Android Label widget can't be used on API 28 or earlier

[freakboy3742]

Describe the bug

The Android Label widget references the LineBreaker class, which wasn't added until API level 29 (Android 10).

If you try to launch an app that uses label on Android 9 or earlier, the app will crash.

Steps to reproduce

1. Launch any Android ap that uses toga.Label
2. See error

(logs provided below)

Expected behavior

The gradle project specifies an API minimum of 21 (5); Toga should adhere to the same minimum.

Screenshots

No response

Environment

• Operating System: Android 8.1
• Python version: Any
• Software versions:
  • Briefcase: 0.3.14
  • Toga: 0.3.1

Logs

04-17 15:29:56.737  6976  6976 E AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.keith_magee.traveltips/org.beeware.android.MainActivity}: com.chaquo.python.PyException: java.lang.NoClassDefFoundError: android.graphics.text.LineBreaker
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2805)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2883)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.ActivityThread.-wrap11(Unknown Source:0)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1613)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:106)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:164)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:6523)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:857)
04-17 15:29:56.737  6976  6976 E AndroidRuntime: Caused by: com.chaquo.python.PyException: java.lang.NoClassDefFoundError: android.graphics.text.LineBreaker
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at com.chaquo.python.PyObject.callAttr(PyObject.java:225)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at org.beeware.android.MainActivity.onCreate(MainActivity.java:85)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.Activity.performCreate(Activity.java:7023)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.Activity.performCreate(Activity.java:7014)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2758)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        ... 9 more
04-17 15:29:56.737  6976  6976 E AndroidRuntime: Caused by: java.lang.NoClassDefFoundError: android.graphics.text.LineBreaker
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at java.lang.Class.classForName(Native Method)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at java.lang.Class.forName(Class.java:453)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.CQPEnv.FindClass(env.pxi:63)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.JavaClass.__new__(class.pxi:79)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.new_class(class.pxi:67)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.jclass(class.pxi:59)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.jclass(class.pxi:53)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.jclass(class.pxi:34)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.toga_android.libs.android.graphics.<module>(graphics.py:17)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.import_override(import.pxi:26)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.toga_android.app.<module>(app.py:9)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.chaquopy.import_override(import.pxi:26)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.toga_android.factory.<module>(factory.py:2)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib._bootstrap._call_with_frames_removed(<frozen importlib._bootstrap>:241)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib._bootstrap_external.exec_module(<frozen importlib._bootstrap_external>:883)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.android.importer.exec_module(importer.py:554)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.java.android.importer.exec_module(importer.py:606)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib._bootstrap._load_unlocked(<frozen importlib._bootstrap>:688)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib._bootstrap._find_and_load_unlocked(<frozen importlib._bootstrap>:1006)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib._bootstrap._find_and_load(<frozen importlib._bootstrap>:1027)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib._bootstrap._gcd_import(<frozen importlib._bootstrap>:1050)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.importlib.import_module(__init__.py:126)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.toga.platform.get_platform_factory(platform.py:122)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.toga.app.__init__(app.py:323)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.traveltips.app.main(app.py:237)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.__main__.<module>(__main__.py:4)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.runpy._run_code(runpy.py:86)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.runpy._run_module_code(runpy.py:96)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.runpy.run_module(runpy.py:224)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.chaquopy_java.call(chaquopy_java.pyx:354)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at <python>.chaquopy_java.Java_com_chaquo_python_PyObject_callAttrThrowsNative(chaquopy_java.pyx:326)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at com.chaquo.python.PyObject.callAttrThrowsNative(Native Method)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at com.chaquo.python.PyObject.callAttrThrows(PyObject.java:232)
04-17 15:29:56.737  6976  6976 E AndroidRuntime:        at com.chaquo.python.PyObject.callAttr(PyObject.java:221)

Additional context

The implementation of rehint() for Label includes a version check against API Level O (26/8.0), to protect against the non-existence of setJustificationMode API; however, the constant that is used in both cases uses the LineBreaker class, which was only introduced in API 29.

The issue isn't just the usage of the constant - it's the import of the LineBreaker class, which won't exist (and thus crashes on app startup).

[mhsmith]

The app doesn't even need to use a Label, because the crash happens while importing toga_android.app.