NAME¶

StateVar - state variable subject base class

SYNOPSIS¶

#include <Unidraw/statevar.h>

DESCRIPTION¶

StateVar is the base class for state variable subjects. State variables provide a standard way to represent and access state that can be modified by the user or through dataflow. State variable subjects store the state, while state variable views provide a graphical interface for examining and potentially modifying the state in their subject. The StateVar class defines the protocol for state variable subjects. It is an abstract class and thus cannot be instantiated.

PUBLIC OPERATIONS¶

Connector* GetBinding()

Return the connector to which the state variable is bound to support dataflow. Data flows through connected connectors with bound state variables: the library automatically assigns one bound state variable's state to another's. The direction of this assignment depends on the participating connectors. See Connector(3U) for details on how to bind state variables to connectors and how to specify the direction of flow.

virtual void Attach(StateVarView*)

virtual void Detach(StateVarView*)

Attach associates the subject with a view, represented by an instance of a StateVarView subclass. Detach dissociates a previously attached view. These operations do not ensure that the argument is an appropriate view of the subject.

virtual void Notify()

Notify iterates through the views, calling each one's Update operation to notify the view that the subject has potentially changed. Notify is usually called by the subject's state-modifying operations.

virtual StateVar& operator = (StateVar&)

The assignment operation should be redefined to carry out subclass-specific assignment semantics. Typically this operator calls the parent classes' assignment operator and then performs additional assignments of its own. This operator is used during dataflow to transfer state variable values.

virtual StateVar* Copy()

Return a copy of the state variable. Subclasses should redefine this operation to return an instance of their type.

virtual void Read(istream&)

virtual void Write(ostream&)

Read and write the state variable's contents to a stream to support catalog operations. Read and write typically call first the corresponding operations defined by their parent class, and then they read or write their class-specific state. Note that you must ensure that the objects are read in the same order they are written.

virtual ClassId GetClassId()

virtual boolean IsA(ClassId)

GetClassId returns the unique class identifier for the StateVar subclass, while IsA returns whether the instance is of a class or subclass corresponding to the given identifier. IsA typically checks the given identifier against the instance's own (as defined by its GetClassId operation) and, failing that, calls its parent classes' IsA operation. All subclasses must redefine GetClassId and IsA to ensure that their identifiers are unique and that instances are written and read properly.

PROTECTED OPERATIONS¶

StateVar()

The constructor is protected to prevent instantiation.

SEE ALSO¶

Catalog(3U), Connector(3U), Creator(3U), StateVarView(3U), classes(3U), istream(3C++), ostream(3C++)