Brand new to WPF and MVVM. My application has a button to browse for a file and a start button to perform a task with the selected file. I only want the start button available to the user if they have selected a file using the browse button. I am using the file path property in the ViewModel as the CommandParameter but this does not work. Any help appreciated.
XAML
<Button Grid.Column="1" Grid.Row="2" Content="Browse File" Margin="0,0,5,5" Command="{Binding Path=CommandBrowseFile}" ></Button> <Button Grid.Column="1" Grid.Row="3" Grid.ColumnSpan="2" Content="Start" Margin="0,0,0,5" Command="{Binding Path=CommandStart}" CommandParameter="{Binding Path=FilePath}"></Button> ViewModel
public class MyViewModel : ViewModelBase { public RelayCommand CommandBrowseFile { get; private set; } public RelayCommand CommandStart { get; private set; } private string _filePath; public MyViewModel() { //L5XPath = "test"; CommandBrowseFile = new RelayCommand(BrowseFile); CommandStart = new RelayCommand(Start, CanStart); } public string FilePath { get { return _filePath; } set { _filePath = value; } } public void BrowseFile(object message) { // Configure open file dialog box OpenFileDialog dlg = new OpenFileDialog(); dlg.FileName = "Document"; // Default file name dlg.DefaultExt = ".l5x"; // Default file extension dlg.Filter = "l5x files (.l5x)|*.l5x"; // Filter files by extension // Show open file dialog box Nullable<bool> result = dlg.ShowDialog(); // Process open file dialog box results FilePath = result == true ? dlg.FileName : null; } public void Start(object message) { //Do something } public bool CanStart(object message) { return message != null ? true : false; } } RelayCommand
public class RelayCommand : ICommand { readonly Action<object> _execute; readonly Predicate<object> _canExecute; public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } public RelayCommand(Action<object> execute, Predicate<object> canExecute) { if (execute == null) { throw new NullReferenceException("execute"); } else { _execute = execute; _canExecute = canExecute; } } //public void RaiseCanExecuteChanged() //{ // if (CanExecuteChanged != null) // CanExecuteChanged(this, new EventArgs()); //} public RelayCommand(Action<object> execute) : this(execute, null) { } public bool CanExecute(object parameter) { return _canExecute == null ? true : _canExecute(parameter); } public void Execute(object parameter) { _execute.Invoke(parameter); } } 
