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
Related
According to this answer I should not need to bother about NotifyPropertyChanges Bubbling up the hierachie, still I can't get it to work with a (simplified test-) structure like that:
a Data-Holding Class
public class TestNotifyChanged : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _Test = "default";
public string Test
{
get
{
return _Test;
}
set
{
if(_Test!=value)
{
_Test = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Test"));
}
}
}
}
A ViewModel that used that Test-Class and Test-Property:
public class ViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private TestNotifyChanged tnc = new TestNotifyChanged(); // only to init, otherwise VS screams at me
public ViewModel(TestNotifyChanged tnc)
{
tnc = tnc; // getting an instance of TestNotifyChanged from "Master" passed in, which hopefully will be replaces by a singleton class.
}
private string _Test;
public string Test
{
get
{
return tnc.Test; // this might be the crucial part!?
}
set
{
if (_Test != value) // never hits that, as I would expect, but you never know..
{
_Test = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Test")); // of course also never hit, as expected
}
}
}
}
And finally my MainWindow cs
public partial class MainWindow : Window
{
TestNotifyChanged tnc;
public MainWindow()
{
InitializeComponent();
tnc = new TestNotifyChanged();
DataContext = new ViewModel(tnc); // pass in my Test-Object that has the Values.
}
private void ButtonGet_Click(object sender, RoutedEventArgs e)
{
tnc.Test = "new Value";
MessageBox.Show($"{tnc.Test}"); // got "new Value" here!
}
}
And in xaml I have besides that one button a simple TextBlock that is bound to the ViewModel's Test Property:
<TextBlock x:Name="OutputId" Text="{Binding Path=Test, Mode=OneWay}"/>
What is happening now:
The default value "default" is shown in TextBlock.
When I click the button the messageBox shows the "new Value"
TextBlock is not updating to "new Value"
What I want to achieve:
seems easy: TextBlock should update to "new Value"
I can easily make this work when I directly set the Test Value on the ViewModel - but this doesn't seem right and is far away from what I thought I could structure my app/code. The future goal is to have a Singleton (static won't work I figured out) "RecordStore" that has most of the data (and gets it from an API, from local Database, or just from Memory if any of these are done)
So the question is:
Why is the NotifyPropertyChange not bubbling up to the View/ViewModel?
Or is there another issue I don't see?
I've read INotifyPropertyChanged bubbling in class hierarchy
and
What is a good way to bubble up INotifyPropertyChanged events through ViewModel properties with MVVM?
and
https://learn.microsoft.com/en-us/dotnet/framework/winforms/how-to-implement-the-inotifypropertychanged-interface
and
OnPropertyChange called but not taking any effect on UI
most of those questions are also quite old...
EDIT:
I tried #MineR 's suggestion that way:
// made tnc public in ViewModel
public TestNotifyChanged tnc = new TestNotifyChanged();
// changed Binding directly to that (and it's Property):
<TextBlock x:Name="OutputId" Text="{Binding Path=tnc.Test, Mode=OneWay}"/>
Unfortunately now I don't even get the default, so I must have misunderstood smth.
EDIT2:
I did one thing wrong in the 1st edit:
// this isn't recognized as bindable parameter:
public TestNotifyChanged tnc = new TestNotifyChanged();
// it instead has to be
public TestNotifyChanged tnc { get; }
And I made it TNC, removed the local Test parameter, bound directly to Path=TNC.Test
So I understood, that PropertyChanges do not bubble up the way I hoped/thought, it's better to bind directly down to the nested object.
"Bubbling" is a concept of routed events. A regular event like PropertyChanged doesn't "bubble up".
Besides the apparent bug tnc = tnc; in the ViewModel (which should be this.tnc = tnc;) the Test properties of the two classes are unrelated. In order to update its own Test property, ViewModel must register a PropertyChanged event handler at tnc. And it must update the property of tnc when its own Test property changes.
public class ViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private TestNotifyChanged tnc;
public ViewModel(TestNotifyChanged t)
{
tnc = t;
tnc.PropertyChanged += (s, e) =>
{
if (e.PropertyName == nameof(Test) || string.IsNullOrEmpty(e.PropertyName))
{
Test = tnc.Test; // update ViewModel.Test from TestNotifyChanged.Test
}
};
}
private string test;
public string Test
{
get
{
return test; // always return own value
}
set
{
if (test != value)
{
test = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Test)));
tnc.Test = Test; // update TestNotifyChanged.Test from ViewModel.Test
}
}
}
}
Alternatively, drop the Test property's backing field and only operate on tnc.Test:
public class ViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private TestNotifyChanged tnc;
public ViewModel(TestNotifyChanged t)
{
tnc = t;
tnc.PropertyChanged += (s, e) =>
{
if (e.PropertyName == nameof(Test) || string.IsNullOrEmpty(e.PropertyName))
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Test)));
}
};
}
public string Test
{
get { return tnc.Test; }
set { tnc.Test = Test; }
}
}
Fortunately, it is not necessary at all.
There could instead just be a public Tnc property like
public class ViewModel
{
public TestNotifyChanged Tnc { get; }
public ViewModel(TestNotifyChanged tnc)
{
Tnc = tnc;
}
}
with a Binding like this:
<TextBlock Text="{Binding Tnc.Test}"/>
I have a listbox which i want to get updated when the items get added to a list. I understand I need to bind the listbox. I was trying to follow this question/answer.
I have a ViewModel which handles the list:
namespace TESTS
{
public class ViewModel : INotifyPropertyChanged
{
private List<Cars> _listCars;
public List<Cars> listCars
{
get
{
return _listCars;
}
set
{
if (_listCars == value)
{
return;
}
this.RaisePropertyChanged("Message");
_listCars = value;
this.RaisePropertyChanged("Message");
}
}
public ViewModel()
{
listCars = new List<Cars>();
}
protected void RaisePropertyChanged(string propertyName)
{
Debug.WriteLine("Property Changed");
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
}
Here is the class Cars:
public class Cars: INotifyPropertyChanged
{
public string model{ get; set; }
public string year{ get; set; }
public event PropertyChangedEventHandler PropertyChanged;
}
So I did the binding of listbox to the property path in my Viewmodel which is listCars.
<ListBox .... ItemsSource="{Binding listCars}">
So when in my Main.xaml.cs. I do a button click and add the item. It does not get added to the listbox even though its bind to the list on view model.
public sealed partial class MainPage : Page
{
public static ViewModel vm = new ViewModel();
public MainPage()
{
this.InitializeComponent();
this.DataContext = vm;
}
private void button_Click(object sender, RoutedEventArgs e)
{
Cars x = new Cars();
x.model = "Ford";
x.Year = "1998";
vm.listCars.Add(x);
}
}
I hope I explained what i implemented well enough. Is there something wrong in my implementation of ViewModel. I am new to MVVM. Please help.
Use ObservableCollection<T>, not List<T>. The former is designed to be used with MVVM, the latter is not. You'll get all your notifications automatically. It's doable with List<T>, but you'll have to write much more code and the performance will be much worse, especially with big collections. Just don't do it.
If you create the collection in the constructor, assign it to a read-only property and never change its instance (and this is the way you should do it), you don't even need to implement INPC.
When implementing INPC, you're expected to call RaisePropertyChanged after you've changed the property, once, and with the property name that has been changed, not a random unrelated string.
I don't understand why when I update a object, my bound controls do not update.
The data displays fine initially, but when I want to refresh the data displayed in the UI nothing happens when I update the object. The object updates fine. The ViewModel does use INotifyPropertyChanged on all fields.
However if I update individual items directly, I can update my UI. As commented below.
I guess I've made a school boy error somewhere here?
UPDATE: I've added the model to the question. While I understand the answers, I don't understand how to implement it. Attempted to implement a collection changed event without success. Can I have some pointers please?
public partial class CisArrivalsPanel : UserControl
{
private ApiDataArrivalsDepartures _theArrivalsDepartures;
public CisArrivalsPanel()
{
InitializeComponent();
_theArrivalsDepartures = new ApiDataArrivalsDepartures();
_theArrivalsDepartures = MakeQuery.LiveTrainArrivals("London Kings Cross");
this.DataContext = _theArrivalsDepartures;
ListBoxArr.ItemsSource = _theArrivalsDepartures.StationMovementList;
}
void Reload()
{
//This does not update the UI**
_theArrivalsDepartures = MakeQuery.LiveTrainArrivals("London Paddington");
//However this (when uncommented, and I comment out the above line) does update the UI**
//_theArrivalsDepartures.StationMovementList[0].OriginName = "test";
//_theArrivalsDepartures.StationMovementList[0].Platform = "0";
//_theArrivalsDepartures.StationMovementList[0].BestArrivalEstimateMins = "999";
//_theArrivalsDepartures.StationName = "test";
}
private void StationHeader_OnPreviewMouseDown(object sender, MouseButtonEventArgs e)
{
Reload();
Debug.WriteLine(_theArrivalsDepartures.StationName);
foreach (var a in _theArrivalsDepartures.StationMovementList)
{
Debug.WriteLine(a.OriginName);
Debug.WriteLine(a.BestArrivalEstimateMins);
}
}
}
EDIT : Added Model
public class ApiDataArrivalsDepartures : INotifyPropertyChanged
{
private string _stationName;
[JsonProperty(PropertyName = "station_name")]
public string StationName {
get
{
return _stationName;
}
set
{
_stationName = value;
NotifyPropertyChanged("StationName");
}
}
private List<StationListOfMovements> _stationMovementList;
public List<StationListOfMovements> StationMovementList
{
get
{
return _stationMovementList;
}
set
{
_stationMovementList = value;
NotifyPropertyChanged("StationMovementList");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
}
public class StationListOfMovements : INotifyPropertyChanged
{
private string _originName;
[JsonProperty(PropertyName = "origin_name")]
public string OriginName {
get
{
return _originName;
}
set
{
_originName = value;
NotifyPropertyChanged("OriginName");
}
}
[JsonProperty(PropertyName = "destination_name")]
public string DestinationName { get; set; }
private string _platform;
[JsonProperty(PropertyName = "Platform")]
public string Platform {
get
{
return _platform;
}
set
{
_platform = value;
NotifyPropertyChanged("Platform");
}
}
private string _bestArrivalEstimateMins;
[JsonProperty(PropertyName = "best_arrival_estimate_mins")]
public string BestArrivalEstimateMins {
get
{
return _bestArrivalEstimateMins;
}
set
{
_bestArrivalEstimateMins = value;
NotifyPropertyChanged("BestArrivalEstimateMins");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
}
There are two pieces here pertaining to your collection (technically three):
If you want a new collection to propagate, the collection property has to raise PropertyChanged (sounds like it does)
If you want add/remove on the collection to propagate, you need to use a collection that implements INotifyCollectionChanged. ObservableCollection is a good choice.
If you want changes to the items in the container to propagate, then those items need to implement INotifyPropertyChanged and raise the PropertyChanged event.
Make sure all those are covered, and the changes should appear on the UI as you expect.
You should update the DataContext and ItemsSource too.
void Reload()
{
//This does not update the UI**
_theArrivalsDepartures = MakeQuery.LiveTrainArrivals("London Paddington");
DataContext = theArrivalsDepartures;
ListBoxArr.ItemsSource = _theArrivalsDepartures.StationMovementList;
}
Use for the collection ObservableCollection , this class notify the ui when change to the collection occurred
your reload function works because the there is PropertyChanged on all the fields include this one
it notify the ui and reload the correct collection
I have an ObservableCollection of items bound to a listbox as the ItemsSource.
Some of these items are also located in another collection on the same ViewModel (call it CollectionTwo).
I want to be able to take the count of the item in Collection2 and display it for the respective item in CollectionOne. When CollectionTwo properties change (ie the Count), it must also be reflected back to CollectionOne.
I would guess the best way to do this in MVVM is to wrap items in CollectionOne with a viewmodel class with an extra Count property on it. Can someone point me to a good example of this? Or perhaps another method to tackle this problem that won't hugely weigh down my ItemsSource performance.
Thanks!
You can use inheritance to create a custom collection along these lines...
public class MyCollection<T> : ObservableCollection<T>, INotifyPropertyChanged
{
// implementation goes here...
//
private int _myCount;
public int MyCount
{
[DebuggerStepThrough]
get { return _myCount; }
[DebuggerStepThrough]
set
{
if (value != _myCount)
{
_myCount = value;
OnPropertyChanged("MyCount");
}
}
}
#region INotifyPropertyChanged Implementation
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string name)
{
var handler = System.Threading.Interlocked.CompareExchange(ref PropertyChanged, null, null);
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
#endregion
}
This is a class that wraps an Observable Collection and puts a custom property in it. The property participates in change notification, but that depends upon your design.
To wire it up, you can do something like this...
public MyCollection<string> Collection1 { get; set; }
public MyCollection<string> Collection2 { get; set; }
public void Initialise()
{
Collection1 = new MyCollection<string> { MyCount = 0 };
Collection2 = new MyCollection<string> { MyCount = 0 };
Collection2.CollectionChanged += (s, a) =>
{
// do something here
};
}
You can also do something like...
Collection1.PropertyChanged += // your delegate goes here
Hi i am trying to use the NotifyPropertyChanged to update all the places where i am binding a property. For what i have searched the INotifyPropertyChanged is indicated to this cases.
So i need help because i don't understand what i have wrong in here. And i really don't know what to do with the PropertyChange event. My question about that is, when he changes? What i have to more with him?
Datagrid:
<ListView Name="listView" ItemsSource="{Binding Categories}"/>
An example when i change my Categories property:
DataTest dtTest = new DataTest();
public MainWindow()
{
InitializeComponent();
this.DataContext = dtTest;
}
private void Button1_Click(object sender, RoutedEventArgs e)
{
//Here i pick up a string from a textBox, where i will insert in a Table of my DB,
//Then i will do a query to my Table, and i will get a DataTable for example
//Then i just put the contents into the DataView, so the value have changed.
dtTest.Categories = dtTable.DefaultView;
dtTest = dtTable.defaultView; (this only an example, i don't this for real.)
//What i have to do now, to wherever i am binding (DataGrid, ListView, ComboBox)
//the property to the new values automatically being showed in all places?
}
My Class:
public class DataTest : INotifyPropertyChanged
{
private DataView categories;
public event PropertyChangedEventHandler PropertyChanged; //What i have to do with this?
private void NotifyPropertyChanged(string str)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(str));
}
}
public DataView Categories
{
get { return categories; }
set
{
if (value != categories)
{
categorias = value;
NotifyPropertyChanged("Categories");
}
}
}
}
My Class with INotifyCollectionChanged:
public class DataTest : INotifyCollectionChanged
{
public event NotifyCollectionChangedEventHandler CollectionChanged;
private void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (CollectionChanged != null)
{
CollectionChanged(this, e);
}
}
public DataView Categories
{
get { return categories; }
set
{
if (value != categories)
{
categories = value;
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, Categories));
}
}
}
}
But why the PropertyChanged is always NULL??? I have to do something more, but i don't know what.
Thanks in advance!
the DataTest class needs to be the DataContext for the Binding. You can set this in code-behind (or a myriad of other ways, but for simplicity - just do it in code-behind)
public MainWindow() // constructor
{
this.DataContext = new DataTest();
}
Then, with the 'Source' of the Binding set, you can specify the 'Path', so your xaml looks like this:
<ListBox ItemsSource="{Binding Categories}" />
Now, if the property 'Categories' is changed in code, the NotifyPropertyChanged code you have written will alert the Binding, which in turn will access the public getter for the property and refresh the view.
Getting the handler prevents the event handler from going to null after you check for null and checking for null will prevent you from getting a null exception if there are no event handlers.
The reason that your PropertyChanged is null is that there are no event handlers attached to it. The reason there are not handlers attached to it is you have not bound your object to anything (which will take care of adding a handler) or you haven't added a handler to it (if you wanted to observe it for some other reason). Once your object is created you need to bind it somewhere.
You are doing all you have to do. An event is just a special kind of delegate. You declare it, you invoke it, clients subscribe to it. That's all there is to it.