The document discusses the Dependency Inversion Principle (DIP), which states that high-level modules should not depend on low-level modules, but that both should depend on abstractions. DIP is important for framework design, as it reduces tight coupling between modules. Violations of DIP include direct instantiation of concrete classes and use of static methods. The document provides examples of how to avoid DIP violations through dependency injection and inversion of dependencies on abstractions rather than concrete classes.

1. SOLID Principles - III
DIP – Dependency Inversion Principle
Maulik Soni

2. Dependency Inversion Principle
 High-level modules should not depend on low-level modules
 Both should depend on abstractions
 Abstractions should not depend on details
 Details should depend on abstractions
Maulik Soni

3. Dependency Inversion Principle
DIP is at the very heart of framework design
Maulik Soni

4. How To Spot DIP Violation ?
 Direct Instantiation
 new SomeObject();
 Static Methods
 ServiceLocator.getObject();
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5. Is DIP Violated Here ?
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6. Resolution
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7. Inverted Dependencies
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8. Demo
 Demo of DIP and Dependency Injection using Unity
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9. Summary
 Depend on abstractions
 No variable should hold a reference to a concrete class
 No class should derive from a concrete class
 No method should override an implemented method of any of its base classes
 Heuristic is typically violated at least once
 Somebody has to create the instances of the concrete classes
 No reason to strictly follow this heuristic for classes that are concrete but non-volatile
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10. End of Presentation
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 End of Introduction to SOLID Principles
 S = Single Responsibility
 O = Open / Closed
 L = Liskov Substitution
 I = Interface Segregation
 D = Dependency Inversion