MVVM show confirmation messagebox before command attached to a button is executed

user_1624552 0
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I have a button attached to a command in the view model. This button deletes the rows current selected in the listview so I would like to show a messagebox of confirmation before proceeding. Is user click ok button (in messagebox) then command is executed, otherwise, if user click cancel button command attached is not called. Is it possible? If so how?

<Button Name="btnDelete" Command="{Binding DeleteRowsCommand}"/>

Another possibility is to call the command on click and in the view model through a property that is attached to a custom message box placed in the view, to make this custom messagebox visible when value of the property is true. But then how can I send back to the view model which button 'Ok' or 'Cancel' has been pressed?

messagebox command icommand mvvm wpf
3 Answers

The view model doesn't often need to know that there is a question for the user before the command is executed. If that's the case, you can create very simple custom button class to just show the message box and if the user click yes, execute the command (or do whatever). 

public class YesNoButton : Button
{
    public string Question { get; set; }

    protected override void OnClick()
    {
        if (string.IsNullOrWhiteSpace(Question))
        {
            base.OnClick();
            return;
        }

        var messageBoxResult = MessageBox.Show(Question, "Confirmation", MessageBoxButton.YesNo);

        if (messageBoxResult == MessageBoxResult.Yes)
            base.OnClick();
    }       
}

In XAML you can use the button like this: 

<components:YesNoButton Content="Delete rows" Command="{Binding DeleteRowsCommand}" Question="Do you really want to delete rows?" />

EDIT: Another way to solve this is to define some MessageBoxService in the ViewModel layer and implement it in View layer. Interface could look like this:

public interface IMessageBoxService
{
    void ShowError(string messageBoxText);

    void ShowWarning(string messageBoxText);

    void ShowInformation(string messageBoxText);
}

This way you can show message boxes directly from the VM without directly referencing WPF libraries.

user_11176860
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