If I bind a TextBox to an object's (Merchandise is the object) property like:
Text="{Binding Path=Merchandise.Quantity, Mode=TwoWay}
<TextBox x:Name="QuantityTextBox" Grid.Column="1" Grid.Row="5" Width="70" Text="{Binding Path=Merchandise.Quantity, Mode=TwoWay, TargetNullValue='0', FallbackValue='0', ValidatesOnExceptions=True, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"/>
The DataContext is set to my ViewModel which contains (among other properties) the declared property of type Merchandise.
Implements INotifyPropertyChanged, IDataErrorInfo
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Public Sub OnPropertyChanged(ByVal e As PropertyChangedEventArgs)
If PropertyChangedEvent IsNot Nothing Then
RaiseEvent PropertyChanged(Me, e)
Select Case e.PropertyName
Case "Merchandise"
DoSomething()
Case Else
End Select
End If
End Sub
Private _Merchandise As DC.SL.Services.WebServiceMerchandise.Merchandise
Public Property Merchandise() As DC.SL.Services.WebServiceMerchandise.Merchandise
Get
Return _Merchandise
End Get
Set(ByVal value As DC.SL.Services.WebServiceMerchandise.Merchandise)
_Merchandise = value
OnPropertyChanged(New PropertyChangedEventArgs("Merchandise"))
End Set
End Property
When I input changes in the TextBox the PropertyChanged event is NOT triggered. The only way I can work around this is by creating duplicate properties in my ViewModel ... i.e. Quantity and then later when Ok button is clicked I assigned the ViewModel properties to my Merchandise object. But this is definitely not efficient seems to defeat the purpose of being able to Bind using Path=SomeObject.Property.
Any hints on how to solve this?
Thanks, Rob.
You need to raise a PropertyChanged event on the properties of your Merchandise class. So that class needs to implement the INotifyPropertyChanged interface as well as your view model class. Otherwise, the UI doesn't know that anything's changed.
Related
So I have a Grid with some checkboxes, etc inside it and wanted to set them all to readonly , I added the IsEnabled part below:
<Grid IsEnabled="{Binding IsFieldReadOny}">
And in the code behind added this:
Private _isFieldReadOnly As Boolean = True
Public Property IsFieldReadOny() As Boolean
Get
Return _isFieldReadOnly
End Get
Set(value As Boolean)
_isFieldReadOnly = value
End Set
End Property
But when I put breakpoint, it does not get hit or do anything.
If I manually hard code a True for the grid, then it works.
I am new to both WPF and VB syntax, so it might be something easy that I am not doing right.
Here is a very simple example of MVVM and binding with one way out of TONS to do things. Binding in and of itself has many many options of traversing a visual tree with 'RelativeSource' and scoping. As well as mode options and other settings. I chose to focus on keeping it simple though. I just want a view that has a textbox, you can change yourself, a button you can hit, a label that will update from the text you changed.
So here is a basic view:
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:SimpleWPF"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<StackPanel>
<TextBox Text="{Binding Text}" Height="30" />
<Button Content="Example" Command="{Binding DoCommand}" />
<Label Content="{Binding Output}" Height="30" />
</StackPanel>
</Window>
I want to set up a single helper class for a 'DelegateCommand'. You can do this many ways but essentially I am saving repeat methods for later reuse for commands to help with an ICommand interface.
Public Class DelegateCommand(Of T)
Implements ICommand
Private _execute As Action(Of T)
Public Sub New(execute As Action(Of T))
_execute = execute
End Sub
Public Event CanExecuteChanged As EventHandler
Private Event ICommand_CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged
Private Function ICommand_CanExecute(parameter As Object) As Boolean Implements ICommand.CanExecute
Return True
End Function
Private Sub ICommand_Execute(parameter As Object) Implements ICommand.Execute
_execute.Invoke(DirectCast(parameter, T))
End Sub
End Class
Now in my Code behind of the view it should be pretty minimal except this:
Class MainWindow
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
Me.DataContext = New MainViewModel()
End Sub
End Class
And my MainViewModel is pretty simple in this case is pretty simple and I am only implementing INotifyPropertyChanged. I would usually do most of my stuff like this in a base class and inherit that on larger solutions.
Imports System.ComponentModel
Public Class MainViewModel
Implements INotifyPropertyChanged
Private _text As String
Public Property Text As String
Get
Return _text
End Get
Set(ByVal value As String)
_text = value
OnPropertyChanged(NameOf(Text))
End Set
End Property
Private _output As String
Public Property Output As String
Get
Return _output
End Get
Set(ByVal value As String)
_output = value
OnPropertyChanged(NameOf(Output))
End Set
End Property
Public Sub New()
_text = "Test"
End Sub
Public ReadOnly Property DoCommand As New DelegateCommand(Of Object)(AddressOf DoIt)
Private Sub DoIt(obj As Object)
Output = $"{Text} {DateTime.Now.ToLongDateString}"
End Sub
#Region "Implement INotifyProperty Changed"
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Public Sub OnPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
#End Region
End Class
When you use a generic binding you are looking at the DataContext of the object and by generic I mean a {Binding PropertyName} without any other parameters. In order to bind to a property within your code behind (which I don't recommend doing) then you need to tell the binding to look at that location. You also need to use a dependency property for binding on UIElements since it's already built in.
So to make this work I've named the Window the Grid is in 'window'. Then I've given the binding expression a direct connection to the property.
<Grid IsEnabled="{Binding IsReadOnlyField, ElementName=window}" />
I've then added a binding to the Checkbox as well to the same thing.
<CheckBox Content="Is Grid Enabled" IsChecked="{Binding IsReadOnlyField, ElementName=window}" />
Then in the code behind I've changed the property to a DependencyProperty.
public bool IsReadOnlyField
{
get { return (bool)GetValue(IsReadOnlyFieldProperty); }
set { SetValue(IsReadOnlyFieldProperty, value); }
}
public static readonly DependencyProperty IsReadOnlyFieldProperty =
DependencyProperty.Register(nameof(IsReadOnlyField), typeof(bool), typeof(MainWindow));
This will get the binding working.
If you are not using the code behind and are binding to a ViewModel or any class you should preferably make that class interface INotifyPropertyChanged (although you can also make that ViewModel inherit from DependencyObject and use the same DependencyPropery... It's just normally used for UI elements). Then write the property as normal and in the setter call the property changed event. However, you will most likely set the binding back to the way you had it and just put that ViewModel as the DataContext.
There's A LOT to explain about binding as it can be very flexible and used many different ways. Once you get it though you got it and learning more ways to bind will be simple. I suggest learning exactly how the binding takes place so that you can manipulate and choose the best binding for any situation.
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
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.
Let's say I have a property called Greeting that is principally composed of two bound properties: LastName and FirstName. Can I subscribe to updates on first and last name so I can force a refresh with OnPropertyChanged() for my Greeting property. Here's a simple example:
View
<TextBox Text="{Binding FirstName}" />
<TextBox Text="{Binding LastName}" />
<TextBlock Text="{Binding Greeting}" />
ViewModel
Public Property FirstName() As String
Get
Return _firstName
End Get
Set(ByVal value As String)
_firstName = value
OnPropertyChanged("FirstName")
End Set
End Property
'... Omitting LastName for brevity ...
Public ReadOnly Property Greeting() As String
Get
Return String.Format("Hello {0} {1}", Firstname, LastName)
End Get
End Property
The way this is currently set up, nothing will ever update the Greeting binding. I could put OnPropertyChanged("Greeting") in the setter for FirstName and LastName, but this feels wrong. In a more complex example, I'd rather each object just take care of refreshing itself when something changes.
Q:) Can I force an update for a ReadOnly Property when one of the Properties it's composed of changes?
You can call PropertyChange of Greetings from setter of FirstName and LastName
Public Property FirstName() As String
Get
Return _firstName
End Get
Set(ByVal value As String)
_firstName = value
OnPropertyChanged("FirstName")
OnPropertyChanged("Greeting")
End Set
End Property
OR
You can subscribe to PropertyChanged of your ViewModel in itself
AddHandler this.PropertyChanged, AddressOf PropertyChanged
and in PropertyChanged you can check which property is changed depending on that you can RaisePropertyChanged for Greeting
Borrowing from nit's answer, just to round it out a little. Here's what I did to fire an update on the Greeting property when FirstName or LastName changes:
Private Sub UpdateGreeting(ByVal sender As Object, ByVal e As PropertyChangedEventArgs) _
Handles Me.PropertyChanged
If e.PropertyName = "FirstName" OrElse e.PropertyName="LastName" Then
OnPropertyChanged("Greeting")
End If
End Sub
It handles the PropertyChanged event that is already implemented as part of the INotifyPropertyChanged interface on the ViewModel.
Then it checks if the PropertyName value of the event argument is equal to "FirstName" or "LastName".
If so, it manually raises the OnPropertyChanged() method for the Greeting property.
I am developing a WPF application using the MVVM design pattern.
I have a ViewModel which implements INotifyPropertyChanged via it's base class. The ViewModel contains a property which is then bound to two text boxes. Relevant code below.
ViewModelBase
Public MustInherit Class ViewModelBase : Implements INotifyPropertyChanged
Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged
Protected Sub onPropertyChanged(propertyName As String)
If Not propertyName Is Nothing Then RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
End Sub
End Class
ViewModel
Public Class TemplateEditVM : Inherits ViewModelBase
Public Property Name As String
Get
Return _Template.Name
End Get
Set(value As String)
If Not _Template.Name = value Then
_Template.Name = value
onPropertyChanged("TemplateEditName")
End If
End Set
End Property
End Class
View
<TextBox Text="{Binding Path=Name}" />
<TextBox Text="{Binding Path=Name}" />
The value of the property Name correctly populates both text boxes when the View is first loaded. The problem is that when I change the text in one of the text boxes the text of the other doesn't change, even though the underlying property has. If I step through it I can see that the PropertyChanged event is being fired.
Can anybody tell me why? Many thanks for any help.
Set your binding mode to Twoway
<TextBox Text="{Binding Path=Name, Mode="TwoWay"}" />
And your on propertyChanged method should math the exact name you bind to