Reference types are raw references to an instance of a component. Unlike interface types you cannot use them to access component methods or handle component events unless you first cast the reference type to a valid interface type. See Interface Types. The actual reference is the opaque values returned when you create an instance of a component using the _createInstance() function. _createInstance() function. 

Reference types in UJML 

In UJML, a reference is a data type with the value stored as a component instance in memory. You can assign a reference variable to another variable. See Variables. You can pass a reference value as a function argument and return one from a function. You can tell a reference to paint itself using the display-instance element. See display-instance. You can cast a reference to an interface type if the reference is null or if the component instance implements that interface. See Interface Types. But you cannot convert a reference type to a different data type or use it in an expression, other than casting to an interface type. See Expressions. State variables may not be of the reference type.

The _castInterface() function converts a reference value to a specific interface type. See _castInterface() function.

You can compare two reference type variables to see if they refer to the same component instance using the _isSameInstance() function. See _isSameInstance() function.

You can determine if an reference type instance refers to a component that implements a specific interface using the _instanceOf() function. See _instanceOf() function.

References may be a special value called 'null'. When a reference is null, it does not refer to any extension instance. It is, essentially, empty. You can test to see if a reference is null by using the _is_null() function. See _is_null() function. You can also assign the literal value 'null' to a reference variable to give the variable the value null.

Because references are an opaque type, there is no such thing as a reference literal except for the value 'null'. See Literals and Constants.

The following example declares a reference variable. It is part of the things.ujml sample.

<var name="ref" type="reference"/>

The following assigns a value returned from a component method to the reference variable declared above. It is part of the things.ujml sample.

ref = mThingEnumerator.getNextItem();

The following example shows how to cast the reference variable declared above to an interface type. It is part of the things.ujml sample.

thing = _castInterface(ref, "IThing");

Data Types, Literals and Constants, Variables, Components, Interfaces, Scripting, Expressions, Using Functions, _createInstance(), _castInterface(), _instanceOf(), _is_null()