Difference between revisions of "How To Use Interfaces"
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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. | 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. | Note if you change the interface type to CORBA it WILL leak. | ||
+ | |||
+ | This example has two unrelated classes, but share the same COM interface. | ||
+ | Since they are instantiated through that interface, destruction is automatic: | ||
<syntaxhighlight lang="pascal">program interfacesygenerics; | <syntaxhighlight lang="pascal">program interfacesygenerics; | ||
{$mode objfpc}{$H+} | {$mode objfpc}{$H+} | ||
Line 11: | Line 14: | ||
end; | end; | ||
− | + | TOneObject = class(TInterfacedObject,ITestInterface) | |
procedure DoSomething; | procedure DoSomething; | ||
procedure DoItAll; | procedure DoItAll; | ||
end; | end; | ||
− | + | TOtherObject = class(TInterfacedObject,ITestInterface) | |
procedure DoSomething; | procedure DoSomething; | ||
procedure DoItAll; | procedure DoItAll; | ||
end; | end; | ||
− | + | ||
− | procedure | + | procedure TOneObject.DoSomething; |
begin | begin | ||
− | Writeln(' | + | Writeln('TOneObject DoSomething !'); |
end; | end; | ||
− | procedure | + | procedure TOneObject.DoItAll; |
begin | begin | ||
− | Writeln(' | + | Writeln('TOneObject DoItAll !'); |
end; | end; | ||
− | procedure | + | |
+ | procedure TOtherObject.DoSomething; | ||
begin | begin | ||
− | Writeln(' | + | Writeln('TOtherObect DoSomething !'); |
end; | end; | ||
− | procedure | + | procedure TOtherObject.DoItAll; |
begin | begin | ||
− | Writeln(' | + | Writeln('TOtherObect DoItAll !'); |
end; | end; | ||
Line 44: | Line 48: | ||
begin | begin | ||
Writeln('Using regular interfaces'); | Writeln('Using regular interfaces'); | ||
− | I := | + | I := TOneObject.Create as ITestInterface; |
+ | if I <> nil then | ||
+ | Writeln('Got interface OK. Calling it'); | ||
+ | I.DoSomething; | ||
+ | I.DoItAll; | ||
+ | I:=nil; // releases TOneObject | ||
+ | I := TOtherObject.Create as ITestInterface; | ||
if I <> nil then | if I <> nil then | ||
Writeln('Got interface OK. Calling it'); | Writeln('Got interface OK. Calling it'); |
Latest revision as of 09:24, 6 October 2021
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.
This example has two unrelated classes, but share the same COM interface. Since they are instantiated through that interface, destruction is automatic:
program interfacesygenerics;
{$mode objfpc}{$H+}
type
ITestInterface = interface
['{3FB19775-F5FA-464C-B10C-D8137D742088}']
procedure DoSomething;
procedure DoItAll;
end;
TOneObject = class(TInterfacedObject,ITestInterface)
procedure DoSomething;
procedure DoItAll;
end;
TOtherObject = class(TInterfacedObject,ITestInterface)
procedure DoSomething;
procedure DoItAll;
end;
procedure TOneObject.DoSomething;
begin
Writeln('TOneObject DoSomething !');
end;
procedure TOneObject.DoItAll;
begin
Writeln('TOneObject DoItAll !');
end;
procedure TOtherObject.DoSomething;
begin
Writeln('TOtherObect DoSomething !');
end;
procedure TOtherObject.DoItAll;
begin
Writeln('TOtherObect DoItAll !');
end;
var
I: ITestInterface = nil;
begin
Writeln('Using regular interfaces');
I := TOneObject.Create as ITestInterface;
if I <> nil then
Writeln('Got interface OK. Calling it');
I.DoSomething;
I.DoItAll;
I:=nil; // releases TOneObject
I := TOtherObject.Create as ITestInterface;
if I <> nil then
Writeln('Got interface OK. Calling it');
I.DoSomething;
I.DoItAll;
end.