Is there a simpeler way to bind many properties?
So if you have a Person class with properties: lastname, firstname, birthday, gender, title, ...
Now I do this for every property on the ViewModel:
public string _LastName;
public string LastName
{
get { return _LastName; }
set { _LastName = value;
RaisePropertyChanged("LastName"); }
}
And on the XAML page this binding:
<TextBlock Text="{Binding FirstName}" />
Now image if Person object has like 20 properties..
So my question is can I do this in a simpeler way?
You only need to raise the PropertyChanged event from the setter of a data-bound property if you actually intend to update the property dynamically at runtime. Otherwise you could use auto-implemented properties without any custom logic:
public FirstName { get; set; }
There is also a NuGet package called Fody that can turn simple public properties into full INotifyPropertyChanged implementations for you automatically: https://github.com/Fody/PropertyChanged
If you use a third party MVVM framework, it also might have a code snippet to create property with INotifyPropertyChanged.
If you use Catel, you can download templates and snippets here:
http://catelproject.com/downloads/general-files/
And here's implementation for Caliburn.Micro:
https://github.com/winterdouglas/propc
The simplest solution is to use the POCO mechanism provided by a free DevExpress MVVM Framework.
POCO will automatically implement INotifyPropertyChanged and raise the PropertyChanged event for all public virtual properties in your view model.
All magic happens when you use the ViewModelSource class to create your view model. You can create your view model in XAML:
<UserControl ...
DataContext="{dxmvvm:ViewModelSource Type=local:MyViewModel}">
Or in code-behind:
this.DataContext = ViewModelSource.Create(() => new MyViewModel());
PREMISE
In a default MVVM scenario, your ViewModel don't have to raise notifications on every property.
Typical case: you get some Person from a database, show them on a View, modify them via TextBoxes and other controls, and click "Save" re-sending them to the database. You can do this by setting the DataContext on the View every time you call the database. This action raises a first update on the bound properties of the control and of every sub-control, so all the getters of the ViewModel's bound properties are called one time and the View get populated with the ViewModel's values. When you modify something on the View, that binding carries the modification to the corresponding ViewModel's property (even a simple plain get-set property).
In this case, you're just fine with something like:
public class Person
{
public string Name { get; set; }
public string Surname { get; set; }
//and so on...
}
You need to raise notifications for the ViewModel's properties only if the View must listen to some property's change. For example, this feature: the Button "Save" is enabled if and only if the Name on the Person is not empty. Here, clearly the Button must be able to see when the Name property changes, so that property setter must raise the PropertyChanged event.
A possible implementation:
Use this as base class for ViewModels:
protected abstract BaseViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
protected void SetAndNotifyIfChanged<T>(
ref T field, T value, [CallerMemberName] string propertyName = null)
{
if (!EqualityComparer<T>.Default.Equals(field, value))
{
field = value;
NotifyPropertyChanged(propertyName);
}
}
}
In a derived class you can write every get-set property like this:
class MyViewModel : BaseViewModel
{
public string MyProp
{
get { return _MyProp; }
set { SetAndNotifyIfChanged(ref _MyProp, value); }
}
private string _MyProp;
}
The type T and the parameter propertyName are automatically inferred.
This is the shortest piece of code you could write, and is not so different from a normal full-property:
public string NormalProp
{
get { return _ NormalProp; }
set { _NormalProp = value; }
}
private string _MyProp;
If you don't want to write all this code every time, use a code snippet.
Related
Can someone explain me why need to use implementation of INotifyPropertyChanged when using binding in wpf?
I can bind properties without implementation of this interface?
For example i have code
public class StudentData : INotifyPropertyChanged
{
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
string _firstName = null;
public string StudentFirstName
{
get
{
return _firstName;
}
set
{
_firstName = value;
OnPropertyChanged("StudentFirstName");
}
}
}
And binding in .xaml
<TextBox Text="{Binding Path=StudentFirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Grid.Row="1"
Grid.Column="2"
VerticalAlignment="Center" />
this code from .xaml.cs
StudentData _studentData = new StudentData { StudentFirstName = "John", StudentGradePointAverage = 3.5};
public MainWindow()
{
InitializeComponent();
this.DataContext = _studentData;
}
why we need to use INotifyPropertyChanged in this case?
It is not my code.
You need INotifyPropertyChanged if you want a wpf form to be automatically updated when a property changes through code. Also some controllers might want to know if edits have been made in order to enable/disable a save-button, for instance. You also might be displaying the same property on different views; in this case INotifyPropertyChanged helps to immediately update the other view when you edit a property.
If you think that your form behaves well without INotifyPropertyChanged, then you can drop it.
Note that binding works even without INotifyPropertyChanged. See: Why does the binding update without implementing INotifyPropertyChanged?
I would implement the properties like this. In some rare cases it can help to avoid endless circular updates. And it is more efficient by the way.
private string _firstName;
public string StudentFirstName
{
get { return _firstName; }
set
{
if (value != _firstName) {
_firstName = value;
OnPropertyChanged("StudentFirstName");
}
}
}
Starting with C#6.0 (VS 2015), you can implement OnPropertyChanged like this:
private void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
When you bind to a property of StudentData such as the StudentFirstName then the binding class tests to see if the StudentData instance provides the INotifyPropertyChanged interface. If so then it will hook into the PropertyChanged event. When the event fires and it fires because of the StudentFirstName property then it knows it needs to recover the source value again because it has changed. This is how the binding is able to monitor changes in the source and reflect them in the user interface.
If you do not provide the INotifyPropertyChanged interface then the binding has no idea when the source value changes. In which case the user interface will not update when the property is changed. You will only see the initial value that was defined when the binding was first used.
It does need to be implemented in order for binding to work but that doesn't mean you always have to do it yourself. There are other options like Castle Dynamic Proxy (which wraps your classes in a proxy and injects INPC into all virtual properties) and Fody (which adds it to the IL in a post-processing step). It's also possible to implement yourself while at the same time reducing code bloat, as demonstrated in my answer to this question.
Can someone explain me why need to use implementation of INotifyPropertyChanged when using binding in wpf?
I can bind properties without implementation of this interface?
For example i have code
public class StudentData : INotifyPropertyChanged
{
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
string _firstName = null;
public string StudentFirstName
{
get
{
return _firstName;
}
set
{
_firstName = value;
OnPropertyChanged("StudentFirstName");
}
}
}
And binding in .xaml
<TextBox Text="{Binding Path=StudentFirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Grid.Row="1"
Grid.Column="2"
VerticalAlignment="Center" />
this code from .xaml.cs
StudentData _studentData = new StudentData { StudentFirstName = "John", StudentGradePointAverage = 3.5};
public MainWindow()
{
InitializeComponent();
this.DataContext = _studentData;
}
why we need to use INotifyPropertyChanged in this case?
It is not my code.
You need INotifyPropertyChanged if you want a wpf form to be automatically updated when a property changes through code. Also some controllers might want to know if edits have been made in order to enable/disable a save-button, for instance. You also might be displaying the same property on different views; in this case INotifyPropertyChanged helps to immediately update the other view when you edit a property.
If you think that your form behaves well without INotifyPropertyChanged, then you can drop it.
Note that binding works even without INotifyPropertyChanged. See: Why does the binding update without implementing INotifyPropertyChanged?
I would implement the properties like this. In some rare cases it can help to avoid endless circular updates. And it is more efficient by the way.
private string _firstName;
public string StudentFirstName
{
get { return _firstName; }
set
{
if (value != _firstName) {
_firstName = value;
OnPropertyChanged("StudentFirstName");
}
}
}
Starting with C#6.0 (VS 2015), you can implement OnPropertyChanged like this:
private void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
When you bind to a property of StudentData such as the StudentFirstName then the binding class tests to see if the StudentData instance provides the INotifyPropertyChanged interface. If so then it will hook into the PropertyChanged event. When the event fires and it fires because of the StudentFirstName property then it knows it needs to recover the source value again because it has changed. This is how the binding is able to monitor changes in the source and reflect them in the user interface.
If you do not provide the INotifyPropertyChanged interface then the binding has no idea when the source value changes. In which case the user interface will not update when the property is changed. You will only see the initial value that was defined when the binding was first used.
It does need to be implemented in order for binding to work but that doesn't mean you always have to do it yourself. There are other options like Castle Dynamic Proxy (which wraps your classes in a proxy and injects INPC into all virtual properties) and Fody (which adds it to the IL in a post-processing step). It's also possible to implement yourself while at the same time reducing code bloat, as demonstrated in my answer to this question.
I have a view that has a group of images I get from a web service
I receive them in a list of this class:
public class ImageModel
{
public int Id { get; set; }
public string Name { get; set; }
public string imageUrl { get; set; }
}
under each image I show an up-vote button, so I added another bool property to the model above:
public bool UpVoted { get; set; }
the ListView that shows these images is bound to an ObservableCollection<ImageModel > , I want to change the voting icon through a converter that convert the value of UpVoted to the corresponding icon, when the user click the voting icon: a command execute this method:
private void OnVoting(ImageModel image)
{
Images.Single(x => x.id == image.id).UpVoted = !image.UpVoted;
}
the problem is that the UI is not updated, and to make sure that I understood the problem I turned the model to a View model and made the required changes to the UpVoted property (I'm using MVVM light library)
bool upVoted;
public bool UpVoted
{
get { return upVoted; }
set
{
Set(ref upVoted, value);
}
}
and it works now,
so I need to bind the UpVoted to the UI, so it's updated whenever it changed
first
your model class must inherit from MvxNotifyPropertyChanged
public class ImageModel : MvxNotifyPropertyChanged
{
public int Id { get; set; }
public string Name { get; set; }
private bool upVoted ;
public bool UpVoted
{
get { return upVoted ; }
set { upVoted = value; RaisePropertyChanged(() => UpVoted ); }
}
}
then with MvxValueConverter you ready to go
Mustafa's answer mentions a class that is specific to MvvmCross library.
Another alternative is TinyMvvm.
If you wish to write your own MVVM (or understand how MVVM works),
the general pattern is to implement INotifyPropertyChanged: Implement Property Change Notification, which I discuss here.
A convenient way to implement INotifyPropertyChanged, is to make a base class that does that implementation, then inherit from that base class. You can use the code in that sample as your base class. Or use a slightly different implementation, that avoids having to manually pass the property name as a string:
using System.ComponentModel;
using System.Runtime.CompilerServices;
// Use this as base class for all your "view model" classes.
// And possibly for your (domain) model classes.
// E.g.: "public class MyLoginViewModel : HasNotifyPropertyChanged".
// OR "public class MyLoginModel : HasNotifyPropertyChanged".
// Give it whatever name you want, for ViewModels I suggest "ViewModelBase".
public class HasNotifyPropertyChanged : INotifyPropertyChanged
{
// --- This is pattern to use to implement each property. ---
// This works for any property type: int, Color, etc.
// What's different from a standard c# property, is the "SetProperty" call.
// You will often write an IValueConverter (elsewhere) to use in XAML to convert from string to your property type,
// or from your property type to a type needed in your UI.
// Comment out this example property if you don't need it.
/// <summary>
/// Set to "true" at end of your initialization.
/// Then can use Property Trigger on Ready value=true in XAML to do something when your instance is ready for use.
/// For example, load something from web, then trigger to update UI.
/// </summary>
private bool _ready;
public bool Ready
{
get => _ready;
set => SetProperty(ref _ready, value);
}
public event PropertyChangedEventHandler PropertyChanged;
protected void SetProperty<T>(ref T property, T value, [CallerMemberName] string propertyName = null)
{
if (property == null || !property.Equals(value))
{
property = value;
RaisePropertyChanged(propertyName);
}
}
protected void RaisePropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Again, an alternative to the above code is to use an existing MVVM library.
For another alternative, that doesn't require writing "SetProperty(..)" or "OnPropertyChanged(..)" in all of your property setters, google for info about using Fody/PropertyChanged. Then you wouldn't need any of the above code; your class would simply inherit from INotifyPropertyChanged. (And in app startup, you call a method that "injects" the needed logic into all properties of all INotifyPropertyChanged classes.)
Acknowledgement: The code pattern in example above is based on one of the open source libraries. It might be from TinyMvvm.
you do not say which sort of container that you are using but not all controls are set to support two way notification by default. so you may have to add a
Mode=TwoWay
to get notifications from the back end that data has changed. Or as the previous answer by Mustafa indicated you may need to verify that your class is implementing the InotifyPropertyChanged event with mvvm light.
I have a problem with two way binding a TextBox content to a property in another class. Searching stackoverflow gave a lot of tips/solutions but none seem to work.
In my XAML code I have:
< TextBox ... Width="336" IsReadOnly="True"
Text="{Binding Path=AssignedClearProgram, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
(... I removed all non important items)
In the accompanies cs code I have:
public CombiWindow(Combi combi)
{
ViewModel = new CombiViewModel(combi);
DataContext = ViewModel;
}
In the CombiViewModel:
[UsedImplicitly]
public string AssignedClearProgram { get; set; }
It seems that the first time I assign AssignedClearProgram, the textbox is filled with the text that I set, however after the window is displayed and AssignedClearProgram gets updated from the code (i.e. the set method is called), the data is not updated in the screen.
Does anybody have a solution to update the textbox when this variable is changed?
Kind regards,
Michel
Your viewmodel class needs to implement INotifyPropertyChanged and you need to raise that interface's event whenever you change the property. Then the binding will spot changes and update the textbox.
Your view model class should implement the INotifyPropertyChanged interface.
Your property would then look like the following:
private string assignedClearProgram;
public string AssignedClearProgram
{
get { return assignedClearProgram; }
set
{
if (assignedClearProgram != value)
{
assignedClearProgram = value;
// Notify property has changed here using PropertyChanged event from INotifyPropertyChanged.
}
}
}
Read this article for an example of how to implement the INotifyPropertyChanged interface and utilize its PropertyChanged event.
I am having a problem with the textbox text updating in my view. I have seen some other threads but cannot find one that is close to my setup.
I have a model with a class of
interface IPerson : INotifyPropertyChanged
{
string FirstName { get; set;}
}
public class Person
{
public event PropertyChangedEventHandler PropertyChanged = delegate { };
private string _firstName;
public string FirstName
{
get {return _firstName;}
set
{
_firstName = value;
PropertyChanged(this , new PropertChangedEventArgs("FirstName"));
}
}
}
This is what my viewModel Looks Like
interface IViewModel : INotifyPropertyChanged
{
string FirstName { get; set;}
IPerson Person { get; set; }
}
public class viewModel : IViewModel
{
public event PropertyChangedEventHandler PropertyChanged = delegate { };
private IPerson _person;
public Person Person
{
get {return _person;}
set
{
_person = value;
PropertyChanged(this , new PropertyChangedEventArgs("Person"));
}
}
public string FirstName
{
get {return Person.FirstName;}
Set
{
Person.FirstName = value;
PropertyChanged(this , new PropertChangedEventArgs("FirstName"));
}
}
}
Xaml Binding Setup
// If i use this binding my model will get updated but my textbox text will never show what the value is in the model
Text="{Binding Path=FirstName ,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay,diag:PresentationTraceSources.TraceLevel=High}"
// This binding works fine both ways
Text="{Binding Path=Person.FirstName ,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay,diag:PresentationTraceSources.TraceLevel=High}"
So if i bind to the Person.First Name everything works great. If I bind to FirstName then it will update my model fine but will not get the data for The TextBox Text. This becomes apparent when i select an item in my list.
Does anyone have an idea why this would happen. I want to be able to bind to the ViewModel Firstname and just have it pass that to my person object.
If your model changes the FirsName value it triggers an PropertyChanged event but that is not extended (relayed) by the ViewModel.
To make the first binding work your ViewModel should subscribe to Person.PropertyChanged and then raise its own event when the nested FirstName changes.
But of course the Path=Person.FirstName binding is preferable anyway.
With this binding "Binding Path=Person.FirstName" the View is listening to your viewModel for the PropertyChanged event. The View is not listening to your model (i.e. Person).
If you are setting the DataContext of your View to the viewModel, then in order for the View to know about changes to your model (i.e. person) you are going to have to have your viewModel listen for the PropertyChanged event of your model. Then, raise the PropertyChanged event from within your viewModel.