General component manipulation¶

You can attach a callback for a component like this:

    sub comp_cb {
        ...
    }
    $component->AddCallback(\%comp_cb);

Exactly when (if ever) the callback is invoked depens on the type of the component.

Yo can tell if a component takes or not focus when traversing a form with the following function:

    $component->TakesFocus($true_or_false);

It is handy to set some arbitrary information on a component for later retrieval. You do this by setting its tag:

    $button->Tag("OK");

If you call this function without an argument, it replies with the actual tag for that component.

In general when the return value of any method of a component isn't described the method returns the component itself to allow constructions like:

    $panel
        ->Add(0,0, $componet1->Set( .... ) )
        ->Add(0,1, Newt::Label( .... ) )
        ->Add(0,2, Newt::Panel( .... )
            ->Add( .... )
            ->Add( .... ) )
        ->Add( .... );

Buttons¶

There are two kinds of buttons: full and compact:

    $normal_button = Newt::Button($text);
    $compact_button = Newt::CompactButton($text);

Labels¶

Labels are quite simple:

    $label = Newt::Label($text);

You can set the text of an existing label like this:

    $label->Set($text);

Entry boxes¶

Entry boxes are used to enter text:

    $entry = Newt::Entry($width, $flags, $initial_text);

The initial text is optional. After an entry has been created, it's contents can be set by using:

    $entry->Set($text, $cursor_at_end);

The last parameter is optional, and signals if the cursor should be moved to the end of the new value.

To get the current value of the entry box, you do this:

    $entry->Get();

You can filter the characters that may be entered by using a callback filter like this:

    sub my_filter {
      my ($proposed_char, $cursor_position) = @_;
      ...
      return(0) if $char_shoud_be_ignored;
      return($proposed_char)    # Accept the char
    }
    $entry->SetFilter(\&my_filter);

As can be seen, filter callbacks receive a char and an integer which indicates the position that the proposed char would take on the entry. The filter function can return the very same char to indicate that it was accepted, but it can also return another char, to actually substitute the original one. If the filter wants to simply reject the keystroke, it only returns 0.

When an entry is created, some flags may be specified. The flags are the following and may be "OR"ed:

"NEWT::NEWT_ENTRY_SCROLL"

If not specified, the user cannot enter text into the entry box which is wider than the entry box itself. This flag removes this limitation, and lets the user enter data of an arbitrary length.

"NEWT::NEWT_FLAG_HIDDEN"

If specified, the value of the entry is not displayed. Useful when an applications needs a password.

"NEWT::NEWT_FLAG_RETURNEXIT"

When specified, the entry will cause the form to stop running if the user pressed return inside the entry box. Nice shortcut for users.

Checkboxes¶

Newt checkboxes are peculiar, since they may have more than two states. To create a normal one (checked or unchecked), do this:

    $check = Newt::Checkbox("Normal checkbox");

But you can create, for example, a checkbox that switches from not checked to checked with an asterisk and then to checked with an 'M':

    $check = Newt::Checkbox("Normal checkbox", " ", " *M");

As you can see, you can use the two optional parameters to tell the default char first and then the possible chars.

To know if a checkbox is checked after the for is ran, you use the following:

    print "Is checked\n" if $check->Checked();

And you can always get the actual state like this:

    $state = $check->Get();

Radio groups¶

You create two kinds of radio button groups, vertical and horizontal, by doing this:

    $radio_group1 = Newt::VRadiogroup('Red', 'Green', 'Blue');
    $radio_group2 = Newt::HRadiogroup('Red', 'Green', 'Blue');

You can put any number of options and the first one will always be preselected. To know the index of the selected option after the form has run, you do this:

    $index = $radio_group->Get();

Listboxes¶

Listboxes are the most complicated components Newt provides. They can allow single or multiple selection, and are easy to update. They are created as follows:

    $listbox = Newt::Listbox($height, $flags);

A listbox is created at a certain position and a given height. The $height is used for two things. First of all, it is the minimum height the listbox will use. If there are less items in the listbox then the height, suggests the listbox will still take up that minimum amount of space. Secondly, if the listbox is set to be scrollable (by setting the "NEWT_FLAG_SCROLL" flag, $height is also the maximum height of the listbox. If the listbox may not scroll, it increases its height to display all of its items.

The following flags may be used when creating a listbox:

"NEWT_FLAG_SCROLL"

The listbox should scroll to display all of the items it contains.

"NEWT_FLAG_RETURNEXIT"

When the user presses return on an item in the list, the form should return.

"NEWT_FLAG_BORDER"

A frame is drawn around the listbox, which can make it easier to see which listbox has the focus when a form contains multiple listboxes.

"NEWT_FLAG_MULTIPLE"

By default, a listbox only lets the user select one item in the list at a time. When this flag is specified, they may select multiple items from the list.

¶

Once a listbox has been created, items are appended to the bottom like this:

    $listbox->Append($item1, $item2, ...);

Appending is not the only way to add items to the list. You can insert items in any position by telling the item that should be before with the following command:

    $listbox->Insert($before, $item1, $item2, ...);

And you can change any item just by telling:

    $listbox->Set($original, $new);

Of course you can delete entries:

    $listbox->Delete($item1, $item2, ...);

Or just clear out the listbox:

    $listbox->Clear();

You can select and unselect items, with the following:

    $listbox->Select($item1, $item2, ...);
    $listbox->Unselect($item1, $item2, ...);
    $listbox->ClearSelection();

but if you did not sepecify the flag "NEWT_FLAG_MULTIPLE" when constructing your listbox, only the last item on the argument list of "Unselect()" will remain selected.

To get a list of the selected items, just issue:

    @selected_items = $listbox->Get();

Scales¶

Scales provide an easy way for telling the user the advance on some lengthy operation. It is a horizontal bar graph which the application updates as the operation continues:

    $scale = Newt::Scale($width, $fullvalue);

It is set as expected:

    $scale->Set($amount);

Textboxes¶

A text box is used for displaying large amounts of text. They are created as follows:

    $textbox = Newt::Textbox($width, $height, $flags, $text, ...);

The $text parameter is optional, and if not supplied, the textbox is created only, but it does not fill it with data. To do so, use:

    $textbox->Set($text, ...);

All the arguments are simply concatenated using the double quote operator.

The flags that can be passed to the constructor are the following:

"NEWT_FLAG_WRAP"

All text in the textbox should be wrapped to fit the width of the textbox. If this flag is not specified, each newline-delimited line in the text is truncated if it is too long to fit.

When Newt wraps text, it tries not to break lines on spaces or tabs. Literal newline characters are respected, and may be used to force line breaks.

"NEWT_FLAG_SCROLL"

The text should be scrollable. When this option is used, the scrollbar which is added increases the width of the area used by the textbox by 2 characters.

Reflowing text¶

When applications need to display large amounts of text, it is common not to know exactly where the linebreaks should go. While textboxes are quite willing to scroll the text, the programmer still must know what width the text will look ``best'' at (where ``best'' means most exactly rectangular; no lines much shorter or much longer then the rest). This common is specially prevalent in internationalized programs, which need to make a wide variety of message string look good on a screen.

To help with this, Newt provides routines to reformat text to look good. It tries different widths to figure out which one will look ``best'' to the user. As these commons are almost always used to format text for textbox components, Newt makes it easy to construct a textbox with reflowed text.

The following function reflows the provided text to a target width. the actual width of the longest line in the returned text is between "$width - $flexdown" and "$width + $flexup"; the actual maximum line length is chosen to make displayed text look rectangular. The function returns a tuple consisting of the reflowed text and the actual width and height of it.

    ($r_text, $width, $height) = Newt::ReflowText($width,
                                                  $flexdown,
                                                  $flexup,
                                                  $text);

When the reflowed text is being placed in a textbox it may be easier to use the following:

    $textbox = Newt::TextboxReflowed($width, $flexdown, 
                                     $flexup, $flags,
                                     $text, ...);

which creates a textbox, reflows the text, and places the reflowed text in the listbox. Its parameters consist of the position of the final textbox, the width and flex values for the text (which are identical to the parameters passed to "Newt::Reflow()", and the flags for the textbox (which are the same as the flags for "Newt::Textbox()". This function does not let you limit the height of the textbox, however, making limiting its use to constructing textboxes which do not need to scroll.

To find out how tall the textbox created by "Newt::TextboxReflowed()" is, use "Newt::GetNumLines()", which returns the number of lines in the textbox. For textboxes created by "Newt::TextboxReflowed()", this is always the same as the height of the textbox.

Please note that the order of the parameters of Newt::ReflowText and Newt::TextboxReflowed differs from the C API to allow lists of text but currently only TextboxReflowed allows this.

Scrollbars¶

Scrollbars may be attached to forms to let them contain more data than they have space for. Currently, there can only be vertical scrollbars:

    $scroll = Newt::VScrollbar($height, 
                               $normalColorset, 
                               $thumbColorset);

When a scrollbar is created, it is given a position on the screen, a height, and two colors. The first color is the color used for drawing the scrollbar, and the second color is used for drawing the thumb. This is the only place in newt where an application specifically sets colors for a component. It s done here to let the colors a scrollbar use match the colors of the component the scrollbar is mated too. When a scrollbar is being used with a form, $normalColorset is often "NEWT_COLORSET_WINDOW" and $thumbColorset "NEWT_COLORSET_ACTCHECKBOX".

If you do not want to bother with colors, you can omit the last two parameters and let Newt use the defaults.

As the scrollbar is normally updated by the component it is mated with, there is no public interface for moving the thumb.

Hotkeys¶

Normally, a panel terminates when the user presses a button, but you can define some keys as "hotkeys" that will make the "Run()" function return with "NEWT_EXIT_HOTKEY". Yo do this by issuing the folowing:

   $panel->AddHotKey(NEWT_KEY_F11);

F12 is always defined to be a hotkey.

Drawing panels instead of running them¶

When you run a panel the terminal is blocked until the user presses a component or a key that causes the panel to exit. Sometimes is useful to present the interface to the user without blocking the execution of code. This can be done by only drawing the panel, not running it. It is easy to show an advance status for a lengthy operation like this:

   $i = 1;
   foreach (@items) {
      $label->Set("Processing item $i");
      $panel->Draw();
      $scale->Set($i);
      process_item($_);
      $i++
   }

Hiding panels¶

Panels can be hidden in case you want by using the following:

    $panel->Hide()