c# - MVVM 光 : RelayCommand : define it lazy or in constructor?

Question

关于如何在 ViewModel 中定义一个 RelayCommand 有几个例子:

选项 1(惰性):

/// <summary>
/// Gets the LogOnCommand.
/// </summary>
/// <value>The LogOnCommand.</value>
public RelayCommand<LogOnUser> LogOnCommand
{
    get
    {
        if (this.logOnCommand == null)
        {
            this.logOnCommand = new RelayCommand<LogOnUser>(
                action =>
                {
                    // Action code...
                },
                g => g != null);
        }

        return this.logOnCommand;
    }
}

选项 2(在构造函数中)

/// <summary>
/// Initializes a new instance of the <see cref="LogOnFormViewModel"/> class.
/// </summary>
public LogOnFormViewModel()
{
    this.logOnCommand = new RelayCommand<LogOnUser>(
                action =>
                {
                    // Action code...
                },
                g => g != null);
}

/// <summary>
/// Gets the LogOnCommand.
/// </summary>
/// <value>The LogOnCommand.</value>
public RelayCommand<LogOnUser> LogOnCommand {get; private set;}

什么是最好/最清晰的设计？

Answer 1

这真的取决于你喜欢什么风格。如果可以避免的话，大多数人不喜欢在属性 getter 中有一堆逻辑。

就个人而言，我更喜欢有一个真正的方法来调用而不是匿名方法。我的 ViewModel 看起来像这样。

public class MyViewModel : ViewModelBase
{
    public RelayCommand<CommandParam> MyCommand { get; private set; }

    public MyViewModel()
    {
        CreateCommands();
    }

    private void CreateCommands()
    {
        MyCommand = new RelayCommand<CommandParam>(MyCommandExecute);
    }

    private void MyCommandExecute(CommandParam parm)
    {
        // Action code...
    }
}

请注意，如果您不使用 enable 命令，则不需要调用设置它的 ctor 重载。