使用 MVVM 和 WPF 通过 OpenFileDialog 更新带有文件名和路径的文本

Question

我有一个带有路径的文件名文本框。用户使用 OpenFileDialog 找到文件后，此文本框应填充文件名。当用户直接输入带有路径的文件名而不是从文件对话框中选择时，此文本也应该起作用。

由于我正在学习 MVVM，我很难弄清楚如何使用文件名/路径更新文本框。我尝试了我能想到的一切。

我期待 onPropertyChanged(“FilenameWithPath”) 应该注意这个问题。有人可以告诉我如何处理这个问题吗？

见下方代码

文件浏览视图.xaml

<TextBox  Height="23" HorizontalAlignment="Left" Margin="113,22,0,0" 
               Name="txtFilenameWithPath" 
               Text="{Binding Path=FilenameWithPath, 
               UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
               VerticalAlignment="Top" Width="300" />
<Button 
        Content="Browse..." 
        Height="30" 
        HorizontalAlignment="Left" 
        Margin="433,20,0,0" 
        Name="btnBrowse" 
        VerticalAlignment="Top"
        Width="142" 
        Command="{Binding Path=BrowseCommand}"  />

文件浏览视图.xaml.cs

public partial class FileBrowseView : Window
{
    public FileBrowseView()
    {
        InitializeComponent();
        DataContext = new FileBrowseViewModel();
    }


}

文件浏览模型

public class FileBrowseModel
{
  private string _filenameWithPath = string.Empty;
    public string FilenameWithPath
    {
        get { return _filenameWithPath; }
        set
        {
            if (value == _filenameWithPath)
                return;
            else
                _filenameWithPath = value;
        }
    }

}

文件浏览视图模型

public class FileBrowseViewModel  : INotifyPropertyChanged 
{   
  private string _filenameWithPath = string.Empty;
  public string FilenameWithPath
  {
        get { return _filenameWithPath; }
        set
        {
            if (value == _filenameWithPath)
                return;
            else
                _filenameWithPath = value;
            OnPropertyChanged("FilenameWithPath"); 
        }
    }

    private ICommand _browseCommand;
    public ICommand BrowseCommand
    {
        get
        {
            if (_browseCommand == null)
                _browseCommand = new DoBrowse();
            return _browseCommand;
        }
        set
        {
            _browseCommand = value;
            OnPropertyChanged("FilenameWithPath"); 
        }
    }


    private class DoBrowse : ICommand
    {
        public bool CanExecute(object parameter) { return true; }
        public event EventHandler CanExecuteChanged;
        public void Execute(object parameter)
        {
            var filedialog = new System.Windows.Forms.OpenFileDialog();
            DialogResult fresult = filedialog.ShowDialog();

            if (fresult == System.Windows.Forms.DialogResult.OK)
            {
                 FilenameWithPath = filedialog.FileName;
                //I am trying to assign value i got from OpenFileDialog to 
                // FilenameWithPath property
                //complier says "Cannot access non static member of outer type 
                   'MyProject.FileBrowseViewModel' via 
                  nested type 'MyProject.FileBrowseViewModel.DoBrowse

                onPropertyChanged(“FilenameWithPath”);                    
            }
        }
    }

   public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

Answer 1

您只需要在命令的 Execute 函数中设置 FileNameWithPath。 FileNameWithPath 的设置器应该调用 OnPropertyChanged。您不必从命令的 Execute 函数中调用它。

Answer 2

编辑：确保将数据上下文设置为视图模型而不是模型，因为两者都具有 FilenameWithPath 属性。如果您这样做，则绑定不会失败，因为仍有要绑定的属性。否则：

进行以下更改：

public string FilenameWithPath
{
   get { return _filenameWithPath; }
   set
   {
       if (value == _filenameWithPath)
           return;
       else
       {
           _filenameWithPath = value;
           OnPropertyChanged("FilenameWithPath");
       }
   }
}

和

if (fresult == System.Windows.Forms.DialogResult.OK)
{
    FilenameWithPath = filedialog.FileName;
}

这应该可以解决您的问题。此外，考虑更改您使用的对话框，因为这是 WPF（如我的评论中所建议的那样）。

Answer 3

最后，我能够通过添加名为 RelayCommand 的新类来解决此问题。我已经修改了 _browseCommand 使用中继命令的 get 块，如下所示。

private ICommand _browseCommand;
public ICommand BrowseCommand
{
  get{
    if (_browseCommand == null){
        _browseCommand = new RelayCommand(
                                         a => this.DoBrowseFolder(),
                                         p => this.CheckCondition());
    }

    return _browseCommand;
   }

    set
    {   _browseCommand = value;
        OnPropertyChanged("FilenameWithPath");
    }
   }


    public bool CheckCondition () {
    //Check condition here if needed        
        return true;
    }


    private void DoBrowseFolder(){
        var filedialog = new System.Windows.Forms.OpenFileDialog();
        DialogResult fresult = filedialog.ShowDialog();

        if (fresult == System.Windows.Forms.DialogResult.OK)
        {
            FilenameWithPath = filedialog.FileName;
            OnPropertyChanged("FilenameWithPath ");
        }

    }

中继命令类

public class RelayCommand : ICommand
{

    #region Fields
    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;
    #endregion // Fields

    #region Constructors      
    public RelayCommand(Action<object> execute, Predicate<object> canExecute){
        if (execute == null)             
            throw new ArgumentNullException("execute");          
        _execute = execute;         
        _canExecute = canExecute;     
    }     

    #endregion // Constructors      
    #region ICommand Members      
    [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);     
    }      
    #endregion // ICommand Members      
}