ICommand是否总是需要对象作为参数?

问题描述

当我实现ICommand接口时，将创建以下方法

When I implement the ICommand interface, the following methods are created

#region ICommand Members

    public bool CanExecute(object parameter)
    {
    }

    public event EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
    }

#endregion

有趣的部分是

public void Execute(object parameter)
{
}

仅因为它指示期望1个参数.如果我不需要传递参数怎么办?在我的ViewModel中，我有以下代码

Simply because it indicates that it expects 1 parameter. What if I don't need to pass a parameter? In my ViewModel I have the following code

public class DownloadViewModel : BaseViewModel
{
    public ICommand BrowseForFile { get; set; }

    public string File { get; set; }

    public DownloadViewModel()
    {
        BrowseForFile = new RelayCommand(new Action<object>(OpenDialog));
    }

    private void OpenDialog(object o)
    {
        var dialog = new System.Windows.Forms.FolderBrowserDialog();
        System.Windows.Forms.DialogResult result = dialog.ShowDialog();
        File = dialog.SelectedPath;
    }
}

OpenDialog方法不需要该参数，但看起来好像我必须这样做，这样我才能满足Interface.

The OpenDialog method does not require the parameter but it appears as if I have to just so I can satisfy the Interface.

我是做对了还是错过了重点?

Am I doing this right or have I missed the point?

推荐答案

是的，ICommand总是需要一个对象，而RelayCommand也总是需要一个对象.如果不需要它，则传递null，并且不要在您的方法中使用它，这很丑陋.

Yes, ICommand always needs an object and RelayCommand too. If you don't need it, you pass null and don't use it in your method, which is ugly.

我会改用Prism的DelegateCommand.它存在于非通用版本中，该版本不使用参数:

I would use Prism's DelegateCommand instead. This exists in a non-generic version, which doesn't take parameters:

Command = new DelegateCommand(DoSomething);
CommandWithParameter = new DelegateCommand<int>(DoSOmethingWithInt);

它在PRISM程序集中，您必须下载并参考.

Its in the PRISM assembly, which you have to download and reference.

using Microsoft.Practices.Prism;

PRISM

或者，使用MVVMLight工具箱，该工具箱提供了一个命令类，其功能基本相同.无论如何，在没有MVVM框架的情况下使用MVVM是没有意义的.我可以推荐PRISM，因为它是DelegateCommand或EventAggregator的基本内容.

Alternatively, use the MVVMLight toolkit, which provides a command class which does basically the same thing. There is no point in using MVVM without a MVVM framework anyway. I can recommend PRISM, also for it's basic stuff like the DelegateCommand or the EventAggregator.

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