Solved

Delphi how to create a new Instance of a Component at runtime. (TStringList)

Posted on 2009-04-11
9
1,548 Views
Last Modified: 2013-11-23
It's like this
 
Click button 1
Button one will create a new Instance of TStringList with Edit1.Text for the Name
It will then take The Items in the ListBox and Add them to the new instance.

Click Button 2

Go through all instances ot TStringList created on Button1 Click and process them to a Textbox for viewing.

if you needf clarification just ask
0
Comment
Question by:jamerslong
  • 5
  • 4
9 Comments
 
LVL 37

Expert Comment

by:Geert Gruwez
ID: 24124860
a TStringList doesn't have a property name.
so you need to create a descendant which does have a property Name

this should work ...
unit Unit1;
 

interface
 

uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls, ContNrs;
 

type

  TNamedStringList = class(TStringList)

  private

    fName: string;

  published

  public

    constructor Create(aName: string); reintroduce;

    property Name: string read fName;

  end;
 

  TForm1 = class(TForm)

    Edit1: TEdit;

    Button1: TButton;

    Button2: TButton;

    Memo1: TMemo;

    ListBox1: TListBox;

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

  private

    fSList: TObjectList;

  public

    constructor Create(AOwner: TComponent); override;

    destructor Destroy; override;

  end;
 

var

  Form1: TForm1;
 

implementation
 

{$R *.dfm}
 

{ TNamedStringList }
 

constructor TNamedStringList.Create(aName: string);

begin

  inherited Create;

  fName := aName;

end;
 

{ TForm1 }
 

constructor TForm1.Create(AOwner: TComponent);

begin

  inherited Create(AOwner);

  fSList := TObjectList.Create(True);

end;
 

destructor TForm1.Destroy;

begin

  FreeAndNil(fSList);

  inherited Destroy;

end;
 

procedure TForm1.Button1Click(Sender: TObject);

var item: TStringList;

  I: Integer;

begin

  for I := 0 to fSList.Count - 1 do

    if SameText(TNamedStringList(fSList.Items[I]).Name, Edit1.Text) then

    begin

      ShowMessage('This name allready exists in the list');

      Exit;

    end;

  item := TNamedStringList.Create(Edit1.Text);

  item.AddStrings(ListBox1.Items);

  fSList.Add(item);

end;
 

procedure TForm1.Button2Click(Sender: TObject);

var I: Integer;

  item: TNamedStringList;

begin

  Memo1.Lines.BeginUpdate;

  try

    Memo1.Lines.Clear;

    for I := 0 to fSList.Count - 1 do

    begin

      item := TNamedStringList(fSList.Items[I]);

      Memo1.Lines.Add(item.Name);

      Memo1.Lines.AddStrings(item);

      Memo1.Lines.Add('');

    end;

  finally

    Memo1.Lines.EndUpdate;

  end;

end;
 

end.

Open in new window

0
 
LVL 4

Author Comment

by:jamerslong
ID: 24124879
that works perfect!, could you do my one flavor and comment in some stuff to explain how it works?
0
 
LVL 37

Accepted Solution

by:
Geert Gruwez earned 500 total points
ID: 24124895
ok,
unit Unit1;

 

interface

 

uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls, ContNrs;

 

type

  TNamedStringList = class(TStringList)

  private

    fName: string;

  published

  public

    constructor Create(aName: string); reintroduce;

    property Name: string read fName;

  end;

 

  TForm1 = class(TForm)

    Edit1: TEdit;

    Button1: TButton;

    Button2: TButton;

    Memo1: TMemo;

    ListBox1: TListBox;

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

  private

    fSList: TObjectList;

  public

    constructor Create(AOwner: TComponent); override;

    destructor Destroy; override;

  end;

 

var

  Form1: TForm1;

 

implementation

 

{$R *.dfm}

 

{ TNamedStringList }

 

constructor TNamedStringList.Create(aName: string);

begin

  // call TStringList constructor

  inherited Create;

  // set Name of object

  fName := aName;

end;

 

{ TForm1 }

 

constructor TForm1.Create(AOwner: TComponent);

begin

  // call TForm constructor

  inherited Create(AOwner);

  // Create container object to hold TStringLists

  // The container object is the owner of the TStringLists 

  fSList := TObjectList.Create(True);

end;

 

destructor TForm1.Destroy;

begin

  // Free the container object, the objects it owns are automatically freed too

  FreeAndNil(fSList);

  // Call the destructor of the form

  inherited Destroy;

end;

 

procedure TForm1.Button1Click(Sender: TObject);

var item: TStringList;

  I: Integer;

begin

  // Find if the name is allready in use (non case sensitive)

  for I := 0 to fSList.Count - 1 do

    if SameText(TNamedStringList(fSList.Items[I]).Name, Edit1.Text) then

    begin

      ShowMessage('This name allready exists in the list');

      Exit;

    end;

  // Create a Named stringlist

  item := TNamedStringList.Create(Edit1.Text);

  // Add the items from the Listbox to the Stringlist

  item.AddStrings(ListBox1.Items);

  // Add the item to the container object

  fSList.Add(item);

end;

 

procedure TForm1.Button2Click(Sender: TObject);

var I: Integer;

  item: TNamedStringList;

begin

  // Start change (don't change display until finished)

  Memo1.Lines.BeginUpdate;

  try

    // Clear all entries

    Memo1.Lines.Clear;

    // Take each Stringlist from the container

    for I := 0 to fSList.Count - 1 do

    begin

      // Typecast the item to a usable TNamedStringList

      item := TNamedStringList(fSList.Items[I]);

      // Add the name to the memo

      Memo1.Lines.Add(item.Name);

      // Add the strings to the memo

      Memo1.Lines.AddStrings(item);

      // Add a blank line to the memo

      Memo1.Lines.Add('');

    end;

  finally

    // After changes, Update the display

    Memo1.Lines.EndUpdate;

  end;

end;

 

end.

Open in new window

0
 
LVL 37

Expert Comment

by:Geert Gruwez
ID: 24125016
The trick is to use a container object,
this can hold anything descending from TObject
when you create it with AOwnsObjects = True then it will free the objects it contains on freeing the container

There is more types of containers in the unit ContNrs
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 4

Author Comment

by:jamerslong
ID: 24126231
Thanks, way more comments then expected. You save me from myself once again!
0
 
LVL 4

Author Comment

by:jamerslong
ID: 24127813
Ok, When i try to Edit a TNamed String List I get a Read address violation... a little help?
if exsists = true then
    else
      begin
      item := TNamedStringList.Create(ListBox1.Items.Strings[ListBox1.ItemIndex]);
      fSList.Add(item);
      end;
item := TNamedStringList(ListBox1.Items.Strings[ListBox1.ItemIndex]);
item.Clear;
for i := 0 to CheckListBox1.Items.Count -1 do
      begin
      If CheckListBox1.Checked[i] = true then
        begin
        item.Add(CheckListBox1.Items.Strings[i]);
        end
      end

Or also would would be better if i would Destroy the instance and remake it?
But i do need to know how to destory the instance if i do not need it anyore.
0
 
LVL 4

Author Comment

by:jamerslong
ID: 24127869
Nevermind, I got it!

for I := 0 to fSList.Count - 1 do
    if SameText(TNamedStringList(fSList.Items[I]).Name, ListBox1.Items.Strings[ListBox1.ItemIndex]) then
    begin
      item := TNamedStringList(fSList.Items[I]);
    end;
0
 
LVL 4

Author Comment

by:jamerslong
ID: 24127873
Allthough I still need to figure out how to delete an instance.
0
 
LVL 37

Expert Comment

by:Geert Gruwez
ID: 24135719
use the Remove function after using your search for finding the NamedStringList

function Remove(AObject: TObject): Integer;

if you set AOwnsObjects to true as i did, the stringlist is freed automatically
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Syntax Check Delphi Seattle IOS app without MAC ? 1 91
Copying WordPress Pages 5 76
Convert a string into a TDateTime 5 50
Syntax Error 2 45
In our object-oriented world the class is a minimal unit, a brick for constructing our applications. It is an abstraction and we know well how to use it. In well-designed software we are not usually interested in knowing how objects look in memory. …
In this tutorial I will show you how to use the Windows Speech API in Delphi. I will only cover basic functions such as text to speech and controlling the speed of the speech. SAPI Installation First you need to install the SAPI type library, th…
This tutorial covers a step-by-step guide to install VisualVM launcher in eclipse.
THe viewer will learn how to use NetBeans IDE 8.0 for Windows to perform CRUD operations on a MySql database.

910 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

21 Experts available now in Live!

Get 1:1 Help Now