I have a checkbox in my view and the binding on it is working fine if i do any modification to my object and trigger the propertyChanged event.
On the other side when i click my checkbox i perform some logic if the property where it is bound to can be changed. If not i change it back to False and trigger the propertyChanged event.
My view is not updating this state of the checbox and it is still checked.
Is this a know problem with any bypass?
Code:
<ctrls:CheckBox
IsChecked="{Binding IsConverted, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
When i change the value and raise the property change event the property is retrieved with the false value:
Private _isConverted As Boolean
Public Property IsConverted As Boolean
Get
Return _isConverted
End Get
Set(value As Boolean)
_isConverted = value
End Set
End Property
In your Binding in Xaml, make sure that Mode is set to TwoWay so the updates work in both directions.
<CheckBox IsChecked="{Binding Path=ViewModelIsChecked, Mode=TwoWay}"/>
Also, now that you posted code, you seem to do things "manually", that should be implemented using the interface INotifyPropertyChanged. Can you drop the UpdateSourceTrigger and just implement INotifyPropertyChanged in your ViewModel?
There is a good guide here.
Edit:
And because the Poster isn't willing or able to read and understand the guide, here comes the code that is posted there:
Public Property PhoneNumber() As String
Get
Return Me.phoneNumberValue
End Get
Set(ByVal value As String)
If Not (value = phoneNumberValue) Then
Me.phoneNumberValue = value
NotifyPropertyChanged() <===== THIS LINE IS DIFFERENT! YOU DON'T HAVE IT. YOU NEED IT.
End If
End Set
End Property
Related
I'm encountering a strange problem. Despite setting everything correctly, the Validation.Error doesn't get fired.
Here are the details:
<DataTemplate x:Key="dtLateComers">
<TextBox Text="{Binding ParticipantTag, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, NotifyOnValidationError=True, NotifyOnSourceUpdated=True}" Validation.Error="Validation_Error" >
</DataTemplate>
Code behind (VB.Net) to set ItemsSource of HeaderedItemsControl:
hicLateComers.ItemsSource = _LateComersViewModels
_LateComersViewModels is ObservableCollection(Of ParticipantViewModel)
Implementation of ParticipantViewMode:
Public Class ParticipantViewModel
Implements INotifyPropertyChanged, IDataErrorInfo
Private _ParticipantTag As String = ""
Public Property ParticipantTag() As String
Get
Return _ParticipantTag
End Get
Set(ByVal value As String)
_ParticipantTag = value
_ParticipantTag= _ParticipantTag.ToUpper
NotifyPropertyChanged("ParticipantTag")
End Set
End Property
Public ReadOnly Property Item(byVal columnName As String) As String Implements IDataErrorInfo.Item
Get
Dim errorString As String = String.Empty
If columnName.Equals("ParticipantTag") Then
If not ParticipantValidationManager.IsValidKeypadTag(_ParticipantTag, True) then
errorString = "Incorrect entry. Please try again."
End If
End If
Return errorString
End Get
End Property
Public ReadOnly Property [Error] As String Implements IDataErrorInfo.Error
Get
Throw New NotImplementedException()
End Get
End Property
End Class
Problem
When I set ItemSource property (as mentioned above in code), Item index is called as many times as there are items in _LaterComersViewModels. Validation works and as a result I get red circle next to TextBox. However, Validation_Error never gets fired until I start typing in Textbox. Typing in TextBox changes the Property binds to it and validate it. Base on validation Validation.Error event is raised, and handled by application. Within that event handler I maintain a count of errors.
So the Question is, why Validation.Error doesn't get raised when one/more items fail on a validation rule during initial data binding? Though it does get raised once property is changed by typing into that TextBox.
Feel free to share any idea, assumption or a solution. Any type of help will be appreciated. Thanks.
Side note: I've a simple C# application which doesn't use data templating. In that application, Validation.Error event gets raised perfectly on start, and on property change. Though in that application, Model is binding to DataContext property of Grid.
Since Validation.Error is an attached event, you could hook up the event handler on the HeaderedItemsControl:
<HeaderedItemsControl x:Name="hicLateComers" ItemTemplate="{StaticResource dtLateComers}" Validation.Error="Validation_Error" />
The result should be pretty much the same since you can easily access both the TextBox and the ParticipantViewModel object in the event handler:
Private Sub Validation_Error(sender As Object, e As ValidationErrorEventArgs)
Dim textBox = CType(e.OriginalSource, TextBox)
Dim participant = CType(textBox.DataContext, ParticipantViewModel)
'...
End Sub
I have a simple viewmodel class with two properties: sEmailAddress and sEmailCompare.
I have a simple view (window) with two text boxes. The data context is set to an instance of the viewmodel. The two text boxes are bound to the two properties on the viewmodel, with the validation properties set, as follows:
Text="{Binding sEmailAddress,
Mode=TwoWay,
NotifyOnValidationError=True,
UpdateSourceTrigger=PropertyChanged,
ValidatesOnDataErrors=True,
ValidatesOnExceptions=True}"
My viewmodel has a Validate method as follows:
Public Function Validate() As Boolean
If Validator.TryValidateObject(Me, New ValidationContext(Me), New List(Of ValidationResult), True) Then
Return True
Else
Validator.ValidateObject(Me, New ValidationContext(Me), True)
Return False
End If
End Function
And Data Annotated properties:
Private _sEmailAddress As String
<Required>
Public Property sEmailAddress As String
Get
Return _sEmailAddress
End Get
Set(ByVal value As String)
If _sEmailAddress <> value Then
_sEmailAddress = value
OnPropertyChanged("sEmailAddress")
End If
End Set
End Property
Private _sEmailAddressConfirm As String
<Required>
<CustomValidation(GetType(MatchingEmailValidator), "ValidateEmail")>
Public Property sEmailAddressConfirm As String
Get
Return _sEmailAddressConfirm
End Get
Set(ByVal value As String)
If _sEmailAddressConfirm <> value Then
_sEmailAddressConfirm = value
OnPropertyChanged("sEmailAddressConfirm")
End If
End Set
End Property
The actual validation part is working correctly- if I leave a field blank or if the two field values do not match, then TryValidateObject returns false. But the UI does not change. So I try calling ValidateObject, and that throws a validation exception, as it should, but I don't know how to handle that exception so that the UI is updated and the textbox is outlined in red as normal.
Can anyone shed some light on what I'm missing here?
There are two ways to do this kind of validation in Silverlight. The first is to throw an exception inside the property setter -- since you have ValidatesOnExceptions=true, that should cause the validation error to appear on the UI. To implement this, you would basically just need to call ValidateObject inside the setter.
The other way, which is useful for more advanced scenarios (ie, when there may be validation rules depending on multiple properties), is to have your view-model implement INotifyDataErrorInfo. This interface has a collection of errors that you maintain, and an event ErrorsChanged that you need to call when an error is added or removed.
Goal
To add a list of a custom class object (DamagedItems) to a DataGrid using the Model, View, ViewModel (MVVM) way of doing things.
I want the user to be able to create entries of damaged parts (deemed improper during inspection of a machine).
What I have done
I have created:
A window: wDamagedItems.xaml in which it's DataContext is set to DamagedItemViewModel
A Model: DamagedItemModel.vb which implements INotifyPropertyChanged
A ViewModel: DamagedItemViewModel.vb where I set properties of classes such as my DamagedItemModel
An ObservableCollection: DamagedItemList.vb which inherits an ObservableCollection(Of DamagedItemModel)
Since my DataContext is set to the DamagedItemViewModel, here is how I setup the properties:
Public Class DamagedItemViewModel
Private _DamagedItem As DamagedItemModel
Private _Add As ICommand
Private _DamagedItems As DamagedItemList
Public Property DamagedItem As DamagedItemModel
Get
Return _DamagedItem
End Get
Set(value As DamagedItemModel)
_DamagedItem = value
End Set
End Property
Public Property DamagedItems As DamagedItemList
Get
Return _DamagedItems
End Get
Set(value As DamagedItemList)
_DamagedItems = value
End Set
End Property
Public Property Add As ICommand
Get
Return _Add
End Get
Set(value As ICommand)
_Add = value
End Set
End Property
Public Sub New()
DamagedItem = New DamagedItemModel("", "", "")
DamagedItems = New DamagedItemList
Add = New DamagedItemAddEntryCommand(Me)
End Sub
Public Function CanUpdate() As Boolean
If DamagedItem.Description = "" Then Return False
If DamagedItem.Initiales = "" Then Return False
Return True
End Function
Public Sub AddEntry()
DamagedItems.Add(DamagedItem) 'Items get added to the datagrid
DamagedItem = New DamagedItemModel 'Does not seem to clear textboxes
End Sub
End Class
Here is how my XAML is set up:
<DataGrid ItemsSource="{Binding Path=DamagedItems}" AutoGenerateColumns="True" HorizontalAlignment="Stretch" Margin="12,90,12,0" Name="DataGrid1" VerticalAlignment="Top" Height="229" / >
<TextBox Text="{Binding DamagedItem.Description, UpdateSourceTrigger=PropertyChanged}" Height="23" HorizontalAlignment="Left" Margin="88,24,0,0" VerticalAlignment="Top" Width="249" />
<TextBox Text="{Binding DamagedItem.Initiales, UpdateSourceTrigger=PropertyChanged}" Height="23" HorizontalAlignment="Left" Margin="88,58,0,0" VerticalAlignment="Top" Width="249" />
As you can see, my textboxes are bound to my Model (which is contained in my ViewModel, which is bound to that Window's DataContext). Whenever I click on my "Add" button, whatever is in the textbox gets added to the DataGrid, but the content in the text boxes stay there.
This step is fine, I write in what I want to add and click on "Add"
After clicking on "Add" i get the following results in the DataGrid, which is fine. The issue is my text boxes are still filled with data yet the Model was cleared (see code after DamagedItemViewModel AddEntry method).
Now when I try to add the following text:
Description: "Part is bent"
Initiales: "A.C"
I get the following result:
The first letter typed in the description gets inputted in the first entry of the DataGrid, then it erases the text in the description textbox. Only then can I keep typing what I want. The same thing occurs for the initiales text box.
Any ideas? If you wish to see more of my code, suggest which portion I should add.
Thank you in advance!
Yup, I remember running into this one. You have to implement iNotifyPropertyCHnaged. This is how the viewmodel class "notifies" the user interface that there has been a change to the underlying property of a binding:
look here:
http://msdn.microsoft.com/en-us/library/ms743695.aspx
You will have to implement this for every property you want reflected back to the view. SO what I do is have a base viewmodel class (ViewModelBase which exposes method RasiePropertyChanged) which implements iNotifyPropertyChanged and then my viewmodles inherit from it. Then I notify the property changed in the property set of the property:
ie:
Public Property Selection As job
Get
Return Me._Selection
End Get
Set(ByVal value As job)
If _Selection Is value Then
Return
End If
_PreviousJob = _Selection
_Selection = value
RaisePropertyChanged(SelectionPropertyName)
End Set
End Property
This seems frustrating at first but is needed to keep the decoupling that MVVM supports. Its easy to implement.
I have created a UserControl, which is to display a converted string value based on the contents of a bound ObservableCollection. Everything works when the application loads; my IValueConverter is called and produces the correct string result, which is displayed correctly in my UserControl. However if the ObservableCollection contents change, my control is not updated.
Also, before I created this control, I had the same behaviour, but binding the Content property of a regular Button control, and this also worked correctly and updated as expected.
Any ideas what I am missing to get the same thing with my UserControl?
The control property looks like;
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(string), typeof(MyUserControl));
public string Text
{
get { return GetValue(TextProperty) as string; }
set { SetValue(TextProperty, value);
}
The relevant section in the UserControl XAML (which displays the converted string value) is;
<TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type Controls:MyUserControl}}, Path=Text}" />
And the control is created in a separate Window like so;
<CoreControls:MyUserControl
Name="myControl"
Text="{Binding Path=ObservableCollectionInstance, Converter={StaticResource MyValueConverter}, Mode=OneWay}" />
I would use ElementName instead of RelativeSource in your binding, since you have named your user control. Also, you are trying to bind a collection to a <Textbox>. a <Textbox> is designed to display a single item. this is probably why its not working. ObservableCollection fires CollectionChanged events, not PropertyChanged. Even if it did respond, you are still going to have problems because ObservableCollection does not notify when an item contained in it has property changes--only when items are added/removed etc (think, the collection itself changes). If this is the behavior you want, you are going to have to write some code.
EDIT
after your comments, it sounds to me like even though you set it to OneWay binding mode, its acting like OneTime binding mode.
I would try this to help you debug it:
add this xmlns:
xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase"
and then, in your binding add this:
diagnostics:PresentationTraceSources.TraceLevel=High
here is an article on debugging bindings.
the other thing you could do is set breakpoints in your converter. see if its actually updating when you add/remove things to your collection. I would be willing to bet that its bc the ObservableCollection is NOT firing PropertyChanged events and that the initial update occurs because its not based on an update event.
ObservableCollection notifies only in case if items get added or removed. It is used to observe a collection. They are more suited for content controls. Read about it here. You are talking about observing a property, which needs INotifyPropertyChanged. Posting more code might help, like how are you changing the value of the collection.
Thanks for the tips guys.
I managed to work out a solution; I can handle the CollectionChanged event on the ObservableCollection and then explicitly update the target with something like;
BindingExpression exp = myControl.GetBindingExpression(MyUserControl.TextProperty);
if (null != exp) exp.UpdateTarget();
As noted, most likely, binding on the Text property is only listening to PropertyChanged events, not NotifyCollectionChanged events, but this solution does the trick.
I cannot get a two-way bind in WPF to work.
I have a string property in my app's main window that is bound to a TextBox (I set the mode to "TwoWay").
The only time that the value of the TextBox will update is when the window initializes.
When I type into the TextBox, the underlying string properties value does not change.
When the string property's value is changed by an external source (an event on Click, for example, that just resets the TextBox's value), the change doesn't propagate up to the TextBox.
What are the steps that I must implement to get two-way binding to work properly in even this almost trivial example?
Most probably you're trying to bind to a .net CLR property instead of a WPF dependencyProperty (which provides Change Notification in addition to some other things).
For normal CLR property, you'd need to implement INotifyPropertyChanged and force update on the textbox in the event handler for PropertyChanged.
So make your object with the property implement this interface, raise the event in the property setter. (So now we have property change notification)
Make sure the object is set as the DataContext property of the UI element/control
This threw me off too when I started learning about WPF data binding.
Update: Well OP, it would have been a waste of time if i was barking up the wrong tree.. anyways now since you had to dig a bit.. you'll remember it for a long time. Here's the code snippet to round off this answer. Also found that updating the textbox happens automatically as soon as I tab-out.. You only need to manually subscribe to the event and update the UI if your datacontext object is not the one implementing INotifyPropertyChanged.
MyWindow.xaml
<Window x:Class="DataBinding.MyWindow" ...
Title="MyWindow" Height="300" Width="300">
<StackPanel x:Name="TopLevelContainer">
<TextBox x:Name="txtValue" Background="AliceBlue" Text="{Binding Path=MyDotNetProperty}" />
<TextBlock TextWrapping="Wrap">We're twin blue boxes bound to the same property.</TextBlock>
<TextBox x:Name="txtValue2" Background="AliceBlue" Text="{Binding Path=MyDotNetProperty}" />
</StackPanel>
</Window>
MyWindow.xaml.cs
public partial class MyWindow : Window, INotifyPropertyChanged
{
public MyWindow()
{
InitializeComponent();
this.MyDotNetProperty = "Go ahead. Change my value.";
TopLevelContainer.DataContext = this;
}
private string m_sValue;
public string MyDotNetProperty
{
get { return m_sValue; }
set
{
m_sValue = value;
if (null != this.PropertyChanged)
{
PropertyChanged(this, new PropertyChangedEventArgs("MyDotNetProperty"));
}
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
}
I feel the need to add some precision:
"Two ways" data binding is more than "One way" data binding.
"One way" data binding is a binding from a source to a dependency property. The source must implement INotifyPropertyChanged, in order to get change propagation from source to target.
To get the " 2 way" , so to get a propagation from Target to Source, it depends on the binding mode which you set on the Binding . If you don't set any BindingMode for your binding, the default Binding mode will be used, and this default mode is a characteristics for your target Dependency Property.
Example:
A Textbox bound to a string property, called "MyTextProperty".
In the code, you bind Textbox.Text DependencyProperty to "MyTextProperty" on object "MyObject"
--> "one way" binding : the setter of "My TextProperty" must raise an event Property Changed,and "MyObject" must implement INotifyPropertyChanged.
--> "2 ways data binding": in addition to what is needed for "One way", bindingMode must be set to "2 ways". In this special case, the Text DependencyProperty for Textbox does have "2 ways" as default mode, so there is nothing else to do !
We might need to see the code. Does your string property raise a PropertyChanged event? Or (even better) is it implemented as a DependencyProperty? If not, the bound TextBox won't know when the value changes.
As for typing into the TextBox and not seeing the property's value change, that may be because your TextBox isn't losing focus. By default, bound TextBoxes don't write their values back to the source property until focus leaves the control. Try tabbing out of it and seeing if the property value changes.
Make sure that the binding specifies two way and when the property has a change, it is immediately transmitted to the holding property.
<TextBox Text="{Binding TextBuffer,
UpdateSourceTrigger=PropertyChanged,
Mode=TwoWay}"/>
The above assures that the TextBox input control Text property binds to, then sends the changes back to the string property named TextBuffer in an immediate, PropertyChanged, and TwoWay fashion.