Question

我想创建一个返回新对象的方法，并将delegate作为参数。代表应该使用该对象。我想不把该对象作为参数并使用返回我的函数的对象。是否可以运行此代码？

    public class ActionContext
    {
        public Action Action;
        public int Variable = 0;
    }

    public ActionContext Create(Action action)
    {
        return new ActionContext(){ Action = action };    
    }

    public void Test()
    {
        // I don't want provide ActionContext through delegate(ActionContext)
        ActionContext context = Create(delegate
        {
            //ERROR: Use of unassigned local variable 'context'
            context.Variable = 10;
        });

        context.Action.Invoke();
    }

Answer 1

将其更改为：

public void Test()
{
    ActionContext context = null; // Set it to null beforehand
    context = Create(delegate
    {
        context.Variable = 10;
    });

    context.Action.Invoke();
}

它编译并正常工作。

在您的代码版本中，编译器在仍未取消分配时尝试使用（ capture ）变量。但是我们知道在调用匿名方法之前正在分配context变量。所以我们可以为它分配一个临时值，这样编译器就不会抱怨。

Answer 2

public class ActionContext
{
    public Action Action;
    public int Variable = 0;
    public delegate void Foo(ref int i);

    public ActionContext(ActionContext.Foo action)
    {
        Action = () => action(ref this.Variable);    
    }
}



public void Test()
{
    // I don't want provide ActionContext through delegate(ActionContext)
    ActionContext context = new ActionContext(
        (ref int variable) => variable = 10);

    context.Action.Invoke();
}

Answer 3

public class ActionContext
{
    public Action Action;
    public int Variable = 0;


   public Func<ActionContext> Create(Action action)
   {
        return (() => { Action = action; return this; });
   }


   public void Test()
   {
      // I don't want provide ActionContext through delegate(ActionContext)
      var context = Create(() => { Variable = 10; });
     context().Action.Invoke();
   }

}

如何从委托访问变量？

3 个答案: