Fired when the browser has shown a menu.
An extension can use this event to update its menu items using information that's only available once the menu is shown. Typically an extension will figure out the update in its
onShown
handler and then call
menus.refresh()
to update the menu itself.
The handler can add, remove, or update menu items.
例如，
menu-labelled-open
example extension adds a menu item that's shown when the user clicks a link, and that, when clicked, just opens the link. It uses
onShown
and
refresh()
to annotate the menu item with the hostname for the link, so the user can easily see where they will go before they click.
Note that an extension should not take too much time before calling
refresh()
, or the update will be noticeable to the user.
The handler is passed some information about the menu and its contents, and some information from the page (such as the link and/or selection text). To get access to the information from the page, your extension must have the host permission for it.
若
onShown
handler calls any asynchronous APIs, then it's possible that the menu has been closed again before the handler resumes execution. Because of this, if a handler calls any asynchronous APIs, it should check that the menu is still being displayed before it updates the menu. For example:
var lastMenuInstanceId = 0;
var nextMenuInstanceId = 1;
browser.menus.onShown.addListener(async function(info, tab) {
var menuInstanceId = nextMenuInstanceId++;
lastMenuInstanceId = menuInstanceId;
// Call an async function
await .... ;
// After completing the async operation, check whether the menu is still shown.
if (menuInstanceId !== lastMenuInstanceId) {
return; // Menu was closed and shown again.
}
// Now use menus.create/update + menus.refresh.
});
browser.menus.onHidden.addListener(function() {
lastMenuInstanceId = 0;
});
Note that it is possible to call menus API functions synchronously, and in this case you don't have to perform this check:
browser.menus.onShown.addListener(async function(info, tab) {
browser.menus.update(menuId, ...);
// Note: Not waiting for returned promise.
browser.menus.refresh();
});
However, if you call these APIs asynchronously, then you do have to perform the check:
browser.menus.onShown.addListener(async function(info, tab) {
var menuInstanceId = nextMenuInstanceId++;
lastMenuInstanceId = menuInstanceId;
await browser.menus.update(menuId, ...);
// must now perform the check
if (menuInstanceId !== lastMenuInstanceId) {
return;
}
browser.menus.refresh();
});
Firefox makes this event available via the
contextMenus
namespace as well as the
menus
名称空间。
browser.menus.onShown.addListener(listener)
浏览器
.
menus
.
onShown
.
removeListener
(
listener
)
浏览器
.
menus
.
onShown
.
hasListener
(
listener
)
Events have three functions:
addListener(listener)
Adds a listener to this event.
removeListener(listener)
Stop listening to this event. The
listener
argument is the listener to remove.
hasListener(listener)
校验是否
listener
is registered for this event. Returns
true
if it is listening,
false
否则。
callback
Function that will be called when this event occurs. The function will be passed the following arguments:
info
对象
. This is just like the
menus.OnClickData
object, except it contains two extra properties:
上下文
: an array of all the
上下文
that are applicable to this menu.
menuIds
: an array of IDs of all menu items belonging to this extension that are being shown in this menu.
Compared with
menus.OnClickData
，
info
object also omits the
menuItemId
and
modifiers
properties, because of course these are not available until a menu item has been selected.
上下文
,
menuIds
,
frameId
，和
editable
properties are always provided. All the other properties in
info
are only provided if the extension has the
host permission
为页面。
tab
tabs.Tab
. The details of the tab where the click took place. If the click did not take place in or on a tab, this parameter will be missing.
BCD tables only load in the browser
This example listens for the context menu to be shown over a link, then updates the
openLabelledId
menu item with the link's hostname:
function updateMenuItem(linkHostname) {
browser.menus.update(openLabelledId, {
title: `Open (${linkHostname})`
});
browser.menus.refresh();
}
browser.menus.onShown.addListener(info => {
if (!info.linkUrl) {
return;
}
let linkElement = document.createElement("a");
linkElement.href = info.linkUrl;
updateMenuItem(linkElement.hostname);
});
最后修改： , 由 MDN 贡献者