Android 8.1 introduces the TextClassfier API that uses machine learning techniques to help developers classify text:
TextClassificationManager tcm = context.getSystemService(TextClassificationManager.class); TextClassifier classifier = tcm.getTextClassifier(); TextSelection selection = classifier.suggestSelection(...); TextClassification classification = classifier.classifyText(...);
Developers may choose to set a custom text classifier:
tcm.setTextClassifier(customTextClassifier);
But if an app developer sets the text classifier to null, a system default text
classifier is returned for getTextClassifier()
.
See: android.view.textclassifier.TextClassifierImpl
TextView and WebView use the TextClassifier for smart selection and smart text share features:
Figure 1. TEXTCLASSIFIER usage.
The Android Open Source Project (AOSP) features a number of neural network models for classifying text. Each model file is trained for a single language. You may choose to install any combination of models. The models are defined in:
external/libtextclassifier/Android.mk
You may specify a bundle of language models and install them on a device:
# ----------------------- # Smart Selection bundles # ----------------------- include $(CLEAR_VARS) LOCAL_MODULE := textclassifier.smartselection.bundle1 LOCAL_REQUIRED_MODULES := textclassifier.smartselection.en.model LOCAL_REQUIRED_MODULES += textclassifier.smartselection.es.model LOCAL_REQUIRED_MODULES += textclassifier.smartselection.de.model LOCAL_REQUIRED_MODULES += textclassifier.smartselection.fr.model include $(BUILD_STATIC_LIBRARY)
For example, in device/google/marlin/device-common.mk
# TextClassifier smart selection model files PRODUCT_PACKAGES += \ textclassifier.smartselection.bundle1
Use ADB to list the files in the directory:
$ adb shell ls -l /etc/textclassifier -rw-r--r-- 1 root root ... textclassifier.smartselection.de.model -rw-r--r-- 1 root root ... textclassifier.smartselection.en.model -rw-r--r-- 1 root root ... textclassifier.smartselection.es.model -rw-r--r-- 1 root root ... textclassifier.smartselection.fr.model
Models can be updated either by having a new model included as part of a system image update,
or dynamically via having a system component that would trigger an update through the
System API ACTION_UPDATE_SMART_SELECTION
intent. By broadcasting this System API
intent, the framework is able to update the language model of the currently set language.
The models themselves contain the supported
language and a version number so the latest appropriate model is used.
So you don't need to preload models for all languages because they can be added later. If no model file is found for the specified language, text classification will return no-op values.
The associated Android Compatibility Test Suite (CTS) tests can be found in:
cts/tests/tests/view/src/android/view/textclassifier/cts/TextClassificationManagerTest.java
cts/tests/tests/widget/src/android/widget/cts/TextViewTest.java
testSmartSelection
testSmartSelection_dragSelection
testSmartSelection_resetSelection