使用 JsonStore 在 kivy android 中保存变量

Question

我想在 kivy 中为 android 应用程序保存一个变量（label.text），当应用程序重新启动时，它应该将变量加载回 label.text。

我尝试使用JsonStore来保存变量https://kivy.org/docs/api-kivy.storage.html#

有没有更好的方法来保存变量？

但是当我运行代码时出现以下错误：

ValueError: 无法解码 JSON 对象

这是我的 ma​​in.py 文件：

from kivy.app import App
from kivy.storage.jsonstore import JsonStore
from kivy.uix.boxlayout import BoxLayout
from kivy.core.window import Window


class Test(BoxLayout):
    Window.clearcolor = (1, 1, 1, 1)
    def save(self):
        store = JsonStore('hello.json')
        store.put('tito', score=label.text)

class MyApp(App):
    def build(self):
        return Test()
    def on_start(self):
        store = JsonStore('hello.json')
        label.text = store.get('tito')['score']


if __name__ == '__main__':
    MyApp().run()

这是我的 my.kv 文件：

<Test>:
    orientation: "vertical"
    BoxLayout:
        Label:
            id: label
            text: '0'
            color: 0,0,0,1
            pos: 250,200
            size: 50,50
            font_size:30
        Button:
            text: 'save'
            on_release: root.save()
        Button:
            text: 'load'
            on_release:

    Button:
        size_hint: 1, .5
        text: 'click me'
        on_press: label.text = str(int(label.text)+1)

这里是完整的错误信息：

 Traceback (most recent call last):
   File "main.py", line 25, in <module>
     MyApp().run()
   File "/usr/lib/python2.7/dist-packages/kivy/app.py", line 823, in run
     self.dispatch('on_start')
   File "kivy/_event.pyx", line 699, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:7394)
   File "main.py", line 20, in on_start
     store = JsonStore('hello.json')
   File "/usr/lib/python2.7/dist-packages/kivy/storage/jsonstore.py", line 25, in __init__
     super(JsonStore, self).__init__(**kwargs)
   File "/usr/lib/python2.7/dist-packages/kivy/storage/__init__.py", line 133, in __init__
     self.store_load()
   File "/usr/lib/python2.7/dist-packages/kivy/storage/jsonstore.py", line 34, in store_load
     self._data = loads(data)
   File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
     return _default_decoder.decode(s)
   File "/usr/lib/python2.7/json/decoder.py", line 364, in decode
     obj, end = self.raw_decode(s, idx=_w(s, 0).end())
   File "/usr/lib/python2.7/json/decoder.py", line 382, in raw_decode
     raise ValueError("No JSON object could be decoded")
 ValueError: No JSON object could be decoded

提前致谢

Answer 1

错误有点笼统，但您的 JSON 似乎无效。您的 JSON 应该类似于：

{"tito": {"score": "3"}}

您可以在Test 类中使用__init__ 方法在启动时加载Json，我认为在这种情况下它比使用on_start 方法最简单。

另一方面，您需要先测试 JSON 文件和密钥是否存在，然后再尝试获取它。否则，您可以提出 KeyError 异常。你可以使用 try-except 。

from kivy.app import App
from kivy.storage.jsonstore import JsonStore
from kivy.uix.boxlayout import BoxLayout
from kivy.core.window import Window
from kivy.lang import Builder
from kivy.properties import ObjectProperty

kv_text = '''\
<Test>:
    orientation: "vertical"
    label: label
    BoxLayout:
        Label:
            id: label
            text: '0'
            color: 0,0,0,1
            pos: 250,200
            size: 50,50
            font_size:30
        Button:
            text: 'save'
            on_release: root.save()
        Button:
            text: 'load'
            on_release: root.load()

    Button:
        size_hint: 1, .5
        text: 'click me'
        on_press: label.text = str(int(label.text)+1)
'''

class Test(BoxLayout):
    label = ObjectProperty()
    Window.clearcolor = (1, 1, 1, 1)

    def __init__(self, **kwargs):
        super(Test,  self).__init__(**kwargs)
        self.store = JsonStore('hello.json')
        self.load()

    def save(self):
        self.store.put('tito', score= self.label.text)

    def load(self):
        try:
            self.label.text = self.store.get('tito')['score']
        except KeyError:
            pass


class MyApp(App):
    def build(self):
        Builder.load_string(kv_text)
        return Test()


if __name__ == '__main__':
    MyApp().run()