In this article I show how to implement the command pattern (https://en.wikipedia.org/wiki/Command_pattern) and include it in a queue
First of all we need the command interface
Interface ICommand
interface ICommand
{
procedure Execute();
}
Because we want to add this to an queue we need a queue entry, i choose a codeunit to this put to be more generic it is also possible to use an interface and an implementing codeunit
Codeunit QueueEntry
codeunit 50102 "QueueEntry"
{
procedure SetValue(var v: Interface ICommand);
begin
value := v;
end;
procedure GetValue(): Interface ICommand;
begin
exit(value);
end;
procedure GetNextEntry(): Codeunit QueueEntry;
begin
exit(NextEntry);
end;
procedure SetNextEntry(var Entry: Codeunit QueueEntry);
begin
NextEntry := Entry;
end;
var
value: Interface ICommand;
NextEntry: Codeunit QueueEntry;
}
Now we need a managing codeunit for this Queue Entry
Codeunit Queue
codeunit 50100 "Queue"
{
procedure Push(var value: Interface ICommand)
var
Entry: Codeunit QueueEntry;
begin
Entry.SetValue(value);
if count = 0 then begin
first := Entry;
last := Entry;
end
else begin
last.SetNextEntry(Entry);
last := Entry;
end;
count += 1;
end;
procedure Pop() value: Interface ICommand;
begin
if count > 0 then begin
value := first.GetValue();
first := first.GetNextEntry();
count -= 1;
end
else
Error('The Queue is empty!');
end;
procedure GetSize(): Integer
begin
exit(count);
end;
var
first: Codeunit QueueEntry;
last: Codeunit QueueEntry;
count: Integer;
}
That’s it!
To this whole example if also implementet a MessageCommander
codeunit 50103 "MessageCommander" implements ICommand
{
procedure SetText(value: Text);
begin
t := value;
end;
procedure Execute()
begin
Message(t);
end;
var
t: Text;
}
page 50100 "Queue Test"
{
PageType = Card;
ApplicationArea = All;
UsageCategory = Administration;
layout
{
area(Content)
{
group(GroupName)
{
field(Input; input)
{
Caption = 'Add Message';
ApplicationArea = All;
}
}
}
}
actions
{
area(Processing)
{
action(AddEntry)
{
ApplicationArea = All;
Caption = 'Add new Message';
trigger OnAction()
var
t: Codeunit MessageCommander;
object: Interface ICommand;
begin
t.SetText(input);
object := t;
queue.Push(object);
end;
}
action(ActionName)
{
ApplicationArea = All;
Caption = 'Execute Next Message';
trigger OnAction()
var
object: Interface ICommand;
begin
if queue.GetSize() > 0 then begin
object := queue.Pop();
object.Execute();
end;
end;
}
}
}
var
input: Text;
queue: Codeunit Queue;
}
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