WPF MVVM按鈕命令獲取文本框值

Question

我在了解按鈕命令的工作方式時遇到了很大的麻煩。 我有這樣的東西

{Binding TxtBox}從模型中獲取價值，假設它是“ aaa”。 我想單擊按鈕，值應該出現在第二個文本框中（帶有{Binding TxtBox2}文本框中）。

這是我的xaml：

<TextBox Text="{Binding TxtBox, Source={StaticResource viewModel}}" />
<TextBox Text="{Binding TxtBox2, Source={StaticResource viewModel}}" />
<Button Command="{Binding ClickCommand}"/>

這是我的ViewModel：

public class CommandHandler : ICommand
{
    private Action _action;
    private bool _canExecute;
    public CommandHandler(Action action, bool canExecute)
    {
        _action = action;
        _canExecute = canExecute;
    }

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

    public event EventHandler CanExecuteChanged;

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

我真的需要這個CommandHandler類嗎？ 我從網上復制了代碼。

public string TxtBox
{
    get { return Model.TxtBoxValue; }
    set { Model.TxtBoxValue = value; }
}
public string TxtBox2 { get; set; }

private ICommand _clickCommand;
public ICommand ClickCommand
{
    get
    {
        return _clickCommand ?? (_clickCommand = new CommandHandler(() => MyAction(), _canExecute)); // I believe that when the button is clicked MyAction() is triggered, right?

    }

}
private bool _canExecute = true;
public void MyAction()
{
    this.TxtBox2 = this.TxtBox; // should something like this work? Because right now it doesn't
}

Answer 1

第二個文本框的綁定永遠不會收到有關其綁定屬性已更改的通知。 設置this.TxtBox2時，應觸發該屬性的propertychanged事件，以便更新綁定。 有關綁定的所有信息，請參見思考鏈接

我不知道您是否使用棱鏡作為mvvm框架，但這是DelegateCommand類附帶的。 我認為.net框架中沒有簡單/輕量級的實現。 有關mvvm框架和委托命令，請參見此鏈接。

Answer 2

視圖通過PropertyChanged事件對綁定更改作出反應，而您沒有事件。 綁定到View實現INotifyPropertyChanged的任何東西，然后在props更改時觸發事件，並且都准備好綁定起作用（一種或兩種方式）。

更改模型使其看起來像這樣，它應該對您有用。

public class MyViewModel : INotifyPropertyChanged
{
    #region INotifyPropertyChanged Members

    [field: NonSerialized]
    public event PropertyChangedEventHandler PropertyChanged = null;

    protected virtual void RaisePropertyChanged(string propName)
    {
        if(PropertyChanged != null)
        {
            Task.Run(() => PropertyChanged(this, new PropertyChangedEventArgs(propName)));
        }
    }

    #endregion

    public string TxtBox
    {
        get { return Model.TxtBoxValue; }
        set
        {
            Model.TxtBoxValue = value;
            RaisePropertyChanged("TxtBox");
        }
    }

    // presuming TxtBox2Value is in Model...else use a field
    public string TxtBox2
    {
        get { return Model.TxtBox2Value; }
        set
        {
            Model.TxtBox2Value = value;
            RaisePropertyChanged("TxtBox2");
        }
    }

    private ICommand _clickCommand;
    public ICommand ClickCommand
    {
        get
        {
            return _clickCommand ?? (_clickCommand = new CommandHandler(() => MyAction(), _canExecute)); // I believe that when the button is clicked MyAction() is triggered, right?

        }

    }
    private bool _canExecute = true;
    public void MyAction()
    {
        this.TxtBox2 = this.TxtBox; // should something like this work? Because right now it doesn't
    }
}

IMO-最好讓模型實現INotifyPropertyChanged，然后直接綁定到它，而不是將其包裝在ViewModel中。 如果Model：INotifyPropertyChanged，則您的ViewModel現在看起來像這樣：

public class MyViewModel
{

    // fire prop changed event here if this model will be swapped out after the ctor...otherwise don't worry about it
    public Model Model { get; set; }

    private ICommand _clickCommand;
    public ICommand ClickCommand
    {
        get
        {
            return _clickCommand ?? (_clickCommand = new CommandHandler(() => MyAction(), _canExecute)); 

        }

    }
    private bool _canExecute = true;
    public void MyAction()
    {
        Model = new Model();

        Model.TxtBox2 = "Some new value"; 
    }
}

...而您的xaml更改為：

<TextBox Text="{Binding Model.TxtBox, Source={StaticResource viewModel}}" />
<TextBox Text="{Binding Model.TxtBox2, Source={StaticResource viewModel}}" />
<Button Command="{Binding ClickCommand}"/>