Simple DataBinding in wpf application

Simple DataBinding in wpf application - c#

Hi I am trying to study simple data binding in wpf. I tried and am not succeeding.. please suggest ways..
<Window x:Class="WpfTestApp.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="250" Width="350">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="70"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="50"/>
<RowDefinition Height="50"/>
<RowDefinition Height="50"/>
<RowDefinition Height="50"/>
</Grid.RowDefinitions>
<Label Content="First Name" Grid.Row="0" Grid.Column="0" Height="25" HorizontalAlignment="Stretch"/>
<Label Content="Last Name" Grid.Row="1" Grid.Column="0" Height="25" HorizontalAlignment="Stretch"/>
<Label Content="Full Name" Grid.Row="2" Grid.Column="0" Height="25" HorizontalAlignment="Stretch"/>
<TextBox x:Name="fName" Text="{Binding FirstName, UpdateSourceTrigger=PropertyChanged}" Grid.Row="0" Grid.Column="1" Height="25" HorizontalAlignment="Stretch"/>
<TextBox x:Name="lName" Text="{Binding LastName, UpdateSourceTrigger=PropertyChanged}" Grid.Row="1" Grid.Column="1" Height="25" HorizontalAlignment="Stretch"/>
<Label x:Name="lblFullName" Content="{Binding FirstName}" Grid.Row="2" Grid.Column="1" Height="25" HorizontalAlignment="Stretch"/>
<Button x:Name="cmdCommand" Content="Command" Grid.Row="3" Grid.Column="1" Margin="2" VerticalAlignment="Center" HorizontalAlignment="Center" Click="cmdCommand_Click"/>
</Grid>
</Window>
Now you see, I want that the label lblFullName to be automatically updated as soon as I type name in textboxes.
Now the my codebehind file looks like this:
public partial class MainWindow : Window, INotifyPropertyChanged
{
private string _firstName;
public string FirstName
{
get { return _firstName; }
set
{
if (value != _firstName)
{
_firstName = value;
OnPropertyChanged("FirstName");
}
}
}
private string _lastName;
public string LastName
{
get { return _lastName; }
set
{
if (value != _lastName)
{
_lastName = value;
OnPropertyChanged("LastName");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Notifies objects registered to receive this event that a property value has changed.
/// </summary>
/// <param name="propertyName">The name of the property that was changed.</param>
protected virtual void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public MainWindow()
{
InitializeComponent();
}
private void cmdCommand_Click(object sender, RoutedEventArgs e)
{
lblFullName.Content = FirstName + " " + LastName;
}
}
needless to say, even clicking the command button is not working...
any suggestions?

Setting the DataContext to point to the window itself will solve the immediate problem:
public MainWindow()
{
InitializeComponent();
this.DataContext = this;
}
The paths in the Binding expressions in the Xaml are all relative to the DataContext of the controls so the DataContext has to be set.
However, I strongly suggest that you put the first name and last name in a separate class (e.g. PersonViewModel) That will make the code easier to read and to maintain.
public class PersonViewModel : INotifyPropertyChanged
{
private string _firstName;
public string FirstName
{
get { return _firstName; }
set
{
if (value != _firstName)
{
_firstName = value;
OnPropertyChanged("FirstName");
}
}
}
private string _lastName;
public string LastName
{
get { return _lastName; }
set
{
if (value != _lastName)
{
_lastName = value;
OnPropertyChanged("LastName");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
var handler = this.PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new PersonViewModel();
}
private void cmdCommand_Click(object sender, RoutedEventArgs e)
{
lblFullName.Content = FirstName + " " + LastName;
}
}
Now the last part of this code does not work anymore. There are two solutions.
The quick and dirty solution:
private void cmdCommand_Click(object sender, RoutedEventArgs e)
{
var person = this.DataContext as PersonViewModel;
if(person == null) return;
lblFullName.Content = string.Format("{0} {1}", person.FirstName, person.LastName);
}
A better way, when trying to do proper MVVM is to put an extra property in the ViewModel (note the change in the First and Last name properties!):
public class PersonViewModel : INotifyPropertyChanged
{
public string FullName
{
get
{
return string.Format("{0} {1}", FirstName, LastName);
}
}
private string _firstName;
public string FirstName
{
get { return _firstName; }
set
{
if (value != _firstName)
{
_firstName = value;
OnPropertyChanged("FirstName");
OnPropertyChanged("FullName");
}
}
}
private string _lastName;
public string LastName
{
get { return _lastName; }
set
{
if (value != _lastName)
{
_lastName = value;
OnPropertyChanged("LastName");
OnPropertyChanged("FullName");
}
}
}
// remainder of the class remains the same
}
Remove the button and its click handler. Bind the label to this new property:
<Label Content="{Binding FullName}"
Grid.Row="2" Grid.Column="1"
Height="25" HorizontalAlignment="Stretch"/>

Related

Control looses focus on UpdateSourceTrigger = PropertyChanged

I have a ListBox with its ItemSource bound to an ObservableCollection. The ListBox has the following (minimalized) ItemTemplate:
<ListBox ItemsSource="{Binding SelectedDirectory.PluginValues}" HorizontalContentAlignment="Stretch">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid HorizontalAlignment="Stretch">
<Grid Height="29" Margin="5" HorizontalAlignment="Stretch">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1*" />
<ColumnDefinition Width="1*" />
</Grid.ColumnDefinitions>
<TextBox Grid.Column="0" Width="Auto"
Text="{Binding Name, Mode=TwoWay
, UpdateSourceTrigger=PropertyChanged}" />
<TextBox Grid.Column="1" Width="Auto"
Text="{Binding Value, Mode=TwoWay
, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
The binding option UpdateSourceTrigger=PropertyChanged causes the TextBoxes to loose the focus after each keypress to the surrounding ListBox. When I remove the option the focus is not lost, but the value in the TextBox is not immediately saved to the property. So when I enter a value and then raise a command (eg via save Button) the property is not updated. Only when I click somewhere else first and then raise the command the value is updated.
Edit
Simplified ViewModel:
public class ViewModel : INotifyPropertyChanged
{
private FbiDirectory selectedDirectory;
public FbiDirectory SelectedDirectory
{
get
{
return this.selectedDirectory;
}
set
{
this.selectedDirectory = value;
this.OnPropertyChanged("SelectedDirectory");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
}
FbiDirectory class (has nothing to do with the Federal Bureau of investigation):
public class FbiDirectory : INotifyPropertyChanged
{
private ObservableCollection<PluginValue> pluginValues = new ObservableCollection<PluginValue>();
public ObservableCollection<PluginValue> PluginValues
{
get
{
return this.pluginValues;
}
set
{
this.pluginValues = value;
this.OnPropertyChanged("PluginValues");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
}
PluginValue class:
public class PluginValue : INotifyPropertyChanged
{
private string name;
private string value;
public string Name
{
get => name;
set
{
name = value;
this.OnPropertyChanged("Name");
}
}
public string Value
{
get => value;
set
{
this.value = value;
this.OnPropertyChanged("Value");
}
}
public PluginValue(string name, string value)
{
this.Name = name;
this.Value = value;
}
public PluginValue()
{
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
}

A simplified code for your problem may look like this:
public class MyViewModel
{
public ObservableCollection<ItemViewModel> Items { get; set; }
public ICommand SaveCommand { get; }
public MyViewModel()
{
SaveCommand = new RelayCommand(OnSaveCommand);
Items = new ObservableCollection<ItemViewModel>();
Items.Add(new ItemViewModel{Name = "test1", Value = "test1"});
Items.Add(new ItemViewModel{Name = "test2", Value = "test2"});
}
private void OnSaveCommand()
{
var message = Items.Aggregate(new StringBuilder(),
(builder, item) => builder.AppendLine($"{item.Name} {item.Value}"));
message.AppendLine("Will be save");
MessageBox.Show(message.ToString());
}
}
public class ItemViewModel : NotifiableObject
{
private string _value;
private string _name;
public string Name
{
get => _name;
set
{
OnPropertyChanged();
_name = value;
}
}
public string Value
{
get => _value;
set
{
OnPropertyChanged();
_value = value;
}
}
}
public class NotifiableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
With this view:
<Grid>
<Grid.RowDefinitions>
<RowDefinition></RowDefinition>
<RowDefinition></RowDefinition>
</Grid.RowDefinitions>
<ListBox ItemsSource="{Binding Items}" Grid.Row="0">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid HorizontalAlignment="Stretch">
<Grid Height="29" Margin="5" HorizontalAlignment="Stretch">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1*" />
<ColumnDefinition Width="1*" />
</Grid.ColumnDefinitions>
<TextBox Grid.Column="0" Text="{Binding Name, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
<TextBox Grid.Column="1" Text="{Binding Value, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button Grid.Row="1" Content="Save" Command="{Binding SaveCommand}"></Button>
</Grid>
Not really sure of what's wrong in your code but:
You should use a NotifableObject for the common RaisePropertyChanged behavior
I don't really understand why you use a FbiDirectory instead of directly put the pluginValues into your ViewModel?
Hope it helps.

copy textbox value to another when click on Button Command in WPF MVVM

I have two text box and want to copy first textbox value to another textbox whenever I click on Button and this should done by using Commands in WPF.
This is my scenario :
First textbox binds the value from Person class.
Button shows simple MsgBox which verifies that Command executed properly.
Well here, I want to pass first textbox value to 2nd textbox (using Command) ?
XML File:
<Window x:Class="PrismDemo.Views.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:PrismDemo.ViewModels"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<vm:Person x:Name="vmmmm1" />
</Window.DataContext>
<Grid>
<TextBox x:Name="fName" Grid.Row="1" Height="30" Width="100" Text="{Binding Path=FirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
<Button Name="Submit" Grid.Row="2" Height="30" Width="100" Content="Submit Me" Command="{Binding submitCommand}" CommandParameter="{Binding Text, ElementName=fName}"/>
<TextBox x:Name="display" Grid.Row="3" Height="30" Width="100" Text="{}" />
Person class (ViewModel):
public class Person:INotifyPropertyChanged
{
private string _firstName;
private string _copyName;
public ICommand submitCommand {get;set;}
public Person()
{
_firstName = "Ronaldo";
submitCommand = new RelayCommand(MyMethod, canExecuteMethod);
}
public string FirstName
{
get
{
return _firstName;
}
set
{
_firstName = value;
OnPropertyUpdated(FirstName);
//OnPropertyUpdated(CopyName);
}
}
public string CopyName
{
get
{
return _copyName;
}
set
{
OnPropertyUpdated(CopyName);
}
}
private void OnPropertyUpdated(string property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
private bool canExecuteMethod(object parameter)
{
return true;
}
private void MyMethod(object parameter)
{
MessageBox.Show("Welcome to Command Demo...");
//if (parameter == null) return;
//_copyName = parameter.ToString();
this._copyName = _firstName;
}
public event PropertyChangedEventHandler PropertyChanged;
}
Any help will be appreciated.
Thank you !!

You were almost right ....Its working at my place properly , Just make following changes in you code
Just remove command parameter... we dont need it and Bind the copied string.
<TextBox Grid.Row="1" Height="30" Width="100" Text="{Binding FirstName}" />
<Button Grid.Row="2" Height="30" Width="100" Content="Submit Me" Command="{Binding submitCommand}"/>
TextBox Grid.Row="3" Height="30" Width="100" Text="{Binding CopyName}" />
In View model make following changes...
public class Person:INotifyPropertyChanged{
private string _firstName;
private string _copyName=string.Empty;
public Person()
{
_firstName = "Ronaldo";
submitCommand = new RelayCommand(MyMethod, canExecuteMethod);
}
public string FirstName
{
get
{
return _firstName;
}
set
{
_firstName = value;
OnPropertyChanged("FirstName");
}
}
public string CopyName
{
get
{
return _copyName;
}
set
{
if (_copyName != value)
{
_copyName = value;
OnPropertyChanged("CopyName");
}
}
}
public ICommand submitCommand { get; set; }
private void MyMethod(object param)
{
MessageBox.Show("Welcome to Command Demo...");
CopyName = FirstName;
}
private bool canExecuteMethod(object parameter)
{
return true;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(params string[] propertyNames)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
foreach (string propertyName in propertyNames) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
handler(this, new PropertyChangedEventArgs("HasError"));
}
}
}

You don't need CommandParameter here.
<Button Name="Submit" Grid.Row="2" Height="30" Width="100" Content="Submit Me" Command="{Binding submitCommand}" />
Add the Display property:
public string Display
{
get
{
return _display;
}
set
{
_display = value;
OnPropertyUpdated(Display);
}
}
Fix the binding in the second TextBox:
<TextBox x:Name="display" Grid.Row="3" Height="30" Width="100" Text="{Binding Display}" />
Update MyMethod:
private void MyMethod(object parameter)
{
MessageBox.Show("Welcome to Command Demo...");
Display = FirstName;
}

Here is how to copy text from one textBox to another.
this is dataContext behinde MainWindow
public class TestVM : INotifyPropertyChanged
{
public TestVM()
{
CopyCommand = new RelayCommand<string>(OnCopyExecuted);
}
private void OnCopyExecuted(string commandParameter)
{
TextUpdate = commandParameter;
}
private string _textUpdate;
public string TextUpdate
{
get { return _textUpdate; }
set
{
if (_textUpdate != value)
{
_textUpdate = value;
OnPropertyChanged();
}
}
}
public RelayCommand<string> CopyCommand { get; private set; }
public event PropertyChangedEventHandler PropertyChanged = delegate { };
public virtual void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
Generic RelayCommand that can take parameters
public class RelayCommand<T> : ICommand
{
private Action<T> _executeMethod;
private Func<T, bool> _canExecuteMethod;
#region RelayCommand ctor
public RelayCommand(Action<T> executeMethod)
{
_executeMethod = executeMethod;
}
public RelayCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
{
_executeMethod = executeMethod;
_canExecuteMethod = canExecuteMethod;
}
#endregion
public void RaiseCanExecuteChanged()
{
CanExecuteChanged(this, EventArgs.Empty);
}
#region ICommand Members
bool ICommand.CanExecute(object parameter)
{
var Tparam = (T)parameter;
if (_canExecuteMethod != null)
return _canExecuteMethod(Tparam);
if (_executeMethod != null)
return true;
return false;
}
void ICommand.Execute(object parameter)
{
if (_executeMethod != null)
_executeMethod((T)parameter);
}
public event EventHandler CanExecuteChanged = delegate { };
#endregion
}
and MainWindow xaml just to show purpose
<Window.DataContext>
<local:TestVM />
</Window.DataContext>
<Grid>
<TextBox x:Name="txt1"
Height="35"
Width="150"
Margin="49,62,318,224" />
<TextBox Text="{Binding TextUpdate}"
Height="35"
Width="150"
Margin="313,62,54,226" />
<Button Command="{Binding CopyCommand}"
CommandParameter="{Binding ElementName=txt1,Path=Text}"
Content="Copy"
Grid.Row="0"
Margin="208,157,198,132" />
</Grid>
It's working. Now you can implement it as it fits your needs.

Binding Enable Property to BindingGroup.IsDirty

I have got a View who's DataContext is set to an Employee.
Further, the view uses a BindingGroup and Validation Rules.
At last the view has got 2 Buttons: Save and Cancel
Save: Validate the users input and in case of success, save the changes.
Cancel: Rollback the user input and restore the original values.
Until this point it works fine.
Now the last requirement and the problem:
For a better User Experience i would like to enable the save Button when the user begins to change data.
To achieve this, I bind the IsDirty Property of the BindingGroup to the Enabled Property of the Button.
Unfortunately it doesn't work. The binding seems to be correct, but the user interface does not recognize the change of IsDirty.
Who can i solve this problem?
My Model:
public class EmployeeModel:ModelBase
{
private int _nr;
private string _firstname;
private string _lastname;
public int Nr
{
get
{
return _nr;
}
set
{
_nr = value;
OnChanged(nameof(Nr));
}
}
public string Firstname
{
get
{
return _firstname;
}
set
{
_firstname = value;
OnChanged(nameof(Firstname));
}
}
public string Lastname
{
get
{
return _lastname;
}
set
{
_lastname = value;
OnChanged(nameof(Lastname));
}
}
}
ModelBase:
public class ModelBase:INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnChanged(string propertyname)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
}
}
ValidationRule:
public class EmployeeValidationRule:ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
BindingGroup bindingGroup = (BindingGroup)value;
if (bindingGroup.Items.Count == 2)
{
EmployeeModel employee = (EmployeeModel)bindingGroup.Items[1];
string firstname = (string)bindingGroup.GetValue(employee, "Firstname");
string lastname = (string)bindingGroup.GetValue(employee, "Lastname");
if (firstname.Length == 0)
return new ValidationResult(false, "Firstname can not be empty.");
if (lastname.Length == 0)
return new ValidationResult(false, "Lastname can not be empty.");
}
return ValidationResult.ValidResult;
}
}
My ViewModel:
public class EmployeeViewModel
{
private EmployeeModel _employeeModel;
public EmployeeModel Employee
{
get
{
return _employeeModel;
}
set
{
_employeeModel = value;
}
}
public EmployeeViewModel()
{
LoadData();
}
private void LoadData()
{
//Employee = (from e in _context.Employee
// where e.Nr == 158
// select e).FirstOrDefault();
Employee = new EmployeeModel() { Firstname = "Billy", Lastname = "Wilder" };
}
public void Save()
{
//_context.SaveChanges();
}
}
At last the View:
<Window x:Class="WpfApplication3_Validation.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:WpfApplication3_Validation"
xmlns:vm="clr-namespace:WpfApplication3_Validation.ViewModel"
xmlns:vr="clr-namespace:WpfApplication3_Validation.ValidationRules"
mc:Ignorable="d"
Title="Employee" Height="250" Width="525"
Validation.ValidationAdornerSite="{Binding ElementName=lbErrors}" Loaded="Window_Loaded">
<Window.DataContext>
<vm:EmployeeViewModel/>
</Window.DataContext>
<Window.BindingGroup>
<BindingGroup x:Name="MyBindingGroup">
<BindingGroup.ValidationRules>
<vr:EmployeeValidationRule/>
</BindingGroup.ValidationRules>
</BindingGroup>
</Window.BindingGroup>
<Grid x:Name="gridMain">
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
<RowDefinition/>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<Label Content="Nr:"/>
<TextBlock Grid.Column="1" Text="{Binding Employee.Nr}"/>
<Label Grid.Row="1" Content="Vorname:" Target="{Binding ElementName=tbFirstname}"/>
<TextBox Grid.Row="1" Grid.Column="1" x:Name="tbFirstname" Text="{Binding Employee.Firstname}"/>
<Label Grid.Row="2" Content="Nachname:" Target="{Binding ElementName=tbLastname}"/>
<TextBox Grid.Row="2" Grid.Column="1" x:Name="tbLastname" Text="{Binding Employee.Lastname}"/>
<Label Grid.Row="4" Grid.Column="0" x:Name="lbErrors" Content="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.ValidationAdornerSiteFor).(Validation.Errors)[0].ErrorContent}"
Foreground="Red" FontWeight="Bold"/>
<StackPanel Grid.Row="4" Grid.Column="1" Orientation="Horizontal" HorizontalAlignment="Right">
<TextBlock x:Name="tbIsDirty"/>
<Button x:Name="btn1" Content="IsDirty?" Click="btn1_Click"/>
<Button x:Name="btnSave" Content="Save1" Click="btnSave_Click" />
<Button x:Name="btnSave1" Content="Save2" Click="btnSave_Click" IsEnabled="{Binding ElementName=MyBindingGroup, Path=IsDirty}"/>
<Button x:Name="btnCancel" Content="Cancel" Click="btnCancel_Click"/>
</StackPanel>
</Grid>
Code Behind:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
this.MyBindingGroup.BeginEdit(); // Not really needed?
}
private void btnSave_Click(object sender, RoutedEventArgs e)
{
if (this.BindingGroup.CommitEdit())
{
EmployeeViewModel vm = (EmployeeViewModel)this.DataContext;
vm.Save();
}
}
private void btnCancel_Click(object sender, RoutedEventArgs e)
{
this.BindingGroup.CancelEdit();
}
private void btn1_Click(object sender, RoutedEventArgs e)
{
tbIsDirty.Text = BindingGroup.IsDirty.ToString();
}
}

Due to the fact that BindingGroup.IsDirty does not Implement INotifyPropertyChanged, it's not a useful source for this type of databinding.
Possible solution:
- Implementing INotifyPropertyChanged in the view
- Creating a own IsDirty in the view, using INotifyPropertyChanged
- Adding an event handler for KeyUp, which sets my IsDirty in case of BindingGroup.IsDirty.
- Binding of Enabled to the new Property
Disadvantage: Need if implementation of INotifyPropertyChanged in the view.
Advantage: It works.
CodeBehind of View:
public partial class MainWindow : Window, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnChanged(string propertyname)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
}
private bool _isDirty;
public bool IsDirty
{
get
{
return _isDirty;
}
set
{
_isDirty = value;
OnChanged(nameof(IsDirty));
}
}
public MainWindow()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
this.MyBindingGroup.BeginEdit(); // Not really needed?
gridMain.KeyUp += GridMain_KeyUp;
}
private void GridMain_KeyUp(object sender, System.Windows.Input.KeyEventArgs e)
{
if (this.MyBindingGroup.IsDirty)
{
IsDirty = true;
}
}
private void btnSave_Click(object sender, RoutedEventArgs e)
{
if (this.BindingGroup.CommitEdit())
{
EmployeeViewModel vm = (EmployeeViewModel)this.DataContext;
vm.Save();
IsDirty = false;
}
}
private void btnCancel_Click(object sender, RoutedEventArgs e)
{
this.BindingGroup.CancelEdit();
IsDirty = false;
}
}
Further improvements:
Now i moved IsDirty to my ViewModel, so I don't have to implement INPC in the view. Another advantage is, that in this way, Commands can consume the property and finally i don't have to use databinding for the enabled Property, because i get it over the command.

WPF Textbox Binding Is Not Updating When Setting Value

I have a small program to test out textbox databinding and it works when I change the value in the textbox itself, but when I try to change the value from the code-behind, the variable is updated but the Textbox is not updated. I have looked around but have not been able to find a solution, as most I have seen are for the textbox updating the variable, which is opposite of what I need. Here is the code:
XAML:
<Grid>
<TextBox Text="{Binding FirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="23" Margin="127,37,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
<TextBox Text="{Binding LastName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="23" Margin="127,88,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
<TextBlock HorizontalAlignment="Left" Margin="28,40,0,0" TextWrapping="Wrap" Text="First Name" VerticalAlignment="Top"/>
<TextBlock HorizontalAlignment="Left" Margin="28,91,0,0" TextWrapping="Wrap" Text="Last Name" VerticalAlignment="Top"/>
<Button x:Name="Name" Content="Name!" HorizontalAlignment="Left" Margin="145,212,0,0" VerticalAlignment="Top" Width="75" Click="Name_Click"/>
</Grid>
And My Code:
namespace WpfApplication1
{
public class UIControls : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _firstName;
private string _lastName;
protected void Notify(string propertyName)
{
if(this.PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public string FirstName
{
get { return _firstName; }
set
{
if (value != _firstName)
{
_firstName = value;
Notify("FirstName");
}
}
}
public string LastName
{
get { return _lastName; }
set
{
if (value != _lastName)
{
_lastName = value;
Notify("LastName");
}
}
}
}
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
UIControls viewModel = new UIControls();
this.DataContext = viewModel;
}
private void Name_Click(object sender, RoutedEventArgs e)
{
UIControls ui = new UIControls();
ui.FirstName = "Mike";
ui.LastName = "Smith";
}
}
}

Well you are creating new UIControls on every button click. New UIControls is not binded to text box. Try to create private filed that is binded to MainWindow, something like this:
public partial class MainWindow : Window
{
private UIControls viewModel;
public MainWindow()
{
InitializeComponent();
viewModel = new UIControls();
this.DataContext = viewModel;
}
private void Name_Click(object sender, RoutedEventArgs e)
{
viewModel.FirstName = "Mike";
viewModel.LastName = "Smith";
}

MVVM viewmodel events (commands?)

I have a MVVM setup that creates a View on my MainWindow. I am not sure how to know when a user Clicks on a specific Notification Item inside the View. Where would I add the event, or a command to know when that happens?
here are is my MVVM code :
MainWindow
cs:
NotificationViewModel notificationViewModel = new NotificationViewModel();
notificationViewModel.AddNoticiation(new NotificationModel() { Message = "Error", Name = "Station 21" });
NotificationView.DataContext = notificationViewModel;
xaml:
<notification:NotificationView x:Name="NotificationView" />
NotificationModel
public class NotificationModel : INotifyPropertyChanged
{
private string _Message;
public string Message
{
get { return _Message; }
set
{
if (_Message != value)
{
_Message = value;
RaisePropertyChanged("Message");
}
}
}
private string _Name;
public string Name
{
get { return _Name; }
set
{
if (_Name != value)
{
_Name = value;
RaisePropertyChanged("Name");
}
}
}
public string TimeStamp
{
get { return DateTime.Now.ToString("h:mm:ss"); }
}
#region PropertChanged Block
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
#endregion
}
NotificationViewModel
public class NotificationViewModel
{
private ObservableCollection<NotificationModel> _Notifications = new ObservableCollection<NotificationModel>();
public ObservableCollection<NotificationModel> Notifications
{
get { return _Notifications; }
set { _Notifications = value; }
}
public void AddNoticiation(NotificationModel notification)
{
this.Notifications.Insert(0, notification);
}
}
NotificationView
<Grid>
<StackPanel HorizontalAlignment="Left" >
<ItemsControl ItemsSource="{Binding Path=Notifications}"
Padding="5,5,5,5">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Border Background="SlateGray"
CornerRadius="4">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="100" />
<ColumnDefinition Width="100" />
<ColumnDefinition Width="100" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0"
Text="{Binding Path=TimeStamp}" />
<TextBlock Grid.Column="1"
Text="{Binding Path=Name}" />
<TextBlock Grid.Column="2"
Text="{Binding Path=Message}" />
</Grid>
</Border>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</Grid>

There's no real selection mechanism built into an ItemsControl. It would probably solve your problem to switch out your ItemsControl for a ListBox.
If you do that, you can bind to SelectedItem, then handle any changes made to SelectedItem using the PropertyChanged event.
Example:
In your view model's constructor:
PropertyChanged += NotificationViewModel_PropertyChanged;
Add a property to your view model to allow the binding:
private string _selectedNotification;
public string SelectedNotification
{
get { return _selectedNotification; }
set
{
if (_selectedNotification != value)
{
_selectedNotification = value;
RaisePropertyChanged("SelectedNotification");
}
}
}
Finally, add the event handler to your view model:
NotificationViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e))
{
if (e.PropertyName = "SelectedNotification") DoStuff();
}
You may find that you don't even need to hook into PropertyChanged if you just want to update another control in your view based on the selected item in your list box. You can just bind directly to the property within xaml.

Develop Reference

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.

Simple DataBinding in wpf application - c#

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MVVM viewmodel events (commands?)

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