Writing Plugins
Plugins modify how Leo works. With plugins you can give Leo new commands, modify how existing commands work, or change any other aspect of Leo's look and feel.
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Plugins can use any of Leo's source code simply by accessing the g global module.
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Plugins can register event handlers just like any other Leo script. For full details, see the section called Handling Events later in this chapter.
The rest of this chapters discusses topics related specifically to plugins.
How to create a plugin
A LeoJS plugin is a VSCode Extensions that uses the API LeoJS exposes.
See the LeoJS Access Sample Extension for more information on how to create a plugin for LeoJS. This sample extension shows how to access and use LeoJS from another extension through its exposed instance of the leoGlobals 'g' object:
const extension = vscode.extensions.getExtension('boltex.leojs');
const g = await extension.activate();
c ivars & properties
For any commander c:
| Property | Value |
|---|---|
| c.p | the presently selected position |
| c.frame | the leoFrame representing the main window. |
| c.frame.body | a NullBody representing the body pane. |
| c.frame.body.wrapper | a StringTextWrapper. |
| c.frame.tree | a NullTree, representing the tree pane |
| c.user_dict | a dictionary for use by scripts and plugins. Does not persist when Leo exists. |
Handling events
Plugins and other scripts can register event handlers (also known as hooks):
g.registerHandler("after-create-leo-frame", onCreate)
g.registerHandler("idle", on_idle)
g.registerHandler(("start2", "open2", "command2"), create_open_with_menu)
As shown above, a plugin may register one or more event handlers with a single call to g.registerHandler. Once a hook is registered, Leo will call the registered function' at the named hook time. For example:
g.registerHandler("idle", on_idle)
causes Leo to call on_idle at "idle" time.
Event handlers must have the following signature:
function myHook (tag: string, keywords: Record<string, any>): any {
// whatever
}
- tag is the name of the hook (a string).
- keywords is a dictionary containing additional information. The following section describes the contents of the keywords dictionary in detail.
Summary of event handlers
The following table tells about each event handler: its name, when it is called, and the additional arguments passed to the hook in the keywords dictionary.
📌 NOTE
For some kind of hooks, Leo will skip its own normal processing if the hook returns anything other than None. The table indicates such hooks with 🛑 in the Stop? column.
| Event name | Stop? | When | Keys in keywords dict |
|---|---|---|---|
| 'after-auto' | after each @auto file loaded | c,p (note 5) | |
| 'after-create-leo-frame' | after creating any frame | c | |
| 'after-redraw-outline' | end of tree.redraw | c (note 4) | |
| 'after-reading-external-file' | after reading each external file | c,p | |
| 'after-reload-settings' | after 'reload-settings' command | c | |
| 'before-create-leo-frame' | before frame.finishCreate | c | |
| 'before-writing-external-file' | before writing each external file | c,p | |
| 'bodykey1' | 🛑 | before body keystrokes | c,p,v,ch,oldSel,undoType |
| 'bodykey2' | after body keystrokes | c,p,v,ch,oldSel,undoType | |
| 'clear-all-marks' | after clear-all-marks command | c,p,v | |
| 'clear-mark' | when mark is set | c,p,v | |
| 'close-frame' | in app.closeLeoWindow | c (note 3) | |
| 'command1' | 🛑 | before each command | c,p,v,label (note 1) |
| 'command2' | after each command | c,p,v,label (note 1) | |
| 'end1' | start of app.quit() | None | |
| 'headclick1' | 🛑 | before normal click in headline | c,p,v,event |
| 'headclick2' | after normal click in headline | c,p,v,event | |
| 'headkey1' | 🛑 | before headline keystrokes | c,p,v,ch (note 4) |
| 'headkey2' | after headline keystrokes | c,p,v,ch (note 4) | |
| 'hoist-changed' | whenever the hoist stack changes | c | |
| 'idle' | periodically (at idle time) | c | |
| 'new' | start of New command | c,old_c | |
| 'open1' | 🛑 | before opening any file | c,old_c,fileName (note 2) |
| 'open2' | after opening any file | c,old_c,fileName (note 2) | |
| 'openwith1' | 🛑 | before Open With command | c,p,v,d (note 6) |
| 'openwith2' | after Open With command | c,p,v,(note 6) | |
| 'recentfiles1' | 🛑 | before Recent Files command | c,p,v,fileName |
| 'recentfiles2' | after Recent Files command | c,p,v,fileName | |
| 'save1' | 🛑 | before any Save command | c,p,v,fileName |
| 'save2' | after any Save command | c,p,v,fileName | |
| 'select1' | 🛑 | before selecting a position | c,new_p,old_p |
| 'select2' | after selecting a position | c,new_p,old_p | |
| 'select3' | after selecting a position | c,new_p,old_p | |
| 'set-mark' | when a mark is set | c,p,v | |
| 'start1' | after app.finishCreate() | None | |
| 'start2' | after opening first Leo window | c,p,v,fileName | |
| 'unselect1' | 🛑 | before unselecting a vnode | c,new_p,old_p |
| 'unselect2' | after unselecting a vnode | c,new_p,old_p | |
| '@url1' | 🛑 | before double-click @url node | c,p,url |
| '@url2' | after double-click @url node | c,p |
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'commands' hooks: The label entry in the keywords dict contains the 'canonicalized' form of the command, that is, the lowercase name of the command with all non-alphabetic characters removed.
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'open1' and 'open2' hooks: These are called with a keywords dict containing the following entries:
- c: The commander of the newly opened window.
- old_c: The commander of the previously open window.
- new_c: (deprecated: use 'c' instead) The commander of the newly opened window.
- fileName: The name of the file being opened.
You can use old_c.p and c.p to get the current position in the old and new windows. Leo calls the 'open1' and 'open2' hooks only if the file is not already open. Leo will also call the 'open1' and 'open2' hooks if: a) a file is opened using the Recent Files menu and b) the file is not already open.
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g.app.closeLeoWindow calls the 'close-frame' hook just before removing the window from g.app.windowList. The hook code may remove the window from app.windowList to prevent g.app.closeLeoWindow from destroying the window.
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Leo calls the 'headkey1' and 'headkey2' when the headline has actually changed.
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p is the new node (position) containing '@auto filename.ext'
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The d argument to the open-with event handlers is a dictionary whose keys are all the tags specified by the user in the body of the @openwith node.