Can 'Shelve' and 'dbm' not be used in Android?

[jlij]

Does Toga have its own caching API？

[jlij]

I tried using JSON, but it was not successful.

[freakboy3742]

No, Toga doesn't have a caching API. Toga is a GUI framework; it leaves tasks that aren't related to GUIs, or device hardware related to GUIs (such as GPS), to other libraries.

And yes - you can use shelve, dbm, JSON, SQLite, or any other builtin data storage library with a Beeware/Toga app on Android. If you're having difficulties, the issue is almost certainly the specification of the filesystem location that you're attempting to use to save the file; however, without details, we can't provide any advice on how to fix problems that you may be having.

[jlij]

E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testoga/org.beeware.android.MainActivity}: com.chaquo.python.PyException: OSError: [Errno 30] Read-only file system: b'mydata.db.dat'

import toga
import shelve
from toga.style import Pack
from toga.style.pack import COLUMN, ROW

class testoga(toga.App):

def shelve_test(self):
    with shelve.open('mydata.db') as db:
        # 存储一个字典
        db['user'] = {'name': 'Alice', 'age': 30}

def startup(self):
    self.shelve_test()
    main_box = toga.Box()
    self.main_window = toga.MainWindow(title=self.formal_name)
    self.main_window.content = main_box
    self.main_window.show()

def main():
return testoga()

[freakboy3742]

As I indicated, the issue is filesystem location. You're specifying a file of mydata.db. That is a relative file location, and as a result, Python will assume the file is in your current working directory. On Android, your current working directory is not a writable location.

You need to specify a writeable file system location, preferably as an absolute path. Since this is a Toga app, the file self.paths.app.data / "mydata.db" will give you a writable location, although you may need to call self.paths.app.data.mkdir(exist_ok=True, parents=True) first to ensure that the directory has been created.

[jlij]

Can you give me some examples?

[freakboy3742]

I have given you an example. Instead of calling:

with shelve.open('mydata.db'):
    ...

call:

self.paths.data.mkdir(exist_ok=True, parents=True)
with shelve.open(self.paths.data / "mydata.db"):
    ...

[jlij]

Please forgive my foolishness, it did not materialize, please help me correct it.

import toga
import shelve
from toga import paths

class testoga(toga.App):

def test_path(self):
    paths.Paths.app.mkdir(exist_ok=True, parents=True)
    with shelve.open(paths.Paths.app.data / "mydata.db") as db:
        db['key1'] = b'This is a value'

        value = db['key1']
        print(value)

def startup(self):
    self.test_path()
    main_box = toga.Box()
    self.main_window = toga.MainWindow(title=self.formal_name)
    self.main_window.content = main_box
    self.main_window.show()

def main():
return testoga()

[freakboy3742]

I can't fix problems if you don't tell me what error you're seeing.

However, as a first guess - the code you've presented isn't what I told you to write. The example code I gave you uses self.paths, not path.Paths. I'll admit there's also a typo in the code that I provided; I've corrected that typo.

[jlij]

Thank you very much for your patient guidance

[jlij]

--------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
E/AndroidRuntime: Process: com.example.testoga, PID: 10803
E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testoga/org.beeware.android.MainActivity}: com.chaquo.python.PyException: OSError: [Errno 30] Read-only file system: b'mydb.dbm.dat'

import toga
import dbm
from toga.style import Pack
from toga.style.pack import COLUMN, ROW

class testoga(toga.App):

with dbm.open('mydb.dbm', 'c') as db:
    # 存储数据
    db['key1'] = b'This is a value'

    value = db['key1']
    print(value)

def startup(self):
    main_box = toga.Box()
    self.main_window = toga.MainWindow(title=self.formal_name)
    self.main_window.content = main_box
    self.main_window.show()

def main():
return testoga()