I've stumbled over the following problem. I've got a checkbox whose IsChecked property is bound to a CLR property in my MainWindow class. Here's the source code.
Code behind (MainWindow.xaml.cs):
namespace MenuItemBindingTest {
public partial class MainWindow : Window, INotifyPropertyChanged {
private bool m_backedVariable = false;
public bool IsPressAndHoldEnabled {
get { return this.m_backedVariable; }
set {
this.m_backedVariable = value;
OnPropertyChanged("IsPressAndHoldEnabled");
MessageBox.Show("Item changed: " + this.m_backedVariable);
}
}
public MainWindow() {
InitializeComponent();
this.m_checkbox.DataContext = this;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName) {
if (this.PropertyChanged != null) {
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
XAML code (MainWindow.xaml):
<Window x:Class="MenuItemBindingTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Binding Problem Test" Width="525" Height="350">
<DockPanel>
<CheckBox x:Name="m_checkbox"
IsChecked="{Binding IsPressAndHoldEnabled}"
HorizontalAlignment="Center" VerticalAlignment="Center"
Content="Is Press and Hold enabled"/>
</DockPanel>
</Window>
The problem now is that the set accessor for the property IsPressAndHoldEnabled is never called (ie. the message box never shows) when the user checks or unchecks the check box. It does, however, work when I rename the property to something else - like IsPressAndHoldEnabled2.
My question now is: Why can't I use IsPressAndHoldEnabled as name for my property? Does this have anything to do with the property Stylus.IsPressAndHoldEnabled existing?
Interesting. I don't have answers why, but I have workarounds:
Seperating the IsPressAndHoldEnabled property out to a seperate ViewModel class worked, unless the class was derived from FrameworkElement.
Also, changing from a regular property to a Dependency Property in the same MainWindow class worked -- the DP changed callback fires.
Have you specified TwoWay as your binding mode? Although I think CheckBox.IsChecked defaults to TwoWay binding mode...
I think you may have messed up your binding context, so that it is not finding the IsPressAndHoldEnabled property. Bindings in WPF fail silently -- a royal pain if you ask me.
Check that the check-box is really bound to that property, and that the binding context really is your MainWindodw class object.
Related
I have a bunch of textboxes I'm trying to bind to strings in my viewmodel. I thought I had everything set up correctly, but nothing is appearing in the textboxes.
Here's my XAML and one of the textboxes I'm trying to bind.
<Window x:Class="Server.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
xmlns:l="clr-namespace:Server"
xmlns:viewmodel="clr-namespace:Server.ViewModels"
Title="MainWindow">
<Window.DataContext>
<viewmodel:MainWindowViewModel />
</Window.DataContext>
<TextBlock Name="ShipLatTB"
FontSize="17"
Text="{Binding Path=CurrentShipLat, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
Here's the viewmodel:
namespace Server.ViewModels
{
class MainWindowViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _currentShipLat;
public string CurrentShipLat
{
get { return _currentShipLat; }
set { _currentShipLat = value; OnPropertyChanged("CurrentShipLat"); }
}
// Create the OnPropertyChanged method to raise the event
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
}
I tested to make sure data is actually in '_currentShipLat' by setting it equal to "test" in a command, and debugged to verify it. Not sure what else is wrong?
Note: This textbox is supposed to be able to dynamically update.
Edit: How about giving a reason for the downvote and voting to close? That doesn't help anyone.
Make sure you set the field _currentShipLat before the WPF window is initialized.
If you do it after initialisation of the window, WPF will never 'see' this change because it doesn't trigger the property changed event. Either make sure the field is set before the window is initialized or use the setter of the property instead of directly setting the field.
I'm pulling what's remaining of my hair out trying to get something to work in Silverlight that works out of the box in WPF.
I have some CheckBoxes on a form which represent items - The Checked property is bound to a bool in my ViewModel (one viewmodel per item). When the checkbox is checked it adds the item to a list in another ViewModel - before this happens I want to perform some validation (in my case count how many items are in the list in the other ViewModel, and if its reached a limit show the user a message) and if this validation fails don't add it to the list and uncheck the box. When it runs, after the validation check is done in the bool property setter I can see the value set back to false, but this is not reflected back in the CheckBox in the UI in Silverlight so the CheckBox remains checked. In WPF this issue does not occur.
The following code demonstrates the issue - for brevity instead of performing the validation I'm just always forcing the box to unchecked when it is checked.
XAML
<UserControl x:Class="CheckboxTest.SL.MainPage"
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"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="400">
<Grid x:Name="LayoutRoot" Background="White">
<CheckBox IsChecked="{Binding IsSelected, Mode=TwoWay}" Margin="20"/>
</Grid>
</UserControl>
Code Behind
namespace CheckboxTest.SL
{
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
this.DataContext = new MainPageViewModel();
}
}
public class MainPageViewModel : INotifyPropertyChanged
{
private bool _isSelected;
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
if (_isSelected) //if checked always uncheck
_isSelected = false; //this does not get reflected in UI in Silverlight
OnPropertyChanged("IsSelected");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler changedEventHandler = this.PropertyChanged;
if (changedEventHandler == null)
return;
changedEventHandler((object)this, new PropertyChangedEventArgs(propertyName));
}
}
}
I know that people used to get round this issue when it was in WPF pre .NET 4.0 by either setting the property binding to Async (not allowed in Silverlight) or to implement a dummy IValueConverter (tried this and it had no effect in Silverlight).
Can anyone suggest a way to get the above to work in Silverlight please?
One way to do this could be to bind the IsEnabled property of the CheckBox to a boolean property in your ViewModel where you can perform the validation.
public bool CanEditCheckBox
{
get
{
// perform validation here
return list.Length < 100;
}
}
Edit
I tested your code, and it seems to work like intended.
I'm trying to convert my console app to a nice WPF GUI. Am getting a little stuck on this code and was wondering if someone can help?
In my xaml I have this:
<CheckBox IsChecked="{Binding CL.LoggedIn}"></CheckBox>
to try and bind the value of the checkbox to the value of CL.LoggedIn. CL is my ConnectionLibrary.cs class in a referenced class library.
In the code behind for the xaml page i declare CL as follows :
public ConnectionLibrary CL = new ConnectionLibrary();
In the connection library class I have added :INotifyPropertyChanged to the class declaration and added the following code:
public event PropertyChangedEventHandler PropertyChanged;
// Create the OnPropertyChanged method to raise the event
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
I have changed the LoggedIn property to now look like this:
private bool loggedIn;
public bool LoggedIn {
get { return loggedIn; }
set { loggedIn = value; OnPropertyChanged("LoggedIn"); }
}
However, it doesnt seem to work in my xaml? I dont get any binding errors in the output window, but it doesnt reflect the value of LoggedIn correctly.
Any ideas?
Thanks!
Have you set the datacontext of your view?
In the code-behind of your XAML file, you need to do:
this.DataContext = CL;
then the binding is:
<CheckBox IsChecked="{Binding LoggedIn}"></CheckBox>
The binding will find the the named path (i.e. LoggedIn) on the object that is in the DataContext.
EDIT: The default binding is one-way, this means it only gets updated from your ViewModel.
For controls that can be inputed data (i.e: TextBox, CheckBox...) you can set the Binding as "TwoWay". The Binding expression becomes:
<CheckBox IsChecked="{Binding LoggedIn, Mode="TwoWay"}"></CheckBox>
Now whenever the Checked state changes in the UI, it is reflected in your ViewModel.
When you use Binding like this, it binds to the current DataContext, not to the page itself.
The easiest way to fix this would be to set DataContext = this at the end of the constructor of the page.
The proper way to fix it would be to use MVVM. That would mean having ConnectionLibrary in a property of another class and set the DataContext to this other class.
<CheckBox IsChecked="{Binding LoggedIn}"></CheckBox>
I like to create a UserControl with own Header Property.
public partial class SomeClass: UserControl, INotifyPropertyChanged
{
public SomeClass()
{
InitializeComponent();
}
private string header;
public string Header
{
get { return header; }
set
{
header = value;
OnPropertyChanged("Header");
}
}
protected void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
}
in UserContol xaml:
Label Name="lbHeader" Grid.Column="0" Content="{Binding Path=Header}"
If I set the value: AA2P.Header = "SomeHeeaderText"; than the label.Caption will not changed. How can I solve that problem?
In Windows xaml:
uc:SomeClass x:Name="AA2P"
If I give directly a value to label (lbHeader.Content = header;) instead of OnPropertyChanged("Header"); its work but, why it does not work with OnPropertyChanged?
I need to use DataContext for somethig else. I try to use dependency property but something is wrong.
public partial class tester : UserControl
{
public tester()
{
InitializeComponent();
}
public string Header
{
get { return (string)GetValue(MyDependencyProperty); }
set { SetValue(MyDependencyProperty, value); }
}
public static readonly DependencyProperty MyDependencyProperty =
DependencyProperty.Register("MyDependencyProperty", typeof(string), typeof(string));
}
<UserControl ... x:Name="mainControl">
<TextBlock Text="{Binding ElementName=mainControl, Path=MyDependencyProperty}"/>
</UserControl>
<Window ...>
<my:tester Header="SomeText" />
</Window>
It does not work. What I do wrong?
Thanks!
The easiest approach is to just the DataContext of your object. One way of doing that is directly in the constructor like this:
public SomeClass()
{
InitializeComponent();
DataContext = this;
}
Setting the DataContext will specify where new data should be fetched from. There are some great tips and information in the article called WPF Basic Data Binding FAQ. Read it to better understand what the DataContex can be used for. It is an essential component in WPF/C#.
Update due to update of the question.
To my understanding you should change the first argument of DependencyProperty.Register to the name of the property that you want to bind to, here "Header" as well as the second argument to the type of your class, here SomeClass. That would leave you with:
public static readonly DependencyProperty MyDependencyProperty =
DependencyProperty.Register("Header", typeof(SomeClass), typeof(string));
But i seldom use dependency properties so I am not positive that this is it, but its worth a try..
If you need the Data context for something else. You can also utilize the ElementName property in the Binding.
<UserControl
x:Class="MyControl.MyUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Name="mainControl">
<TextBlock Text="Binding ElementName=mainControl, Path=MyDependencyProperty}"/>
</UserControl>
[Edit]
I should add something. Make the "Header" property a dependency property, this will make your live much easier. In UI Controls you should make property almost always a dependency property, every designer or user of your control will thank you.
The UserControl itself needs the DataContext of where it is used later. But the controls inside the UserControl need the UserControl as their DataContext, otherwise they also will inherit the DataContext from the later usage context. The trick is to set the DataContext of the UserControl's child to that of the UserControl, so it now can use the dependency properties of the UserControl.
<UserControl x:Class="MyControl.MyUserControl">
<Grid DataContext="{Binding RelativeSource={RelativeSource FindAncestor,
AncestorType=UserControl,AncestorLevel=1}}">...</Grid>
</UserControl>
If you do this this way the children of the Grid can have simple {Binding dp's name} without additionally ElementName parameters.
In WPF I have a collection of bool? values and I want to bind each of these to a separate checkbox programmatically. I want the bindings to be TwoWay so that changing the value of the individual item in the collection in code updates the check box and vice versa.
I have spent ages trying to figure out how to do this and I am completely stuck. With the following code the checkbox only gets the right value when the window is loaded and that's it. Changing the check box doesn't even update the value in the collection. (UPDATE: this appears to be a bug in .NET4 as the collection does get updated in an identical .NET3.5 project. UPDATE: Microsoft have confirmed the bug and that it will be fixed in the .NET4 release.)
Many thanks in advance for your help!
C#:
namespace MyNamespace
{
public partial class MyWindow : Window, INotifyPropertyChanged
{
public MyWindow()
{
InitializeComponent();
DataContext = this;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public List<bool?> myCollection = new List<bool?>
{ true, false, true, false, true, false };
public List<bool?> MyCollection
{
get { return myCollection; }
set { myCollection = value; }
}
}
}
XAML:
<CheckBox IsChecked="{Binding Path=MyCollection[0], Mode=TwoWay}">
There are a few things that need changing here to get this to work. Firstly you'll need to wrap your boolean value in an object that implements the INotifyPropertyChanged interface in order to get the change notification that you are looking for. Currently you are binding to boolean values in your collection which do not implement the interface. To do this you could create a wrapper class like so :
public class Wrapper: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private bool val = false;
public bool Val
{
get { return val; }
set
{
val = value;
this.OnPropertyChanged("Val");
}
}
public Wrapper(bool val)
{
this.val = val;
}
}
You'll then want to create these objects in your form instead of a list of booleans. You may also want to use an observable collection instead of a list so that notification of items being added and removed are sent. This is shown below:
public Window1()
{
InitializeComponent();
this.DataContext = this;
}
private ObservableCollection<Wrapper> myCollection = new ObservableCollection<Wrapper>()
{new Wrapper(true), new Wrapper(false), new Wrapper(true)};
public ObservableCollection<Wrapper> MyCollection
{
get { return myCollection; }
}
The next thing to do is to display a list of check boxes in your ui. To do this WPF provides itemscontrols. ListBox is an itemscontrol so we can use this as a starting point. Set the itemssource of a listbox to be MyCollection. We then need to define how each Wrapper object is going to be displayed in the list box and this can be done with a datatemplate which is created in the windows resources. This is shown below :
<Window.Resources>
<DataTemplate x:Key="myCollectionItems">
<CheckBox IsChecked="{Binding Path=Val, Mode=TwoWay}"></CheckBox>
</DataTemplate>
</Window.Resources>
<Grid>
<ListBox ItemsSource="{Binding Path=MyCollection}" ItemTemplate="{StaticResource myCollectionItems}"></ListBox>
</Grid>
This should get you up and running with a simple demo of checkboxes that have values bound to a list of booleans.
What makes you think it's not working? It's working for me :)
Here's my test XAML:
<UniformGrid>
<CheckBox IsChecked="{Binding Path=MyCollection[0], Mode=TwoWay}"/>
<ListBox ItemsSource="{Binding MyCollection}"/>
<Button Content="Test" Click="Button_Click"/>
</UniformGrid>
Here's my code behind:
private void Button_Click(object sender, RoutedEventArgs e)
{
}
(the rest is the same as yours)
I placed a breakpoint on Button_Click and checked MyCollection[0] it was updated according to the IsChecked value of the CheckBox.
Try changing your collection type from List<bool?> to ObservableCollection<bool?> perhaps that is the reason you think it's not working for you (the fact that changes to the collection are not reflected anywhere else in your view).
Change your List<bool?> to an ObservableCollection<bool?>. A List does not raise the change notifications that WPF needs to update the UI. An ObservableCollection does. This handles the case where the list entry is changed and the CheckBox needs to update accordingly.
In the other direction, it works for me even with a List<bool?> -- i.e. toggling the checkbox modifies the value in the collection. Your binding syntax is certainly correct.