NAME

Tk::Adjuster - Allow size of packed widgets to be adjusted by user

SYNOPSIS

use Tk::Adjuster;

$adjuster = $widget->Adjuster(?options?);

Name: restore
Class: Restore
Switch: -restore: Specifies a boolean value that determines whether the Adjuster should forcibly attempt to make room for itself (by reducing the size of its managed widget) when it is unmapped (for example, due to a size change in a top level window). The default value is 1.
Name: side
Class: Side
Switch: -side: Specifies the side on which the managed widget lies relative to the Adjuster. In conjunction with the pack geometry manager, this relates to the side of the master against which the managed widget and the Adjuster are packed. Must be left, right, top, or bottom. Defaults to top.
Name: widget
Class: Widget
Switch: -widget: Specifies the widget which is to be managed by the Adjuster.

DESCRIPTION

Tk::Adjuster is a Frame containing a "line" and a "blob".

Dragging with Mouse Button-1 results in a line being dragged to indicate new size. Releasing Button-1 submits GeometryRequests on behalf of the managed widget which will cause the packer to change the widget's size.

If Drag is done with Shift button down, then GeometryRequests are made in "real time" so that text-flow effects can be seen, but as a lot more work is done behaviour may be sluggish.

If widget is packed with -side => left or -side => right then width is adjusted. If packed -side => top or -side => bottom then height is adjusted.

packPropagate is turned off for the master window to prevent adjustment changing overall window size. Similarly packPropagate is turned off for the managed widget if it has things packed inside it. This is so that the GeometryRequests made by Tk::Adjuster are not overridden by pack.

In addition, the managed widget is made non-expandable to prevent the geometry manager reallocating freed space in the master back to the managed widget. Note however that expansion is turned off only after the Adjuster is mapped, which allows the managed widget to expand naturally on window creation.

The Tk::Widget method, packAdjust, calls pack on the widget, then creates an instance of Tk::Adjuster, and packs that "after" the widget. Its use has two disadvantages however: the Adjuster widget is not made available to the caller, and options cannot be set on the Adjuster. For these reasons, the Tk::Adjuster method, packAfter is preferred, but packAdjust is retained for backwards compatibility.

WIDGET METHODS

$adjuster->packAfter(managed_widget, ?pack_options?): This command configures the Adjuster's -widget and -side options respectively to managed_widget and the -side value specified in pack_options (top if not specified). It then packs the Adjuster after managed_widget, with -fill set to x or y as appropriate.
$adjuster->packForget?(boolean)?: This command calls Tk::Widget::packForget on the Adjuster. If a parameter is provided and it has a true boolean value, then packForget is also called on the managed widget.
$adjuster->slave: This command returns the value $adjuster->cget('-widget'), ie. the reference to the managed widget.

EXAMPLES

Using an Adjuster to separate two widgets, whereby the left widget is managed, and right widget expands to fill space on a window resize

a) Using packAfter (preferred interface)

  use Tk;
  use Tk::Adjuster;
  my $f = MainWindow->new;
  my $lst1 = $f->Listbox();
  my $adj1 = $f->Adjuster();
  my $lst2 = $f->Listbox();
  my $side = 'left';
  $lst1->pack(-side => $side, -fill => 'both', -expand => 1);
  $adj1->packAfter($lst1, -side => $side);
  $lst2->pack(-side => $side, -fill => 'both', -expand => 1);
  MainLoop;

b) Using packAdjust

  use Tk;
  use Tk::Adjuster;
  my $f = MainWindow->new;
  my $lst1 = $f->Listbox();
  my $lst2 = $f->Listbox();
  my $side = 'left';
  $lst1->packAdjust(-side => $side, -fill => 'both');
  $lst2->pack      (-side => $side, -fill => 'both', -expand => 1);
  MainLoop;

c) Using the standard Tk::Widget::pack

  use Tk;
  use Tk::Adjuster;
  my $f = MainWindow->new;
  my $side = 'left';
  my $lst1 = $f->Listbox();
  my $adj  = $f->Adjuster(-widget => $lst1, -side => $side);
  my $lst2 = $f->Listbox();
  $lst1->pack(-side => $side, -fill => 'both', -expand => 1);
  $adj->pack (-side => $side, -fill => 'y');
  $lst2->pack(-side => $side, -fill => 'both', -expand => 1);
  MainLoop;

Changing the above examples so that $side has the value 'right' means the left widget expands to fill space on a window resize.

Changing the above examples so that $side has the value 'top' produces a testcase with a horizontal Adjuster. Here the bottom widget expands to fill space on a window resize. Packing to the 'bottom' makes the top widget expand to fill space on window resize.

Using -restore => 0 for multiple columns

In the case of multiple columns (or rows) the "restore" functionality of the Adjuster can be inconvenient. When the user adjusts the width of one column and thereby pushes the Adjuster of another column off the window, this adjuster tries to restore itself by reducing the size of its managed widget. This has the effect that column widths shrink; and the original size is not restored when the user reverses the originating change. The -restore option can be used to turn off this functionality. (It makes some sense, however, to leave -restore turned on for the first-packed Adjuster, so that at least one Adjuster always remains visible.)

  use Tk;
  use Tk::Adjuster;
  my $f = MainWindow->new;
  my $lst1 = $f->Listbox();
  my $adj1 = $f->Adjuster();
  my $lst2 = $f->Listbox();
  my $adj2 = $f->Adjuster(-restore => 0);
  my $lst3 = $f->Listbox();
  my $side = 'left';
  $lst1->pack(-side => $side, -fill => 'both', -expand => 1);
  $adj1->packAfter($lst1, -side => $side);
  $lst2->pack(-side => $side, -fill => 'both', -expand => 1);
  $adj2->packAfter($lst2, -side => $side);
  $lst3->pack(-side => $side, -fill => 'both', -expand => 1);
  MainLoop;

BUGS

It is currently not possible to configure the appearance of the Adjuster. It would be nice to be able to set the width and relief of the Adjuster "line" and the presence/absence of the "blob" on the Adjuster.

Tk::Adjuster works theoretically with the grid geometry manager but there are currently some problems which seem to be due to bugs in grid:

  a) There's never an Unmap event for the adjuster, so the "restore"
     functionality has no effect.
  b) After adjusting, widgets protrude into the border of the master.
  c) grid('Propagate', 0) on MainWindow has no effect - window shrinks/grows
     when widgets are adjusted.
  d) Widgets shuffle to correct position on startup

2020-11-09