>
/// File status
/// </summary>
public int Filestatus
{
get { return (int)GetValue(FilestatusProperty); }
set { SetValue(FilestatusProperty, value); }
}
public static readonly DependencyProperty FilestatusProperty =
DependencyProperty.Register(
"Filestatus",
typeof(int),
typeof(MyUserControl),
new PropertyMetadata(0, OnFilestatusPropertyChanged));
private static void OnFilestatusPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MyUserControl control = (MyUserControl)d;
if (e.NewValue != null)
{
}
}
edit:2015/09/21
Add the get/set methods:
public static readonly DependencyProperty FileStatusProperty = DependencyProperty.RegisterAttached(
"FileStatus", typeof(int), typeof(FileStatusIconControl), new PropertyMetadata(0, PropertyChangedCallback));
public static int GetFileStatus(DependencyObject source)
{
return (int)source.GetValue(FileStatusProperty);
}
public static void SetFileStatus(DependencyObject target, int value)
{
target.SetValue(FileStatusProperty, value);
}
private static void PropertyChangedCallback(
DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
FileStatusIconControl fsic = dependencyObject as FileStatusIconControl;
if(fsic != null)
wahahahahaha;
}
edit end
I used this userControl in my mainPage like this:
<mainPage ...
...>
<Grid>
<MyUserControl Filestatus={Binding Bproperty.status} />
<TextBox Text={Binding Bproperty.status} />
</Grid>
</mainPage>
The datacontext of mainPage is an instance of Class A.
My question is:
When status is changed, the text of textbox is changed, but the OnFilestatusPropertyChanged method only was called once when Usercontrol is loaded. Why?
Thanks.

I will start by saying that while I was looking into your question I ran into some problems with the code you have provided. I appreciate that somewhere you have some real code which has a problem and you cannot share this code with us so have tried to reproduce the problem in a smaller set of files.
However, if you do do this, please at least verify that the code you have provided runs and exhibits the problem. It is evident that you haven't tried to run your sample code (particularly the XAML) as there are problems with it:
attribute values should be surrounded in double-quotes,
the binding path Bproperty.status should be BProperty.status (first P capitalised).
All these things slow down someone trying to help you. Worse still, when I do find a problem with your code I can't be sure whether it's a genuine problem that your real code also has or whether it's something you introduced putting together your sample code. So all I can do is point out all the problems I find in the hope that one of them is the problem you have in your real code.
Firstly, your TextBox's Text property binding doesn't contain Mode=TwoWay. In WPF, this binding is TwoWay by default, but in Silverlight all bindings are OneWay by default. If you are familiar with WPF, this may be why you omitted Mode=TwoWay.
Secondly, I don't see why you have implemented class B as you have, apparently leaving it up to class A to fire property-changed events on its behalf. This approach doesn't work: when Silverlight updates the value in the status property of a B instance, it does so by calling the status setter of the B instance. Your B class has only an autogenerated property setter, which certainly doesn't fire the PropertyChanged event. Because this event wasn't fired, Silverlight doesn't know that is has some updates to do, and furthermore your A class isn't aware that it has changed either.
I would implement INotifyPropertyChanged in the usual way in class B, by calling OnPropertyChanged in the status setter. I would also remove the BProperty_PropertyChanged event handler in class A as I don't think it does you any favours.

"Bindable Method" with OneWayToSource mode

I need to write a custom control that looks like a TextBox and that contains a method called Refresh() which main purpose will be to clear the Text and to roll back few other values.
The method shall become bindable somehow so that others can bind a property from their ViewModel with it. Hence why I am thinking that inside my custom control I will need an dependency property of type Action.
So far so logical but next problem is the method/dp may no get overriden on control side once users sets a two way binding on it. Basically I always have to deliver the method wrapper as Action to ViewModel and inside ViewModel other users may call it.
How do I do all this? It seems to me that I have to somehow get the binding of the method work like OneWayToSource.
I apologize in case its a duplicate. Futhermore thanks in advance guys.
EDIT: Please no alternative solutions. Those are the requirements and I have to stick to them.

I think that the simplest thing you can do here is to expose a bool property, maybe called IsCleared, and just call your method from that property when it becomes true. Exposing ICommand and/or delegate objects transfers the functionality out of your control, so you can't use those.
#ninjahedgehog, why can't you use a bool 'switch' property? Your requirement says 'so that others can bind a property from their ViewModel with it'... they can bind to a bool property from their view model. In my opinion, it seems to be your only option. As I said earlier, you can't use ICommand and/or delegate objects as that would transfer the functionality out of your control - that would enable other developers to write their own functionality rather than to just call yours.
What you really want is a method on your control that they could call from their view model... but view models shouldn't have any knowledge about the view controls, so you can't do that. The next best thing to that is creating a method that is called when a property is given a certain value. Here you have a few choices.
If you really don't like the bool switch idea, then how about an enum property? Create an enum with specific values like ClearText and whatever other functionality you would like to expose. Then the other developers simply set this property to the relevant instance to instantiate that functionality... I only suggested the bool switch property because it seems as if you only want to expose one piece of functionality.
One last point to note about using the bool switch property... as it is a switch, you need to reset it after use, or just never actually set it:
public bool IsTextClear
{
get { if (value) ClearText(); }
}

I dont know why you need this coz the person who is using your control can directly call the method from the code behind. But if you want that there should be some property like ClearMe on control and when set to true it should clear the control then you can define the dependency property and listen to its change in control like below and call Refresh from there.
public static readonly DependencyProperty ClearMeProperty = DependencyProperty.Register
(
"ClearMe",
typeof(bool),
typeof(MyControl),
new FrameworkPropertyMetadata(false, OnClearMeChanged)
);
public bool ClearMe
{
get { return (bool)GetValue(ClearMeProperty); }
set { SetValue(ClearMeProperty, value); }
}
private static void OnClearMeChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var control = sender as MyControl;
if((bool)e.NewValue)
{
control.Refresh()
}
}
and you can bind this property to your ViewModel property. whenever ViewModel property will change to true. Property Change will be fired in control and will refersh it.

I editted my answer, as I wasn't understanding what you wanted. The only way I could come up with to do what you want was to use an Action DependencyProperty on the CustomControl and bind that to the ViewModel using a OneWayToSource binding, that way the Action from the control gets sent to the viewmodel. Within your customcontrol, you can test to make sure that only OneWayToSource binding is used and do something if not.. in this case, I add some text and made the background red.
View
<UserControl x:Class="WpfApplication1.Views.TestView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:WpfApplication1.ViewModels"
xmlns:controls="clr-namespace:WpfApplication1.Controls">
<UserControl.Resources>
<vm:TestViewModel x:Key="TestViewModel" />
</UserControl.Resources>
<StackPanel DataContext="{StaticResource TestViewModel}">
<StackPanel Orientation="Horizontal" Height="30">
<controls:CustomTextBox Width="300" Refresh="{Binding RefreshAction, Mode=OneWayToSource}" />
<Button Content="Refresh" Width="80" Command="{Binding RefreshFromView}" />
</StackPanel>
</StackPanel>
ViewModel
using System;
using System.ComponentModel;
namespace WpfApplication1.ViewModels
{
public class TestViewModel : INotifyPropertyChanged
{
public TestViewModel()
{
RefreshFromView = new RelayCommand(ExecuteRefreshFromView);
}
public Action RefreshAction { get; set; }
public RelayCommand RefreshFromView { get; set; }
private void ExecuteRefreshFromView(object parameter)
{
if (RefreshAction != null)
RefreshAction();
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyOfPropertyChange(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Custom Control
using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
namespace WpfApplication1.Controls
{
public class CustomTextBox : TextBox
{
public CustomTextBox()
{
this.Loaded += CustomTextBox_Loaded;
}
void CustomTextBox_Loaded(object sender, RoutedEventArgs e)
{
BindingExpression bindingExpression = GetBindingExpression(RefreshProperty);
BindingMode mode = bindingExpression.ParentBinding.Mode;
if (mode != BindingMode.OneWayToSource)
{
Text = "Use OneWayToSource Binding only!";
Background = new SolidColorBrush(Colors.Red);
}
Refresh = new Action(DoRefresh);
}
private void DoRefresh()
{
Text = null;
}
public Action Refresh
{
get { return (Action)GetValue(RefreshProperty); }
set { SetValue(RefreshProperty, value); }
}
public static readonly DependencyProperty RefreshProperty = DependencyProperty.Register("Refresh", typeof(Action), typeof(CustomTextBox));
}
}

You could use a Command:
public class Command : ICommand
{
public void Execute(object parameter)
{
// Do whatever you have to do
}
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
}
In your ViewModel:
public ICommand Command { get; set; }
In your XAML (assuming that your Custom Control is composed of a TextBox and a Button for example):
<Button Click="{Binding Command}" />

Variable Bindings in WPF

I’m creating a UserControl for a rich TreeView (one that has context menus for renaming nodes, adding child nodes, etc.). I want to be able to use this control to manage or navigate any hierarchical data structures I will create. I currently have it working for any data structure that implements the following interface (the interface need not actually be implemented, however, only the presence of these members is required):
interface ITreeItem
{
string Header { get; set; }
IEnumerable Children { get; }
}
Then in my UserControl, I use templates to bind my tree to the data structure, like so:
<TextBlock x:Name="HeaderTextBlock" Text="{Binding Path=Header}" />
What I would like to do is define the name of each of these members in my RichTreeView, allowing it to adapt to a range of different data structures, like so:
class MyItem
{
string Name { get; set; }
ObservableCollection<MyItem> Items;
}
<uc:RichTreeView ItemSource={Binding Source={StaticResource MyItemsProvider}}
HeaderProperty="Name" ChildrenProperty="Items" />
Is there any way to expose the Path of a binding inside a UserControl as a public property of that UserControl? Is there some other way to go about solving this problem?

Perhaps this might help:
Create a new Binding when you set the HeaderProperty property on the Header dependency property:
Header property is your normal everyday DependencyProperty:
public string Header
{
get { return (string)GetValue(HeaderProperty); }
set { SetValue(HeaderProperty, value); }
}
public static readonly DependencyProperty HeaderProperty =
DependencyProperty.Register("Header", typeof(string), typeof(ownerclass));
and the property of your HeaderProperty works as follows:
public static readonly DependencyProperty HeaderPropertyProperty =
DependencyProperty.Register("HeaderProperty", typeof(string), typeof(ownerclass), new PropertyMetadata(OnHeaderPropertyChanged));
public string HeaderProperty
{
get { return (string)GetValue(HeaderPropertyProperty); }
set { SetValue(HeaderPropertyProperty, value); }
}
public static void OnHeaderPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
if (args.NewValue != null)
{
ownerclass c = (ownerclass) obj;
Binding b = new Binding();
b.Path = new PropertyPath(args.NewValue.ToString());
c.SetBinding(ownerclass.HeaderProperty, b);
}
}
HeaderProperty is your normal everyday DependencyProperty, with a method that is invoked as soon as the HeaderProperty changes. So when it changes , it creates a binding on the Header which will bind to the path you set in the HeaderProperty. :)