Purpose of Activator CreateInstance with example

Question

Can someone explain Activator CreateInstance   purpose in detail

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The Activator CreateInstance method creates an instance of a specified type using the constructor that best matches the specified parameters   For example  let s say that you have the type name as a string  and you want to use the string to create an instance of that type  You could use Activator CreateInstance for this   string objTypeName    Foo   Foo foo    Foo Activator CreateInstance Type GetType objTypeName      Here s an MSDN article that explains it s application in more detail   http   msdn microsoft com en-us library wccyzw83 aspx

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Say you have a class called MyFancyObject like this one below   class MyFancyObject    public int A   get set       It lets you turn   String ClassName    MyFancyObject     Into   MyFancyObject obj    Using  obj    MyFancyObject Activator CreateInstance  MyAssembly   ClassName     and can then do stuff like   obj A   100    That s its purpose  It also has many other overloads such as providing a Type instead of the class name in a string  Why you would have a problem like that is a different story  Here s some people who needed it    Createinstance   - Am I doing this right  C  Using Activator CreateInstance Creating an object without knowing the class name at design time

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A good example could be next  for instance you have a set of Loggers and you allows user to specify type to be used in runtime via configuration file    Then   string rawLoggerType   configurationService GetLoggerType    Type loggerType   Type GetType rawLoggerType   ILogger logger   Activator CreateInstance loggerType GetType    as ILogger    OR another case is when you have a common entities factory  which creates entity  and is also responsible on initialization of an entity by data received from DB    pseudocode   public TEntity CreateEntityFromDataRow lt TEntity gt  DataRow row   where TEntity   IDbEntity  class      MethodInfo methodInfo   typeof T  GetMethod  BuildFromDataRow       TEntity instance   Activator CreateInstance typeof TEntity   as TEntity     return methodInfo Invoke instance  new object     row     as TEntity

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My good friend MSDN can explain it to you  with an example  Here is the code in case the link or content changes in the future   using System   class DynamicInstanceList       private static string instanceSpec    System EventArgs System Random              System Exception System Object System Version        public static void Main                 string   instances   instanceSpec Split               Array instlist   Array CreateInstance typeof object   instances Length           object item          for  int i   0  i  lt  instances Length  i                             create the object from the specification string             Console WriteLine  Creating instance of   0    instances i                item   Activator CreateInstance Type GetType instances i                 instlist SetValue item  i                     Console WriteLine   nObjects and their default values  n            foreach  object o in instlist                        Console WriteLine  Type       0  nValue      1  nHashCode   2  n                   o GetType   FullName  o ToString    o GetHashCode                           This program will display output similar to the following          Creating instance of  System EventArgs     Creating instance of  System Random     Creating instance of  System Exception     Creating instance of  System Object     Creating instance of  System Version         Objects and their default values          Type      System EventArgs     Value     System EventArgs     HashCode  46104728         Type      System Random     Value     System Random     HashCode  12289376         Type      System Exception     Value     System Exception  Exception of type  System Exception  was thrown      HashCode  55530882         Type      System Object     Value     System Object     HashCode  30015890         Type      System Version     Value     0 0     HashCode  1048575

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Building off of deepee1 and this  here s how to accept a class name in a string  and then use it to read and write to a database with LINQ  I use  dynamic  instead of deepee1 s casting because it allows me to assign properties  which allows us to dynamically select and operate on any table we want   Type tableType   Assembly GetExecutingAssembly   GetType  NameSpace TableName    ITable itable   dbcontext GetTable tableType      prints contents of the table foreach  object y in itable        string value    string y GetType   GetProperty  ColumnName   GetValue y  null       Console WriteLine value        inserting into a table dynamic tableClass   Activator CreateInstance tableType     Alternative to using tableType  using Tony s tips dynamic tableClass   Activator CreateInstance null   NameSpace TableName   Unwrap    tableClass Word   userParameter  itable InsertOnSubmit tableClass   dbcontext SubmitChanges       sql equivalent dbcontext ExecuteCommand  INSERT INTO  TableNme   ColumnName   VALUES   0     userParameter

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Why would you use it if you already knew the class and were going to cast it  Why not just do it the old fashioned way and make the class like you always make it  There s no advantage to this over the way it s done normally  Is there a way to take the text and operate on it thusly    label1 txt    Pizza   Magic label1 txt  p   new Magic lablel1 txt  arg1  arg2  arg3   p method1    p method2      If I already know its a Pizza there s no advantage to    p    Pizza somefancyjunk  Pizza    over Pizza p   new Pizza      but I see a huge advantage to the Magic method if it exists

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Coupled with reflection  I found Activator CreateInstance to be very helpful in mapping stored procedure result to a custom class as described in the following answer

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You can also do this -  var handle   Activator CreateInstance  AssemblyName                     Full name of the class including the namespace and class name    var obj   handle Unwrap

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Well i can give you an example why to use something like that  Think of a game where you want to store your level and enemies in an XML file  When you parse this file  you might have an element like this    lt Enemy X  10  Y  100  Type  MyGame OrcGuard   gt    what you can do now is  create dynamically the objects found in your level file   foreach XmlNode node in doc     var enemy   Activator CreateInstance null  node Attributes  Type       This is very useful  for building dynamic enviroments  Of course its also possible to use this for Plugin or addin scenarios and alot more

[c#] Purpose of Activator.CreateInstance with example?

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