When and where to use GetType or typeof

Question

Why this works  if  mycontrol GetType      typeof TextBox         and this do not   Type tp   typeof mycontrol     But this works  Type tp   mycontrol GetType      I myself use is operator for checking type but my understanding fails when I use typeof   and GetType    Where and when to use GetType   or typeof

User · Answer

typeOf is a C  keyword that is used when you have the name of the class  It is calculated at compile time and thus cannot be used on an instance  which is created at runtime  GetType is a method of the object class that can be used on an instance

User · Answer

You may find it easier to use the is keyword   if  mycontrol is TextBox

User · Answer

typeof is applied to a name of a type or generic type parameter known at compile time  given as identifier  not as string   GetType is called on an object at runtime  In both cases the result is an object of the type System Type containing meta-information on a type   Example where compile-time and run-time types are equal  string s    hello    Type t1   typeof string   Type t2   s GetType         t1    t2                       gt  true   Example where compile-time and run-time types are different  object obj    hello    Type t1   typeof object         gt  object Type t2   obj GetType           gt  string       t1    t2                       gt  false   i e   the compile time type  static type  of the variable obj is not the same as the runtime type of the object referenced by obj     Testing types  If  however  you only want to know whether mycontrol is a TextBox then you can simply test  if  mycontrol is TextBox    Note that this is not completely equivalent to  if  mycontrol GetType      typeof TextBox         because mycontrol could have a type that is derived from TextBox  In that case the first comparison yields true and the second false  The first and easier variant is OK in most cases  since a control derived from TextBox inherits everything that TextBox has  probably adds more to it and is therefore assignment compatible to TextBox   public class MySpecializedTextBox   TextBox      MySpecializedTextBox specialized   new MySpecializedTextBox    if  specialized is TextBox           gt  true  if  specialized GetType      typeof TextBox             gt  false     Casting  If you have the following test followed by a cast and T is nullable      if  obj is T        T x    T obj     The casting tests  whether obj is T again                  you can change it to      T x   obj as T  if  x    null                Testing whether a value is of a given type and casting  which involves this same test again  can both be time consuming for long inheritance chains  Using the as operator followed by a test for null is more performing   Starting with C  7 0 you can simplify the code by using pattern matching   if  obj is T t           t is a variable of type T having a non-null value              Btw   this works for value types as well  Very handy for testing and unboxing  Note that you cannot test for nullable value types   if  o is int  ni      gt  does NOT compile    This is because either the value is null or it is an int  This works for int  o as well as for object o   new Nullable lt int gt  x     if  o is int i      gt  OK    I like it  because it eliminates the need to access the Nullable lt T gt  Value property

User · Answer

typeof is an operator to obtain a type known at compile-time  or at least a generic type parameter   The operand of typeof is always the name of a type or type parameter - never an expression with a value  e g  a variable   See the C  language specification for more details   GetType   is a method you call on individual objects  to get the execution-time type of the object   Note that unless you only want exactly instances of TextBox  rather than instances of subclasses  you d usually use   if  myControl is TextBox           Whatever     Or  TextBox tb   myControl as TextBox  if  tb    null           Use tb

[c#] When and where to use GetType() or typeof()?

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