c# - 最佳重载方法匹配...有一些无效参数 [byref/byval]

Question

我正在从 asp.net 应用程序调用一个 dll(用 vb6 编写)。我正在调用 dll 的以下函数:

Public Function FamIdentify_BYTE(strName As String, strDatabaseTemplate As Variant, len_of_data As Long, strIdentifyTemplate As String, strIP As String) As Boolean

以下 C# 代码调用上述函数:

public Boolean VerifyFinger(String name , String SampleModel, String REMOTE_ADDR)
        {

            try
            {
                Connect();
                OracleCommand command = connection.CreateCommand();  
                string sql = "SELECT FINGER_DATA,DATA_LENGTH,SERIAL_NO FROM FP_BIOMETRIC_DATA WHERE CUST_NO =" + name.Trim();
                command.CommandText = sql;
                OracleDataReader reader = command.ExecuteReader();

                bool fingerMatched = false;
                FamServer.FamApp famApp = new FamServer.FamApp();
                while (reader.Read())
                {
                    Object[] values = new object[3];
                    int numColumns = reader.GetValues(values);
                    byte[] fingerData = values[0] as byte[];
                    string result = System.Text.Encoding.UTF8.GetString(fingerData);

                    int length_of_data =  Convert.ToInt32(values[1]);
                    int serial_no = Convert.ToInt32(values[2]);

                    //                     FamIdentify_BYTE(ref string, ref object, ref int, ref string, ref string)
                    fingerMatched = famApp.FamIdentify_BYTE(name, fingerData, length_of_data, SampleModel, REMOTE_ADDR);

               //     if (fingerMatched)
                       // break;
                }
                famApp.Termination();
               // famApp = null;
                GC.Collect();

                Close();
                return fingerMatched;
            }
            catch (Exception e)
            {
                HttpContext.Current.Response.Write("<br>" + e.GetBaseException() + "<br>");
                return false;
            }
        }

但是当我在 IIS express 中运行应用程序时，出现了这个错误:

The best overloaded method match for 'FamServer._FamApp.FamIdentify_BYTE(ref string, ref object, ref int, ref string, ref string)'
 has some invalid arguments ASPNET(1)

这是完整的错误列表:

F:\ASP.NET Projects\ASPNET\App_Code\Global.asax.cs(180,37): error CS1502: The best overloaded method match for 'FamServer._FamApp.FamIdentify_BYTE(ref string, ref object, ref int, ref string, ref string)' has some invalid arguments
F:\ASP.NET Projects\ASPNET\App_Code\Global.asax.cs(180,61): error CS1620: Argument '1' must be passed with the 'ref' keyword
F:\ASP.NET Projects\ASPNET\App_Code\Global.asax.cs(180,67): error CS1503: Argument '2': cannot convert from 'byte[]' to 'ref object'
F:\ASP.NET Projects\ASPNET\App_Code\Global.asax.cs(180,79): error CS1620: Argument '3' must be passed with the 'ref' keyword
F:\ASP.NET Projects\ASPNET\App_Code\Global.asax.cs(180,95): error CS1620: Argument '4' must be passed with the 'ref' keyword
F:\ASP.NET Projects\ASPNET\App_Code\Global.asax.cs(180,108): error CS1620: Argument '5' must be passed with the 'ref' keyword

如果我在 IIS 服务器上运行上面的应用程序，重定向时间太长了。我不明白为什么会这样。请帮我 。

Answer 1

关于 MSDN Library 的传递参数机制的一个小问题:

In Visual Basic 6.0, if you do not specify ByVal or ByRef for a procedure parameter, the passing mechanism defaults to ByRef. This allows the variable passed into the procedure to be modified in the calling program.

使用上面的解释，默认情况下，DLL 库方法对所有输入变量使用按引用传递，这与 C# 的默认值(而不是按值传递)具有不同的行为。因此，ref 关键字对于方法调用中的每个传递变量都是强制性的，如下所示:

fingerMatched = famApp.FamIdentify_BYTE(ref name, ref fingerData, ref length_of_data, ref SampleModel, ref REMOTE_ADDR);

在这一点上，它似乎工作正常但仍然有第二个问题，它包含在传递输入参数期间从字节数组到 object(VB 6 中的 Variant)的无效转换.您必须先将该字节数组转换为 object:

byte[] fingerData = values[0] as byte[];

// Variant in VB 6 translated as Object into C#
// Therefore, a conversion to Object type is required
object fingerObject = fingerData;

那么，上面的方法调用应该改成这样:

fingerMatched = famApp.FamIdentify_BYTE(ref name, ref fingerObject, ref length_of_data, ref SampleModel, ref REMOTE_ADDR);

注意:您不能调用带有引用参数的方法，而不是完全指定的参数类型，并且ref参数必须包含任何可分配的值。

相关引用:

Passing Objects By Reference or Value in C#

Why use the 'ref' keyword when passing an object?

Passing Parameters (MSDN Library)

Cannot convert from 'ref byte[]' to 'ref object'