WPF using SaveFileDialog in MVVM

Question

I'm struggling with using SaveFileDialog in MVVM.

I'm using RelayCommand class and launch SaveAsFileCommand. Within the SaveAsFileCommand, using lambda expression I split two arguments to have:

Instance of RichTextBox control and targeted path (filePath)

Then I call DataIO.SaveAsFile(arguments[0], arguments[1]), using above arguments.

To create the SaveDialogBox in the View Layer I'm using 3 classes: DialogBox, FileDialogBox and SaveFileDialogBox

In the XAML I create the SaveDialogBox and try to call SaveAsFileCommand using MultiBinding to pass those two Command Parameters.

To show the SaveDialogBox I use the button which is bindded to SaveDialogBox

The problem is: At this place the compiler complains that it can't execute multibinding for my SaveDialogBox because of being non-DependencyObject and non-DependencyProperty.
How can I solve that problem and correctly save the file using that DialogBox being in accordance with MVVM in my case???

XAML parts of code:

<Button Command="{Binding ElementName=SaveFileDB, Path=Show}" > 
    <Button.ToolTip>
        <ToolTip Style="{StaticResource styleToolTip}" >
            <TextBlock Text="Save" Style="{StaticResource styleTextBlockTP}" />
        </ToolTip>
    </Button.ToolTip>
    <Image Source="Icon\Save.png"/>
</Button>


<local:SaveFileDialogBox x:Name="SaveFileDB" Caption="Save content to file..."
                             Filter="Text files (*.txt)|*.txt|All files(*.*)|*.*"
                             FilterIndex="0" DefaultExt="txt"
                             CommandFileOK="{Binding SaveAsFileCommand}" >
        <local:SaveFileDialogBox.CommandParemeter>
            <MultiBinding Converter="{StaticResource parametersConverter}">
                <Binding ElementName="MainRichTextBox" />
                <Binding ElementName="SaveFileDB" Path="Show" />
            </MultiBinding>
        </local:SaveFileDialogBox.CommandParemeter>
    </local:SaveFileDialogBox>

SaveAsFileCommand:

private ICommand _SaveAsFileCommand;
public ICommand SaveAsFileCommand
{
    get
    {
        if (_SaveAsFileCommand == null)
        {
            _SaveAsFileCommand = new RelayCommand(
            argument =>
                {
                    var arguments = (object[])argument;
                    DataIO.SaveAsFile(arguments[0], arguments[1]); 
                }
                );
        }
        return _SaveAsFileCommand;
    }
}

DataIO.SaveAsFile method:

    public static void SaveAsFile(object argument0, object argument1)
    {
        System.Windows.Controls.RichTextBox richTB = argument0 as System.Windows.Controls.RichTextBox;
        string path = (string)argument1;


        using (FileStream fileStream = new FileStream(path, FileMode.Create))
        {
            TextRange textRange = new TextRange(richTB.Document.ContentStart, richTB.Document.ContentEnd);
            textRange.Save(fileStream, DataFormats.Text);

        }
    }

RelayCommand class:

class RelayCommand : ICommand
{
    private readonly Action<object> _Execute;
    private readonly Func<object, bool> _CanExecute;

    public RelayCommand(Action<object> execute, Func<object, bool> canExecute)
    {
        if (execute == null) throw new ArgumentNullException("execute");
        _Execute = execute;
        _CanExecute = canExecute;
    }

    public RelayCommand(Action<object> execute)
    {
        if (execute == null) throw new ArgumentNullException("execute");
        _Execute = execute;
    }

    public bool CanExecute(object parameter)
    {
        return _CanExecute == null ? true : _CanExecute(parameter);
    }

    public event EventHandler CanExecuteChanged
    {
        add
        {
            if (_CanExecute != null) CommandManager.RequerySuggested += value;
        }
        remove
        {
            if (_CanExecute != null) CommandManager.RequerySuggested -= value;
        }
    }

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

DialogBox class:

public abstract class DialogBox : FrameworkElement, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string parameter)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(parameter));
    }

    protected Action<object> execute = null;

    public string Caption { get; set; }

    protected ICommand show;
    public virtual ICommand Show
    {
        get
        {
            if (show == null)
                show = new RelayCommand(execute);
            return show;
        }
    }
}

FileDialogBox class:

public abstract class FileDialogBox : CommandDialogBox
{
    public bool? FileDialogResult { get; protected set; }
    public string FilePath { get; set; }
    public string Filter { get; set; }
    public int FilterIndex { get; set; }
    public string DefaultExt { get; set; }

    protected Microsoft.Win32.FileDialog fileDialog = null;

    protected FileDialogBox()
    {
        execute =
            o =>
            {
                var values = (object[])o;
                RelayCommand relCom1 = (RelayCommand)values[1];

                fileDialog.Title = Caption;
                fileDialog.Filter = Filter;
                fileDialog.FilterIndex = FilterIndex;
                fileDialog.DefaultExt = DefaultExt;

                string filePath = "";

                if (FilePath != null) filePath = FilePath; else FilePath = "";
                //if (o != null) filePath = (string)o;
                //if (o != null) filePath = (string)values[1];
                if (o != null) filePath = relCom1.ToString();
                if (!String.IsNullOrWhiteSpace(filePath))
                {
                    fileDialog.InitialDirectory = System.IO.Path.GetDirectoryName(filePath);
                    fileDialog.FileName = System.IO.Path.GetFileName(filePath);
                }

                FileDialogResult = fileDialog.ShowDialog();
                OnPropertyChanged("FileDialogResult");
                if (FileDialogResult.HasValue && FileDialogResult != null)
                {
                    FilePath = fileDialog.FileName;
                    OnPropertyChanged("FilePath");
                    ExecuteCommand(CommandFileOK, FilePath);
                };
            };
    }

    public static DependencyProperty CommandFileOKProperty =
        DependencyProperty.Register("CommandFileOK", typeof(ICommand), typeof(FileDialogBox));

    public ICommand CommandFileOK
    {
        get { return (ICommand)GetValue(CommandFileOKProperty); }
        set { SetValue(CommandFileOKProperty, value); }
    }
}

SaveFileDialogBox class:

public class SaveFileDialogBox : FileDialogBox
{
    public SaveFileDialogBox()
    {
        fileDialog = new SaveFileDialog();
    }
}

Answer 1

The way I handle a requirement for user input in a dialog is to use a control which goes in the view but has no UI.
I split the command to be done into two pieces.
Essentially these are show the dialog and invoke a command when you finish.
The control shows a dialog which grabs data and then invokes a command you give it via binding.
Since this is control you can bind fine and it's in the visual tree so it can get a reference to the window.

Please see confirmationrequestor in this:

https://gallery.technet.microsoft.com/WPF-User-Notification-MVVM-98940828

That's intended for confirming the deletion of a record but the same principle can be extended to a file picker with a little modification.

From that, the command invoked once the user clicks and closes the dialogue can capture any variables you need. If you bind them:

private RelayCommand _confirmCommand;
public RelayCommand ConfirmCommand
{
    get
    {
        return _confirmCommand
          ?? (_confirmCommand = new RelayCommand(
               () =>
               {
                   confirmer.Caption = "Please Confirm";
                   confirmer.Message = "Are you SURE you want to delete this record?";
                   confirmer.MsgBoxButton = MessageBoxButton.YesNo;
                   confirmer.MsgBoxImage = MessageBoxImage.Warning;
                   OkCommand = new RelayCommand(
                       () =>
                       {
                           // You would do some actual deletion or something here
                           UserNotificationMessage msg = new UserNotificationMessage { Message = "OK.\rDeleted it.\rYour data is consigned to oblivion.", SecondsToShow = 5 };
                           Messenger.Default.Send<UserNotificationMessage>(msg);
                       });
                   RaisePropertyChanged("OkCommand");
                   ShowConfirmation = true;
               }));
    }
}

From the confirmationrequestor, invoking that command:

    public static readonly DependencyProperty ShowConfirmDialogProperty =
        DependencyProperty.Register("ShowConfirmDialog",
                    typeof(bool?),
                    typeof(ConfirmationRequestor),
                    new FrameworkPropertyMetadata(null
                        , new PropertyChangedCallback(ConfirmDialogChanged)
                        )
                    { BindsTwoWayByDefault = true }
                    );
    private static void ConfirmDialogChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if ((bool?)e.NewValue != true)
        {
            return;
        }
        ConfirmationRequestor cr = (ConfirmationRequestor)d;
        Window parent = Window.GetWindow(cr) as Window;
        MessageBoxResult result = MessageBox.Show(parent, cr.Message, cr.Caption, cr.MsgBoxButton, cr.MsgBoxImage);
        if (result == MessageBoxResult.OK || result == MessageBoxResult.Yes)
        {
            if (cr.Command != null)
            {
                cr.Command.Execute(cr.CommandParameter);
            }
        }
        cr.SetValue(ShowConfirmDialogProperty, false);
    }