I'm trying to create an instance of specified Type whatever user wants to have. For a quick illustration of my purpose please see the code below:
static void Main(string[] args)
{
object o = GetInstance(typeof(int));
Console.WriteLine("Created type: {0}", o.GetType().FullName);
}
public static object GetInstance(Type t)
{
Console.WriteLine("Creating instance of {0}", t.FullName);
return Activator.CreateInstance(t);
}
The problem is Activator.CreateInstance() returns object by default. There is also an overload of this method like T Activator.CreateInstance<T>() which is parameterless and returns the type you specify as T.
However, the problem is T should be hard-coded while calling this method and thus should be a fixed value. I am trying to create an instance of desired class and return it as its type.
Right now if you use this method you should write something like:
int i = GetInstance(typeof(int)) as int
I'm trying to reduce this to:
int i = GetInstance(typeof(int))
Is there a way that I can do casting inside the GetInstance and get rid of that as int repetition? By this way, my return type (and also the type I cast the object to) will be unknown at compile time.
Seemed impossible by design to me but I'd really appreciate if you figure it out.
EDIT: Where I'm stuck is e.g. while you're casting, you can do return (T) result if you are in a generic method, but you can't do Type t = ...; return (t) result this doesn't work. You cannot cast to a type which is passed to you as a parameter which is not known at compile time.
Follow a known pattern
This is not a new problem. It is a problem facing any API that allows type-specific return values. For example, a JSON parsing library like Newtonsoft (which is, to wit, the single most popular .NET package downloaded by .NET programmers in 2019) must be able to parse a string and return a type-specific object, which may or may not be known at compile time. It might make sense to follow their example.
Newtonsoft exposes three ways to specify the type when deserializing. You could do as you are currently doing:
//Cast required
var result = JsonConvert.DeserializeObject(text, typeof(MyType)) as MyType;
You can use a generic method:
//No cast required, but you have to hardcode a type as a type parameter
var result = JsonConvert.DeserializeObject<MyType>(text);
Or you can use an instance as a template, which is great for anonymous types, although you can use it with non-anonymous classes as well. This one works via generic type inference:
//No cast required and no need to specify type; the type is inferred from the argument
var result = JsonConvert.DeserializeAnonymousType(text, new MyType());
Here's how you'd do it:
So for you to make this work, your code might look like this:
public object GetInstance(Type type)
{
return Activator.CreateInstance(type);
}
int i = GetInstance(typeof(int)) as int;
public T GetInstance<T>()
{
return Activator.CreateInstance<T>();
}
int i = GetInstance<int>();
public T GetInstance<T>(T template)
{
return Activator.CreateInstance<T>();
}
int i = GetInstance(0);
If you do it this way, it's hard to imagine any programmer would have trouble using your library, as the approach should already be familiar to them.
Actually you could write GetInstance like this:
static T GetInstance<T>()
{
return Activator.CreateInstance<T>();
}
And use it:
int j = GetInstance<int>();
This might help you to create instance of desired type:
public class ConcreteFactory<T> : AbstractFactory<T>
{
public override T CreateInstance(string typeName,params object[] parameters)
{
var path = Assembly.GetExecutingAssembly().CodeBase;
var assembly = Assembly.LoadFrom(path);
var type = assembly.GetTypes().SingleOrDefault(t => t.Name == typeName);
return (T)Activator.CreateInstance(type, parameters);
}
}
Key here is generic type T can be used to cast the created instance, this can be used as a template to create instance of any type with parameterized constructor
Related
I am passing a string of the name of the entity type I want to query and getting the type based on the string. I want to get the DbSet back and return an IQueryable. The problem is where I am doing (DbSet<tableEntity>) and getting the following error:
tableEntity is a variable but used like a type
when trying to cast. Is there a way to resolve this?
public object GetList(string tableEntity)
{
Type tableEntity = Type.GetType("TestProject." + typeName + ", TestProject");
var dbObject = (DbSet<tableEntity>)typeof(DbContext).GetMethod("Set", Type.EmptyTypes)
.MakeGenericMethod(tableEntity)
.Invoke(databaseContext, null);
return dbObject.AsQueryable();
}
EDIT
Just to add I don't have access to the type that's we I am passing the name through a string.
So it turns out that the entity type is literally not known, or knowable, at compile time. It has to be a string.
The only place you're using the type at compile time is in the cast to (DbSet<tableEntity>). Well, you may not need that. All you need from that type is to call AsQueryable(), and AsQueryable() is an extension method for IEnumerable, with generic and non-generic versions. IF we call it through non-generic IEnumerable, that's non-generic AsQueryable(), returning non-generic IQueryable. But we're returning object anyway, so hey. For the result of this thing to be useful, something somewhere must be doing a fair amount of reflection on it anyway, so the declared type is likely to be of little consequence.
See if this works:
public object GetList(string typeName)
{
Type tableEntity = Type.GetType("TestProject." + typeName + ", TestProject");
var dbObject = (System.Collections.IEnumerable)
typeof(DbContext).GetMethod("Set", Type.EmptyTypes)
.MakeGenericMethod(tableEntity)
.Invoke(databaseContext, null);
return dbObject.AsQueryable();
}
If it turns out you need generic IQueryable<TEntityType>, we'll have to use reflection to get MethodInfo for AsQueryable<TEntityType> for the unknown (at compile time) entity type, and call MakeGenericMethod(tableEntity) on that.
First try:
In the language, type parameters to generics must be actual types, not instances of the Type class. That's because they're resolved at compile time.
But that's no problem; to pass a type parameter to a generic method, simply write a generic method with a type parameter.
You can't do this:
var stuff = GetList("MyTableEntityClass");
But this is just as good:
var stuff = GetList<MyTableEntityClass>();
...
public object GetList<TTableEntity>()
{
var dbObject = (DbSet<TTableEntity>)typeof(DbContext)
.GetMethod("Set", Type.EmptyTypes)
.MakeGenericMethod(typeof(TTableEntity))
.Invoke(databaseContext, null);
return dbObject.AsQueryable();
}
Reflection is different; that's why we pass typeof(TTableEntity) to MakeGenericMethod().
And once we're using an actual type that the compiler can check, we can do better with our return type, too:
public IQueryable<TTableEntity> GetList<TTableEntity>()
{
var dbObject = (DbSet<TTableEntity>)typeof(DbContext)
.GetMethod("Set", Type.EmptyTypes)
.MakeGenericMethod(typeof(TTableEntity))
.Invoke(databaseContext, null);
return dbObject.AsQueryable();
}
Since, as Ed mentioned, you don't use the table entity type at compile time, why not just use the non-generic databaseContext.Set (tableEntity).AsQueryable ()? But if you've set your heart on Set<>, try this:
public object GetList(string tableEntity)
{
Type tableEntity = Type.GetType("TestProject." + typeName + ", TestProject");
return GetType ()
.GetMethod ("GetListHelper")
.MakeGenericMethod (tableEntity)
.Invoke (this) ;
}
public object GetListHelper<T> () where T : class
{
var dbObject = databaseContext.Set<T> (null) ;
return dbObject.AsQueryable();
}
In C# can I cast a variable of type object to a variable of type T where T is defined in a Type variable?
Here is an example of a cast and a convert:
using System;
public T CastObject<T>(object input) {
return (T) input;
}
public T ConvertObject<T>(object input) {
return (T) Convert.ChangeType(input, typeof(T));
}
Edit:
Some people in the comments say that this answer doesn't answer the question. But the line (T) Convert.ChangeType(input, typeof(T)) provides the solution. The Convert.ChangeType method tries to convert any Object to the Type provided as the second argument.
For example:
Type intType = typeof(Int32);
object value1 = 1000.1;
// Variable value2 is now an int with a value of 1000, the compiler
// knows the exact type, it is safe to use and you will have autocomplete
int value2 = Convert.ChangeType(value1, intType);
// Variable value3 is now an int with a value of 1000, the compiler
// doesn't know the exact type so it will allow you to call any
// property or method on it, but will crash if it doesn't exist
dynamic value3 = Convert.ChangeType(value1, intType);
I've written the answer with generics, because I think it is a very likely sign of code smell when you want to cast a something to a something else without handling an actual type. With proper interfaces that shouldn't be necessary 99.9% of the times. There are perhaps a few edge cases when it comes to reflection that it might make sense, but I would recommend to avoid those cases.
Edit 2:
Few extra tips:
Try to keep your code as type-safe as possible. If the compiler doesn't know the type, then it can't check if your code is correct and things like autocomplete won't work. Simply said: if you can't predict the type(s) at compile time, then how would the compiler be able to?
If the classes that you are working with implement a common interface, you can cast the value to that interface. Otherwise consider creating your own interface and have the classes implement that interface.
If you are working with external libraries that you are dynamically importing, then also check for a common interface. Otherwise consider creating small wrapper classes that implement the interface.
If you want to make calls on the object, but don't care about the type, then store the value in an object or dynamic variable.
Generics can be a great way to create reusable code that applies to a lot of different types, without having to know the exact types involved.
If you are stuck then consider a different approach or code refactor. Does your code really have to be that dynamic? Does it have to account for any type there is?
Other answers do not mention "dynamic" type. So to add one more answer, you can use "dynamic" type to store your resulting object without having to cast converted object with a static type.
dynamic changedObj = Convert.ChangeType(obj, typeVar);
changedObj.Method();
Keep in mind that with the use of "dynamic" the compiler is bypassing static type checking which could introduce possible runtime errors if you are not careful.
Also, it is assumed that the obj is an instance of Type typeVar or is convertible to that type.
Here is my method to cast an object but not to a generic type variable, rather to a System.Type dynamically:
I create a lambda expression at run-time using System.Linq.Expressions, of type Func<object, object>, that unboxes its input, performs the desired type conversion then gives the result boxed. A new one is needed not only for all types that get casted to, but also for the types that get casted (because of the unboxing step). Creating these expressions is highly time consuming, because of the reflection, the compilation and the dynamic method building that is done under the hood. Luckily once created, the expressions can be invoked repeatedly and without high overhead, so I cache each one.
private static Func<object, object> MakeCastDelegate(Type from, Type to)
{
var p = Expression.Parameter(typeof(object)); //do not inline
return Expression.Lambda<Func<object, object>>(
Expression.Convert(Expression.ConvertChecked(Expression.Convert(p, from), to), typeof(object)),
p).Compile();
}
private static readonly Dictionary<Tuple<Type, Type>, Func<object, object>> CastCache
= new Dictionary<Tuple<Type, Type>, Func<object, object>>();
public static Func<object, object> GetCastDelegate(Type from, Type to)
{
lock (CastCache)
{
var key = new Tuple<Type, Type>(from, to);
Func<object, object> cast_delegate;
if (!CastCache.TryGetValue(key, out cast_delegate))
{
cast_delegate = MakeCastDelegate(from, to);
CastCache.Add(key, cast_delegate);
}
return cast_delegate;
}
}
public static object Cast(Type t, object o)
{
return GetCastDelegate(o.GetType(), t).Invoke(o);
}
Note that this isn't magic. Casting doesn't occur in code, as it does with the dynamic keyword, only the underlying data of the object gets converted. At compile-time we are still left to painstakingly figure out exactly what type our object might be, making this solution impractical. I wrote this as a hack to invoke conversion operators defined by arbitrary types, but maybe somebody out there can find a better use case.
Putting boxing and unboxing aside for simplicity, there's no specific runtime action involved in casting along the inheritance hierarchy. It's mostly a compile time thing. Essentially, a cast tells the compiler to treat the value of the variable as another type.
What you could do after the cast? You don't know the type, so you wouldn't be able to call any methods on it. There wouldn't be any special thing you could do. Specifically, it can be useful only if you know the possible types at compile time, cast it manually and handle each case separately with if statements:
if (type == typeof(int)) {
int x = (int)obj;
DoSomethingWithInt(x);
} else if (type == typeof(string)) {
string s = (string)obj;
DoSomethingWithString(s);
} // ...
After not finding anything to get around "Object must implement IConvertible" exception when using Zyphrax's answer (except for implementing the interface).. I tried something a little bit unconventional and worked for my situation.
Using the Newtonsoft.Json nuget package...
var castedObject = JsonConvert.DeserializeObject(JsonConvert.SerializeObject(myObject), myType);
How could you do that? You need a variable or field of type T where you can store the object after the cast, but how can you have such a variable or field if you know T only at runtime? So, no, it's not possible.
Type type = GetSomeType();
Object #object = GetSomeObject();
??? xyz = #object.CastTo(type); // How would you declare the variable?
xyz.??? // What methods, properties, or fields are valid here?
When it comes to casting to Enum type:
private static Enum GetEnum(Type type, int value)
{
if (type.IsEnum)
if (Enum.IsDefined(type, value))
{
return (Enum)Enum.ToObject(type, value);
}
return null;
}
And you will call it like that:
var enumValue = GetEnum(typeof(YourEnum), foo);
This was essential for me in case of getting Description attribute value of several enum types by int value:
public enum YourEnum
{
[Description("Desc1")]
Val1,
[Description("Desc2")]
Val2,
Val3,
}
public static string GetDescriptionFromEnum(Enum value, bool inherit)
{
Type type = value.GetType();
System.Reflection.MemberInfo[] memInfo = type.GetMember(value.ToString());
if (memInfo.Length > 0)
{
object[] attrs = memInfo[0].GetCustomAttributes(typeof(DescriptionAttribute), inherit);
if (attrs.Length > 0)
return ((DescriptionAttribute)attrs[0]).Description;
}
return value.ToString();
}
and then:
string description = GetDescriptionFromEnum(GetEnum(typeof(YourEnum), foo));
string description2 = GetDescriptionFromEnum(GetEnum(typeof(YourEnum2), foo2));
string description3 = GetDescriptionFromEnum(GetEnum(typeof(YourEnum3), foo3));
Alternatively (better approach), such casting could look like that:
private static T GetEnum<T>(int v) where T : struct, IConvertible
{
if (typeof(T).IsEnum)
if (Enum.IsDefined(typeof(T), v))
{
return (T)Enum.ToObject(typeof(T), v);
}
throw new ArgumentException(string.Format("{0} is not a valid value of {1}", v, typeof(T).Name));
}
I will never understand why you need up to 50 reputation to leave a comment but I just had to say that #Curt answer is exactly what I was looking and hopefully someone else.
In my example, I have an ActionFilterAttribute that I was using to update the values of a json patch document. I didn't what the T model was for the patch document to I had to serialize & deserialize it to a plain JsonPatchDocument, modify it, then because I had the type, serialize & deserialize it back to the type again.
Type originalType = //someType that gets passed in to my constructor.
var objectAsString = JsonConvert.SerializeObject(myObjectWithAGenericType);
var plainPatchDocument = JsonConvert.DeserializeObject<JsonPatchDocument>(objectAsString);
var plainPatchDocumentAsString= JsonConvert.SerializeObject(plainPatchDocument);
var modifiedObjectWithGenericType = JsonConvert.DeserializeObject(plainPatchDocumentAsString, originalType );
public bool TryCast<T>(ref T t, object o)
{
if (
o == null
|| !typeof(T).IsAssignableFrom(o.GetType())
)
return false;
t = (T)o;
return true;
}
If you need to cast objects at runtime without knowing destination type, you can use reflection to make a dynamic converter.
This is a simplified version (without caching generated method):
public static class Tool
{
public static object CastTo<T>(object value) where T : class
{
return value as T;
}
private static readonly MethodInfo CastToInfo = typeof (Tool).GetMethod("CastTo");
public static object DynamicCast(object source, Type targetType)
{
return CastToInfo.MakeGenericMethod(new[] { targetType }).Invoke(null, new[] { source });
}
}
then you can call it:
var r = Tool.DynamicCast(myinstance, typeof (MyClass));
even cleaner:
public static bool TryCast<T>(ref T t, object o)
{
if (!(o is T))
{
return false;
}
t = (T)o;
return true;
}
var type = data.ClientBaseObject.GetType();
var newClientObject = GetDataContextedObject(type, data.ClientBaseObject);
private object GetDataContextedObject(Type type, object jobObject)
{
switch (type.Name.ToUpper())
{
case "JOBNUMBER":
{
return GetObjectFromDataContext<JobNumber>(jobObject);
}
case "NA_HEADER":
{
return GetObjectFromDataContext<NA_Header>(jobObject);
}
}
return null;
}
private object GetObjectFromDataContext<T>(object jobObject) where T: class, IJobID
{
var newObject = jobObject as T;
return _dc.GetTable<T>().FirstOrDefault(j => j.JobID == newObject.JobID);
}
In the above code, I am wondering if there is a way I can make the GetObjectFromDataContext into GetObjectFromDataContext<type>, instead of having to get the type.Name for each class and creating a case for each one. Can this be done?
Let me know if the question is not clear.
You can write it this way:
private object GetDataContextedObject<T>(object jobObject)
{
return GetObjectFromDataContext<T>(jobObject);
}
Do all of the allowable types implement a common interface? If so, then yes; change GetObjectFromDataContext to accept the base type as a generic argument.
However, a generic argument must be determined at compile time. Otherwise how would the feature provide type safety? You may as well just be passing everything around as an object at that point.
EDIT: Per your update.
I you must be able to pass in a Type parameter at runtime, then no, you can't do what you want. Since this is all occurring at runtime you will have to selectively call the generic version. You cannot use the overload of GetTable that takes a Type argument for the same reason; you'll need a cast as it returns an ITable.
Do you really need to do this dynamically using a Type parameter?
I have a Type object.
I want to get the object isntance from this type. (just to use the ToString() method from this object).
see:
public class P
{
public string s;
}
class Program
{
static void Main(string[] args)
{
P p = new P();
p.s = "foobar";
Type t = p.GetType();
P p2 = ((t.ToObjet()) as P).s;
Console.WriteLine(p2.s);
}
}
Activator.CreateInstance is what you want.
Type givenType;
var obj = Activator.CreateInstance(givenType);
...
var obj = Activator.CreateInstance(givenType) as GivenType;
EDIT: Based on your edits, the extension method on Type you want (ToObject) is effectively the code above. It must create a new one because you can't be certain the source object still exists and even with the type, you could hit a scenario where that type has multiple instances.
You cannot get the instance back. The type is shared between all the instances, so what you want is impossible.
For example: if you know that something is an integer, you don't know which exactly value it has. (Integer is your type, value is a concrete instance.)
There is no way to do that. One reason is that GetType will return the same Type instance for all instances of the same type.
You can test this like so:
// this will print "True"
Console.WriteLine(object.ReferenceEquals("one".GetType(), "two".GetType()));
Calling GetType on those two different string instances returns the same Type instance, so it is clearly impossible to get one of them back based only on that Type instance.
In C# can I cast a variable of type object to a variable of type T where T is defined in a Type variable?
Here is an example of a cast and a convert:
using System;
public T CastObject<T>(object input) {
return (T) input;
}
public T ConvertObject<T>(object input) {
return (T) Convert.ChangeType(input, typeof(T));
}
Edit:
Some people in the comments say that this answer doesn't answer the question. But the line (T) Convert.ChangeType(input, typeof(T)) provides the solution. The Convert.ChangeType method tries to convert any Object to the Type provided as the second argument.
For example:
Type intType = typeof(Int32);
object value1 = 1000.1;
// Variable value2 is now an int with a value of 1000, the compiler
// knows the exact type, it is safe to use and you will have autocomplete
int value2 = Convert.ChangeType(value1, intType);
// Variable value3 is now an int with a value of 1000, the compiler
// doesn't know the exact type so it will allow you to call any
// property or method on it, but will crash if it doesn't exist
dynamic value3 = Convert.ChangeType(value1, intType);
I've written the answer with generics, because I think it is a very likely sign of code smell when you want to cast a something to a something else without handling an actual type. With proper interfaces that shouldn't be necessary 99.9% of the times. There are perhaps a few edge cases when it comes to reflection that it might make sense, but I would recommend to avoid those cases.
Edit 2:
Few extra tips:
Try to keep your code as type-safe as possible. If the compiler doesn't know the type, then it can't check if your code is correct and things like autocomplete won't work. Simply said: if you can't predict the type(s) at compile time, then how would the compiler be able to?
If the classes that you are working with implement a common interface, you can cast the value to that interface. Otherwise consider creating your own interface and have the classes implement that interface.
If you are working with external libraries that you are dynamically importing, then also check for a common interface. Otherwise consider creating small wrapper classes that implement the interface.
If you want to make calls on the object, but don't care about the type, then store the value in an object or dynamic variable.
Generics can be a great way to create reusable code that applies to a lot of different types, without having to know the exact types involved.
If you are stuck then consider a different approach or code refactor. Does your code really have to be that dynamic? Does it have to account for any type there is?
Other answers do not mention "dynamic" type. So to add one more answer, you can use "dynamic" type to store your resulting object without having to cast converted object with a static type.
dynamic changedObj = Convert.ChangeType(obj, typeVar);
changedObj.Method();
Keep in mind that with the use of "dynamic" the compiler is bypassing static type checking which could introduce possible runtime errors if you are not careful.
Also, it is assumed that the obj is an instance of Type typeVar or is convertible to that type.
Here is my method to cast an object but not to a generic type variable, rather to a System.Type dynamically:
I create a lambda expression at run-time using System.Linq.Expressions, of type Func<object, object>, that unboxes its input, performs the desired type conversion then gives the result boxed. A new one is needed not only for all types that get casted to, but also for the types that get casted (because of the unboxing step). Creating these expressions is highly time consuming, because of the reflection, the compilation and the dynamic method building that is done under the hood. Luckily once created, the expressions can be invoked repeatedly and without high overhead, so I cache each one.
private static Func<object, object> MakeCastDelegate(Type from, Type to)
{
var p = Expression.Parameter(typeof(object)); //do not inline
return Expression.Lambda<Func<object, object>>(
Expression.Convert(Expression.ConvertChecked(Expression.Convert(p, from), to), typeof(object)),
p).Compile();
}
private static readonly Dictionary<Tuple<Type, Type>, Func<object, object>> CastCache
= new Dictionary<Tuple<Type, Type>, Func<object, object>>();
public static Func<object, object> GetCastDelegate(Type from, Type to)
{
lock (CastCache)
{
var key = new Tuple<Type, Type>(from, to);
Func<object, object> cast_delegate;
if (!CastCache.TryGetValue(key, out cast_delegate))
{
cast_delegate = MakeCastDelegate(from, to);
CastCache.Add(key, cast_delegate);
}
return cast_delegate;
}
}
public static object Cast(Type t, object o)
{
return GetCastDelegate(o.GetType(), t).Invoke(o);
}
Note that this isn't magic. Casting doesn't occur in code, as it does with the dynamic keyword, only the underlying data of the object gets converted. At compile-time we are still left to painstakingly figure out exactly what type our object might be, making this solution impractical. I wrote this as a hack to invoke conversion operators defined by arbitrary types, but maybe somebody out there can find a better use case.
Putting boxing and unboxing aside for simplicity, there's no specific runtime action involved in casting along the inheritance hierarchy. It's mostly a compile time thing. Essentially, a cast tells the compiler to treat the value of the variable as another type.
What you could do after the cast? You don't know the type, so you wouldn't be able to call any methods on it. There wouldn't be any special thing you could do. Specifically, it can be useful only if you know the possible types at compile time, cast it manually and handle each case separately with if statements:
if (type == typeof(int)) {
int x = (int)obj;
DoSomethingWithInt(x);
} else if (type == typeof(string)) {
string s = (string)obj;
DoSomethingWithString(s);
} // ...
After not finding anything to get around "Object must implement IConvertible" exception when using Zyphrax's answer (except for implementing the interface).. I tried something a little bit unconventional and worked for my situation.
Using the Newtonsoft.Json nuget package...
var castedObject = JsonConvert.DeserializeObject(JsonConvert.SerializeObject(myObject), myType);
How could you do that? You need a variable or field of type T where you can store the object after the cast, but how can you have such a variable or field if you know T only at runtime? So, no, it's not possible.
Type type = GetSomeType();
Object #object = GetSomeObject();
??? xyz = #object.CastTo(type); // How would you declare the variable?
xyz.??? // What methods, properties, or fields are valid here?
When it comes to casting to Enum type:
private static Enum GetEnum(Type type, int value)
{
if (type.IsEnum)
if (Enum.IsDefined(type, value))
{
return (Enum)Enum.ToObject(type, value);
}
return null;
}
And you will call it like that:
var enumValue = GetEnum(typeof(YourEnum), foo);
This was essential for me in case of getting Description attribute value of several enum types by int value:
public enum YourEnum
{
[Description("Desc1")]
Val1,
[Description("Desc2")]
Val2,
Val3,
}
public static string GetDescriptionFromEnum(Enum value, bool inherit)
{
Type type = value.GetType();
System.Reflection.MemberInfo[] memInfo = type.GetMember(value.ToString());
if (memInfo.Length > 0)
{
object[] attrs = memInfo[0].GetCustomAttributes(typeof(DescriptionAttribute), inherit);
if (attrs.Length > 0)
return ((DescriptionAttribute)attrs[0]).Description;
}
return value.ToString();
}
and then:
string description = GetDescriptionFromEnum(GetEnum(typeof(YourEnum), foo));
string description2 = GetDescriptionFromEnum(GetEnum(typeof(YourEnum2), foo2));
string description3 = GetDescriptionFromEnum(GetEnum(typeof(YourEnum3), foo3));
Alternatively (better approach), such casting could look like that:
private static T GetEnum<T>(int v) where T : struct, IConvertible
{
if (typeof(T).IsEnum)
if (Enum.IsDefined(typeof(T), v))
{
return (T)Enum.ToObject(typeof(T), v);
}
throw new ArgumentException(string.Format("{0} is not a valid value of {1}", v, typeof(T).Name));
}
I will never understand why you need up to 50 reputation to leave a comment but I just had to say that #Curt answer is exactly what I was looking and hopefully someone else.
In my example, I have an ActionFilterAttribute that I was using to update the values of a json patch document. I didn't what the T model was for the patch document to I had to serialize & deserialize it to a plain JsonPatchDocument, modify it, then because I had the type, serialize & deserialize it back to the type again.
Type originalType = //someType that gets passed in to my constructor.
var objectAsString = JsonConvert.SerializeObject(myObjectWithAGenericType);
var plainPatchDocument = JsonConvert.DeserializeObject<JsonPatchDocument>(objectAsString);
var plainPatchDocumentAsString= JsonConvert.SerializeObject(plainPatchDocument);
var modifiedObjectWithGenericType = JsonConvert.DeserializeObject(plainPatchDocumentAsString, originalType );
public bool TryCast<T>(ref T t, object o)
{
if (
o == null
|| !typeof(T).IsAssignableFrom(o.GetType())
)
return false;
t = (T)o;
return true;
}
If you need to cast objects at runtime without knowing destination type, you can use reflection to make a dynamic converter.
This is a simplified version (without caching generated method):
public static class Tool
{
public static object CastTo<T>(object value) where T : class
{
return value as T;
}
private static readonly MethodInfo CastToInfo = typeof (Tool).GetMethod("CastTo");
public static object DynamicCast(object source, Type targetType)
{
return CastToInfo.MakeGenericMethod(new[] { targetType }).Invoke(null, new[] { source });
}
}
then you can call it:
var r = Tool.DynamicCast(myinstance, typeof (MyClass));
even cleaner:
public static bool TryCast<T>(ref T t, object o)
{
if (!(o is T))
{
return false;
}
t = (T)o;
return true;
}