I'm trying to simplify some code by putting the ViewModel models into the code behind and binding the DataContext as "this", but it seems to work differently, in the following example:
Why is it when the button is clicked, the TextBlock bound to "Message" does not change, even though OnPropertyChanged("Message") is called?
XAML:
<Window x:Class="TestSimple223.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel HorizontalAlignment="Left">
<Button Content="Button"
Click="button1_Click" />
<TextBlock
Text="{Binding Path=Message, Mode=TwoWay}"/>
<TextBlock
x:Name="Message2"/>
</StackPanel>
</Window>
Code Behind:
using System.Windows;
using System.ComponentModel;
namespace TestSimple223
{
public partial class Window1 : Window
{
#region ViewModelProperty: Message
private string _message;
public string Message
{
get
{
return _message;
}
set
{
_message = value;
OnPropertyChanged("Message");
}
}
#endregion
public Window1()
{
InitializeComponent();
DataContext = this;
Message = "original message";
Message2.Text = "original message2";
}
private void button1_Click(object sender, RoutedEventArgs e)
{
Message = "button was clicked, message changed";
Message2.Text = "button was click, message2 changed";
}
#region INotify
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}
}
You haven't marked your class as being available for property change notification. Change the heading to
public partial class Window1 : Window, INotifyPropertyChanged
Just because you implement the methods doesn't mean that WPF knows that a class supports change notification - you need to tell it by marking it with INotifyPropertyChanged. This way, the binding mechanism can identify your class as a potential update target.
Related
I'm trying to simplify some code by putting the ViewModel models into the code behind and binding the DataContext as "this", but it seems to work differently, in the following example:
Why is it when the button is clicked, the TextBlock bound to "Message" does not change, even though OnPropertyChanged("Message") is called?
XAML:
<Window x:Class="TestSimple223.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel HorizontalAlignment="Left">
<Button Content="Button"
Click="button1_Click" />
<TextBlock
Text="{Binding Path=Message, Mode=TwoWay}"/>
<TextBlock
x:Name="Message2"/>
</StackPanel>
</Window>
Code Behind:
using System.Windows;
using System.ComponentModel;
namespace TestSimple223
{
public partial class Window1 : Window
{
#region ViewModelProperty: Message
private string _message;
public string Message
{
get
{
return _message;
}
set
{
_message = value;
OnPropertyChanged("Message");
}
}
#endregion
public Window1()
{
InitializeComponent();
DataContext = this;
Message = "original message";
Message2.Text = "original message2";
}
private void button1_Click(object sender, RoutedEventArgs e)
{
Message = "button was clicked, message changed";
Message2.Text = "button was click, message2 changed";
}
#region INotify
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}
}
You haven't marked your class as being available for property change notification. Change the heading to
public partial class Window1 : Window, INotifyPropertyChanged
Just because you implement the methods doesn't mean that WPF knows that a class supports change notification - you need to tell it by marking it with INotifyPropertyChanged. This way, the binding mechanism can identify your class as a potential update target.
I have a problem with data binding. A test application that I have looks as follows:
There's a mainwindow:
<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:Controls="clr-namespace:WpfApplication2"
x:Name="main"
Title="MainWindow" >
<StackPanel >
<Button Content="Button" Click="Button_Click"/>
<Controls:UserControl1 />
</StackPanel>
</Window>
And a user control:
<UserControl x:Class="WpfApplication2.UserControl1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
x:Name="uc"
>
<Grid >
<TextBox Width="40" Text="{Binding ElementName=main,
Path=Status, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
</Grid>
</UserControl>
I want to click the button on the main window to have the value of text box in user control updated:
The code of MainWindow file:
namespace WpfApplication2
{
public partial class MainWindow : Window, INotifyPropertyChanged
{
public MainWindow()
{
InitializeComponent();
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
private string _status;
public string Status
{
get { return _status; }
set
{
if (value != _status)
{
_status = value;
RaisePropertyChanged("Status");
}
}
}
private void Button_Click(object sender, RoutedEventArgs e)
{
if (Status == "one")
Status = "two";
else
Status = "one";
}
}
}
And the code of UserControl:
namespace WpfApplication2
{
public partial class UserControl1 : UserControl, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null) PropertyChanged(this, e: new PropertyChangedEventArgs(propertyName));
}
public UserControl1()
{
InitializeComponent();
}
}
}
I don't understand why doesn't it work, but the PropertyChanged is always null. The example is in the simplest form I can imagine...
You are trying to access the parent window using the ElementName binding, as far as I am aware, that is not possible. You can however use a relative source binding to get the parent window:
<TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType=Window}, Path=Status}" ... />
Follow up edit:
Your child user control should look like this:
<UserControl
...
x:Name="usr">
<Grid>
<TextBlock Text="{Binding Message, ElementName=usr}"/>
</Grid>
</UserControl>
You will then need to create a dependency property called 'Message' (This is just an example, I'm not sure what you want to call this property).
public partial class YourUserControl: UserControl
{
public string Message
{
get { return (string)GetValue(MessageProperty); }
set { SetValue(MessageProperty, value); }
}
// Using a DependencyProperty as the backing store for Message. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MessageProperty =
DependencyProperty.Register("Message", typeof(string), typeof(YourUserControl), new PropertyMetadata(""));
public UserControl1()
{
InitializeComponent();
}
}
Then, when you declare this in your parent user control, simply set the binding of the Message property to whatever property you need to bind to in your parent user control:
<YourNamespace:YourUserControl Message="{Binding PropertyName, ElementName=elementName}" />
A simple WPF window with a label on it:
<Window x:Name="MainWindow1" x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:A="clr-namespace:WpfApplication1"
xmlns:System="clr-namespace:System;assembly=mscorlib"
Title="MainWindow" Height="384" Width="669.114" Icon="alarmclock.ico" Closing="OnClosing" Loaded="OnLoaded" >
<Grid x:Name="Grid1">
<Label x:Name="Label1" Content="{Binding AlarmStatus}" HorizontalAlignment="Left" Margin="10,314,0,0" VerticalAlignment="Top"/>
</Grid>
</Window>
Wire up an object so that the object can be bound to the labels content property. Yes I see the text Off on the window:
public class PropertyChangedBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
//Raise the PropertyChanged event on the UI Thread, with the relevant propertyName parameter:
Application.Current.Dispatcher.BeginInvoke((Action)(() =>
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}));
}
}
public class UserViewModel : PropertyChangedBase
{
private string _alarmStatus = "Off";
public string AlarmStatus
{
get { return _alarmStatus; }
set
{
_alarmStatus = value;
OnPropertyChanged("AlarmStatus"); //This is important!!!
}
}
}
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
I thought I would be able to change the value of the label like this:
private void OnLoaded(object sender, RoutedEventArgs e)
{
//Im setting a value but the UI does not change. The label still says Off
UserViewModel aaaa = new UserViewModel();
aaaa.AlarmStatus = "On";
}
You're creating a new instance of the ViewModel, but the View has no "connection" to that.
the aaaa instance dies (goes out of scope and is de-referenced) immediately after the OnLoaded() method finishes executing, and is garbage collected a moment later.
What you need is to grab the actual instance of the ViewModel that's currently being used by the Window:
private void OnLoaded(object sender, RoutedEventArgs e)
{
var viewModel = this.DataContext as UserViewModel;
viewModel.AlarmStatus = "On";
}
I suggest you read Rachel's Article to better understand the concept of DataContext in WPF.
I'm trying to do a simple binding but I'm having some problems. I have a text block and a button. The textblock is binded to a property called "word". When you press the button the value of word changes and I want to automacally update the text block. This is a classic example, please explain me what I'm doing wrong:
namespace WpfApplication5
{
public partial class MainWindow : Window, INotifyPropertyChanged
{
private string _word;
public string word
{
get { return _word; }
set
{
_word= value;
RaisePropertyChanged(word);
}
}
private void change_Click(object sender, RoutedEventArgs e)
{
word= "I've changed!";
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}
}
And my XAML with the binding:
<Window x:Class="WpfApplication5.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<TextBlock HorizontalAlignment="Left" Margin="210,152,0,0" TextWrapping="Wrap" Text="{Binding word}" VerticalAlignment="Top"/>
<Button x:Name="change" Content="Change" HorizontalAlignment="Left" Margin="189,235,0,0" VerticalAlignment="Top" Width="75" Click="change_Click"/>
</Grid>
</Window>
You are raising a PropertyChanged event for a property named I've changed!, because you pass the value of the property word to RaisePropertyChanged. You need to pass the name of the property instead:
RaisePropertyChanged("word");
This answer assumes that the data context is set correctly. If not, you need to fix that too:
DataContext = this;
I have this custom wpf user control:
ShowCustomer.xaml:
<UserControl x:Class="TestControlUpdate2343.Controls.ShowCustomer"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid>
<TextBlock Text="{Binding Message}"/>
</Grid>
</UserControl>
ShowCustomer.xaml.cs:
using System.Windows.Controls;
using System;
using System.ComponentModel;
namespace TestControlUpdate2343.Controls
{
public partial class ShowCustomer : UserControl, INotifyPropertyChanged
{
#region ViewModelProperty: Message
private string _message;
public string Message
{
get
{
return _message;
}
set
{
_message = value;
OnPropertyChanged("Message");
}
}
#endregion
public ShowCustomer()
{
InitializeComponent();
DataContext = this;
Message = "showing test customer at: " + DateTime.Now.ToString();
}
#region INotifiedProperty Block
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
}
And I display it from this XAML:
Window1.xaml:
<Window x:Class="TestControlUpdate2343.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:controls="clr-namespace:TestControlUpdate2343.Controls"
Title="Window1" Height="300" Width="300">
<StackPanel HorizontalAlignment="Left" Margin="10">
<controls:ShowCustomer x:Name="ShowCustomerControl" Margin="0 0 0 10"/>
<Button Content="Refresh Control"
Click="Button_RefreshControls_Click"
Margin="0 0 0 10"/>
</StackPanel>
</Window>
And I would like to update the control (i.e. in this example show the current time) from my event handler in code behind:
using System.Windows;
namespace TestControlUpdate2343
{
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
}
private void Button_RefreshControls_Click(object sender, RoutedEventArgs e)
{
//ShowCustomerControl.Refresh()???
}
}
}
How can I force a refresh of my custom control from code behind, or force it to reload somehow so when I click the button it shows the current time?
in Window1.xaml.cs -
private void Button_RefreshControls_Click(object sender, RoutedEventArgs e)
{
ShowCustomerControl.Refresh();
}
in ShowCustomer.xaml.cs -
public ShowCustomer()
{
InitializeComponent();
DataContext = this;
Refresh();
}
public void Refresh()
{
Message = "showing test customer at: " + DateTime.Now.ToString();
}
Hope this helps!!
Or have a LastUpdate property on ShowWindow and set that, which then regenerates the Message property.