WPF MVVM按钮命令获取文本框值

Question

我在了解按钮命令的工作方式时遇到了很大的麻烦。 我有这样的东西

{Binding TxtBox}从模型中获取价值，假设它是“ aaa”。 我想单击按钮，值应该出现在第二个文本框中（带有{Binding TxtBox2}文本框中）。

这是我的xaml：

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

这是我的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();
    }
}

我真的需要这个CommandHandler类吗？ 我从网上复制了代码。

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

第二个文本框的绑定永远不会收到有关其绑定属性已更改的通知。 设置this.TxtBox2时，应触发该属性的propertychanged事件，以便更新绑定。 有关绑定的所有信息，请参见思考链接

我不知道您是否使用棱镜作为mvvm框架，但这是DelegateCommand类附带的。 我认为.net框架中没有简单/轻量级的实现。 有关mvvm框架和委托命令，请参见此链接。

Answer 2

视图通过PropertyChanged事件对绑定更改作出反应，而您没有事件。 绑定到View实现INotifyPropertyChanged的任何东西，然后在props更改时触发事件，并且都准备好绑定起作用（一种或两种方式）。

更改模型使其看起来像这样，它应该对您有用。

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-最好让模型实现INotifyPropertyChanged，然后直接绑定到它，而不是将其包装在ViewModel中。 如果Model：INotifyPropertyChanged，则您的ViewModel现在看起来像这样：

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更改为：

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