Question

我正在为BackAndroid添加一个新的监听器：

componentWillMount () {
  BackAndroid.addEventListener('hardwareBackPress', backAndroidHandler.bind(this));
}

我正在删除侦听器：

componentWillUnmount () {
  BackAndroid.removeEventListener('hardwareBackPress', backAndroidHandler);
}

function backAndroidHandler () {
  ...
}

但是当我卸载组件并再次安装它时，有两个相同的功能，同一个事件会触发两次。任何线索？

Answer 1

修正了它

componentWillMount () {
  this.androidBackHandler = backAndroidHandler.bind(this);
  BackAndroid.addEventListener('hardwareBackPress', this.backAndroidHandler);
}

componentWillUnmount () {
  BackAndroid.removeEventListener('hardwareBackPress', this.androidBackHandler);
}


function backAndroidHandler () {
  ...
}

我尝试直接在组件上声明函数，但this没有绑定，它是undefined

Answer 2

class DocStringInheritor(type):
    """
    A variation on
    http://groups.google.com/group/comp.lang.python/msg/26f7b4fcb4d66c95
    by Paul McGuire
    """
    def __new__(meta, name, bases, clsdict):
        if not('__doc__' in clsdict and clsdict['__doc__']):
            for mro_cls in (mro_cls for base in bases for mro_cls in base.mro()):
                doc=mro_cls.__doc__
                if doc:
                    clsdict['__doc__']=doc
                    break
        for attr, attribute in clsdict.items():
            if not attribute.__doc__:
                for mro_cls in (mro_cls for base in bases for mro_cls in base.mro()
                                if hasattr(mro_cls, attr)):
                    doc=getattr(getattr(mro_cls,attr),'__doc__')
                    if doc:
                        if isinstance(attribute, property):
                            clsdict[attr] = property(attribute.fget, attribute.fset, attribute.fdel, doc)
                        else:
                            attribute.__doc__=doc
                        break
        return type.__new__(meta, name, bases, clsdict)


class X(object):
    __metaclass__ = DocStringInheritor

    """
    some doc
    """
    x = 20

    def please_implement(self):
        """
        I have a very thorough documentation
        :return:
        """
        raise NotImplementedError

    @property
    def speed(self):
        """
        Current speed in knots/hour.
        :return:
        """
        return 0

    @speed.setter
    def speed(self, value):
        """

        :param value:
        :return:
        """
        pass

class SpecialX(X):

    def please_implement(self):
        return True

    @property
    def speed(self):
        return 10

    @speed.setter
    def speed(self, value):
        self.sp = value


class VerySpecial(X):
    p = 0
    """doc"""

    def please_implement(self):
        """

        :return bool: Always false.
        """
        return False

    def not_inherited(self):
        """
        Look at all these words!
        :return:
        """

help(X.speed)
help(SpecialX.speed)
help(SpecialX.please_implement)
help(VerySpecial.please_implement)
help(VerySpecial.not_inherited)

应该是这样的。

React Native BackAndroid不会删除侦听器

2 个答案: