I can't seem to bind a control's value to an object. I want to bind a TextBox to a string object, the idea is that when textbox's text changes, it should automatically change the object as well. couldn't figure out what I'm doing wrong. Here is what I have tried:
MainWindow.xaml.cs:
public partial class MainWindow : Window
{
string str;
public MainWindow()
{
InitializeComponent();
this.DataContext = str;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
}
}
and MainWindow.xaml:
<Window x:Class="WpfApp1.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:WpfApp1"
mc:Ignorable="d"
Title="MainWindow" Height="150" Width="150">
<Grid Margin="0,0,642,319">
<TextBox HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" Text="{Binding str}" VerticalAlignment="Top" Width="120" Margin="0,0,-120,-46" />
<Button Content="Button" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Click="Button_Click" Height="23" Margin="0,28,-75,-51" RenderTransformOrigin="0.423,2.257" />
</Grid>
</Window>
So, when I enter something to the textbox and click the button, I should see the text in str while debugging but it is always null
Change the str to a auto property:
public string str { get; set; }
Change the DataContext to:
DataContext = this;
The DataContext is the class which will hold your binding properties/commands/events.
The properties/commands/events need to be public in order to be accessible by your view.
For the two-way binding to work, you have to notify to the UI binding that the property has been changed and for that you need to implement the INotifyPropertyChanged interface for the class which holds the properties which have been bound in the UI. You will need a private property and you cannot notify from a auto-property.
Simple Example:
public class Sample : INotifyPropertyChanged
{
private string _str;
public string Str
{
get { return _str; }
set
{
_str = value;
NotifyPropertyChanged(nameof(Str));
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged(string propName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
}
}
First, data bindings in WPF only work with public properties. So you must explicitely declare one in your code behind (instead of string str;)
public string str { get; set; }
Second, the DataContext property of a view defines the object / class in which the property will be searched for the bindings. The line this.DataContext = str; in your example means that you want your bindings in the view to be looked for inside the str object (which is a string). You should replace this line by
this.DataContext = this;
so that the bindings will be searched inside the code behind of this view itself.
Remark
You could also stay with the line this.DataContext = str; if str is a public property and bind using an expression such as
<TextBox Text="{Binding .}" />
which will bind to the value of the DataContext property.
Maybe you can use MVVM light to do the binding.
Related
In a simple trying-to-learn-WPF experiment I'm trying to bind a property ("InternalName") of an instance of MyModel to the contents of TextBlock "MainWindowTextBlock". Clicking the ``ChangeNameButton" changes the InternalName property of mymodel, but that property change never makes it through to the TextBlock. Nothing happens. What am I doing wrong?
XMAL
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:UserControlExperiments"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<StackPanel Grid.Row ="0">
<Button Width="100" Height="20" Name="ChangeName" Content="Change the Name" Click="ChangeNameButtonClick"/>
<TextBlock Text=""/>
<TextBlock Name="MainWindowTextBox" Width="100" Height="20" Text="{Binding Path = mymodel.InternalName, Mode=TwoWay}"/>
</StackPanel>
</Grid>
</Window>
CODE BEHIND
public partial class MainWindow : Window
{
public MyModel mymodel;
public MainWindow()
{
InitializeComponent();
DataContext = this.DataContext;
mymodel = new MyModel("The old name");
}
private void ChangeNameButtonClick(object sender, RoutedEventArgs e)
{
mymodel.InternalName = "A new name!";
}
}
public class MyModel : INotifyPropertyChanged
{
private string internalname;
public event PropertyChangedEventHandler PropertyChanged;
public MyModel(string nm)
{
InternalName = nm;
}
protected void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public string InternalName
{
get { return internalname; }
set
{
if (internalname != value)
{
internalname = value;
OnPropertyChanged("InternalName");
}
}
}
}
}
The following markup tries to bind to a property named "mymodel" of the current DataContext of the TextBlock, which is inherited from the parent window:
<TextBlock Name="MainWindowTextBox"
Text="{Binding Path = mymodel.InternalName}"/>
So you need to set the DataContext of the window to itself:
DataContext = this;
And you also need to make mymodel a public property since you cannot bind to fields:
public MyModel mymodel { get; }
Then it should work but you probably also want to change the name of the property to comply with the C# naming standards.
You can also remove Mode=TwoWay from the binding. It makes no sense for a TextBlock.
This question already has answers here:
Issue with DependencyProperty binding
(3 answers)
Closed 4 years ago.
I would like to be able to bind complex model (many properties) to UserControl through DependencyProperty, and if model would be edited in UserControl I would like to see this edited information inside my binded model.
Example application: Model, UserControl (xaml + cs), MainWindow (xaml + cs). I have no ViewModel to simplify idea.
Model:
public class MyModel : INotifyPropertyChanged
{
private string _surname;
private string _name;
public string Name
{
get => _name;
set
{
_name = value;
OnPropertyChanged();
}
}
public string Surname
{
get => _surname;
set
{
_surname = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
MyModelEditor.xaml (inside Grid):
<DockPanel>
<TextBox Text="{Binding MyModel.Name}"/>
<TextBox Text="{Binding MyModel.Surname}"/>
</DockPanel>
Also contains this line in UserControl root element:
DataContext="{Binding RelativeSource={RelativeSource Self}}"
MyModelEditor.xaml.cs:
public partial class MyModelEditor : UserControl
{
public MyModel MyModel
{
get => (MyModel)GetValue(MyModelProperty);
set => SetValue(MyModelProperty, value);
}
public static readonly DependencyProperty MyModelProperty =
DependencyProperty.Register("MyModel", typeof(MyModel), typeof(MyModelEditor), new FrameworkPropertyMetadata(null));
public MyModelEditor()
{
InitializeComponent();
}
}
MainWindow.xaml (inside Grid):
<DockPanel>
<Button DockPanel.Dock="Bottom" Content="Press Me!" Click="ButtonBase_OnClick"/>
<controls:MyModelEditor MyModel="{Binding MyModel}"/>
</DockPanel>
MainWindow.xaml.cs:
public partial class MainWindow : Window, INotifyPropertyChanged
{
private MyModel _myModel;
public MyModel MyModel
{
get => _myModel;
set
{
_myModel = value;
OnPropertyChanged();
}
}
public MainWindow()
{
InitializeComponent();
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
MessageBox.Show(MyModel?.Name);
}
}
My test scenario: type text in textbox, press button.
Current behavior: Message after pressing button is empty.
Expected behavior: Message after pressing button is same like in textbox.
I wold not like to bind to all properties separately, because in future I will have much more then two properties.
Why current approach does not work?
How can I achieve my goal?
You are apparently not using the UserControl instance as Binding source in your UserControl's XAML. One way to do this would be to set the Binding's RelativeSource:
<TextBox Text="{Binding MyModel.Name,
RelativeSource={RelativeSource AncestorType=UserControl}}"/>
However, you don't need a new dependency property at all for this purpose. Just bind the UserControl's DataContext to a MyModel instance, like
<controls:MyModelEditor DataContext="{Binding MyModel}"/>
The Bindings in the UserControl's XAML would automatically work with the MyModel object, like this:
<DockPanel>
<TextBox Text="{Binding Name}"/>
<TextBox Text="{Binding Surname}"/>
</DockPanel>
For both of your TextBox controls, you should define their Binding with a TwoWay mode (ms docs on binding modes). Which, basically, would assure that the data flow is working in both direction (i.e. from the view model into the view and the other way around):
<DockPanel>
<TextBox Text="{Binding MyModel.Name, Mode=TwoWay}"/>
<TextBox Text="{Binding MyModel.Surname, Mode=TwoWay}"/>
</DockPanel>
As a good practice, you should always explicitly define what is the mode of the the Binding (NOTE: by default it's OneWay TwoWay - how to know which is the default?).
Another tip would be to go ahead and use MvvmHelpers nuget (github project), which could spare you the time of implementing INotifyPropertyChanged. Besides, you shouldn't re-invent the wheel
EDIT: Fixes are in your GitHub repo
Two things to note here
You have not instantiated your ViewModel (i.e. MyModel), so it was always null
You don't need to create DependencyPropery every time you want to pass some information to your UserControl. You could simply bind the DataContext itself
The ViewModel:
public class ConnectionStatusViewModel : BindableBase
{
private string _txtConn;
public string TextConn
{
get { return _txtConn; }
set { SetProperty(ref _txtConn, value); }
}
}
The XAML:
<UserControl x:Class="k7Bot.Login.Views.ConnectionStatus"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:prism="http://www.codeplex.com/prism"
prism:ViewModelLocator.AutoWireViewModel="True" Width="300">
<Grid x:Name="LayoutRoot">
<Label Grid.Row="1" Margin="10,0,10,0">connected:</Label>
<TextBlock Text="{Binding TextConn}" Grid.Row="1" Grid.Column="1" Margin="10,0,10,0" Height="22" />
</Grid>
</UserControl>
The View:
public partial class ConnectionStatus : UserControl
{
public ConnectionStatus()
{
InitializeComponent();
}
}
In another module, I have an event listener, that eventually runs this code:
ConnectionStatusViewModel viewModel = _connectionView.DataContext as ConnectionStatusViewModel;
if (viewModel != null)
{
viewModel.TextConn = "Testing 123";
}
The code runs but the TextConn is updated and does not display in the UI
Are you sure TextConn does not update? Because it can update but the display could not change. You should implement the INotifyPropertyChanged interface and after you make any changes to TextConn call the implemented OnPropertyChanged("TextConn"); or whatever you name the function. This will tell the UI that the value has changed and it needs to update.
The UserControl's DataContext gets its value when the UC is initialized. Then you get a copy of the DataContext, cast it to a view model object, and change the property. I don't believe that the UC gets its original DataContext updated in this scenario.
Probably you need to use a message mediator to communicated changes between different modules.
After some troubleshooting, this code works, the issue was that I was running this code:
ConnectionStatusViewModel viewModel = _connectionView.DataContext as ConnectionStatusViewModel;
if (viewModel != null)
{
viewModel.TextConn = "Testing 123";
}
before the view was actually activated. Silly, but maybe it will help someone down the line.
I've got some problem I need some help with. I want to bind the visibility properties from a view model to the xaml elements so I get some visually changes (collapse or show in this case) by just changing the value in the viewmodel.
I got this xaml
<Window x:Class="PampelMuse.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:welcome="clr-namespace:PampelMuse.Views.Welcome"
xmlns:backend="clr-namespace:PampelMuse.Views.Backend"
xmlns:pampelMuse="clr-namespace:PampelMuse" xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d"
Title="PampelMuse" Height="670" Width="864">
<Grid>
<Image HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Source="Resources/Images/Backgrounds/4.jpg" Stretch="UniformToFill" />
<welcome:WelcomeScreen x:Name="UIWelcome" HorizontalAlignment="Center" VerticalAlignment="Center" Visibility="{Binding ElementName=UiWelcomeVisibility}" />
<backend:BackendUI x:Name="UIBackend" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Visibility="{Binding ElementName=UiBackendVisibility}" />
</Grid>
The visibilities as you can see are binded to the properties UiWelcomeVisibility and UiBackendVisibility in the UIModel. These properties are now defined as followed:
public partial class MainWindow : Window
{
private ViewModel.ViewModel ViewModel = PampelMuse.ViewModel.ViewModel.GetInstance();
public MainWindow()
{
InitializeComponent();
DataContext = ViewModel; // Setting the data context what effects all the xaml elements in this component too, including UIWelcome and BackendUI
ViewModel.UIModel.UiBackendVisibility = Visibility.Collapsed;
}
The ViewModel:
public class ViewModel
{
private static ViewModel instance = new ViewModel();
public UIModel UIModel = UIModel.GetInstance();
public static ViewModel GetInstance()
{
return instance;
}
}
And the UIModel:
public class UIModel
{
private static UIModel instance = new UIModel();
public Visibility UiWelcomeVisibility { get; set; }
public Visibility UiBackendVisibility { get; set; }
public static UIModel GetInstance()
{
return instance;
}
}
I just don't see any coding mistakes here (and I don't get some at runtime in fact) but the BackendUI-visibility-property is not changed by the UiBackendVisibility of UIModel.
Any ideas? Thanks so far.
You are doing the binding wrong. Visibility="{Binding ElementName=UiWelcomeVisibility}" sets the visibility of an element equal to another visual element named "UiWelcomeVisibility". There are two problems with this:
There is no element named "UiWelcomeVisibility" in the first place.
Even if there were, a visual element itself is not a valid value for the Visibility property.
What you want is to databind to the viewmodel instead. Assuming that you have already set the DataContext to the viewmodel, just use
<welcome:WelcomeScreen ... Visibility="{Binding UiWelcomeVisibility}" />
I know a way to do MVC binding of one string to one TextBox. That's how it can be done:
C#:
namespace WpfApplication4
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = Model;
}
public ModelClass Model = new ModelClass();
private void button1_Click(object sender, RoutedEventArgs e)
{
Model.Output += "Setting New Output! ";
}
public class ModelClass : INotifyPropertyChanged
{
string _output;
public event PropertyChangedEventHandler PropertyChanged =
delegate { };
public string Output
{
get { return _output; }
set { _output = value;
PropertyChanged(this,
new PropertyChangedEventArgs("Output"));
}
}
}
}
}
XAML:
<Window x:Class="WpfApplication4.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>
<Button Content="Button" VerticalAlignment="Top"
Name="button1" Click="button1_Click" />
<TextBox VerticalAlignment="Bottom"
Name="textBox1" Text="{Binding Path=Output}" />
</Grid>
</Window>
But I can't find a way to bind a two-dimensional array (or List) to a Grid or DataGrid. Can you help me with it? I couldn't find a working example on SO.
Consider using a DataGrid to display your two-dimensional array, assuming you can store your data as a List<ColumnData> where ColumnData is a class with one property per table column.
The WPF SDK contains a DataGrid, and there are several data grids from vendors available that have additional features.
if you wanna bind data to a datagrid you should be read something about the following.
ICollectionView, BindingListCollectionView
if you have somekind of collection you simply set the itemssource.
<DataGrid ItemsSource="{Binding Path=MyCollection, Mode=OneWay}" />
Collection types are mostly ObservableCollection or DataSet/DataTable. if your collection supports editing and so on, you can do it with the datagrid.