通过合并其他三个具有优先级来创建对象 (C# .NET 3.5)

Question

我有三个C#(使用.NET 3.5作为旧版sw(的同一类(A，B，C(对象，具有所有公共属性(字符串，整数，短整型，字节，日期时间，双精度( 我需要通过合并"三个"对象来创建第四个 (D(。 如果 A 设置了一个属性(不是 null 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。 最有效和最优雅的方法是什么？ 我读过关于反思是正确的方法吗？

Answer 1

反射是一种方法。 下面是一个示例;可能不是最优雅的，但它可以建立在：

使用系统 使用系统反射;
命名空间测试 { 班级课程 { 静态空 主(字符串[] 参数( { 车 A = 新车 { 品牌 ="沃尔沃" };
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，您可以在此处使基于反射的解决方案工作，但您可能不需要它。如果你知道要合并的类型，你可以编写一个非常简单的映射函数来处理这个问题。

例如，给定一个简单的类...

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://learn.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;
}

并这样称呼它...

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

您可以使用反射来实现此目的。例如，请检查以下代码(内联注释添加到解释该方法的方法中(

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;
}

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

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

演示代码