插件如何增强Anki的JavaScript？

Question

Anki允许卡片使用JavaScript。例如，一张卡片可以包含如下内容：

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

当显示卡时，JavaScript代码将被执行。

为了允许这种脚本与Anki后端交互(例如，为了更改便笺字段的值、添加标记、影响调度等等)，我想为Anki编写一个插件(版本2)，它将实现一些后端函数，并使卡片的JavaScript脚本能够调用它们。

例如，假设我的插件中有一个(Python)函数，它与Anki的对象交互：

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

我希望允许卡片的JavaScript调用该函数，例如，在卡片中有这样的东西：

<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事件调用我的插件函数，但我希望允许卡内的JavaScript这样做。这一切都能做到吗?如果是的话，那怎么做呢？谢谢!

Answer 1

在阅读了由@Louis链接的帖子，并与一些同事讨论了这个问题，并尝试了各种不同的事情之后，我终于想出了一个解决方案：

这个想法可以概括在以下两个要点(和两个子关键点)：

• 插件可以创建一个或多个对象，这些对象将被“公开”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--就好像它们是脚本范围的一部分一样。

- in order to do it the objects must be instances of a specific class (or subclass thereof), and each method and property that is to be exposed to card scripts must be declared as such with a proper PyQt decorator.

​

和

• PyQt提供了将这些对象“注入”到the视图的功能。

- The plug-in has to ensure this injection occurs every time Anki's reviewer's webview is (re-)initialised.

​

下面的代码显示了如何实现这一点。它为卡片脚本提供了一种检查当前状态的方法(“问题”或“答案”)，以及访问(读，更重要的是写)便条字段的方法。

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!安装了这样一个插件后，卡内的JavaScript脚本可以使用pluginObject.state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(也可以通过使用设置变量的脚本在答案模板中包装问题部分来实现，但这更整洁)，pluginObject.field(名称)从备注中获得字段的值(也可以通过使用Anki的预处理器将字段直接注入JavaScript代码)和pluginObject.field(名称、值)来设置注释中字段的值(直到现在才能完成，据我所知)。当然，许多其他功能可以被编程到我们的CardScriptObject中，以允许卡片脚本做更多的事情(读取/更改配置、实现另一种问答机制、与调度程序交互等等)。

如果有人能提出改进的话，我很想听听。具体来说，我感兴趣的是：

• 有否更清晰的方法公开方法和属性，使签名更具灵活性；及
• 是否有一种不那么麻烦的方法来执行注入。