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.NET Forum / Languages / C# / April 2008How to convert to an object of a certain type?
Hello, Imagine, that I've got a string variable containing a value of each possible value type (string, int32, double, ...). Now I want to convert the string to an object of the right type, where the correct type is given by a Type variable. So given is: string strValue; Type typeValue; And I want to call something like object value = Convert.ToType(strValue, typeValue); Is there a simple way to do that? Thank you, Norbert See below; Marc string src = "12345"; Type dest = typeof(int); // simple int value1 = (int)Convert.ChangeType(src, dest); // more versatile but more complex // (and you might need to look at src->ConvertTo) int value2 = (int)TypeDescriptor.GetConverter(dest).ConvertFrom(src); Hi Marc, > string src = "12345"; > Type dest = typeof(int); [quoted text clipped - 5 lines] > // (and you might need to look at src->ConvertTo) > int value2 = (int)TypeDescriptor.GetConverter(dest).ConvertFrom(src); That's good, thank you. Do you have an idea how to convert an array of string into an array of a certain type given by a Type variable. ChangeType only works for non array variables. Thank you, Norbert If you know the destination type at compile-time (perhaps via generics), the following works: string[] data = {"12345", "3154", "15012"}; // C# 2 (VS2005) int[] values1 = Array.ConvertAll<string, int>(data, delegate(string value) { // of your chosen method from last post... return int.Parse(value); }); // C# 3 (VS2008) int[] values = Array.ConvertAll(data, value => int.Parse(value)); Again - you would be able to use this with generics (T[], etc). If you don't know the type (and generics aren't available), you could either use an object[], or ues Array.CreateInstance to create an array (of cited type), then loop over it setting values. My first choice would be: refactor the code so that you can use generics. Hard to say "how" without more detail... Marc Hi Marc, > Again - you would be able to use this with generics (T[], etc). If you > don't know the type (and generics aren't available), you could either [quoted text clipped - 3 lines] > My first choice would be: refactor the code so that you can use > generics. Hard to say "how" without more detail... I would like use generics, but how??? I've got a Type variable, e.g. Type type = typeof(System.Int32); How can I instantiate a generic list using that type variable? List<type> list = new List<type>(); does not work. The compiler needs something like that: List<Int32> list = new List<Int32>(); That's static. I need a dynamic way. Any idea? Kind regards, Norbert You can use reflection to invoke the generic method dynamically: using System; using System.ComponentModel; using System.Reflection; static class Program { static void Main() { string[] values = {"12345", "123", "5142"}; foreach (int value in CreateData(typeof(int), values)) { Console.WriteLine(value); } } // get the method-template (i.e. this points to CreateData<T>, but without the "T" yet) private static readonly MethodInfo genericMethod = typeof(Program).GetMethod("CreateData", BindingFlags.NonPublic | BindingFlags.Static, null, new Type[] { typeof(string[]) }, null); // actually returns an array of the correct type, but arrays are covariant static Array CreateData(Type destinationType, string[] values) { // invoke the generic method (after supplying a specific "T") object[] args = { values }; return (Array)genericMethod.MakeGenericMethod(destinationType).Invoke(null, args); } static T[] CreateData<T>(string[] values) { TypeConverter converter = TypeDescriptor.GetConverter(typeof(T)); return Array.ConvertAll<string, T>(values, delegate(string val) { return (T)converter.ConvertFrom(val); }); } } > If you know the destination type at compile-time (perhaps via > generics), the following works: [quoted text clipped - 14 lines] > use an object[], or ues Array.CreateInstance to create an array (of > cited type), then loop over it setting values. You could do this, however I would expect it to be very slow because it has to re-test the destination type and re-plan the conversion for each element. Array dest = Array.CreateInstance(t, src.Length); Array.ConvertAll<string, object>(delegate (string value) { Convert.ChangeType(value, t); }).CopyTo(dest, src.Length); > My first choice would be: refactor the code so that you can use > generics. Hard to say "how" without more detail... > > Marc Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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