说来话长）：我有一些类型看起来像这样：
public class Model {
private readonly SomeType _member;
private readonly AnotherType _member2;
public Model(SomeType member, AnotherType member2) {
_member = member;
_member2 = member2;
}
public SomeType Member { get { return _member; } }
public AnotherType Member2 { get { return _member2; } }
}
我正在尝试创建一些表达式来创建类的实例，从其他一些对象（通常是匿名对象）读取属性，并将值写入创建的实例的私有字段 - 基于显示的命名约定：Prop 具有字段名称： _prop。
我的意思是我想将以下对象写入以下对象的新实例Model：
var anon1 = new { Member = "something" };
// expected: new Model with _member = "something"
var anon2 = new { Member2 = "something" };
// expected: new Model with _member2 = "something"
var anon3 = new { Member = "something", Member2 = "something else" };
// expected: new Model with _member = "something" and _member2 = "something else"
我在下面创建了代码，它创建了新实例，但对字段不做任何事情。你能帮我找出我做错的地方吗？
public class InstanceCreator {
static public readonly Func<FieldInfo, PropertyInfo, bool> NamingConvention;
static InstanceCreator() {
NamingConvention = (f, p) => {
var startsWithUnderscope = f.Name.StartsWith("_");
var hasSameName = p.Name.Equals(f.Name.Remove(0, 1), StringComparison.OrdinalIgnoreCase);
var hasSameType = f.FieldType == p.PropertyType;
return startsWithUnderscope && hasSameName && hasSameType &&
f.IsInitOnly && !p.CanWrite;
};
}
private readonly Type _type;
private readonly Func<dynamic, dynamic> _creator;
public InstanceCreator(Type type) {
_type = type;
var ctor = GetCtor(type);
var propertyToFieldWriters = MakeWriters(type);
_creator = MakeCreator(type, ctor, propertyToFieldWriters);
}
private Expression GetCtor(Type type) {
if (type == typeof(string)) // ctor for string
return Expression.Lambda<Func<dynamic>>(
Expression.Constant(string.Empty));
if (type.IsValueType || // type has a parameterless ctor
type.GetConstructor(Type.EmptyTypes) != null)
return Expression.Lambda<Func<dynamic>>(Expression.New(type));
var info = typeof(FormatterServices).GetMethod("GetUninitializedObject");
var call = Expression.Call(info, Expression.Constant(type));
return call;
//return Expression.Lambda<Func<dynamic>>(call);
}
private IEnumerable<PropertyToFieldMapper> MakeWriters(Type type) {
var properties = type.GetProperties(BindingFlags.Instance | BindingFlags.Public);
var fields = type.GetFields(BindingFlags.Instance | BindingFlags.NonPublic);
var list = (from field in fields
let property = properties.FirstOrDefault(prop => NamingConvention(field, prop))
where property != null
select new PropertyToFieldMapper(field, property)).ToList();
foreach (var item in list) {
var sourceParameter = Expression.Parameter(type, "sourceParameter");
var propertyGetter = Expression.Property(sourceParameter, item.Property.Name);
var targetParameter = Expression.Parameter(type, "targetParameter");
var setterInfo = item.Field.GetType().GetMethod("SetValue", new[] { typeof(object), typeof(object) });
var setterCall = Expression.Call(Expression.Constant(item.Field), setterInfo,
new Expression[] {
Expression.Convert(targetParameter,typeof(object)),
Expression.Convert(propertyGetter,typeof(object))
});
var call = Expression.Lambda(setterCall, new[] { targetParameter, sourceParameter });
item.Call = call;
}
return list;
}
private Func<dynamic, dynamic> MakeCreator(
Type type, Expression ctor,
IEnumerable<PropertyToFieldMapper> writers) {
var list = new List<Expression>();
// creating new target
var targetVariable = Expression.Variable(type, "targetVariable");
list.Add(Expression.Assign(targetVariable, Expression.Convert(ctor, type)));
// find all properties in incoming data
var sourceParameter = Expression.Parameter(typeof(object), "sourceParameter");
var sourceTypeVariable = Expression.Variable(typeof(Type));
var sourceTypeGetter = Expression.Call(sourceParameter, "GetType", Type.EmptyTypes);
list.Add(Expression.Assign(sourceTypeVariable, sourceTypeGetter));
var sourcePropertiesVariable = Expression.Variable(typeof(PropertyInfo[]));
var sourcePropertiesGetter = Expression.Call(sourceTypeVariable, "GetProperties", Type.EmptyTypes);
list.Add(Expression.Assign(sourcePropertiesVariable, sourcePropertiesGetter));
// itrate over writers and add their Call to block
foreach (var writer in writers) {
var param = Expression.Parameter(typeof(PropertyInfo));
var prop = Expression.Property(param, "Name");
var eq = Expression.Equal(Expression.Constant(writer.Property.Name), prop);
var any = CallAny.Call(sourcePropertiesVariable, Expression.Lambda(eq, param));
var predicate = Expression.IfThen(any,
Expression.Lambda(writer.Call, new[] { targetVariable, sourceParameter }));
list.Add(predicate);
}
list.Add(targetVariable);
var block = Expression.Block(new[] { targetVariable, sourceTypeVariable, sourcePropertiesVariable }, list);
var lambda = Expression.Lambda<Func<dynamic, dynamic>>(
block, new[] { sourceParameter }
);
return lambda.Compile();
}
public dynamic Create(dynamic data) {
return _creator.Invoke(data);
}
private class PropertyToFieldMapper {
private readonly FieldInfo _field;
private readonly PropertyInfo _property;
public PropertyToFieldMapper(FieldInfo field, PropertyInfo property) {
_field = field;
_property = property;
}
public FieldInfo Field {
get { return _field; }
}
public PropertyInfo Property {
get { return _property; }
}
public Expression Call { get; set; }
}
}
另外，我有这个CallAny类，从这里创建的。
public class CallAny {
public static Expression Call(Expression collection, Expression predicate) {
Type cType = GetIEnumerableImpl(collection.Type);
collection = Expression.Convert(collection, cType);
Type elemType = cType.GetGenericArguments()[0];
Type predType = typeof(Func<,>).MakeGenericType(elemType, typeof(bool));
// Enumerable.Any<T>(IEnumerable<T>, Func<T,bool>)
var anyMethod = (MethodInfo)
GetGenericMethod(typeof(Enumerable), "Any", new[] { elemType },
new[] { cType, predType }, BindingFlags.Static);
return Expression.Call(anyMethod, collection, predicate);
}
static MethodBase GetGenericMethod(Type type, string name, Type[] typeArgs, Type[] argTypes, BindingFlags flags) {
int typeArity = typeArgs.Length;
var methods = type.GetMethods()
.Where(m => m.Name == name)
.Where(m => m.GetGenericArguments().Length == typeArity)
.Select(m => m.MakeGenericMethod(typeArgs));
return Type.DefaultBinder.SelectMethod(flags, methods.ToArray(), argTypes, null);
}
static Type GetIEnumerableImpl(Type type) {
// Get IEnumerable implementation. Either type is IEnumerable<T> for some T,
// or it implements IEnumerable<T> for some T. We need to find the interface.
if (IsIEnumerable(type))
return type;
Type[] t = type.FindInterfaces((m, o) => IsIEnumerable(m), null);
Debug.Assert(t.Length == 1);
return t[0];
}
static bool IsIEnumerable(Type type) {
return type.IsGenericType
&& type.GetGenericTypeDefinition() == typeof(IEnumerable<>);
}
}
这是用法：
var inst = new InstanceCreator(typeof (Model)).Create(new {MyData});