请考虑以下代码
var currentType = Type.GetType("Some.Type, Some");
dynamic myDynamic = new System.Dynamic.ExpandoObject();
myDynamic.A = "A";
var objectInCorrectType = ???
我该如何将动态类型转换为当前类型?
请考虑以下代码
var currentType = Type.GetType("Some.Type, Some");
dynamic myDynamic = new System.Dynamic.ExpandoObject();
myDynamic.A = "A";
var objectInCorrectType = ???
我该如何将动态类型转换为当前类型?
正如 @Lasse 评论所述,您不能将动态对象强制转换为特定类型。
但是,由于您的问题涉及“反射”,因此我怀疑您正在寻找一种简单映射属性值的方法(例如在 Lasse 的评论中提到的“创建新 X 并复制值等”):
...
myDynamic.A = "A";
// get settable public properties of the type
var props = currentType.GetProperties(BindingFlags.Public | BindingFlags.Instance)
.Where(x => x.GetSetMethod() != null);
// create an instance of the type
var obj = Activator.CreateInstance(currentType);
// set property values using reflection
var values = (IDictionary<string,object>)myDynamic;
foreach(var prop in props)
prop.SetValue(obj, values[prop.Name]);
dynamic
是 鸭子类型 的变量(即将类型检查延迟到运行时)。它仍然持有一个类型化对象,但在编译时不进行检查。
因此,由于 ExpandoObject
是一种类型,无论您将其分配给类型化或动态引用,您都不能将 ExpandoObject
强制转换或转换为类型,只是因为它与目标类型共享相同的成员。
顺便说一下,由于 ExpandoObject
实现了 IDictionary<string,object>
,您可以通过扩展方法实现从 ExpandoObject
实例到目标类型的即时映射,其中成员作为匹配项:
public static class ExpandObjectExtensions
{
public static TObject ToObject<TObject>(this IDictionary<string, object> someSource, BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.Public)
where TObject : class, new ()
{
Contract.Requires(someSource != null);
TObject targetObject = new TObject();
Type targetObjectType = typeof (TObject);
// Go through all bound target object type properties...
foreach (PropertyInfo property in
targetObjectType.GetProperties(bindingFlags))
{
// ...and check that both the target type property name and its type matches
// its counterpart in the ExpandoObject
if (someSource.ContainsKey(property.Name)
&& property.PropertyType == someSource[property.Name].GetType())
{
property.SetValue(targetObject, someSource[property.Name]);
}
}
return targetObject;
}
}
现在,尝试以下代码,它将按照您的预期工作:
public class A
{
public int Val1 { get; set; }
}
// Somewhere in your app...
dynamic expando = new ExpandoObject();
expando.Val1 = 11;
// Now you got a new instance of A where its Val1 has been set to 11!
A instanceOfA = ((ExpandoObject)expando).ToObject<A>();
实际上,我基于其他问答的答案来回答这个问题,那里我可以解决类似将对象映射到字典和反之的问题:将对象映射到字典和反之.
我遇到了这个问题,因为我需要上这样的课程:
public class PropertyChange
{
[JsonProperty("name")]
public string PropertyName { get; set; }
[JsonProperty("value")]
public string PropertyValue { get; set; }
[JsonProperty("arrayValue")]
public dynamic[] PropertyArray { get; set; }
}
将对象的 PropertyArray
属性(使用Newtonsoft库从JSON反序列化)转换为特定类型的对象数组,其中类型可以由 PropertyName
推导出来。
我写了这个名为 DynamicCast <>
的助手类,并决定在这里发布,以防其他人与我处于相同的情况。
此助手类允许您编写以下代码:
public class MyType
{
public string A { get; set; }
}
var myCast = new DynamicCast<MyType>();
dynamic dyn = ExpandoObject();
dyn.A = "Hello";
var myType = myCast.Cast(dyn);
Console.WriteLine(myType.A); // prints 'Hello'
这是我如何使用它来解决我的反序列化问题的示例:
public class JsonTest
{
[JsonProperty("theArray")]
public dynamic[] TheArray { get; set; }
}
var json = "{'theArray':[{'a':'First'},{'a':'Second'}]}";
var jsonTest = JsonConvert.DeserializeObject<JsonTest>(json);
var myCast = new DynamicCast<MyType>();
var myTypes = myCast.Cast(jsonTest.TheArray).ToArray();
Console.WriteLine(myTypes[0].A); // prints 'First'
根据其他答案,他编写了DynamicCast
类。代码如下:
public class DynamicCast<T> where T: class, new()
{
private Property[] _proprties;
public DynamicCast()
{
_proprties = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance)
.Where(x => x.GetSetMethod() != null)
.Where(x => x.GetGetMethod() != null)
.Select(p =>
{
var property = new Property
{
PropertyInfo = p,
Name = p.Name
};
foreach (var attribute in p.GetCustomAttributes(false))
{
if (attribute.GetType() == typeof(JsonPropertyAttribute))
{
var jsonProperty = (JsonPropertyAttribute)attribute;
property.Name = jsonProperty.PropertyName;
break;
}
if (attribute.GetType() == typeof(JsonIgnoreAttribute))
{
return null;
}
}
return property;
})
.Where(p => p != null)
.ToArray();
}
public T Cast(IDictionary<string, object> d)
{
var t = new T();
Fill(d, t);
return t;
}
public T Cast(JObject d)
{
var t = new T();
Fill(d, t);
return t;
}
public dynamic Cast(T t)
{
dynamic d = new ExpandoObject();
Fill(t, d);
return d;
}
public IEnumerable<T> Cast(IEnumerable<JObject> da)
{
return da.Select(e => Cast(e));
}
public IEnumerable<T> Cast(IEnumerable<object> da)
{
return da.Select(e =>
{
if (e is JObject) return Cast((JObject)e);
if (e is IDictionary<string, object>) return Cast((IDictionary<string, object>)e);
return null;
});
}
public void Fill(IDictionary<string, object> values, T target)
{
foreach (var property in _proprties)
if (values.TryGetValue(property.Name, out var value))
property.PropertyInfo.SetValue(target, value, null);
}
public void Fill(JObject values, T target)
{
foreach (var property in _proprties)
{
if (values.TryGetValue(property.Name, out var value))
{
if (value is JValue jvalue)
{
var propertyValue = Convert.ChangeType(jvalue.Value, property.PropertyInfo.PropertyType);
property.PropertyInfo.SetValue(target, propertyValue, null);
}
}
}
}
public void Fill(T obj, IDictionary<string, object> target)
{
foreach (var property in _proprties)
target[property.Name] = property.PropertyInfo.GetValue(obj, null);
}
private class Property
{
public PropertyInfo PropertyInfo;
public string Name;
}
}
你可以在 .Net Fiddle 上自己尝试一下,链接在这里:https://dotnetfiddle.net/J1JXgU