[英]Copying the contents of a base class from a derived class
我目前有一个派生类和一个基类。 如何使派生类的基类等于我拥有的基类? 浅拷贝会起作用吗?
class Base
{
private string name;
public string Name { get; set; }
private string address;
public string Address { get; set; }
}
class Derived:Base
{
private string field;
public String field { get; set; }
}
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Base b = new Base();
b.Address = "Iliff";
b.Name = "somename";
Derived d = new Derived();
//How can I make the base class of d equal to b ?
}
}
}
为基类创建一个复制构造函数,为此您还需要创建一个无参数的构造函数,并且通过添加复制构造函数,编译器将不再生成默认构造函数。 然后在派生类中调用基类的复制构造函数。
public class Base
{
public int Name { get; set; }
public string Address { get; set; }
public Base()
{ }
public Base(Base toCopy)
{
this.Name = toCopy.Name;
this.Address = toCopy.Address;
}
}
public class Derived : Base
{
public String Field { get; set; }
public Derived(Base toCopy)
: base (toCopy)
{ }
// if desired you'll need a parameterless constructor here too
// so you can instantiate Derived w/o needing an instance of Base
public Derived()
{ }
}
另一种方法是将基类映射到派生类:
/// <summary>
/// Maps the source object to target object.
/// </summary>
/// <typeparam name="T">Type of target object.</typeparam>
/// <typeparam name="TU">Type of source object.</typeparam>
/// <param name="target">Target object.</param>
/// <param name="source">Source object.</param>
/// <returns>Updated target object.</returns>
public static T Map<T, TU>(this T target, TU source)
{
// get property list of the target object.
// this is a reflection extension which simply gets properties (CanWrite = true).
var tprops = target.GetProperties();
tprops.Where(x=>x.CanWrite == true).ToList().ForEach(prop =>
{
// check whether source object has the the property
var sp = source.GetType().GetProperty(prop);
if (sp != null)
{
// if yes, copy the value to the matching property
var value = sp.GetValue(source, null);
target.GetType().GetProperty(prop).SetValue(target, value, null);
}
});
return target;
}
例子:
var derivedClass = new DerivedClass();
derivedClass.Map(baseClass);
如果我理解正确,这将起作用:
class Derived : Base
{
// all the code you had above, plus this:
public Derived(Base toCopy)
{
this.name = toCopy.name;
this.address = toCopy.address;
}
}
Derived d = new Derived(b);
您必须手动将Base
实例的字段复制到新的Derived
实例。
一种常见的方法是提供一个复制构造函数:
public Derived(Base other)
{
if (other == null) {
throw new ArgumentNullException("other");
}
this.name = other.name;
this.address = other.address;
}
关于您的代码的另一个注意事项:
private string field;
public string Field { get; set; }
这没有多大意义(其他属性也是如此)。
public string Field { get; set; }
public string Field { get; set; }
表示编译器会自动创建一个私有字段。 您的field
将永远不会被使用。
要么只写public string Field { get; set; }
public string Field { get; set; }
public string Field { get; set; }
,因为私有字段将自动创建。 或者以某种方式声明Field
属性,以便使用您的私有字段:
private string field;
public string Field {
get {
return field;
}
set {
field = value;
}
}
您始终可以使用 Object.MemberwiseClone 来复制它。
http://msdn.microsoft.com/en-us/library/system.object.memberwiseclone.aspx
或者实现IClonable接口: http : //msdn.microsoft.com/en-us/library/system.icloneable.aspx
我想出了一个很好的模式来处理这种情况。
public class Base
{
public int BaseField;
/// <summary>
/// Apply the state of the passed object to this object.
/// </summary>
public virtual void ApplyState(Base obj)
{
BaseField = obj.BaseField;
}
}
public class Derived : Base
{
public int DerivedField;
public override void ApplyState(Base obj)
{
var src = srcObj as Derived;
if (src != null)
{
DerivedField = src.DerivedField;
}
base.ApplyState(srcObj);
}
}
给定任何两个共享类型“Base”的对象,您可以将 A 应用于 B 或 B 应用于 A。
根据mnyarar代码,有必要更新获取属性的方式:
public static T Map<T, TU>(this T target, TU source)
{
// list of writable properties of the destination
List<PropertyInfo> tprops = typeof(T).GetTypeInfo().DeclaredProperties
.Where(x => x.CanWrite == true).ToList();
tprops.ForEach(prop =>
{
// check whether source object has the the property
var sp = source.GetType().GetProperty(prop.Name);
if (sp != null)
{
// if yes, copy the value to the matching property
var value = sp.GetValue(source, null);
target.GetType().GetProperty(prop.Name).SetValue(target, value, null);
}
});
}
我意识到其他几个答案可能涉及到这个解决方案,但我想更完整地说明它。
我找到的解决方案是填充基类,然后将该基类传递给派生类的构造函数。 派生类的构造函数根据基类填充其字段。
class Base
{
private string name;
public string Name { get; set; }
private string address;
public string Address { get; set; }
}
class Derived:Base
{
Derived(Base toCopy)
{
this.Name = toCopy.Name;
this.Address = toCopy.Address;
}
private string field;
public String field { get; set; }
}
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Base b = new Base();
b.Address = "Iliff";
b.Name = "somename";
//You are now passing the base class into the constructor of the derived class.
Derived d = new Derived(b);
}
}
}
我发现 EMIT 可以为您提供帮助。
因为我们会在反射上花费太长时间,但我们可以在 Emit 上快速。
private static void CloneObjectWithIL<T>(T source, T los)
{
var dynamicMethod = new DynamicMethod("Clone", null, new[] { typeof(T), typeof(T) });
ILGenerator generator = dynamicMethod.GetILGenerator();
foreach (var temp in typeof(T).GetProperties().Where(temp=>temp.CanRead&&temp.CanWrite))
{
generator.Emit(OpCodes.Ldarg_1);// los
generator.Emit(OpCodes.Ldarg_0);// s
generator.Emit(OpCodes.Callvirt,temp.GetMethod);
generator.Emit(OpCodes.Callvirt, temp.SetMethod);
}
generator.Emit(OpCodes.Ret);
var clone = (Action<T, T>) dynamicMethod.CreateDelegate(typeof(Action<T, T>));
clone(source, los);
}
它可以用作此代码:
public class Base
{
public string BaseField;
}
public class Derived : Base
{
public string DerivedField;
}
Base base = new Base();
//some alother code
Derived derived = new Derived();
CloneObjectWithIL(base, derived);
更快的代码是缓存它。
// ReSharper disable once InconsistentNaming
public static void CloneObjectWithIL<T>(T source, T los)
{
//See http://lindexi.oschina.io/lindexi/post/C-%E4%BD%BF%E7%94%A8Emit%E6%B7%B1%E5%85%8B%E9%9A%86/
if (CachedIl.ContainsKey(typeof(T)))
{
((Action<T, T>) CachedIl[typeof(T)])(source, los);
return;
}
var dynamicMethod = new DynamicMethod("Clone", null, new[] { typeof(T), typeof(T) });
ILGenerator generator = dynamicMethod.GetILGenerator();
foreach (var temp in typeof(T).GetProperties().Where(temp => temp.CanRead && temp.CanWrite))
{
if (temp.GetAccessors(true)[0].IsStatic)
{
continue;
}
generator.Emit(OpCodes.Ldarg_1);// los
generator.Emit(OpCodes.Ldarg_0);// s
generator.Emit(OpCodes.Callvirt, temp.GetMethod);
generator.Emit(OpCodes.Callvirt, temp.SetMethod);
}
generator.Emit(OpCodes.Ret);
var clone = (Action<T, T>) dynamicMethod.CreateDelegate(typeof(Action<T, T>));
CachedIl[typeof(T)] = clone;
clone(source, los);
}
private static Dictionary<Type, Delegate> CachedIl { set; get; } = new Dictionary<Type, Delegate>();
只要改变这个。
Derived d = (Derived)b;
此外,您的姓名数据类型应该是字符串,而不是 int
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