c# - 将模型绑定(bind)到 View ，但按钮单击工作

Question

全部，
绑定(bind)的完整模型，值显示在控件中，但无法让按钮单击工作......有什么建议吗？我错过了什么或做错了什么？谢谢

<Window x:Class="test" Title="test" Height="350" Width="525">
    <StackPanel Name="abc" Orientation="Vertical" DataContext="{Binding Path=EMP, Mode=TwoWay}" Margin="4" Height="153">
        <Label Content="Last Name:" Margin="0,0,4,0"/>
        <TextBox Width="250" Text="{Binding Path=LastName}" Height="20"/>
        <Button Grid.Row="2" Margin="0,0,4,0" Height="40" Width="40" 
                 Command="{Binding Path=SaveCommand}" />
    </StackPanel>
</Window>

class EmployeeVM: ViewModelBase
{
    private bool _Execute = true;
    public EmployeeVM()
    {
        emp = new Model.Employee { FirstName = "abc", LastName = "xyz" };
    }
    private string sFirstName;
    private string sLastName;
    private Model.Employee emp;

    public Model.Employee EMP
    {
        get{return emp;}
        set{emp = value;
            OnPropertyChanged("EMP");}
    }
    public string LastName
    {
        get { return sLastName; }
        set 
        { 
            sLastName = value;
            OnPropertyChanged("LastName");
        }
    }

    #region Commands
    private ICommand _SaveCommand;
    public ICommand SaveCommand
    {
        get
        {
            return _SaveCommand = new CommandHandler(Save, _Execute);
        }
    }
    #endregion

    private void Save(object param)
    {
        ObservableCollection<Model.Employee> newIM = new ObservableCollection<Model.Employee>();
        foreach(Model.Employee e in newIM)
        {
            string a = e.FirstName;
            string b = e.LastName;
        }
    }
}


public class CommandHandler : ICommand
{
    Action<object> _act;
    bool _canExecute;

    public CommandHandler(Action<object> act, bool canExecute)
    {
        _act = act;
        _canExecute = canExecute;
    }

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

    public event EventHandler CanExecuteChanged;

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

Answer 1

您可以编写自己的命令。

这是我用于命令的基类。

它有一些非常基本的东西，让生活更轻松。

Execute方法接受一个对象，因此您将能够传递数组

可以很容易地传入一个 View 模型，即您将在命令中使用的 View 模型(大多数情况下，如果您不需要它，请将其滑出)

更改后的处理程序利用 CommandManager。这真的很有帮助

也许你想改变一些事情。我添加的所有内容都在那里，因为它非常有帮助。 (尤其是 View 模型)

public abstract class CommandBase : ICommand
{
    public abstract bool CanExecute(object o);
    public abstract void Execute(object o);

    public PropertyChangedBase ViewModel { get; set; }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }
}

你会有像这样的实现

public class ExampleCommand : CommandBase
{
    public ExampleCommand (PropertyChangedBase viewModel)
    {
        this.ViewModel = viewModel;
    }

    public override void Execute(object o)
    {
        // something like
        var settings = UnityContainer.Resolve<ISettings>();
        settings.MagicValue = (this.ViewModel as ConcreteViewModel).MagicValue;
    }

    public override bool CanExecute(object o)
    {
        return true;
    }
}

在您的 ViewModel 中，您通过拥有一个属性将命令公开给 View :

public class ExampleViewModel : PropertyChangedBase
{
    public ExampleViewModel ()
    {
        this.DoThisAndThatCommand = new ExampleCommand(this);
    }

    public CommandBase DoThisAndThatCommand { get; set; }
}


// and in XAML, you can use it like
<Button x:Name="Ok"
            Command="{Binding DoThisAndThatCommand }" />

(假设您通过设置 ViewModel 的 View 正确连接了 DataContext 和 View)

现在，每当单击按钮时，都会调用命令的执行方法。

您的 ViewModel 位于 Command ，因此您可以轻松地使用它。

在命令内或 ViewModel 内有按钮是非常不寻常的。 .
MVVM 的诀窍是将View 分开。来自 ViewModel并且没有UIElements在 ViewModel .

如果您没有 PropertyChangedBase(这个是 Caliburn.Micro 附带的)，那么我建议您使用一些简单的 INotifyPropertyChanged 实现。

I found this one here, should be german though

公共(public)抽象类 NotifyPropertyChangedBase : INotifyPropertyChanged
{
#region < INotifyPropertyChanged > 成员

    /// <summary>
    /// Is connected to a method which handle changes to a property (located in the WPF Data Binding Engine)
    /// </summary>

    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Raise the [PropertyChanged] event
    /// </summary>
    /// <param name="propertyName">The name of the property</param>

    protected void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }


    #endregion

    private Dictionary<string, object> propertyValueStorage;


    #region Constructor

    public NotifyPropertyChangedBase()
    {
        this.propertyValueStorage = new Dictionary<string, object>();
    }


    #endregion



    /// <summary>
    /// Set the value of the property and raise the [PropertyChanged] event
    /// (only if the saved value and the new value are not equal)
    /// </summary>

    /// <typeparam name="T">The property type</typeparam>
    /// <param name="property">The property as a lambda expression</param>
    /// <param name="value">The new value of the property</param>

    protected void SetValue<T>(Expression<Func<T>> property, T value)
    {
        LambdaExpression lambdaExpression = property as LambdaExpression;

        if (lambdaExpression == null)
        {
            throw new ArgumentException("Invalid lambda expression", "Lambda expression return value can't be null");
        }

        string propertyName = this.getPropertyName(lambdaExpression);

        T storedValue = this.getValue<T>(propertyName);

        if (!object.Equals(storedValue, value))
        {
            this.propertyValueStorage[propertyName] = value;

            this.OnPropertyChanged(propertyName);
        }
    }


    /// <summary> Get the value of the property </summary>
    /// <typeparam name="T">The property type</typeparam>
    /// <param name="property">The property as a lambda expression</param>
    /// <returns>The value of the given property (or the default value)</returns>
    protected T GetValue<T>(Expression<Func<T>> property)
    {
        LambdaExpression lambdaExpression = property as LambdaExpression;

        if (lambdaExpression == null)
        {
            throw new ArgumentException("Invalid lambda expression", "Lambda expression return value can't be null");
        }

        string propertyName = this.getPropertyName(lambdaExpression);
        return getValue<T>(propertyName);
    }

    /// <summary>
    /// Try to get the value from the internal dictionary of the given property name
    /// </summary>
    /// <typeparam name="T">The property type</typeparam>
    /// <param name="propertyName">The name of the property</param>
    /// <returns>Retrieve the value from the internal dictionary</returns>

    private T getValue<T>(string propertyName)
    {
        object value;

        if (propertyValueStorage.TryGetValue(propertyName, out value))
        {
            return (T)value;
        }
        else
        {
            return default(T);
        }
    }


    /// <summary>
    /// Extract the property name from a lambda expression
    /// </summary>
    /// <param name="lambdaExpression">The lambda expression with the property</param>
    /// <returns>The extracted property name</returns>
    private string getPropertyName(LambdaExpression lambdaExpression)
    {
        MemberExpression memberExpression;

        if (lambdaExpression.Body is UnaryExpression)
        {
            var unaryExpression = lambdaExpression.Body as UnaryExpression;
            memberExpression = unaryExpression.Operand as MemberExpression;
        }
        else
        {
            memberExpression = lambdaExpression.Body as MemberExpression;
        }

        return memberExpression.Member.Name;
    }
} 

这是非常容易使用!

在您的 ViewModel 中，您必须为 Binding 提供公共(public)属性(这很重要)并发出更改通知。

这是一个如何使用 INPC (INotifyPropertyChanged) 的基本实现的示例

public class LoginViewModel : NotifyPropertyChangedBase
{
    public string UserName { get;set; }
}

这个 INPC 实现会为您调用 NotifyOfPropertyChange，您不必关心它!但是您必须检查最适合您的情况。

在您的问题中，您已经有一个 ViewModelBase。也许您想使用这个而不是上面的。