TListBox with Item ID's
lazarus / 31-LCL

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Weitentaaal · 2021-05-04 06:49

Hello Guys

Lately i was about to rewrite Some of my Code.

I Had 2 ListBoxes where 1 should display all selected items and the
other the non-selected items.
All fine until i had to sort it by relevance. So i had to Idetnify my
items so i could write a proper sorting logarithm for my items.

Is it somehow possible to make something like this happen ?:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i      TSZ =
Object      ID : integer;      Name : String;  end;  procedure
TForm1.FormShow(Sender: TObject);var   sz : Array of TSZ;   Tests :
TSZ;   i : Integer;begin   for i := 0 to 10 - 1 do begin     
//Tests.setName('Test' + i.ToString);      //Tests.setID(i);     
Tests.Name:= 'Test'+ i.ToString;      Tests.ID := i;      sz[i] :=
Tests;   end;    for i := 0 to SizeOf(sz) - 1 do begin     
ListBox1.Items.AddObject(sz[i].Name, sz[i]);  //<--- Error   end;end; 
Just wanted To have an "ID" property on my Items, so i dont have to
compare them by Name and detect wich item it is by Name. Is there any
other (better) Component then ListBox ?

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alpine · 2021-05-04 09:08

You can use ListBox1.Items.AddObject() for that, just use proper type
casting:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
ListBox1.Items.AddObject(ItemName, TObject(ItemId)); // ItemId is an
integer...ItemId := Integer(ListBox1.Items.Objects[index_of_item]); 
Your sample code is wrong also for another reason - because you use
local variable sz it will cease to exist when you exit the FormShow()
method.

If you decide to use Object[] property to point to something useful it
must be allocated on heap or at least to be a pointer to a global
variable.

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Weitentaaal · 2021-05-04 09:14

Illegal type conversion (Attached Picture of Errors)

and btw. i "sz" is Global. This is just a new Project to test ListBox

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korba812 · 2021-05-04 09:22

If you are using the 64 bit compiler then you must first cast to the
appropriate integer type. It is best to use PtrInt, which is defined
separately for each platform.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
ListBox1.Items.AddObject(ItemName, TObject(PtrInt(ItemId))); // ItemId
is an integer...ItemId :=
PtrInt(ListBox1.Items.Objects[index_of_item]);

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ASerge · 2021-05-04 10:32

Quote from: Weitentaaal on May 04, 2021, 08:49:30 amJust wanted To
have an "ID" property on my Items, so i dont have to compare them by
Name and detect wich item it is by Name. Is there any other (better)
Component then ListBox ?
For me, the data and its representation should be separated.

Let's take, for example, some data:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type 
TMyItem = record    Id: SizeInt;    Name: string;  end;   TMyItemArray
= array of TMyItem;
And somehow initialize them:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
PrepareData(out Data: TMyItemArray);const  CCount = 10000;var  i:
SizeInt;  N: SizeInt;begin  SetLength(Data, CCount);  for i := 0 to
CCount - 1 do  begin    N := Random(CCount);    Data[i].Id := N;   
Data[i].Name := Format('Item %.4d', [N]);  end;end;
To represent the data, we take TListView in virtual mode:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
PrepareListViewAsVirtual(AListView: TListView; ACount: SizeInt);begin 
AListView.ColumnClick := False;  AListView.HideSelection := False; 
AListView.OwnerData := True;  AListView.ReadOnly := True; 
AListView.RowSelect := True;  AListView.ShowColumnHeaders := False; 
AListView.ViewStyle := vsReport;  AListView.Columns.Add; 
AListView.Items.Count := ACount;end;
Now let's link the data to the view:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   TForm1 =
class(TForm)    ListView1: TListView;...  private    FData:
TMyItemArray;...procedure TForm1.FormCreate(Sender: TObject);begin 
PrepareData(FData);  PrepareListViewAsVirtual(ListView1,
Length(FData));end; procedure TForm1.ListView1Data(Sender: TObject;
Item: TListItem); // OnData Eventvar  i: SizeInt;begin  i :=
Item.Index;  if Math.InRange(i, 0, High(FData)) then    Item.Caption
:= FData[i].Name;end;
For a better display, we'll adjust it a little:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormShow(Sender: TObject);begin  ListView1.AutoWidthLastColumn
:= True;  if ListView1.ItemIndex < 0 then    ListView1.ItemIndex :=
Low(FData);end;
Now, suppose we want to sort the array by ID. Let's use STL
garrayutils unit:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type 
TMyItemSortWrapper = record    class function c(const Left, Right:
TMyItem): Boolean; static; // Left < Right  end; class function
TMyItemSortWrapper.c(const Left, Right: TMyItem): Boolean;begin 
Result := Left.Id < Right.Id;end; {$PUSH}{$WARN 6058 off : Call to
subroutine "$1" marked as inline is not inlined}procedure
SortDataById(var Data: TMyItemArray);type  TSorter = specialize
TOrderingArrayUtils<TMyItemArray, TMyItem, TMyItemSortWrapper>;begin 
TSorter.Sort(Data, Length(Data));end;{$POP}
And assign the sorting to some button:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);begin  SortDataById(FData); 
ListView1.Refresh;end;
To see all this in action, create an empty project, add a ListView and
a Button to the Form. Add the code specified above to the desired
events.
Don't forget to specify {$MODESWITCH ADVANCEDRECORDS} in the header
and add "uses Math, garrayutils" in the implementation.

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Weitentaaal · 2021-05-04 10:42

@Korba812 and @y.ivanov with ur Suggestions it worked ! Thanks

@ASerge Thanks for your reply
 you are right data and gui should definitely be separated so i guess
i will have a look at ur work. It realy looks easy and will also
provide me a better overview.

Thanks to all of u again

Edit: Why do i need Advanced Records(Only for Sorting method ? wich i
will write on my won so i dont have to use modeswitch ?) and Why
should the list be virtual ?
Edit2: is it possible to use listBox instead of listView ?

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Weitentaaal · 2021-05-04 13:38

What happens to the Item index when i implement a drag and drop. Will
this still work wich drag and drop ?

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howardpc · 2021-05-04 13:42

Quote from: Weitentaaal on May 04, 2021, 12:42:04 pmEdit: Why do i
need Advanced Records(Only for Sorting method ? wich i will write on
my won so i dont have to use modeswitch ?) and Why should the list be
virtual ?
Edit2: is it possible to use listBox instead of listView ?
Advanced records are needed only for the sorting record wrapper which
contains a method.
It is certainly possible to use a listbox. See the attached project
which is an adaptation of ASerge's code.

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Weitentaaal · 2021-05-04 13:51

Yes thanks .. that was what i was looking for ? so my (hopefully) last
question then is about doing this with DragDrop. I Have lets say 100
items wich will be initialized like we did in the First ListBox or
Listview. But how do i keep my ID's correct when i drop some items
from 1 into 2 . Is it possible to make a DataField  for both ListViews
? maybe witch a property wich tells if Parent is ListView 1 or 2.

Thanks