Design Patterns & Refactoring Chain of Responsibility Oliver - - PowerPoint PPT Presentation

▶

Mar 10, 2023 161 likes •259 views

Design Patterns & Refactoring Chain of Responsibility Oliver Haase HTWG Konstanz Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 1 / 9 Description Classification : Object-based behavioral pattern Purpose : Build a chain of

SLIDE 1

Design Patterns & Refactoring

Chain of Responsibility Oliver Haase

HTWG Konstanz

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 1 / 9

SLIDE 2

Description

Classification: Object-based behavioral pattern Purpose: Build a chain of possible receivers of a request. Delegate request along the chain until one receiver handles it.

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 2 / 9

SLIDE 3

Motivation

Imagine a context-sensitive help system for a GUI Each graphical component may (or may not) have associated with it a help text. On, e.g., right mouse click, the most specific help text of the clicked-on component is displayed to the user.

aPrintButton aMouseListener handleHelpReq aPrintDialog handleHelpReq aTopLevelContainer handleHelpReq Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 3 / 9

SLIDE 4

Idea

Chain-up potential receivers in descending order from most specific to least specific Upon reques, each receiver can decide to handle it ot to propagate it to its successor.

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 4 / 9

SLIDE 5

Description

Applicability: Use the chain-of-responsibility pattern if several objects could handle a request, and it is unknown at development time which one actually will. the set of possible receivers is to be configured dynamically

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 5 / 9

SLIDE 6

Structure

Client + handleRequest() Handler + handleRequest() ConcreteHandler1 + handleRequest() ConcreteHandler2 successor Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 6 / 9

SLIDE 7

Consequences

Loose Coupling: the chain-of-responsibility pattern decouples the sender of a request from the receiver. No Processing Guarantee: Because each receiver may decide not to handle a request, it might fall off the chain unprocessed.

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 7 / 9

SLIDE 8

Implementation

The successor chain can either use a pre-existing linkage of the receiver objects,

r be built separately.

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 8 / 9

SLIDE 9

Related Patterns

Composite: Often, the parent object of a composite is used as the successor object for a chain of responsibility.

Oliver Haase (HTWG Konstanz) Design Patterns & Refactoring 9 / 9