如何從委託訪問變量？

Question

我想創建一個返回新對象並將委託作爲參數的方法。 代表應該使用該對象進行操作。 我想不把該對象作爲參數，並使用返回我的函數的對象。 是否有可能使這段代碼運行？

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

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 2

它改成這樣：

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

    context.Action.Invoke(); 
} 

並將其編譯和工作正常。

在您的代碼版本中，編譯器嘗試使用（capture）該變量仍未分配時。但是我們知道context變量在匿名方法被調用之前被分配。所以我們可以給它分配一個臨時值，以便編譯器不會抱怨。

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(); 
    } 

}