ICommand MVVM 实现 [英] ICommand MVVM implementation

问题描述

所以在我正在做的这个特定的 MVVM 实现中，我需要几个命令.我真的厌倦了一个一个地实现 ICommand 类，所以我想出了一个解决方案，但我不知道它有多好，所以在这里任何 WPF 专家的输入将不胜感激.如果你能提供更好的解决方案，那就更好了.

So in this particular MVVM implementation I'm doing, I need several commands. I really got tired of implementing the ICommand classes one by one, so I came up with a solution, but I don't know how good it is, so the input of any WPF expert here will be greatly appreciated. And if you could provide a better solution, even better.

我所做的是一个 ICommand 类和两个将对象作为参数的委托，一个委托是 void(对于 OnExecute)，另一个是 bool(对于 OnCanExecute).因此，在 ICommand 的构造函数(由 ViewModel 类调用)中，我发送了两个方法，并在每个 ICommand 方法上调用了委托的方法.

What I did is a single ICommand class and two delegates which take an object as a parameter, one delegate is void (for OnExecute), the other bool (for OnCanExecute). So in the constructor of my ICommand (which is called by the ViewModel class) I send the two methods, and on each ICommand method I invoke the delegates' methods.

它确实很好用，但我不确定这是否是一种糟糕的方法，或者是否有更好的方法.下面是完整的代码，任何输入将不胜感激，即使是负面的，但请建设性.

It works really good, but I'm not sure if this is a bad way to do it, or if there's a better way. Below is the complete code, any input will be greatly appreciated, even negative, but please be constructive.

视图模型:

public class TestViewModel : DependencyObject
{
    public ICommand Command1 { get; set; }
    public ICommand Command2 { get; set; }
    public ICommand Command3 { get; set; }

    public TestViewModel()
    {
        this.Command1 = new TestCommand(ExecuteCommand1, CanExecuteCommand1);
        this.Command2 = new TestCommand(ExecuteCommand2, CanExecuteCommand2);
        this.Command3 = new TestCommand(ExecuteCommand3, CanExecuteCommand3);
    }

    public bool CanExecuteCommand1(object parameter)
    {
        return true;
    }

    public void ExecuteCommand1(object parameter)
    {
        MessageBox.Show("Executing command 1");
    }

    public bool CanExecuteCommand2(object parameter)
    {
        return true;
    }

    public void ExecuteCommand2(object parameter)
    {
        MessageBox.Show("Executing command 2");
    }

    public bool CanExecuteCommand3(object parameter)
    {
        return true;
    }

    public void ExecuteCommand3(object parameter)
    {
        MessageBox.Show("Executing command 3");
    }
}

ICommand:

public class TestCommand : ICommand
{
    public delegate void ICommandOnExecute(object parameter);
    public delegate bool ICommandOnCanExecute(object parameter);

    private ICommandOnExecute _execute;
    private ICommandOnCanExecute _canExecute;

    public TestCommand(ICommandOnExecute onExecuteMethod, ICommandOnCanExecute onCanExecuteMethod)
    {
        _execute = onExecuteMethod;
        _canExecute = onCanExecuteMethod;
    }

    #region ICommand Members

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

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

    public void Execute(object parameter)
    {
        _execute.Invoke(parameter);
    }

    #endregion
}

推荐答案

这几乎与 Karl Shifflet 演示了一个 RelayCommand，其中 Execute 触发预定的 Action;.如果你问我，这是一个一流的解决方案.

This is almost identical to how Karl Shifflet demonstrated a RelayCommand, where Execute fires a predetermined Action<T>. A top-notch solution, if you ask me.

public class RelayCommand : ICommand
{
    private readonly Predicate<object> _canExecute;
    private readonly Action<object> _execute;

    public RelayCommand(Predicate<object> canExecute, Action<object> execute)
    {
        _canExecute = canExecute;
        _execute = execute;
    }

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

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

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

这可以用作...

public class MyViewModel
{
    private ICommand _doSomething;
    public ICommand DoSomethingCommand
    {
        get
        {
            if (_doSomething == null)
            {
                _doSomething = new RelayCommand(
                    p => this.CanDoSomething,
                    p => this.DoSomeImportantMethod());
            }
            return _doSomething;
        }
    }
}

阅读更多:
Josh Smith(RelayCommand 的介绍者):模式 - WPF 应用使用 MVVM 设计模式

Read more:
Josh Smith (introducer of RelayCommand): Patterns - WPF Apps With The MVVM Design Pattern

这篇关于ICommand MVVM 实现的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！