插件如何增强Anki的JavaScript？

Question

Anki使卡片可以使用JavaScript.例如,卡片可以包含以下内容:

<script>
//JavaScript code here
</script>

并且当显示卡时将执行JavaScript代码.

为了通过启用此类脚本与Anki后端进行交互(例如,为了更改注释字段的值,添加标签,影响调度等),允许更多的灵活性,我想写一个插件-in for Anki(版本2),它将实现一些后端功能并使卡的JavaScript脚本能够调用它们.

例如,假设我的插件中有一个(Python)函数与Anki的对象进行交互:

def myFunc():
# use plug-in's ability to interact with Anki's objects to do stuff

我希望能够允许卡的JavaScript调用该功能,例如在卡中有这样的东西:

<script>
myFunc(); // This should invoke the plug-in's myFunc().
</script>

我知道如何添加钩子,以便各种Anki事件调用我的插件的功能,但我想允许卡内的JavaScript这样做.这可以完成,如果是这样,那么如何？谢谢!

Answer 1

读了后通过@Louis联系,并与一些同事讨论了这个问题,并四处乱尝试不同的东西出来,我终于成功地想出了一个解决方案:

这个想法可以归纳为这两个关键点(和两个子关键点):

• 插件可以创建一个或多个对象,这些对象将"暴露"到卡片的JavaScript脚本中,这样卡片脚本就可以访问这些对象 - 它们的字段和方法 - 就像它们是脚本范围的一部分一样.

  • 为了做到这一点,对象必须是特定类(或其子类)的实例,并且必须使用适当的PyQt装饰器声明要暴露给卡片脚本的每个方法和属性.

和

• PyQt提供了将这些对象"注入"webview的功能.

  • 插件必须确保每次Anki的审阅者的webview(重新)初始化时都会发生这种注入.

以下代码显示了如何实现此目的.它为卡片脚本提供了检查当前状态("问题"或"答案")的方法,并提供了一种访问(读取,更重要的是 - 写入)笔记字段的方法.

from aqt import mw              # Anki's main window object
from aqt import mw QObject      # Our exposed object will be an instance of a subclass of QObject.
from aqt import mw pyqtSlot     # a decorator for exposed methods
from aqt import mw pyqtProperty # a decorator for exposed properties

from anki.hooks import wrap     # We will need this to hook to specific Anki functions in order to make sure the injection happens in time.

# a class whose instance(s) we can expose to card scripts
class CardScriptObject(QObject):
    # some "private" fields - card scripts cannot access these directly 
    _state = None
    _card = None
    _note = None

    # Using pyqtProperty we create a property accessible from the card script.
    # We have to provide the type of the property (in this case str).
    # The second argument is a getter method.
    # This property is read-only. To make it writeable we would add a setter method as a third argument.
    state = pyqtProperty(str, lambda self: self._state)

    # The following methods are exposed to the card script owing to the pyqtSlot decorator.
    # Without it they would be "private".
    @pyqtSlot(str, result = str) # We have to provide the argument type(s) (excluding self),
                                 # as well as the type of the return value - with the named result argument, if a value is to be returned.
    def getField(self, name):
        return self._note[name]

    # Another method, without a return value:
    @pyqtSlot(str, str)
    def setField(self, name, value):
        self._note[name] = value
        self._note.flush()

    # An example of a method that can be invoked with two different signatures -
    # pyqtSlot has to be used for each possible signature:
    # (This method replaces the above two.
    # All three have been included here for the sake of the example.)
    @pyqtSlot(str, result = str)
    @pyqtSlot(str, str)
    def field(self, name, value = None): # sets a field if value given, gets a field otherwise
        if value is None: return self._note[name]
        self._note[name] = value
        self._note.flush()

cardScriptObject = CardScriptObject() # the object to expose to card scripts
flag = None # This flag is used in the injection process, which follows.

# This is a hook to Anki's reviewer's _initWeb method.
# It lets the plug-in know the reviewer's webview is being initialised.
# (It would be too early to perform the injection here, as this method is called before the webview is initialised.
# And it would be too late to do it after _initWeb, as the first card would have already been shown.
# Hence this mechanism.)
def _initWeb():
    global flag
    flag = True

# This is a hook to Anki's reviewer's _showQuestion method.
# It populates our cardScriptObject's "private" fields with the relevant values,
# and more importantly, it exposes ("injects") the object to the webview's JavaScript scope -
# but only if this is the first card since the last initialisation, otherwise the object is already exposed.
def _showQuestion():
    global cardScriptObject, flag
    if flag:
        flag = False
        # The following line does the injection.
        # In this example our cardScriptObject will be accessible from card scripts
        # using the name pluginObject.
        mw.web.page().mainFrame().addToJavaScriptWindowObject("pluginObject", cardScriptObject)
    cardScriptObject._state = "question"
    cardScriptObject._card = mw.reviewer.card
    cardScriptObject._note = mw.reviewer.card.note()

# The following hook to Anki's reviewer's _showAnswer is not necessary for the injection,
# but in this example it serves to update the state.
def _showAnswer():
    global cardScriptObject
    cardScriptObject._state = "answer"

# adding our hooks
# In order to already have our object injected when the first card is shown (so that its scripts can "enjoy" this plug-in),
# and in order for the card scripts to have access to up-to-date information,
# our hooks must be executed _before_ the relevant Anki methods.
mw.reviewer._initWeb = wrap(mw.reviewer._initWeb, _initWeb, "before")
mw.reviewer._showQuestion = wrap(mw.reviewer._showQuestion, _showQuestion, "before")
mw.reviewer._showAnswer = wrap(mw.reviewer._showAnswer, _showAnswer, "before")

就是这个!安装了这样的插件后,来自卡内的JavaScript脚本可以使用pluginObject.state来检查它是作为问题的一部分运行还是作为答案的一部分运行(也可以通过将问题部分包装在答案模板中来实现)使用设置变量的脚本,但这是更整洁的),pluginObject.field(name)从注释中获取字段的值(也可以通过使用Anki的预处理器将字段直接注入JavaScript代码来实现)和pluginObject.field(name,value)来设置注释中字段的值(据我所知,到目前为止还无法完成).当然,许多其他功能可以编程到我们的CardScriptObject中,以允许卡脚本执行更多操作(读取/更改配置,实现另一个问题/答案机制,与调度程序交互等).

如果有人能提出改进建议,我有兴趣听听.具体来说,我感兴趣的是:

• 是否有更简洁的方法来公开方法和属性,以便提供更多的签名灵活性; 和
• 是否有一种不那么麻烦的方式来进行注射.