I'm using ObservableCollection<MyItemViewModel> myItemVMList as the ItemsSouce. I am able to bind Command perfectly but the INotifyPropertyChanged isn't working. Here's my code:
public class MyItemViewModel: INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name) {
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) {
handler(this, new PropertyChangedEventArgs(name));
}
}
public MyItem MyItem { set; get; }
private RelayCommand _ChangeMyItemPropertyValue;
public ICommand ChangeMyItemPropertyValueCommand {
get {
if (_ChangeMyItemPropertyValue == null) _ChangeMyItemPropertyValue = new RelayCommand(o => ChangeMyItemPropertyValue());
return _ChangeMyItemPropertyValue;
}
}
private ChangeMyItemPropertyValue() {
MyItem.SomeProperty = someDifferentValue;
// NEITHER OF THESE CALLS WORK
OnPropertyChanged("MyItem.SomeProperty");
OnPropertyChagned("SomeProperty");
}
}
Needless to say, the binding is set as Content="{Binding MyItem.SomeProperty}" inside the DataTemplate, and it shows the correct value. Problem is it isn't updated when I run the function.
SideNote: If I implement the INotifyPropertyChanged inside MyItem it works, but I want it on the ViewModel.
If I implement the INotifyPropertyChanged inside MyItem it works, but I want it on the ViewModel
Yes, because that's how it's designed. How it's supposed to know it should listen to your ViewModel's property changed event? It doesn't bind to it, it binds to the model, so it listens to the changes on the model.
You have two choices basically:
Implement INotifyPropertyChanged on MyItem
Bind to the ViewModel
Content="{Binding SomeProperty}"
And add a wrapper property:
public string SomeProperty
{
get { return MyItem.SomeProperty; }
set
{
MyItem.SomeProperty = value;
OnPropertyChanged("SomeProperty");
}
}
You should prefer binding to the ViewModel if you want to follow MVVM practices.
Side note: If you add [CallerMemberName] to OnPropertyChanged like this:
protected void OnPropertyChanged([CallerMemberName] string name = null) {
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(name));
}
You'll be able to skip the property name altogether:
public string SomeProperty
{
get { return MyItem.SomeProperty; }
set
{
MyItem.SomeProperty = value;
OnPropertyChanged(); // <-- no need for property name anymore
}
}
Related
I am using MVVM light in WPF. The Model class properties are constantly changed due to changes of the underlying data-access layer.
Model:
public class SBE_V1_Model : ViewModelBase
{
public SBE_V1_Model(String name)
{
Name = "MAIN." + name;
SetupClient();
}
private void SetupClient()
{
client = new ConnectionHelper(this);
client.Connect(Name);
}
public Boolean Output
{
get
{
return _Output;
}
set
{
if (value != this._Output)
{
Boolean oldValue = _Output;
_Output = value;
RaisePropertyChanged("Output", oldValue, value, true);
}
}
}
}
If Output property changes, then bindings will be notified, so this works. But what is the correct way to update the property from the data-access source, which knows the new value?
public class ConnectionHelper : ViewModelBase
{
public Boolean Connect(String name)
{
Name = name;
tcClient = new TcAdsClient();
try
{
dataStream = new AdsStream(4);
binReader = new AdsBinaryReader(dataStream);
tcClient.Connect(851);
SetupADSNotifications();
return true;
}
catch (Exception ee)
{
return false;
}
}
private void tcClient_OnNotification(object sender, AdsNotificationEventArgs e)
{
String prop;
notifications.TryGetValue(e.NotificationHandle, out prop);
switch (prop)
{
case "Output":
Boolean b = binReader.ReadBoolean();
RaisePropertyChanged("Output", false,b, true);
break;
}
}
}
Why doesnt the RaisePropertyChanged call in connectionhelper update the property of the model? If this is the wrong way, should I set up some kind of listener?
In your SBE_V1_Model class you should subscribe to receive PropertyChange notifications from the ConnectionHelper ViewModel.
// Attach EventHandler
ConnectionHelper.PropertyChanged += OnConnectionHelperPropertyChanged;
...
// When property gets changed, raise the PropertyChanged
// event of the ViewModel copy of the property
OnConnectionHelperPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "Something") //your ConnectionHelper property name
RaisePropertyChanged("Ouput");
}
Also look into MVVM light messenger. Here is a link you might be interested from StackOverflow.
You should only use PropertyChanged in the ViewModel, not in the Model.
You can use PropertyChanged in Models only in special times.
RaisePropertyChanged("Output", false,b, true);
In that PropertyChanged you are always saying that Output Property was changed.
I recommend you implement INotifyPropertyChanged
class MyClass : INotifyPropertyChanged
{
public bool MyProperty{ get; set; }
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
}
To notify any property change you have to use:
OnPropertyChanged("MyProperty");
I have the visibility of a progress bar bound to The following property within my viewmodel:
public string CalcProgVisibility
{
get
{
return Calculation.CalcProgVisibility;
}
set
{
}
}
Calculation is my model, which can change the value. When the value changes within the model, what do I need to do to make sure the view is aware of this change?
EDIT:
Here is the property within my model too. I am using onpropertychanged but its not making it to the view.
I am changing the value within the model, the view is bound to my viewmodel and the viewmodel si trying to return a value taken from the model. I am updating the value on the model, and cannot push the fact that it has updated the value all the way down to the view, I can only get the viewmodel to see it has changed...
I updated the entire code. I hope it's clear now.
Define your control BindingMode = TwoWay
<TextBox Visibility="{Binding Path=CalcProgVisibility, Mode=TwoWay}"...
and call the OnPropertyChanged method on the setter of the property in your view model and also in your model
//Model
public class Calculation : INotifyPropertyChanged
{
private string _calcProgVisibility;
public string CalcProgVisibility
{
get { return _calcProgVisibility; }
set
{
_calcProgVisibility = value;
OnPropertyChanged("CalcProgVisibility");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
RaisePropertyChanged(propertyName);
}
private void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler == null) return;
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
//ViewModel
public class ViewModel : INotifyPropertyChanged
{
public ViewModel(Calculation model)
{
this.CalcProgVisibility = model.CalcProgVisibility;
model.PropertyChanged += (s, e) => UpdateEntity(s as Calculation);
}
private void UpdateEntity(Calculation source)
{
CalcProgVisibility = source.CalcProgVisibility;
}
private string _calcProgVisibility;
public string CalcProgVisibility
{
get { return _calcProgVisibility; }
set
{
_calcProgVisibility = value;
OnPropertyChanged("CalcProgVisibility");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
RaisePropertyChanged(propertyName);
}
private void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler == null) return;
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
Your Viewmodel has to implement the INotifyPropertyChanged Interface. To fire it in your case your viewmodel must also be aware of changes in your model object. So your model object could also implement INotifyPropertyChanged, or you use some form of the observer pattern.
If your model implements INotifyPropertyChanged, your viewmodel must manually register for this event and implement an handler. This could in turn trigger the PropertyChange event of the viewmodel then.
Another but in my opinion ugly way would be to scan (per timer or background thread) through your viemodel and check if a value changed since the last scan and then trigger a property changed event.
The first solution could look like this:
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace StackOverflow
{
[TestClass]
public class IntegrationTest
{
[TestMethod]
public void NotifyPropertyChangeShouldFireOnViewModelWhenModelChanges()
{
//Arrange
Model model = new Model();
ViewModel sut = new ViewModel(model);
bool notifyPropertyChangeOnViewModelWasCalled = false;
sut.PropertyChanged += (sender, e) => { notifyPropertyChangeOnViewModelWasCalled = true; };
//Act
model.CalcValue = 4711;
//Assert
Assert.IsTrue(notifyPropertyChangeOnViewModelWasCalled, "NotifyPropertyChange was not fired on ViewModel");
}
}
public class ObjectWithNotifyPropertyChanged : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChanged([CallerMemberName]string propertyName = "")
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public class Model : ObjectWithNotifyPropertyChanged
{
private double calcValue;
public double CalcValue
{
get
{
return calcValue;
}
set
{
if (calcValue != value)
{
calcValue = value;
RaisePropertyChanged();
}
}
}
}
public class ViewModel : ObjectWithNotifyPropertyChanged
{
public ViewModel(Model model)
{
this.model = model;
model.PropertyChanged += model_PropertyChanged;
}
void model_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
switch (e.PropertyName)
{
case "CalcValue":
RaisePropertyChanged("CalcValue");
break;
}
}
private Model model;
public double CalcValue
{
get
{
return model.CalcValue;
}
}
}
}
I am relatively new to WPF and having a problem with data binding. I am binding a dependency property of a user control to a class property in my code behind. During intantiation of the class entity in my code behind the UI is sucessfully updated through INotifyPropertyChanged. However when subsequently changing the value in my code behind the OnPropertyChangedEventHandler fires, but the OnPropertyChanged method does no longer answer to this. Below the details. It would be great if someone could give me some hints what I am doing wrong.
I implemented a user control that I am binding to a property CurrentAccProp.DiscountRate of my partial class in code behind:
<local:doubleUEdit x:Name="InterestRate" LabelField="Interest rate" MinimumValue="0" MaximumValue="1" FormatStringForNumbers="P2" IncrementSize="0.01" UncertainValue="{Binding ElementName=RibbonWindow, Path=CurrentAccProp.DiscountRate, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
The class of which CurrentAccProp is an instance implements INotifyPropertyChanged to inform the UI about value changes
//Event to inform data grid about changes
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
OnPropertyChanged is called in the setter for the DiscountRate property:
doubleU discountingrate;
public doubleU DiscountRate
{
get {return discountingrate;}
set
{
discountingrate = value;
OnPropertyChanged("DiscountingRate");
}
}
The property of my user control that I am binding to is implemented as a dependency property:
//Property for data binding to doubleU
[Description("The formatstring for the double boxes"), Category("Default")]
public doubleU UncertainValue
{
get { return new doubleU(0, 0, (double)doubleUSupremum.Value, (double)doubleUSupremum.Value); }
set { doubleURangeSlider.LowerValue = value.Interval.Infimum; doubleURangeSlider.HigherValue = value.Interval.Supremum; doubleUInfimum.Value = value.Interval.Infimum; doubleUSupremum.Value = value.Interval.Supremum; }
}
public static readonly DependencyProperty UncertainValueProperty =
DependencyProperty.Register(
"UncertainValue",
typeof(doubleU),
typeof(doubleUEdit),
new PropertyMetadata(default(doubleU), OnItemsPropertyChanged));
private static void OnItemsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
doubleUEdit MydblUEdt = d as doubleUEdit;
MydblUEdt.UncertainValue = e.NewValue as doubleU;
}
When I am instantiating CurrentAccProp in my code behind the OnPropertyChanged informs the UI and the value is updated.
AccountingProperties currentaccprop = new AccountingProperties(new doubleU(0.0));
public AccountingProperties CurrentAccProp { get { return currentaccprop; } set { currentaccprop = value; } }
However, when I later update the value of DiscountRate
CurrentAccProp.DiscountRate = new doubleU(1.0);
OnPropertyChanged gets executed, but the UI is no longer updated. Does anyone have a clue what I am doing wrong here?
The typo pointed out by HighCore and zaknotzach was indeed the problem. Thanks for your help! I implemented the approach in the thread referenced by HighCore to avoid this and it works like a charm. Below the changed AccountingProperties class from which CurrentAccProp is instantiated for reference:
public class AccountingProperties : INotifyPropertyChanged
{
doubleU discountrate;
public doubleU DiscountRate
{
get {return discountrate;}
set { SetField(ref discountrate, value, () => DiscountRate); }
}
//------------------------------------------------
//constructors
public AccountingProperties(doubleU discountrate)
{
DiscountRate = discountrate;
}
//Event to inform data grid about changes
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
protected virtual void OnPropertyChanged<T>(Expression<Func<T>> selectorExpression)
{
if (selectorExpression == null)
throw new ArgumentNullException("selectorExpression");
MemberExpression body = selectorExpression.Body as MemberExpression;
if (body == null)
throw new ArgumentException("The body must be a member expression");
OnPropertyChanged(body.Member.Name);
}
protected bool SetField<T>(ref T field, T value, Expression<Func<T>> selectorExpression)
{
if (EqualityComparer<T>.Default.Equals(field, value)) return false;
field = value;
OnPropertyChanged(selectorExpression);
return true;
}
}
You need to first change the string in
OnPropertyChanged("DiscountingRate");
to "DiscountRate". The string you are giving your OnPropertyChanged function must match the property name. That is most likely the issue you are having.
As already answered, the problem is OnPropertyChanged("DiscountingRate"); providing the event with an incorrect property name.
In order to prevent errors like this, you can avoid using string literals all together. In your OnPropertyChanged parameter, use CallerMemberName. You can modify your OnPropertyChanged signature to
public void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
// Do your stuff
}
Then in your setters, you just call this.OnPropertyChanged();. The method will be given the property name that was changed.
public doubleU DiscountRate
{
get {return discountingrate;}
set
{
discountingrate = value;
OnPropertyChanged();
}
}
The benefit to this is that you can refactor your code and not worry about breaking your property changed events.
What is the best way to bind a property to a control so that when the property value is changed, the control's bound property changes with it.
So if I have a property FirstName which I want to bind to a textbox's txtFirstName text value. So if I change FirstName to value "Stack" then the property txtFirstName.Text also changes to value "Stack".
I know this may sound a stupid question but I'll appreciate the help.
You must implement INotifyPropertyChanged And add binding to textbox.
I will provide C# code snippet. Hope it helps
class Sample : INotifyPropertyChanged
{
private string firstName;
public string FirstName
{
get { return firstName; }
set
{
firstName = value;
InvokePropertyChanged(new PropertyChangedEventArgs("FirstName"));
}
}
#region Implementation of INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
public void InvokePropertyChanged(PropertyChangedEventArgs e)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, e);
}
#endregion
}
Usage :
Sample sourceObject = new Sample();
textbox.DataBindings.Add("Text",sourceObject,"FirstName");
sourceObject.FirstName = "Stack";
A simplified version of the accepted answer that does NOT require you to type names of properties manually in every property setter like OnPropertyChanged("some-property-name"). Instead you just call OnPropertyChanged() without parameters:
You need .NET 4.5 minimum.
CallerMemberName is in the System.Runtime.CompilerServices namespace
public class Sample : INotifyPropertyChanged
{
private string _propString;
private int _propInt;
//======================================
// Actual implementation
//======================================
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
//======================================
// END: actual implementation
//======================================
public string PropString
{
get { return _propString; }
set
{
// do not trigger change event if values are the same
if (Equals(value, _propString)) return;
_propString = value;
//===================
// Usage in the Source
//===================
OnPropertyChanged();
}
}
public int PropInt
{
get { return _propInt; }
set
{
// do not allow negative numbers, but always trigger a change event
_propInt = value < 0 ? 0 : value;
OnPropertyChanged();
}
}
}
Usage stays the same:
var source = new Sample();
textbox.DataBindings.Add("Text", source, "PropString");
source.PropString = "Some new string";
Hope this helps someone.
I have created WPF MVVM application, and set WPFToolkit DataGrid binding to DataTable so I want to know how to implement DataTable property to notify changed. Currently my code is like below.
public DataTable Test
{
get { return this.testTable; }
set
{
...
...
base.OnPropertyChanged("Test");
}
}
public void X()
{
this.Test.Add(...); // I suppose this line will call to getter first (this.Test = get Test) and then it will call add letter, this mean that setter scope will never fire.
base.OnPropertyChanged("Test"); // my solution is here :) but I hope it has better ways.
}
Is it has another solution for this problem?
There are 2 ways your Table data could change: Either an element could be added/removed from the collection, or some properties from within an element could change.
The first scenario is easy to handle: make your collection an ObservableCollection<T>. Invoking .Add(T item) or .Remove(item) on your table will fire a change notification through to the View for you (and the table will update accordingly)
The second scenario is where you need your T object to implement INotifyPropertyChanged...
Ultimately your code should look something like this:
public class MyViewModel
{
public ObservableCollection<MyObject> MyData { get; set; }
}
public class MyObject : INotifyPropertyChanged
{
public MyObject()
{
}
private string _status;
public string Status
{
get { return _status; }
set
{
if (_status != value)
{
_status = value;
RaisePropertyChanged("Status"); // Pass the name of the changed Property here
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
var e = new PropertyChangedEventArgs(propertyName);
handler(this, e);
}
}
}
Now set the datacontext of your View to be an instance of your ViewModel, and bind to the collection, like:
<tk:DataGrid
ItemsSource="{Binding Path=MyData}"
... />
Hope this helps :)
Ian