I don't know if this is possible or not, but here is the code to explain the question in the title:
public class LogicClass : INotifyPropertyChanged
{
private String _myText;
public String MyText
{
get{return _myText;}
set
{
_myText = value;
PropertyChanged(this, new PropertyChangedEventArgs("MyText"));
}
}
...
}
public partial class Window1: Window, INotifyPropertyChanged
{
private LogicClass _logic;
public String LogicText
{
get{return _logic.MyText;}
}
...
}
<ContentControl Name="contentControl1" >
<Binding ElementName="MainWindow" Path="LogicText"/>
</ContentControl>
Is there any way to make this work, without having to expose my LogicClass variable and make use of its implementation of INotifyPropertyChanged. I guess I want to know if this can bubble up, or anything other than having to have a redundant set in my UI code-behind (which is how I am doing this now)
Yes, you need to either handle the PropertyChanged event from _logic and then raise an equivalent PropertyChanged notification on LogicText, or you need to add a standard event on MyText, so you would have a MyTextChanged event, handle this and then raise the PropertyChanged for LogicText.
So if LogicClass if never bound to directly in the Xaml, you wouldn't need to implement INotifyPropertyChanged on LogicClass and you would do (something like) this:
public class LogicClass
{
private String _myText;
public event EventHandler MyTextChanged;
public String MyText
{
get{return _myText;}
set
{
_myText = value;
var handler = MyTextChanged;
if(handler != null){ MyTextChanged(this, EventArgs.Empty); }
}
}
...
}
public partial class Window1: Window, INotifyPropertyChanged
{
private LogicClass _logic;
public Window1()
{
_logic = ... initialised;
_logic.MyTextChanged += (s,e) => RaisePropertyChanged("LogicText");
}
public String LogicText
{
get{return _logic.MyText;}
}
...
}
If what you're asking is if you can essentially say "this property represents another property on another class, so you need to look and see if it changes" in some declarative fashion, then no, that's not possible. You can, however, mimic this behavior yourself. Just attach to the PropertyChanged event on your logic class and when the MyText property changes, raise the window's PropertyChanged event by calling OnPropertyChanged.
Note that this is almost certainly better suited to something that goes in your ViewModel, not something in the codebehind on the window.
Related
I am trying to create simple imitation of MVVM using Winforms.
I have alreadt created binding from ViewModel to Form as below:
public class FirstViewModel : ViewModel
{
private string _name;
[Bind(nameof(TextBox.Text), "ExampleTextBox", typeof(ExampleConverter))]
public string Name
{
get => _name;
set
{
_name = value;
RaisePropertyChanged();
}
}
public FirstViewModel()
{
Test();
}
private async void Test()
{
await Task.Delay(TimeSpan.FromSeconds(1));
Name = "Binding working...";
}
}
In above example inside ViewModel class I am calling related Form then find control with given name and set the value.
I am wondering how could I do this as 'generic' as there with return value back to property.
The solution could be to listen TextChanged event for given "ExampleTextBox" but this is not best solution since I would have to know that Text property is realted with OnTextChanged event in this control.
Maybe it is possible to listen for Text property changed and does not matter which one eventhandler will raise that, or maybe I'm going to wrong direction? Did somone faced with that?
Thanks in advance.
The way I've done it in WinForms is by adding the data bindings inside the form itself:
textBox1.DataBindings.Add("Text", _viewModel, "PropertyName");
There are several techniques you can use in order to avoid magic strings.
I would also implement the interface INotifyPropertyChanged in the model:
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
I'm sure this is a very basic question but I don't even know the technical term / jargon to Google and self-educate on.
I have created a simple model implementing INotifyPropertyChanged.
public class PushNotes : INotifyPropertyChanged
{
public string CompletePushNotes { get; set; }
}
Binding in cs:
evt_pushNotes = new PushNotes()
{
CompletePushNotes = "HelloThere"
};
this.DataContext = evt_pushNotes;
//snip later in code
Helpers.UpdateCompletePushNotes();
In XAML:
<xctk:RichTextBox x:Name="PushEmail" Text="{Binding Path=CompletePushNotes, Mode=OneWay}" ScrollViewer.VerticalScrollBarVisibility="Auto" Margin="40,398,40,40">
<xctk:RichTextBox.TextFormatter>
<xctk:PlainTextFormatter />
</xctk:RichTextBox.TextFormatter>
</xctk:RichTextBox>
Helper:
internal static class Helpers
{
internal static void UpdateCompletePushNotes()
{
//duhhhh what do I do now??
//If I create a new PushNotes it will be a different instantiation....???
}
}
Now this is all fine but I have a method in a helper class that needs to change the CompletePushNotes.
Again I know this is a simplistic / newbie question but I don't know what I need to learn.
So do I make my PushNotes class static, or singleton. Is there some global binding "tree" I can walk to find my instantiated and bound PushNotes class that is attached to the UI element?
Not looking for an a handout just need to know what it is I'm looking for.
TIA
Your PushNotes class does not implement the INotifyPropertyChanged interface. Once you have implemented it, you need to modify your CompletePushNotes property to have a backing field and in the setter of the property you can raise the PropertyChanged event to notify the UI of the source property update.
public class PushNotes : INotifyPropertyChanged
{
string completePushNotes;
public string CompletePushNotes
{
get
{
return completePushNotes;
}
set
{
completePushNotes = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
Making the PushNotes class static will not help you. You seem to have a variable of some sort to the PushNotes instance (evt_pushNotes), so just do:
evt_pushNotes.CompletePushNotes = something;
If you have a helper class that does something, call the method in the helper class and get the value back or pass the PushNotes instance into the helper class as a parameter.
internal static class Helpers
{
internal static void UpdateCompletePushNotes(PushNotes pushNotes)
{
pushNotes.CompletePushNotes = something;
}
}
I know that the proper course of action is to create a class, make an event in said class, then use said class in another part of the program where the variable would be changed (e.g. Use said class in the equal button of a calculator, so that an event handler knows that a variable has been changed because an event would be fired). But, trying to streamline my code, I'm looking for a way to monitor a variable directly without an infinite loop/timer and raise an event when it changes. Is there such a thing? If not, are there any other alternatives aside for the one I mentioned?
Here is what I'm trying to mention:
Code that changes a variable -> Another piece of code (not a loop) watching for changes then throws an event if there are changes -> Event handler
You can't do it with fields but with properties:
class SomeClass : INotifyPropertyChanged
{
private string someProperty;
public string SomeProperty
{
get { return someProperty; }
set { someProperty = value; OnPropertyChanged(); }
}
private void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged = delegate {};
}
Edit (.net 4.0)
class SomeClass : INotifyPropertyChanged
{
private string someProperty;
public string SomeProperty
{
get { return someProperty; }
set { someProperty = value; OnPropertyChanged("SomeProperty"); }
}
private void OnPropertyChanged(string propertyName)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged = delegate {};
}
Edit (Winforms example)
public partial class Form1 : Form
{
private SomeClass theObject = new SomeClass(); //keep a reference of the object.
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//here we do the binding... we want the 'Text' Property of the control to change if the 'SomeProperty' changes OnPropertyChanged
textBox1.DataBindings.Add("Text",theObject,"SomeProperty",false,DataSourceUpdateMode.OnPropertyChanged);
}
private void button1_Click(object sender, EventArgs e)
{
theObject.SomeProperty = "This works!"; //just a test button that changes the property...
}
}
Though I know that it is an often undesired practice here at Stack Overflow, you may find my project NMF Expressions interesting: http://nmfexpressions.codeplex.com/
Basically, the project aims to allow you to write such as follows:
var myObservedVariable = Observable.Expression(() => whatever you want)
In this scenario, myObservedVariable will be of INotifyValue<T> which provides a ValueChanged event. Alternatively, you can use the query syntax. Alternatively, you may have a look at other similar frameworks like Obtics, BindableLINQ or ContinuousLINQ. A comparison of the latter was done in Bindable Linq vs. Continuous Linq.
However, this only works under pretty strong assumptions like all the object models that you are working with completely support INotifyPropertyChanged and INotifyCollectionChanged.
In addition to #Florian's answer, you can inject an implementation of the INotifyPropertyChanged interface at compile time using Fody.PropertyChanged.
I have a simple class with a string property and a List property and I have the INofityPropertyChanged event implemented, but when I do an .Add to the string List this event is not hit so my Converter to display in the ListView is not hit. I am guessing the property changed is not hit for an Add to the List....how can I implement this in a way to get that property changed event hit???
Do I need to use some other type of collection?!
Thanks for any help!
namespace SVNQuickOpen.Configuration
{
public class DatabaseRecord : INotifyPropertyChanged
{
public DatabaseRecord()
{
IncludeFolders = new List<string>();
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
protected void Notify(string propName)
{
if (this.PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
#endregion
private string _name;
public string Name
{
get { return _name; }
set
{
this._name = value;
Notify("Name");
}
}
private List<string> _includeFolders;
public List<string> IncludeFolders
{
get { return _includeFolders; }
set
{
this._includeFolders = value;
Notify("IncludeFolders");
}
}
}
}
You should use ObservableCollection<string> instead of List<string>, because unlike List, ObservableCollection will notify dependents when its contents are changed.
And in your case I'd make _includeFolders readonly - you can always work with one instance of the collection.
public class DatabaseRecord : INotifyPropertyChanged
{
private readonly ObservableCollection<string> _includeFolders;
public ObservableCollection<string> IncludeFolders
{
get { return _includeFolders; }
}
public DatabaseRecord()
{
_includeFolders = new ObservableCollection<string>();
_includeFolders.CollectionChanged += IncludeFolders_CollectionChanged;
}
private void IncludeFolders_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
Notify("IncludeFolders");
}
...
}
The easiest way to make WPF's list binding work is to use a collection that implements INotifyCollectionChanged. A simple thing to do here is to replace or adapt your list with an ObservableCollection.
If you use ObservableCollection, then whenever you modify the list, it will raise the CollectionChanged event - an event that will tell the WPF binding to update. Note that if you swap out the actual collection object, you will want to raise the propertychanged event for the actual collection property.
Your List is not going to fire the NotifyPropertyChanged event automatically for you.
WPF controls that expose an ItemsSource property are designed to be bound to an ObservableCollection<T>, which will update automatically when items are added or removed.
You should have a look at ObservableCollection
In my mvvm ViewModel I have such field
public int Delta { get; private set; }
However when I update it like that:
Delta = newValue;
UI is not refreshed.
I was thinking that databinding will do that for me. For example I can declare collection as ObservableCollection and then databinding will work.
However there are no ObservableInt, how to say View that it need to be refreshed then?
Probably I should raise some event "notify property changed" or something?
You have two choices:
Implement the INotifyPropertyChanged interface on your class.
Inherit from DependencyObject and implement Delta as a DependencyProperty.
The simplest option is #1. You can implement the INotifyPropertyChanged interface on your class quite easily:
public class YourClass : INotifyPropertyChanged
{
private int _delta;
public int Delta
{
get { return _delta; }
set { _delta = value; PropertyChanged?.Invoke(nameof(Delta)); }
}
public event PropertyChangedEventHandler PropertyChanged;
}
You can read more about using and implementing dependency properties on MSDN.
While we're at it with improving the answer, some of the other new additions of c# 6.0 and 7.0 help make it ever more compact:
public class Prop<T> : INotifyPropertyChanged
{
private T _value;
public T Value
{
get => _value;
set { _value = value; NotifyPropertyChanged(nameof(Value)); }
}
public event PropertyChangedEventHandler PropertyChanged;
internal void NotifyPropertyChanged(string propertyName) =>
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
This way, you aren't using any "embedded values" (i.e - the property's name) and are keeping the code refactor-safe.
And there's also no need for redundant code blocks due to c# 6.0 and 7.0's new Expression body features
Using #LBushKin's Answer, i modified it to
public class Prop<T> : INotifyPropertyChanged
{
private T _value;
public T Value
{
get { return _value; }
set { _value = value; NotifyPropertyChanged("Value"); }
}
public event PropertyChangedEventHandler PropertyChanged;
internal void NotifyPropertyChanged(String propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
and to set it up:
class MainWindow ...
// a bool with initial value of true
public static Prop<bool> optionBool { get; set; } = new Prop<bool>{ Value = true };
private void Window_Loaded(object sender, RoutedEventArgs e)
{
// connect UI to be able to use the Prop
DataContext = this;
}
and to use it:
<Grid ...
<CheckBox Content="Da Check" ... IsChecked="{Binding optionBool.Value}"/>
There is also a Collection and 2-Properties version here:
Utils.ObservableProperties.cs (this repo contains several related classes)
Just implement INotifyPropertyChanged Interface in your class and use it to raise a PropertyChanged for your Property and then UI will update. If you are using an MVVM project template then there is a good chance you already have a helper method implemented you only need to use it.
MSDN INotifyPropertyChanged
GalaSoft MVVM Light Toolkit
The ObservableCollection raises events automatically but for your own properties you have to raise the events yourself.
A good example is here: http://www.codeproject.com/Tips/228352/Naming-Properties-in-MVVM?display=Print
I'd suggest using mvvm light: http://mvvmlight.codeplex.com, I used it in silverlight and wpf applications. Very easy to use and provides a messageing system between model, view model and view.
Adding on to https://stackoverflow.com/a/8316100/5725669, there is a new and easy way to do this without remembering to keep track of PropertyChanged?.Invoke(nameof(Delta)); in every location
public class YourClass : INotifyPropertyChanged
{
private int _delta;
public int Delta
{
get { return _delta; }
set {
_delta = value;
// Call OnPropertyChanged whenever the property is updated
OnPropertyChanged();
}
}
// Declare the event
public event PropertyChangedEventHandler PropertyChanged;
public YourClass()
{
}
// Create the OnPropertyChanged method to raise the event
// The calling member's name will be used as the parameter.
protected void OnPropertyChanged([CallerMemberName] string name = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
}
It makes use of CallerMemberName for skipping manual entries for property name. More details on this MSDN Doc