How To Use Interfaces: what changed
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Title: How To Use Interfaces
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| 1 | + | Copy the text below and it will demonstrate how to use [[Interfaces]] to write less code, avoid code repetition,..., this is a fully working program. The default interface in FPC is COM, which makes that once a class with an interface is instantiated as that interface it will automatically be released. Note if you change the interface type to CORBA it WILL leak. | |
| 2 | + | ||
| 3 | + | This example has two unrelated classes, but share the same COM interface. Since they are instantiated through that interface, destruction is automatic: | |
| 4 | + | ||
| 5 | + | ``` pascal | |
| 6 | + | program interfacesygenerics; | |
| 7 | + | {$mode objfpc}{$H+} | |
| 8 | + | type | |
| 9 | + | ITestInterface = interface | |
| 10 | + | ['{3FB19775-F5FA-464C-B10C-D8137D742088}'] | |
| 11 | + | procedure DoSomething; | |
| 12 | + | procedure DoItAll; | |
| 13 | + | end; | |
| 14 | + | ||
| 15 | + | TOneObject = class(TInterfacedObject,ITestInterface) | |
| 16 | + | procedure DoSomething; | |
| 17 | + | procedure DoItAll; | |
| 18 | + | end; | |
| 19 | + | ||
| 20 | + | TOtherObject = class(TInterfacedObject,ITestInterface) | |
| 21 | + | procedure DoSomething; | |
| 22 | + | procedure DoItAll; | |
| 23 | + | end; | |
| 24 | + | ||
| 25 | + | procedure TOneObject.DoSomething; | |
| 26 | + | begin | |
| 27 | + | Writeln('TOneObject DoSomething !'); | |
| 28 | + | end; | |
| 29 | + | ||
| 30 | + | procedure TOneObject.DoItAll; | |
| 31 | + | begin | |
| 32 | + | Writeln('TOneObject DoItAll !'); | |
| 33 | + | end; | |
| 34 | + | ||
| 35 | + | procedure TOtherObject.DoSomething; | |
| 36 | + | begin | |
| 37 | + | Writeln('TOtherObect DoSomething !'); | |
| 38 | + | end; | |
| 39 | + | ||
| 40 | + | procedure TOtherObject.DoItAll; | |
| 41 | + | begin | |
| 42 | + | Writeln('TOtherObect DoItAll !'); | |
| 43 | + | end; | |
| 44 | + | ||
| 45 | + | var | |
| 46 | + | I: ITestInterface = nil; | |
| 47 | + | begin | |
| 48 | + | Writeln('Using regular interfaces'); | |
| 49 | + | I := TOneObject.Create as ITestInterface; | |
| 50 | + | if I <> nil then | |
| 51 | + | Writeln('Got interface OK. Calling it'); | |
| 52 | + | I.DoSomething; | |
| 53 | + | I.DoItAll; | |
| 54 | + | I:=nil; // releases TOneObject | |
| 55 | + | I := TOtherObject.Create as ITestInterface; | |
| 56 | + | if I <> nil then | |
| 57 | + | Writeln('Got interface OK. Calling it'); | |
| 58 | + | I.DoSomething; | |
| 59 | + | I.DoItAll; | |
| 60 | + | end. | |
| 61 | + | ``` | |
| 62 | + | ||
| 63 | + | ## See also | |
| 64 | + | ||
| 65 | + | - [[Accessing the Interfaces directly]] | |
| 66 | + | - [[Interfaces]] | |
| 67 | + | - [[Understanding Interfaces]] | |
| 68 | + | ||
| 69 | + | --- | |
| 70 | + | *From the Free Pascal wiki, page "How To Use Interfaces", as it stood on 2021-10-06 after a change by Thaddy, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).* | |
| 71 | + | Category: Example programs | |
| 72 | + | Category: Interfaces | |
| 73 | + | Category: Pascal |