CanExecute () does not enable the button when the condition is met

Question

I have a very simple application with TextBoxand a Button. When the text entered in TextBoxexceeds 5 characters, the button will be turned on. Here is the code for my ViewModel:

private string _text { get; set; }
public string Text
{
    get { return _text; }
    set
    {
        _text = value;
        OnPropertyChanged("Text");
    }
}

private ICommand _buttonCommand;
public ICommand ButtonCommand
{
    get
    {
        if (_buttonCommand == null)
        {
            _buttonCommand = new RelayCommand(
                param => this.ButtonCommandExecute(), 
                param => this.ButtonCommandCanExecute()
            );
        }
        return _buttonCommand;
    }
}

private bool ButtonCommandCanExecute()
{
    if (this.Text.Length < 5)
    {
        return false;
    }
    else
    {
        return true;
    }
}

private void ButtonCommandExecute()
{
    this.Text = "Text changed";
}

public MainWindowViewModel()
{
    //
}

TextBoxand Buttonrelated by this XAML:

<Button Content="Button" HorizontalAlignment="Left" 
                Margin="185,132,0,0" VerticalAlignment="Top" Width="120"
                Command="{Binding Path=ButtonCommand}" />

<TextBox HorizontalAlignment="Left" Height="23" 
         Margin="185,109,0,0" TextWrapping="Wrap" 
         Text="{Binding Path=Text, Mode=TwoWay}" VerticalAlignment="Top" Width="120"/>

DataContext It looks correct, but here it is only because I am starting WPF:

private MainWindowViewModel view_model;

public MainWindow()
{
    InitializeComponent();

    view_model = new MainWindowViewModel();

    this.DataContext = view_model;
}

When I enter in TextBox, it Buttonnever turns on.

Answer 1

Bool IsEnabled Button. true, - Setter of Text. , TextBox.

: - , , , , #, , Viewmodel/Page.cs. . .

: -

private string _text { get; set; }
public string Text
{
    get { return _text; }
    set
    {
        _text = value;

        if(_text.Length  > 5)
        // Enable button here
        // and command does not enable Buttons they are basically report the clicks events.
        IsButtonEnabled = true;

        OnPropertyChanged("Text");
    }
}

Bool IsButtonEnabled Button Xaml.

private bool _IsButtonEnabled { get; set; }
public bool IsButtonEnabled
{
    get { return _IsButtonEnabled ; }
    set
    {
        _IsButtonEnabled = value;
        OnPropertyChanged("IsButtonEnabled");
    }
}

Xaml: -

<Button Content="Button" HorizontalAlignment="Left" 

             IsEnabled="{Binding IsButtonEnabled}"

            Margin="185,132,0,0" VerticalAlignment="Top" Width="120"
            Command="{Binding Path=ButtonCommand}" />

Answer 2

ICommand , "CanExecute" . RelayCommand class (MVVM Light) .

private string _text;
public string Text
{
    get { return _text; }
    set
    {
        _text = value;
        OnPropertyChanged("Text");

        // There is a special RelayCommand method to notify "CanExecute" changed.
        // After this call, the "CanExecute" state is "re-evaluated" automatically by binding using CanExecute Func passed into RelayCommand constructor.
        _buttonCommand.RaiseCanExecuteChanged();
    }
}

private RelayCommand _buttonCommand;
public ICommand ButtonCommand
{
    get
    {
        if (_buttonCommand == null)
        {
            _buttonCommand = new RelayCommand(
                param => this.ButtonCommandExecute(), 
                param => this.ButtonCommandCanExecute()
            );
        }
        return _buttonCommand;
    }
}

: CanExecuteChanged ?

Answer 3

Try this small modification of your code and tell me if it works:

private string _text { get; set; }
public string Text
{
    get { return _text; }
    set
    {
        _text = value;
        OnPropertyChanged("Text");
        ButtonCommandCanExecute();
    }
}

private ICommand _buttonCommand;
public ICommand ButtonCommand
{
    get
    {
        if (_buttonCommand == null)
        {
            _buttonCommand = new RelayCommand(
                param => this.ButtonCommandExecute(), 
                param => this.ButtonCommandCanExecute()
            );
        }
        return _buttonCommand;
    }
}

private bool ButtonCommandCanExecute()
{
    if (this.Text.Length < 5)
    {
        return false;
    }
    else
    {
        return true;
    }
}

private void ButtonCommandExecute()
{
    this.Text = "Text changed";
}

public MainWindowViewModel()
{
    //
}