7

以下代码导致 C3867（...函数调用缺少参数列表...）和 C3350（...委托构造函数需要 2 个参数...）。我究竟做错了什么？

    public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        bool IsEven(int i){
            return (i % 2) == 0;
        }

        Form1(void)
        {
            numbers = gcnew array<int>{
                1, 2, 3, 4, 5, 6, 7, 8, 9, 10
            };

            array<int> ^even = Array::FindAll(
                numbers, gcnew Predicate<int>(IsEven));
        }
    };
4

2 回答 2

13

在 C++/CLI 中，您必须传递包含函数的类型的实际实例：

 array<int> ^even = Array::FindAll(
    numbers, gcnew Predicate<int>(this, &Test::IsEven));

（或制作你的IsEven方法static）

于 2009-03-16T08:48:54.577 回答
0

以下简单的控制台应用程序提供了使用.NET C++/CLI的FindAll()方法示例。array

这适用于不支持 lambdas 的 Visual Studio 2005。由于您的示例使用的是 Windows 窗体，因此我在此 Windows 控制台应用程序中提供了一个额外的类，Predicate以在FindAll().

此示例显示了提供谓词的三种不同机制：

  • 使用没有对象的类静态函数
  • 使用需要在使用之前创建对象的类方法
  • 一个简单的 C 风格函数，它不是类中的方法

这是一个非常基本的示例，int但它也适用于更复杂的数据结构。

// _scrap_net.cpp : main project file.

#include "stdafx.h"

using namespace System;

    public ref class Thing1
    {
    private:
        int     iDiv;                  // divisor if specified
    public:
        static bool IsEven(int i){      // static usable without creating an object
            return (i % 2) == 0;        // even number if division has no remainder
        }
        static bool IsOdd(int i){       // static usable without creating an object
            return (i % 2) != 0;        // odd numbered if division has remainder
        }
        bool IsDivisibleBy (int i) {    // non-static must create object before using
            return (i % iDiv) == 0;     // check if division has remainder
        }
        bool IsNotDivisibleBy (int i) { // non-static must create object before using
            return (i % iDiv) != 0;     // check if division has remainder
        }

        Thing1(void) { iDiv = 2; }      // standard constructor
        Thing1(int i) { iDiv = i; }     // constructor with argument to use IsDivisibleBy()
    };

    // standalone function used rather than a class function
    bool IsLessThan10 (int i) {
        return i < 10;
    }

int main(array<System::String ^> ^args)
{
    // sample array of some integers for our example
    array<int> ^numbers = gcnew array<int>{
        1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
    };

    // our format string to use when printing the array values
    String ^ fmt = gcnew String(L" {0,6}");

    // use a static function in a class as the predicate so object not needed
    array<int> ^even = Array::FindAll(numbers, gcnew Predicate<int>(&Thing1::IsEven));

    Console::WriteLine (L"\n even ");
    for each (int jj in even) {
        Console::Write(fmt, jj);
    }

    // use a standard function as the predicate so class not needed
    array<int> ^lessThan10 = Array::FindAll(numbers, gcnew Predicate<int>(&IsLessThan10));

    Console::WriteLine (L"\n lessThan10 ");
    for each (int jj in lessThan10) {
        Console::Write(fmt, jj);
    }


    // use a special divisor so create an object with that value and use it.
    Thing1 ^ myDiv = gcnew Thing1(3);

    // need to specify the object for the object method in the predicate
    array<int> ^divBy3 = Array::FindAll(numbers, gcnew Predicate<int>(myDiv, &Thing1::IsDivisibleBy));

    Console::WriteLine (L"\n divBy3 ");
    for each (int jj in divBy3) {
        Console::Write(fmt, jj);
    }


    // need to specify the object for the object method in the predicate
    array<int> ^notDivBy3 = Array::FindAll(numbers, gcnew Predicate<int>(myDiv, &Thing1::IsNotDivisibleBy));

    Console::WriteLine (L"\n notDivBy3 ");
    for each (int jj in notDivBy3) {
        Console::Write(fmt, jj);
    }

    Console::WriteLine (L"\nEnd");
    return 0;
}

该程序的输出如下所示：

 even
      2      4      6      8     10     12     14
 lessThan10
      1      2      3      4      5      6      7      8      9
 divBy3
      3      6      9     12
 notDivBy3
      1      2      4      5      7      8     10     11     13     14
End
于 2015-06-29T05:15:10.827 回答