If have an own user control with a DependencyProperty and the corresponding callback method like below:
public partial class PieChart : UserControl
{
public static readonly DependencyProperty RatesProperty = DependencyProperty.Register("Rates", typeof(ObservableCollection<double>), typeof(PieChart),
new PropertyMetadata(new ObservableCollection<double>() { 1.0, 1.0 }, new PropertyChangedCallback(OnRatesChanged)));
[...]
public static void OnRatesChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((PieChart)d).drawChart();
}
When using this user control, I bind an ObservableCollection called "Rates" to the RatesProperty. Rates and the related methods look like this:
private ObservableCollection<double> rates;
public ObservableCollection<double> Rates
{
get { return this.rates; }
set
{
if (this.rates != value)
{
this.rates = value;
OnPropertyChanged("Rates");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
When I change the ObservableCollection Rates (e.g. with this.Rates = new ObservableCollection<double>() { 1.0, 2.0 }) the OnRatesChanged() method of the user-control is called like expected. But when I execute the following, it is not called:
this.Rates[0] = (double)1;
this.Rates[1] = (double)2;
OnPropertyChanged("Rates");
I expected that when I raise the PropertyChanged event with the correct property name, the corresponding callback in the user control is always called. Is that wrong?
I found this thread: Getting PropertyChangedCallback of a dependency property always - Silverlight
which covers silverlight but I think then that the same is true in WPF.
So the Framework in the background checks if the bound property (in my example "Rates") changed and only if it changed, it calls the associated callback, correct? Thus changing the elements of my collection has no effect, I always have to change the complete collection?
Thank you!
Your conclusion is right, your OnRatesChanged callback will only be called when the Rates dependency property is set to a new collection (or null).
In order to get notified about changes in the collection, you would also have to register a NotifyCollectionChangedEventHandler:
private static void OnRatesChanged(
DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var pieChart = (PieChart)d;
var oldRates = e.OldValue as INotifyCollectionChanged;
var newRates = e.NewValue as INotifyCollectionChanged;
if (oldRates != null)
{
oldRates.CollectionChanged -= pieChart.OnRatesCollectionChanged;
}
if (newRates != null)
{
newRates.CollectionChanged += pieChart.OnRatesCollectionChanged;
}
pieChart.drawChart();
}
private void OnRatesCollectionChanged(
object sender, NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
...
}
drawChart();
}
Related
I'm looking at using databinding - and the simplest thing to do seems to be to use a BindingSource to wrap my data objects.
However - while the CurrentItemChanged event tells me when a property has changed, it doesn't tell me which one - and that's a vital part of what I need.
Is there any way to find out which property is changing?
Your data objects need to implement the INotifyPropertyChanged interface:
public class MyObject : INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
private string textData = string.Empty;
protected void OnPropertyChanged(string propertyName) {
if (PropertyChanged != null) {
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public string TextData {
get { return textData; }
set {
if (value != textData) {
textData = value;
OnPropertyChanged("TextData");
}
}
}
}
Then if you use BindingList, you can use the BindingSource's ListChanged event to see which property changed:
BindingList<MyObject> items = new BindingList<MyObject>();
BindingSource bs = new BindingSource();
protected override void OnLoad(EventArgs e) {
base.OnLoad(e);
items.Add(new MyObject() { TextData = "default text" });
bs.DataSource = items;
bs.ListChanged += bs_ListChanged;
items[0].TextData = "Changed Text";
}
void bs_ListChanged(object sender, ListChangedEventArgs e) {
if (e.PropertyDescriptor != null) {
MessageBox.Show(e.PropertyDescriptor.Name);
}
}
Also see Implementing INotifyPropertyChanged - does a better way exist?
Recently i was developing a custom control in Silverlight, I created custom dependency property which is of type ObservableCollection. I have another 2 custom dependency properties of type strings. My requirement is on addition of any item to collection, I have to fire collectionChanged Event , in this event handler, i want to update the other 2 dependency properties.
public static readonly DependencyProperty itemsProperty = DependencyProperty.Register("Items", typeof(ObservableCollection<ValidationErrorMessage>), typeof(SummaryUserControl), new PropertyMetadata(new ObservableCollection<ValidationErrorMessage>(), new PropertyChangedCallback(fun1)));
public ObservableCollection<ValidationErrorMessage> Items
{
get
{
return (ObservableCollection<ValidationErrorMessage>)base.GetValue(itemsProperty);
}
set
{
base.SetValue(itemsProperty, value);
}
}
public static void fun1(object sender, DependencyPropertyChangedEventArgs evt)
{
var newValue = evt.NewValue as ObservableCollection<ValidationErrorMessage>;
if(newValue!=null)
newValue.CollectionChanged += new NotifyCollectionChangedEventHandler(CollectionChangedHandler);
var oldValue = evt.OldValue as ObservableCollection<ValidationErrorMessage>;
if(oldValue!=null)
oldValue.CollectionChanged -= new NotifyCollectionChangedEventHandler(CollectionChangedHandler);
}
static void CollectionChangedHandler(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
var newItems = e.NewItems as ObservableCollection<ValidationErrorMessage>;
foreach (var item in newItems)
{
item.PropertyChanged += new PropertyChangedEventHandler(item_PropertyChanged);
}
}
}
static void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
}
public static readonly DependencyProperty headerProperty = DependencyProperty.Register("Header", typeof(String), typeof(SummaryUserControl), new PropertyMetadata(String.Empty, null));
public String Header
{
get
{
return (String)base.GetValue(headerProperty);
}
set
{
base.SetValue(headerProperty, value);
RaisePropertyChange("Header");
}
}
public static readonly DependencyProperty messageTypeProperty =
DependencyProperty.Register("MessageType", typeof(MessageEnumType), typeof(SummaryUserControl), new PropertyMetadata(MessageEnumType.Error, null));
public MessageEnumType MessageType
{
get { return (MessageEnumType)GetValue(messageTypeProperty); }
set { SetValue(messageTypeProperty, value); RaisePropertyChange("MessageType"); }
}
How can I change the values of the dependency properties messageType and Header? I'm unable to access those properties in either the CollectionChanged or NotifyPropertyChanged event since all those events are static. I cannot access the instance within these static event handlers.
I tried to fix the problem with a converter, but my curosity on Silverlight makes me want to use the above approach. How can I set values for those dependency properties within CollectionChanged event or NotifyPropertyChanged events?
The sender in your static fun1 method should be the instance of the class which declares the itemsProperty DependencyProperty. Therefore you can access the concrete instance with casting the sender to your class.
public static void fun1(object sender, DependencyPropertyChangedEventArgs evt)
{
MyClass concreteInstance = sender as MyClass;
if(concreateInstance != null)
{
[...your code...]
}
}
I have a attached property of type ObservableCollection on a control. If I add or remove items from the collection, the ui does not update. However if I replace the collection within with a new one the ViewModel the ui does update.
Can someone give me an example of what I need to do within the Dependency object so that it can handle changes within the collection?
Part of the dependency object is listed below:
public class RadCalendarBehavior : DependencyObject
{
private static void OnSpecialDaysChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var calendar = d as RadCalendar;
if (e.NewValue != null)
{
calendar.DayTemplateSelector = new SpecialDaySelector((ObservableCollection<DateTime>)e.NewValue, GetSpecialDayTemplate(d));
}
}
public static ObservableCollection<DateTime> GetSpecialDays(DependencyObject obj)
{
return (ObservableCollection<DateTime>)obj.GetValue(SpecialDaysProperty);
}
public static void SetSpecialDays(DependencyObject obj, ObservableCollection<DateTime> value)
{
obj.SetValue(SpecialDaysProperty, value);
}
public static readonly DependencyProperty SpecialDaysProperty =
DependencyProperty.RegisterAttached("SpecialDays", typeof(ObservableCollection<DateTime>), typeof(RadCalendarBehavior), new UIPropertyMetadata(null, OnSpecialDaysChanged));
}
}
I understand that I need to register that the collection has changed, but I am unsure how to do this within the dependency property
A change within the collection won't trigger the OnSpecialDaysChanged callback, because the value of the dependency property hasn't changed. If you need to react to detect changes with the collection, you need to handle the event CollectionChanged event manually:
private static void OnSpecialDaysChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var calendar = d as RadCalendar;
if (e.OldValue != null)
{
var coll = (INotifyCollectionChanged)e.OldValue;
// Unsubscribe from CollectionChanged on the old collection
coll.CollectionChanged -= SpecialDays_CollectionChanged;
}
if (e.NewValue != null)
{
var coll = (ObservableCollection<DateTime>)e.NewValue;
calendar.DayTemplateSelector = new SpecialDaySelector(coll, GetSpecialDayTemplate(d));
// Subscribe to CollectionChanged on the new collection
coll.CollectionChanged += SpecialDays_CollectionChanged;
}
}
private static void SpecialDays_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
// handle CollectionChanged
}
This is just to add to the answer by Thomas. In my code I do interact with the DependencyObject's properties by creating a handler object localy like below:
private static void OnSpecialDaysChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var action = new NotifyCollectionChangedEventHandler(
(o, args) =>
{
var calendar = d as RadCalendar;
if (calendar!= null)
{
// play with calendar's properties/methods
}
});
if (e.OldValue != null)
{
var coll = (INotifyCollectionChanged)e.OldValue;
// Unsubscribe from CollectionChanged on the old collection
coll.CollectionChanged -= action;
}
if (e.NewValue != null)
{
var coll = (ObservableCollection<DateTime>)e.NewValue;
// Subscribe to CollectionChanged on the new collection
coll.CollectionChanged += action;
}
}
Hope this is helpful to someone.
If you have a collection-type dependency property keep the following in mind:
If your property is a reference type, the default value specified in dependency property metadata is not a default value per instance; instead it is a default value that applies to all instances of the type. [...]
To correct this problem, you must reset the collection dependency property value to a unique instance, as part of the class constructor call.
(see MSDN Collection-Type Dependency Properties)
To answer Sam's question (I just ran into the same problem):
Make your CollectionChanged-handler non-static and unsubscribe/re-subscribe on instance-level.
private static void OnSpecialDaysChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var calendar = (RadCalendar)d;
if (e.OldValue != null)
{
var coll = (INotifyCollectionChanged)e.OldValue;
// Unsubscribe from CollectionChanged on the old collection of the DP-instance (!)
coll.CollectionChanged -= calendar.SpecialDays_CollectionChanged;
}
if (e.NewValue != null)
{
var coll = (ObservableCollection<DateTime>)e.NewValue;
calendar.DayTemplateSelector = new SpecialDaySelector(coll, GetSpecialDayTemplate(d));
// Subscribe to CollectionChanged on the new collection of the DP-instance (!)
coll.CollectionChanged += calendar.SpecialDays_CollectionChanged;
}
}
private void SpecialDays_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
// handle CollectionChanged on instance-level
}
I'm currently struggling with one of the bindings I'm trying to add to my WPF project.
In the app I have a model with a bool property that cannot be used for databinding. Behind that property is a .NET remoting object that does some validation and writes the new value into the DB.
The requirement ist that the property should be displayed as checkbox, and as the user changes the value the new value should be immediatly provided to the .NET remoting object.
My approach so far:
I've created in my ViewModel with a DependencyProperty that is bound to my checkbox.
In the propertychanged handler of the DP, I'm writting the value to the property of the remoting object.
The problems I have with this approach:
if the validation within the .net remoting object raises an exception, this exception is swallowed. In addition the checkbox state and what's in the DB is not in sync. I tried to reset the value of the DP in case of an exception, but the checkbox doesn't reflect that.
What makes the situation even worse is the fact, that this WPF controls is integrated into an existing WinForms app.
So I would like to have the same behavior for these exceptions as I have implemented in my Application.ThreadException handler.
any ideas how to approach this?
The problem is that I heard only solutions for .NET 4.0 so far, but I'm working with 3.5SP1.
tia
Martin
Short demo code:
class TestVM : DependencyObject
{
private Model _m;
public TestVM()
{
_m = new Model();
}
public bool Value
{
get { return (bool)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
// Using a DependencyProperty as the backing store for Value. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value",
typeof(bool),
typeof(TestVM),
new FrameworkPropertyMetadata(
false,
FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
((sender, e) => ((TestVM)sender).Apply(e))));
private bool _suppress = false;
private void Apply(DependencyPropertyChangedEventArgs e)
{
if (_suppress) return;
try
{
_m.Value = this.Value;
}
catch
{
_suppress = true;
this.Value = _m.Value;
this.OnPropertyChanged(e);
}
finally
{
_suppress = false;
}
}
}
You don't need to use a DependencyObject as your ViewModel. You just need to implement INotifyPropertyChanged to get data binding support:
class TestVM
: INotifyPropertyChanged
{
private Model _m;
public TestVM()
{
_m = new Model();
}
public bool Value
{
get { return _m.Value; }
set
{
_m.Value = this.Value;
OnPropertyChanged("Value");
}
}
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
Note that if you expect the setter to throw exceptions, you may want to use an ExceptionValidationRule on the binding in your view.
Update: It sounds like your problem is that the Binding won't respond to PropertyChanged events within the call to set the source. One way to get around this is to use an asynchronous binding by setting IsAsync=True in the XAML for your binding. WPF will process the PropertyChanged event after it has finished updating the source value and won't think it is a reentrant call.
You can also get around this by using a Converter and turning off updates on PropertyChanged by doing UpdateSourceTrigger=LostFocus, but I don't think you would want that behavior.
I found a solution for my problem. I'm now deriving my own binding class that does the job.
public class ExceptionBinding : Binding
{
public ExceptionBinding(string name)
: base(name)
{
Construct();
}
public ExceptionBinding()
: base()
{
Construct();
}
private void Construct()
{
this.ValidatesOnExceptions = true;
this.UpdateSourceExceptionFilter = new UpdateSourceExceptionFilterCallback(OnException);
}
private object OnException(object bindExpression, Exception exception)
{
// ... custom error display ...
var exp = (BindingExpressionBase)bindExpression;
exp.UpdateTarget();
return null; // null needed to avoid display of the default error template
}
}
I haven't implement this pattern for a while (and when I did it was in 2, as opposed to 3), and I have several examples that all seem straight forward, but I can't work out what I have done wrong in the below piece of code (The Items are not updated when the property event fires):
public partial class Index : Page
{
private IndexViewModel _vm;
public Index()
{
InitializeComponent();
_vm = new IndexViewModel(19);
this.TheDataGrid.ItemsSource = _vm.Rows;
}
public class IndexViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged = delegate { };
protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
{
this.PropertyChanged(this, e);
}
public SortableCollectionView Rows
{
get
{
return _rows;
}
set
{
if (_rows == value)
return;
_rows = value;
this.OnPropertyChanged(new PropertyChangedEventArgs("Rows"));
}
}
This does not refresh my datagrid... as a 'hack' I have had to pass the datagrid object into my viewmodel and bind it there:
public IndexViewModel(int containerModelId, DataGrid shouldNotNeed)
{
ContainerModelId = containerModelId;
LoadOperation<vwColumn> headings = _ttasContext.Load(_ttasContext.GetRecordColumnsQuery(ContainerModelId));
headings.Completed += (sender2, e2) =>
{
//load data
LoadOperation<vwDataValue> data = _ttasContext.Load(_ttasContext.GetRecordsQuery(ContainerModelId, null));
data.Completed += (sender3, e3) =>
{
Rows = FormatData(data, headings);
shouldNotNeed.ItemsSource = Rows;
};
};
}
Assigning _vm.Rows to TheDataGrid.ItemsSource does not wire any change notification callback automatically. Try this:
in xaml:
<... x:Name=TheDataGrid ItemsSource={Binding Rows}>
In code:
this.DataContext = _vm;
As Codism points out your main problem is you need to use binding to take advantage of an INotifyPropertyChanged. However I would recommend this implementation pattern:-
public event PropertyChangedEventHandler PropertyChanged;
void NotifyPropertyChanged(string name)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(name);
}
...
set
{
if (_rows != value)
{
_rows = value;
NotifyPropertyChanged("Rows");
}
}
Note that this approach minimises the impact on a an object instance whose properties are not being observed. In the original pattern you create instances of PropertyChangedEventArgs and calls to the event delegate going off regardless of whether anything is actually listening.
this.TheDataGrid.ItemsSource = _vm.Rows
When a collection is assigned as the ItemsSource of a DataGird , any changes made to the collection can be observed by the DataGrid if the source implements INotifyCollectionChanged.
From your code sample , I can't tell if the type SortableCollectionView implements INotifyCollectionChanged or inherits from ObservableCollection.
Implementing INotifyCollectionChanged would mean that you can't reset the backing field _rows for property Rows , you can clear items in the collection and add them as needed.
Hope this helps