Check if instance is of a type

Using this to check if c is an instance of TForm.

c.GetType().Name.CompareTo("TForm") == 0 

Is there a more type safe way to do it besides using a string as a param to CompareTo()?

9 Answers

The different answers here have two different meanings.

If you want to check whether an instance is of an exact type then

if (c.GetType() == typeof(TForm)) 

is the way to go.

If you want to know whether c is an instance of TForm or a subclass then use is/as:

if (c is TForm) 

or

TForm form = c as TForm; if (form != null) 

It's worth being clear in your mind about which of these behaviour you actually want.

if(c is TFrom) { // Do Stuff } 

or if you plan on using c as a TForm, use the following example:

var tForm = c as TForm; if(tForm != null) { // c is of type TForm } 

The second example only needs to check to see if c is of type TForm once. Whereis if you check if see if c is of type TForm then cast it, the CLR undergoes an extra check. Here is a reference.

Edit: Stolen from Jon Skeet

If you want to make sure c is of TForm and not any class inheriting from TForm, then use

if(c.GetType() == typeof(TForm)) { // Do stuff cause c is of type TForm and nothing else } 

Yes, the "is" keyword:

if (c is TForm) { ... } 

See details on MSDN: (VS.80).aspx

Checks if an object is compatible with a given type. For example, it can be determined if an object is compatible with the string type like this:

Also, somewhat in the same vein

Type.IsAssignableFrom(Type c) 

"True if c and the current Type represent the same type, or if the current Type is in the inheritance hierarchy of c, or if the current Type is an interface that c implements, or if c is a generic type parameter and the current Type represents one of the constraints of c."

From here:

A little more compact than the other answers if you want to use c as a TForm:

if(c is TForm form){ form.DoStuff(); } 

Try the following

if (c is TForm) { ... } 

As others have mentioned, the "is" keyword. However, if you're going to later cast it to that type, eg.

TForm t = (TForm)c; 

Then you should use the "as" keyword.

e.g. TForm t = c as TForm.

Then you can check

if(t != null) { // put TForm specific stuff here } 

Don't combine as with is because it's a duplicate check.

Or

c.getType() == typeOf(TForm) 

bool isValid = c.GetType() == typeof(TForm) ? true : false; 

or simpler

bool isValid = c.GetType() == typeof(TForm);