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无法将类型'void'隐式转换为System.Action <int>

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我正在尝试使用输入参数int创建.net标准委托，Action . 但我得到“不能隐式地将类型'void'转换为System.Action” . 我了解到可以将相同的返回类型方法添加到多播委托 . 以下是我的代码 . 这段代码有什么问题？如果我写lambda表达式，我没有看到编译错误 .

static void Main(strng[] args)
    {

    Action<int> AddBook = AddBookwithId(15); // Here is the error
    AddBook += x => Console.WriteLine("Added book with :{0}" , x ); // No compile error here
    AddBook += AddBookwithISBN(56434);// of course, the same error here too.
    }
    public static void AddBookwithId(int y)
    {
        Console.WriteLine( "Added Book to the shelf with the ID : {0} ", y ); 
    }

    public static void AddBookwithISBN(int y)
    {
        Console.WriteLine("Added Book to the shelf  with the ISBN: {0} ", y + 2);
    }
c# delegates action

3 回答

  • 2

    下面的代码编译...调用Action时，应该传递整数 .

    Action<int> AddBook = AddBookwithId; // Here is the error
       AddBook += x => Console.WriteLine("Added book with :{0}", x); // No compile error here
       AddBook += AddBookwithISBN;// of course, the same error here too.
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  • 1
    delegate void AddBook(int y);

    static void Main()
    {

        AddBook addBook;
        bool IsISBN = false;

        if (IsISBN)
        {
            addBook = AddBookwithISBN;
        }
        else
        {
            addBook = AddBookwithId;
        }
        addBook += x => Console.WriteLine("Added book with :{0}", x);
    }
    public static void AddBookwithId(int y)
    {
        Console.WriteLine("Added Book to the shelf with the ID : {0} ", y);

    }

    public static void AddBookwithISBN(int y)
    {
        Console.WriteLine("Added Book to the shelf  with the ISBN: {0} ", y + 2);
    }
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  • 0

    为什么不使用Lambda expressions？实际上，您已经在这行代码中使用过它：

    AddBook += x => Console.WriteLine("Added book with :{0}" , x ); // No compile error here

    这将导致：

    Action<int> AddBook = (x) => AddBookwithId(x); // Here is the error
AddBook += (x) => Console.WriteLine("Added book with :{0}" , x ); // No compile error here
AddBook += (x) => AddBookwithISBN(x);// of course, the same error here too.
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