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# persistentSelection(n) 1.0 tklib "Enhanced PRIMARY selection"

## Name

persistentSelection - Enhanced PRIMARY selection

## Synopsis

- package require Tcl 8.5
- package require Tk 8.5
- package require persistentSelection ?1.0?

- persistentSelection::fixText
- persistentSelection::getClassicPrimarySel ?displayOf? ?withOthers?
- persistentSelection::getPrimarySel ?displayOf?
- persistentSelection::report type pathName

## Description

Consider a Tk widget that sets its -exportselection option to boolean true, thereby exporting its selection. When the selection in the widget is canceled, by default Tk also cancels the PRIMARY selection. In this situation, an attempt to read the PRIMARY selection, e.g. by a <<PasteSelection>> event, will fail.

The persistentSelection package offers more convenient behavior. It will sustain as the PRIMARY selection the last non-empty value set by any Tk widget that it monitors, as long as the PRIMARY selection is not claimed by another process, or by a widget that it does not monitor.

The persistentSelection package works by binding to the <<Selection>> event on the widgets of interest, and using this binding to monitor any change of the selection in the widget. Its commands are confined to the namespace ::persistentSelection.

## COMMANDS

persistentSelection::fixText

  Call this command once to resolve problems with text widgets that use the default Text bindtag (rather than Ntext). See Text widgets for an explanation.

  The command adjusts some Text bindings to generate <<Selection>> events; and it re-orders calls to the text widget tag command in the private command ::tk::TextSelectTo, so that this command cooperates better with persistentSelection.

  These adjustments are needed only to older versions of Tk. The command persistentSelection::fixText has no effect on sufficiently recent releases. It can safely be called for any version of Tk.

persistentSelection::getClassicPrimarySel ?displayOf? ?withOthers?

  - displayOf - a Tk window path on the display to be interrogated (optional, default {.})

  - withOthers - whether to return the PRIMARY selection if it is owned by another process or interpreter (optional, boolean, default false)

  A command to return the classic (non-persistent) form of the PRIMARY selection. If the selection does not exist, or is sustained only by persistentSelection, the command returns the empty string.

persistentSelection::getPrimarySel ?displayOf?

  - displayOf - a Tk window on the display to be interrogated (optional, default {.})

  A command to return the value of the PRIMARY selection. If the selection does not exist, the command returns the empty string. The usual Tk commands are perfectly valid, but they raise an error if the selection does not exist.

persistentSelection::report type pathName

  - type - (value text or entry) classification of the widget whose selection has changed

  - pathName - the Tk window path of the widget whose selection has changed

  To make package persistentSelection monitor a widget, this command must be bound to the <<Selection>> event on that widget. The command records changes in the widget's selection, and uses the information to sustain a non-empty PRIMARY selection on each display.

## USAGE

### Script requirements

For each widget that will be monitored by persistentSelection, the command persistentSelection::report must be bound to event <<Selection>> in one of the widget's binding tags.

For example, the developer may wish to use persistentSelection with every text and entryPlus widget in an application: this can be achieved by adding the <<Selection>> binding to the Text and EntryPlus bindtags. See EXAMPLES.

If persistentSelection is not required for all widgets of a particular class, the binding can be added to per-widget bindtags. See EXAMPLES.

### Widget requirements

To be capable of being monitored by persistentSelection, a widget must satisfy three conditions:

- It must have an -exportselection option that allows it to export its selection to the PRIMARY selection.

- It must generate a <<Selection>> event whenever its selection changes.

- its bindings to other events should be suitable - specifically, in versions of Tk older than 8.6.6, a GUI event that extends or reduces the selection from one non-empty value to another should not use an intermediate state that has an empty selection, because this confuses persistentStore.

The Tk and Ttk widgets that can export their selection are text, entry, listbox, spinbox, ttk::entry, ttk::spinbox, and ttk::combobox.

### Text widgets

In versions of Tk older than 8.6.9, the text widget does not generate <<Selection>> events in a few "corner cases" in which its selection changes. These omissions can be corrected by changes to the Text bindings, in order to satisfy the second condition of Widget requirements.

In addition, versions of Tk older than 8.6.6 process selection events slightly differently from newer versions, and in combination with the Text bindings this confuses persistentStore. If an upgrade to the current version of Tcl/Tk is not feasible, this problem can be resolved by making a slight modification to the widget bindings, in order to satisfy the third condition of Widget requirements.

Either the script should call the command persistentSelection::fixText to adjust the Text bindings and the commands that they call; or the widget can use the Ntext binding tag (for ntext version 1.0 or above) instead of the default Text bindtag.

In either case, the argument type supplied to command persistentSelection::report should have the value text.

### Entry, spinbox, ttk::entry, ttk::spinbox, and ttk::combobox widgets

The entry, spinbox, ttk::entry, ttk::spinbox, and ttk::combobox widgets do not generate a <<Selection>> event when their selection changes, and therefore require modification.

The package widgetPlus provides snit wrappers widgetPlus::entryPlus, widgetPlus::spinboxPlus, widgetPlus::ttkEntryPlus, widgetPlus::ttkSpinboxPlus, and widgetPlus::ttkComboboxPlus respectively. Each widgetPlus widget generates the required <<Selection>> events.

In all these cases, the argument type supplied to command persistentSelection::report should have the value entry. This argument determines how persistentSelection will inspect the widget's selection, and the commands that do so are the same for all these widgets.

### Listbox widgets

A similar wrapper has not been created for the listbox widget, which has the complication of permitting multiple selections.

## TO DO

- Test on a system with multiple displays.

## BUGS

This version of persistentSelection is intended to be compatible with all releases of Tk 8.5- and 8.6, and with the branches core-8-5-branch, core-8-6-branch, revised_text, and trunk in the source code repository for Tk. Any incompatibility with any of these versions, for any Tk windowing system, should be reported as a bug. Please report such in the category persistentSelection of the Tklib Trackers.

## EXAMPLES

Each example uses persistentSelection to retain the last non-empty value of the selection in certain widgets. Each example also includes the creation of sample widgets.

Monitor all entryPlus widgets.

    package require widgetPlus
    widgetPlus::entryPlus .ep
    pack .ep
    package require persistentSelection
    bind EntryPlus <<Selection>> {::persistentSelection::report entry %W}

Monitor all text widgets that use the default Text bindings.

    text .t
    pack .t
    package require persistentSelection
    ::persistentSelection::fixText
    bind Text <<Selection>> {::persistentSelection::report text %W}

Monitor all text widgets that use the default Text bindings, and all entryPlus widgets.

    text .t
    pack .t
    package require widgetPlus
    widgetPlus::entryPlus .ep
    pack .ep
    package require persistentSelection
    ::persistentSelection::fixText
    bind Text <<Selection>> {::persistentSelection::report text %W}
    bind EntryPlus <<Selection>> {::persistentSelection::report entry %W}

Monitor all text widgets that use Ntext bindings.

    text .t
    pack .t
    package require ntext
    bindtags .t {.t Ntext . all}
    package require persistentSelection
    bind Ntext <<Selection>> {::persistentSelection::report text %W}

Monitor a single entryPlus widget .ep

    package require widgetPlus
    widgetPlus::entryPlus .ep
    pack .ep
    package require persistentSelection
    bind .ep <<Selection>> {::persistentSelection::report entry %W}

Monitor a single text widget .t

    text .t
    pack .t
    package require persistentSelection
    bind .t <<Selection>> {::persistentSelection::report text %W}

## See Also

bindtags, ntext, text, widgetPlus