通过合并其他三个具有优先级的对象来创建对象 (C# .NET 3.5)

Question

我有三个相同 class（A、B、C）的 C#（将 .NET 3.5 用于遗留软件）对象，它们具有所有 public 属性（string、int、short , 字节, 日期时间, 双) 我需要通过合并 "three" 个对象来创建第四个 (D)。如果 A 有一个属性集（非空或空），我必须在 D 中设置它，否则我必须检查 B，然后作为最后一个 C。最有效和优雅的方法是什么？我读过反射是正确的方法吗？

Answer 1

反思是一种方法。下面是一个例子；可能不是最优雅的，但它可以建立在：

using System
using System.Reflection;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            Car A = new Car
            {
                Make = "Volvo"
            };

        Car B = new Car
        {
            Year = 2001,
            CreateDate = DateTime.Now
        };

        Car C = new Car
        {
            ShortValue = 1,
            MSRP = 20000,
            ByteValue = 10
        };

        Car D = new Car();

        Mapper mapobj = new Mapper();

        D = mapobj.Map<Car>(A);
        D = mapobj.Compare<Car>(B, D);
        D = mapobj.Compare<Car>(C, D);

        // Car D now has all the initialized properties of A,B,C
    }

    public class Mapper
    {
        public T Map<T>(T data)
        {
            var _result = (T)Activator.CreateInstance(typeof(T), new object[] { });

            foreach (PropertyInfo propertyInfo in typeof(T).GetProperties())
            {
                if (typeof(T).GetProperty(propertyInfo.Name) != null)
                    typeof(T)
                        .GetProperty(propertyInfo.Name,
                            BindingFlags.IgnoreCase |
                            BindingFlags.Instance |
                            BindingFlags.Public)
                        .SetValue(_result,
                            propertyInfo.GetValue(data));
            }

            return _result;
        }
        public T Compare<T>(T data, T data2)
        {
            var _result = (T)Activator.CreateInstance(typeof(T), new object[] { });

            foreach (PropertyInfo propertyInfo in typeof(T).GetProperties())
            {

                if (typeof(T).GetProperty(propertyInfo.Name) != null)
                {
                    bool isnullvalue = false;
                    DateTime zerodate = new DateTime();

                    switch (propertyInfo.PropertyType.Name)
                    {
                        case "String":
                            if ((string)propertyInfo.GetValue(data) != null && (string)propertyInfo.GetValue(data2) == null)
                                isnullvalue = true;
                            break;

                        case "Int32":
                            if ((Int32)propertyInfo.GetValue(data) != 0 && (Int32)propertyInfo.GetValue(data2) == 0)
                                isnullvalue = true;
                            break;
                        case "Int16":
                            if ((Int16)propertyInfo.GetValue(data) != 0 && (Int16)propertyInfo.GetValue(data2) == 0)
                                isnullvalue = true;
                            break;
                        case "Byte":
                            if ((Byte)propertyInfo.GetValue(data) != 0 && (Byte)propertyInfo.GetValue(data2) == 0)
                                isnullvalue = true;
                            break;
                        case "Double":
                            if ((Double)propertyInfo.GetValue(data) != 0 && (Double)propertyInfo.GetValue(data2) == 0)
                                isnullvalue = true;
                            break;
                        case "DateTime":  // DateTime.Compare(date1, date2)
                            DateTime time1 = (DateTime)propertyInfo.GetValue(data);
                            DateTime time2 = (DateTime)propertyInfo.GetValue(data2);
                            if (DateTime.Compare(time1, zerodate) != 0 && DateTime.Compare(time2, zerodate) == 0)
                                isnullvalue = true;
                            break;

                        default:
                            Console.WriteLine("No handler for type {} found");
                            Console.ReadLine();
                            Environment.Exit(-1);
                            break;
                    }


                    if (isnullvalue)
                    {
                        typeof(T).GetProperty(propertyInfo.Name,
                                BindingFlags.IgnoreCase |
                                BindingFlags.Instance |
                                BindingFlags.Public)
                            .SetValue(_result,
                                propertyInfo.GetValue(data));
                    }
                    else
                    {
                        typeof(T).GetProperty(propertyInfo.Name,
                                BindingFlags.IgnoreCase |
                                BindingFlags.Instance |
                                BindingFlags.Public)
                            .SetValue(_result,
                                propertyInfo.GetValue(data2));
                    }
                }
            }
            return _result;
        }
    }

    public class Car
    {
        public string Make { get; set; }
        public int Year { get; set; }
        public short ShortValue { get; set; }
        public byte ByteValue { get; set; }
        public DateTime CreateDate { get; set; }
        public double MSRP { get; set; }
    }
}

}

Answer 2

毫无疑问，您可以在这里使用基于反射的解决方案，但您可能不需要它。如果你提前知道合并的类型，你可以写一个非常简单的映射函数来处理这个。

例如，给定一个简单的 class...

class MyClassToMap
{
    public string MyString { get; set; }
    public int MyInt { get; set; }
}

你可以写一个简单的方法...

MyClassToMap Map(params MyClassToMap[] toMap)
{
    var mapped = new MyClassToMap();

    foreach (var m in toMap)
    {
        // 'default' is shorthand for a type's uninitalized value. In the case of
        // string, it resolves to "null", and in the case of int, it resolves to 0.
        // You could also use the literal values here, if you prefer.
        // Note that for C# versions < 7.1, you must specify the type--eg "default(string)".
        // See: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/default
        if (m.MyString != default) mapped.MyString = m.MyString;
        if (m.MyInt != default) mapped.MyInt = m.MyInt;
    }

    return mapped;
}

然后这样称呼它...

var a = new MyClassToMap { MyString = "foo", MyInt = 0 };
var b = new MyClassToMap { MyString = "bar", MyInt = 100 };
var c = new MyClassToMap { MyString = null, MyInt = 0 };

var mapped = Map(a, b, c);

Console.WriteLine($"MyString = {mapped.MyString}, MyInt = {mapped.MyInt}");
// prints: { MyString = "bar", MyInt = 100 };

Answer 3

您可以为此目的使用反射。例如，请检查以下代码（添加到解释方法的方法中的内联注释）

public T AssignProperties<T>(params T[] sources)
{
    // Types of properties that has to be copied
    var filteredPropertyTypes = new []{typeof(int),typeof(string),typeof(short),typeof(byte),typeof(DateTime),typeof(double)};
    // Create Default Instance of T
    var newInstance = (T)Activator.CreateInstance(typeof(T));
    // Iterate through each property
    foreach(var property in typeof(T).GetProperties().Where(x=>filteredPropertyTypes.Contains(x.PropertyType)))
    {
        // Get the default Value of the Type and get the first instance in sources, which has a non-default value for the property
        var defaultValue = property.PropertyType.IsValueType ? Convert.ChangeType(Activator.CreateInstance(property.PropertyType),property.PropertyType) : null;
        if(sources.Any(x=>!Convert.ChangeType(property.GetValue(x),property.PropertyType).Equals(defaultValue)))
        {
            var newValue = property.GetValue(sources.First(x=>!Convert.ChangeType(property.GetValue(x),property.PropertyType).Equals(defaultValue)));
            property.SetValue(newInstance,newValue);
        }
    }
    return newInstance;
}

您现在可以将该方法用于 N 个实例（A、B、C...），实例按需要处理的顺序传递。

var newInstance = AssignProperties(instanceA,instanceB,instanceC);

Demo Code

通过合并其他三个具有优先级的对象来创建对象 (C# .NET 3.5)

Create object by merging other three with priority (C# .NET 3.5)

c#

.net

object

reflection

.net-3.5