# TListBox

Deutsch (de) English (en) suomi (fi) français (fr)

A TListBox is a component that shows a (scrollable) list of (short) strings where user is to select one. It is available from the Standard tab of the Component Palette.

In the TListBox, the stored strings are stored in the property Items, that is of type TStrings. Thus you can assign or remove strings in the ListBox, as in a TStringList or its parent TStrings.

Here are a few examples of how to use a TListBox ListBox1 on a form Form1:

## Fill ListBox

### by the Object Inspector

• Select the ListBox on your form with one click.
• Go in the Object Inspector in the Properties tab on the property Items.
• Click on the button with the three dots. The String Editor opens.

### by code in button click

Add your form a TButton with the name btnFill and caption fill ListBox. In the event handler OnClick of the button, you write the following code:

procedure TForm1.btnFillClick(Sender: TObject);
begin
ListBox1.Items.Clear;             //Delete all existing strings
end;

## Assignment of a StringList

Add your form a TButton with the name btnFill and caption fill ListBox. In the event handler OnClick of the button, you write the following code:

procedure TForm1.btnFillClick(Sender: TObject);
var
myStringList: TStringList;
begin
myStringList:=TStringList.Create;               //Create my StringList
myStringList.Add('This is the second first line.');
ListBox1.Items.Assign(myStringList);            //assign the ListBox1 the text content of my StringList
myStringList.Free;                              //Free my StringList in memory
end;

• Extend the example Fill ListBox by code in button click to a TEdit and a TButton with the name btnAdd and caption add string. Change of Edit1 the property Text to "" - empty string.
• In the event handler OnClick of the button, you write the following code:
procedure TForm1.btnAddClick(Sender: TObject);
begin
Edit1.Text:='';
end;

## Delete string

By default is set that you can select only one row in your list box. Do you want to select several of the lines in your ListBox, you would have the property MultiSelect to make True.

### at ItemIndex

• Extend the example Add string to a TButton with the name "btnDel" and caption "delete string".
• In the event handler OnClick of the button, you write the following code:
procedure TForm1.btnDelClick(Sender: TObject);
begin
if ListBox1.ItemIndex > -1 then    //Delete only when a string in the listbox is selected
ListBox1.Items.Delete(ListBox1.ItemIndex);
end;

### all selected strings

• Extend the example Add string to a TButton with the name "btnDel" and caption "delete string".
• In the event handler OnClick of the button, you write the following code:
procedure TForm1.btnDelClick(Sender: TObject);
var
i: Integer;
begin
if ListBox1.SelCount > 0 then                 //Delete only if at least one string in the list box is selected
for i:=ListBox1.Items.Count - 1 downto 0 do //Iterate through all the items
if ListBox1.Selected[i] then              //If selected...
ListBox1.Items.Delete(i);               //...delete the item (String)
end;

## Owner-drawn ListBox

In general, it is advantageous to let the ListBox follow the theme set by the user. In some cases (for example, to program a game with a colorful surface), you can deviate from this standard and draw the control according to your own choice. You can try this now:

• You can modify the previous sample or create a new application with a TListBox ListBox1.
• In the Object Inspector, change ListBox1 property Style to lbOwnerDrawFixed.
• With the Object Inspector, tab events, create the event handler for the event OnDrawItem, by clicking on the button [...].
• You add the following code to the handler:
procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer;
ARect: TRect; State: TOwnerDrawState);
var
aColor: TColor;                       //Background color
begin
if (Index mod 2 = 0)                  //Index tells which item it is
then aColor:=$FFFFFF //every second item gets white as the background color else aColor:=$EEEEFF;               //every second item gets pink background color
if odSelected in State then aColor:=\$0000FF;  //If item is selected, then red as background color
ListBox1.Canvas.Brush.Color:=aColor;  //Set background color
ListBox1.Canvas.FillRect(ARect);      //Draw a filled rectangle

ListBox1.Canvas.Font.Bold:=True;      //Set the font to "bold"
ListBox1.Canvas.TextRect(ARect, 2, ARect.Top+2, ListBox1.Items[Index]);  //Draw Itemtext
end;

Note: Parameters of ListBoxDrawItem:

Control:
If multiple controls (E.g. multiple ListBoxes) access this event handle, you know which threw this event. You could in our example, instead of ListBox1.Canvas.FillRect(ARect) also TListBox(Control).Canvas.FillRect(ARect) write, where you should query still possible before, whether it is a TListBox:

  if Control is TListBox then
TListBox(Control).Canvas.FillRect(ARect);

Index: Specifies the item location, so you have access to the string <ListBox>.Items[Index].
ARect: Describes the rectangle, which is necessary for drawing the background.
State: Status of the items, whether normal, focused, selected etc.

• Your example could look like:

->