TextBox and button - binding and command

Question

I am using the MVVM pattern. I have

• A text field whose Text property is bound to the ViewModel (VM supports the INotifyProperyChange property) Text property
• A button whose command is bound to the ICommand VM property type

You can think of it as SearchTextBox and SearchButton

The problem I am facing is that when I enter the text in the SearchTextBox and click on the SearchButton, only the implementation of the property of the property setfor SearchTextBox is called, but the button Commandfor SearchButton is never executed (Note: ICommand CanExecute handleralways returns True)

It works fine if I either exit the SearchTextBox using the TAB key, or use the mouse to move the focus from the SearchTextBox, and then click SearchButton. This means that you need to perform two separate actions to trigger both events separately. Ideally, clicking on SearchButton should result in the absence of the SearchTextBox focus, invoking the property set, and clicking on the search button translates into the execution of the command.

Code below

XAML:

<TextBox Text="{Binding Path=SearchText,Mode=TwoWay}"/>

<Button Content="Search" Width="100" Command="{Binding MySearchCommand}"/>

WITH#:

public String _SearchText;
public String SearchText
{
   get { return _SearchText; }
   set 
   {
     _SearchText = value;
     OnPropertyChanged("SearchText"); 
    }
 }

ICommandan implementation is a standard implementation without fake code, and the handler CanExecutealways returns True

Answer 1

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Answer 2

.

Debug.Writeline SearchText - MySearchCommandExecute.

, SearchText - Set. , SearchText - Set, . - VS 2008, .

class SearchViewModel : ViewModelBase
    {
        public SearchViewModel() 
        {

        }

        public String _SearchText;
        public String SearchText
        {
            get { return _SearchText; }
            set
            {
                System.Diagnostics.Debug.WriteLine("Set Membership called");

                OnPropertyChanged("SearchText");
            }
        }

        #region Commands
        RelayCommand _SearchCommand;

        public ICommand SearchCommand
        {
            get
            {
                if (_SearchCommand == null)
                {
                    _SearchCommand = new RelayCommand(param => this.MySearchCommandExecute(), param => this.MySearchCommandCanExecute);
                }
                return _SearchCommand;
            }
        }

        public void MySearchCommandExecute()
        {
            System.Diagnostics.Debug.WriteLine("MySearchCommandExecute called");

            // Do Search
        }

        public bool MySearchCommandCanExecute
        {
            get
            {
                return true;
            }
        }

        #endregion
    }

SearchView.xaml

<UserControl x:Class="WpfApplication2.SearchView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="300" Width="300">
    <StackPanel>
        <StackPanel Orientation="Vertical" HorizontalAlignment="Left" Margin="4">
            <Label Foreground="Black"  FontFamily="Calibri" Width="155" Margin="4,0,4,0" Content="SearchText"/>
            <TextBox Foreground="Black"  FontFamily="Calibri" Width="155" Margin="4,0,4,0" Text="{Binding Path=SearchText}"/>
        </StackPanel>
        <Button HorizontalAlignment="Left" Content="Search" Width="100" Command="{Binding SearchCommand}" Margin="8"/>
    </StackPanel>
</UserControl>

RelayCommand.cs

// Reference: MSDN sample
    class RelayCommand : ICommand
    {
        readonly Action<object> _execute;
        readonly Predicate<object> _canExecute;

        public RelayCommand(Action<object> execute)
            : this(execute, null)
        {
        }

        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("relaycommand execute");

            _execute = execute;
            _canExecute = canExecute;
        }

        [DebuggerStepThrough]
        public bool CanExecute(object parameter)
        {
            return _canExecute == null ? true : _canExecute(parameter);
        }

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public void Execute(object parameter)
        {
            _execute(parameter);
        }
    }

Answer 3

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, , . , ( , ), , , , ( ). , . xaml, Window:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        this.DataContext = new TempViewModel();
    }
}

public class TempViewModel : INotifyPropertyChanged
{
    private String _searchText;
    private ICommand _searchCommand;

    #region Commands

    protected class Search : ICommand
    {
        private TempViewModel _viewModel;

        public bool CanExecute(object parameter)
        {
            return true;
        }

        public event EventHandler CanExecuteChanged
        {
            add { }
            remove { }
        }

        public void Execute(object parameter)
        {
            //MessageBox in VM is just for demonstration
            MessageBox.Show("command executed with search string: " + this._viewModel._searchText);
        }

        public Search(TempViewModel viewModel)
        {
            this._viewModel = viewModel;
        }
    }

    #endregion //Commands

    #region INotifyPropertyChanged

    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(String propertyName)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion //INotifyPropertyChanged

    #region Public properties

    public String SearchText
    {
        get
        {
            return this._searchText;
        }
        set
        {
            this._searchText = value;
            OnPropertyChanged("SearchText");
        }
    }

    public ICommand SearchCommand
    {
        get
        {
            return this._searchCommand;
        }
        set
        {
            this._searchCommand = value;
            OnPropertyChanged("SearchCommand");
        }
    }

    #endregion //Public properties

    public TempViewModel()
    {
        this.SearchCommand = new Search(this);
        this.SearchText = "Sample string";
    }
}

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EDIT: , , Command="{Binding SearchCommand}" Command="{Binding Path=SearchCommand}"