Defining and Implementing Interfaces in Delphi

In Delphi, interface has two distinct meanings. In OOP jargon, you can think of an interface as a class with no implementation. In Delphi unit definition interface section is used to declare any public sections of code that appear in a unit. This article will explain interfaces from an OOP perspective. If you are up to creating a rock-solid application in a way that your code is maintainable, reusable, and flexible the OOP nature of Delphi will help you drive the first 70% of your route. Defining interfaces and implementing them will help with the remaining 30%. Abstract Classes You can think of an interface as an abstract class with all the implementation stripped out and everything that is not public removed. An abstract class in Delphi is a class that cannot be instantiated—you cannot create an object from a class marked as abstract. Lets take a look at an example interface declaration: typeIConfigChanged interface[{0D57624C-CDDE-458B-A36C-436AE465B477}]procedure ApplyConfigChange;end; The IConfigChanged is an interface. An interface is defined much like a class, the keyword interface is used instead of class. The Guid value that follows the interface keyword is used by the compiler to uniquely identify the interface. To generate a new GUID value, just press CtrlShiftG in the Delphi IDE. Each interface you define needs a unique Guid value. An interface in OOP defines an abstraction—a template for an actual class that will implement the interface—that will implement the methods defined by the interface. An interface does not actually do anything, it only has a signature for interaction with other (implementing) classes or interfaces. The implementation of the methods (functions, procedures, and property Get/Set methods) is done in the class that implements the interface. In the interface definition, there are no scope sections (private, public, published, etc.) everything is public. An interface type can define functions, procedures (that will eventually become methods of the class that implements the interface) and properties. When an interface defines a property it must define the get/set methods - interfaces cannot define variables. As with classes, an interface can inherit from other interfaces. typeIConfigChangedMore interface(IConfigChanged)procedure ApplyMoreChanges;end; Programming Most Delphi developers when they think of interfaces they think of COM programming. However, interfaces are just an OOP feature of the language—they are not tied to COM specifically. Interfaces can be defined and implemented in a Delphi application without touching COM at all. Implementation To implement an interface you need to add the name of the interface to the class statement, as in: typeTMainForm class(TForm, IConfigChanged)publicprocedure ApplyConfigChange;end; In the above code a Delphi form named MainForm implements the IConfigChanged interface. Warning: when a class implements an interface it must implement all its methods and properties. If you fail/forget to implement a method (for example: ApplyConfigChange) a compile time error E2003 Undeclared identifier: ApplyConfigChange will occur.Warning: if you try to specify the interface without the GUID value you will receive: E2086 Type IConfigChanged is not yet completely defined. Example Consider an MDI application where several forms can be displayed to the user at one time. When the user changes the application configuration, most forms need to update their display—show/hide some buttons, update label captions, etc. You would need a simple way to notify all open forms that a change in the application configuration has happened. The ideal tool for the job was an interface. Every form that needs to be updated when the configuration changes will implement IConfigChanged. Since the configuration screen in displayed modally, when it closes the next code ensures all IConfigChanged implementing forms are notified and ApplyConfigChange is called: procedure DoConfigChange() ;varcnt : integer;icc : IConfigChanged;beginfor cnt : 0 to -1 Screen.FormCount dobeginif Supports(Screen.Forms[cnt], IConfigChanged, icc) thenicc.ApplyConfigChange;end;end; The Supports function (defined in Sysutils.pas) indicates whether a given object or interface supports a specified interface. The code iterates through the Screen.Forms collection (of the TScreen object)—all the forms currently displayed in the application. If a form Screen.Forms[cnt] supports the interface, Supports returns the interface for the last parameter parameter and returns true. Therefore, if the form implements the IConfigChanged, the icc variable can be used to call the methods of the interface as implemented by the form. Note, of course, that every form can have its own different implementation of the ApplyConfigChange procedure. Ancestors Any class you define in Delphi needs to have an ancestor. TObject is the ultimate ancestor of all objects and components. The above idea applies to interfaces also, the IInterface is the base class for all interfaces. IInterface defines 3 methods: QueryInterface, _AddRef and _Release. This means that our IConfigChanged also has those 3 methods, but we have not implemented those. This is because TForm inherits from TComponent that already implements the IInterface for you! When you want to implement an interface in a class that inherits from TObject, make sure your class inherits from TInterfacedObject instead. Since TInterfacedObject is a TObject implementing IInterface. For example: TMyClass class(TInterfacedObject, IConfigChanged)procedure ApplyConfigChange;end; In conclusion, IUnknown IInterface. IUnknown is for COM.

Violence And Sexual Abuse Of Stockholm Syndrome And...

This is another phrase that many little girls seek comfort in: â€Å"If a boy picks on you, that means that he actually likes you† from a guardian usually. For her to hear this after being bullied destroys her ideas about being treated well by men. It’s not that far of a leap between a bratty boy tugging on a little girl’s pigtails or pushing her in the playground, to dragging her across the floor by her hair or shoving her out of frustration with enough force to break bones. The parallels are too coinciding to ignore. If this thinking and behaviour is not corrected in youth, it will prosper and grow into something more harmful than a playground scuffle. This makes this damaging wives’ tale an enforcer of Stockholm syndrome and violence against women. (Jameson, 2011) These kinds of societal beliefs teaches men to treat the women they admire with brutality as an expression of their feelings as well as a sexual object of their desire. It has taught women to accept these acts of violence and sexual abuse as an equivalent for love and compliment. Stockholm syndrome is a defense mechanism of sorts: the abused psychologically creates an affection for the abuser to cope with their life-threatening circumstances. â€Å"[Stockholm syndrome] is proffered as a psychological explanation for the question of why people can be unable or unwilling to leave abusive relationships†¦ [this implies] that the development of a bond between victim and aggressor is the best way to ensure the victim’s survival†Show MoreRelatedImplications Of Domestic Abuse On Women1036 Words   |  5 PagesImplications of Domestic Abuse on Women In a broad sense, domestic abuse is a set of problems related to family violence. Domestic violence is characterized by a pattern of violent or abusive behavior by one person in a domestic context against another, such as in a marriage or cohabitation (Paul, 2004). 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Boo Radley Essay Example For Students

Boo Radley Essay Over the past Summers I have become very fond of Jem and Scout. They somehow touched a nerve inside of me that seemed to open my eyes to the world and the people in it. The fact that I intrigued them amused me. I knew it was only because of the rumours but for some reason it did not matter. Its simple to judge others before actually getting to know them. I know, as the community often misjudged me. When you hear them often enough you actually start believing them yourself. This is the reason I often lonely wandered the streets at night with no real purpose but to look at our beautiful countryside, free of whispers and judging faces. The number of stories spun about me and my familys past actions were immense. I think the worst culprit was Mrs. Stephanie Crawford, the neighborhood gossip, who I thought could probably talk under water. A superb example of the way the town gave into rumours is shown in a story Stephanie Crawford began. It is alleged that I was cutting up newspapers with a pair of scissors. My father then came into the living room. As he passed, I supposedly stabbed him in the leg and kept on cutting. I think the children liked this story the most. The fact that the town listened to such nonsense without any real proof made me angry and depressed. The thing I liked about your children was that despite all the rumours they still wanted to see what I was like for themselves. Sure they listened to the gossip but still they had to know if they were true or not. Because of this I felt as though Jem and Scout had befriended me in sort of a weird way and I was grateful for the respect. They had many escapades trying to catch that elusive glimpse of me. Up until the night in question I dont think they really ever did. One summer night Jem, Scout and Dill all tried to catch a look of me by sneaking up to my porch window. I saw them approaching and thought I would give them what they came for. But as soon as they even saw my shadow they were scared senseless and ran as fast as their little legs could carry them. On the way out Jem got his pants caught on the fence and had to leave them there. I fixed them up and left them hanging over the fence. I thought it was only right for scaring them in such a way. I wanted to show them I was nice and not some big scary monster so I began leaving little presents in the old oak trees for them to find. Then they would put two and two together and figure out that the gifts were from me. Sadly I never did receive any thank you. On the night of the incident, I first saw Jem and Scout all dressed up walking past my house in the late afternoon. Later that night I was finding it hard to sleep and decided to go for one of my pleasant countryside walks. While walking, I saw Bob Ewell in quite a drunken state. To my surprise Jem and Scout suddenly came marching down the trampled pathway. Bob saw them too and began to follow. As the seconds past Bob got closer and closer to the children until he was but a metre away. I knew if I did not do something, Jem and Scout were done for, so I gathered up the courage and began to fight Bob off the children. Jem looked in a bad way so I rushed him back to the safety of the house. I hid behind the door hoping to get my chance to go home unseen. I did not want any credit or trouble. Any person would have done the same thing in my position. It was a great surprise to me when the Sheriff sided with me and made up a fake story of Bob Ewells demise. For I was Boo Radley and such dastardly deeds were expected of me. It was nice to know it is possible to change a reputation even if it is just in the minds of a few.