Stas Petrov Stas Petrov - 25 days ago 6
C# Question

WPF Fire PropertyChanged when ui update with mvvm

I am trying to implement mvvm in my application. I have bindings to commands, and i need to fire event when user input some data to textbox for force update

CanExecute
in command
My viewmodel

public class AddEditWindowViewModel: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
......
public ConfirmCommand ConfirmCommand { get; set; }
public string Path{ get; set; }

public AddEditWindowViewModel()
{
WindowTitle = "Add new item";
ConfirmCommand = new ConfirmCommand(this);
}

[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}


My command

public class ConfirmCommand: ICommand
{
private AddEditWindowViewModel _model;

public ConfirmCommand(AddEditWindowViewModel model)
{
_model = model;
_model.PropertyChanged += ModelOnPropertyChanged;
}

private void ModelOnPropertyChanged(object sender, PropertyChangedEventArgs args)
{
if (args.PropertyName.Equals("Path"))
{
CanExecuteChanged?.Invoke(this, EventArgs.Empty);
}
}

public bool CanExecute(object parameter)
{
return !string.IsNullOrEmpty(_model.Path);
}

public void Execute(object parameter)
{
.....
}

public event EventHandler CanExecuteChanged;
}


My view

<Window x:Class="NameSpace.Views.AddEditWindow"
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:vm="clr-namespace:NameSpace.ViewModels"
mc:Ignorable="d"
Title="{Binding Path=WindowTitle}"
Height="200"
Width="500"
WindowStyle="SingleBorderWindow">
<Window.DataContext>
<vm:AddEditWindowViewModel />
</Window.DataContext>
.....
<TextBox Name="Path" Text="{Binding Path=Path, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Margin="2" Grid.Column="0" Grid.Row="1"></TextBox>
.....
Button IsDefault="True" Command="{Binding Path=ConfirmCommand}" Margin="5" HorizontalAlignment="Right" Width="100" Grid.Row="2" Grid.Column="0" Content="Ok"></Button>
<Button IsCancel="True" Margin="5" HorizontalAlignment="Left" Width="100" Grid.Row="2" Grid.Column="1" Content="Cancel"></Button>
.....




When textbox updated by user in ui,
PorpertyChanged
event in
ConfirmCommand
doesn't firing. Why?
Where i got wrong?

Answer

Try to call OnPropertyChanged in your Path property setter:

private string _path;

public string Path
{
    get 
    {
        return _path;
    }
    set
    { 
        _path = value;
        OnPropertyChanged();
    }
}