Android -- 开源库文本识别 ML Kit 的基本使用
Posted Kevin-Dev
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前言
机器学习套件是一个移动 SDK，将 Google 的设备端机器学习专业知识运用于 android 和 ios 应用。使用我们强大而易用的 Vision API 和 Natural Language API 解决应用中的常见挑战，或打造全新的用户体验。所有功能均由 Google 一流的机器学习模型提供支持，可免费使用。
学习指南：https://developers.google.cn/ml-kit/guides?hl=zh-cn
效果图
书写识别
准备工作
1. 在 app/build.gradle 添加如下依赖
implementation 'com.google.mlkit:digital-ink-recognition:18.0.0'
2. 创建 StrokeManager.java
/**
* author: Kevin-Dev
* date: 2023/2/2
* desc:
*/
public class StrokeManager
/** Interface to register to be notified of changes in the recognized content. */
public interface ContentChangedListener
/** This method is called when the recognized content changes. */
void onContentChanged();
/** Interface to register to be notified of changes in the status. */
public interface StatusChangedListener
/** This method is called when the recognized content changes. */
void onStatusChanged();
/** Interface to register to be notified of changes in the downloaded model state. */
public interface DownloadedModelsChangedListener
/** This method is called when the downloaded models changes. */
void onDownloadedModelsChanged(Set<String> downloadedLanguageTags);
@VisibleForTesting
static final long CONVERSION_TIMEOUT_MS = 1000;
private static final String TAG = "MLKD.StrokeManager";
// This is a constant that is used as a message identifier to trigger the timeout.
private static final int TIMEOUT_TRIGGER = 1;
// For handling recognition and model downloading.
private RecognitionTask recognitionTask = null;
@VisibleForTesting ModelManager modelManager = new ModelManager();
// Managing the recognition queue.
private final List<RecognitionTask.RecognizedInk> content = new ArrayList<>();
// Managing ink currently drawn.
private Ink.Stroke.Builder strokeBuilder = Ink.Stroke.builder();
private Ink.Builder inkBuilder = Ink.builder();
private boolean stateChangedSinceLastRequest = false;
@Nullable
private ContentChangedListener contentChangedListener = null;
@Nullable private StatusChangedListener statusChangedListener = null;
@Nullable private DownloadedModelsChangedListener downloadedModelsChangedListener = null;
private boolean triggerRecognitionAfterInput = true;
private boolean clearCurrentInkAfterRecognition = true;
private String status = "";
public void setTriggerRecognitionAfterInput(boolean shouldTrigger)
triggerRecognitionAfterInput = shouldTrigger;
public void setClearCurrentInkAfterRecognition(boolean shouldClear)
clearCurrentInkAfterRecognition = shouldClear;
// Handler to handle the UI Timeout.
// This handler is only used to trigger the UI timeout. Each time a UI interaction happens,
// the timer is reset by clearing the queue on this handler and sending a new delayed message (in
// addNewTouchEvent).
private final Handler uiHandler =
new Handler(
msg ->
if (msg.what == TIMEOUT_TRIGGER)
Log.i(TAG, "Handling timeout trigger.");
commitResult();
return true;
// In the current use this statement is never reached because we only ever send
// TIMEOUT_TRIGGER messages to this handler.
// This line is necessary because otherwise Java's static analysis doesn't allow for
// compiling. Returning false indicates that a message wasn't handled.
return false;
);
private void setStatus(String newStatus)
status = newStatus;
if (statusChangedListener != null)
statusChangedListener.onStatusChanged();
private void commitResult()
if (recognitionTask.done() && recognitionTask.result() != null)
content.add(recognitionTask.result());
setStatus("Successful recognition: " + recognitionTask.result().text);
if (clearCurrentInkAfterRecognition)
resetCurrentInk();
if (contentChangedListener != null)
contentChangedListener.onContentChanged();
reset();
public void reset()
Log.i(TAG, "reset");
resetCurrentInk();
content.clear();
if (recognitionTask != null && !recognitionTask.done())
recognitionTask.cancel();
setStatus("");
private void resetCurrentInk()
inkBuilder = Ink.builder();
strokeBuilder = Ink.Stroke.builder();
stateChangedSinceLastRequest = false;
public Ink getCurrentInk()
return inkBuilder.build();
/**
* This method is called when a new touch event happens on the drawing client and notifies the
* StrokeManager of new content being added.
*
* <p>This method takes care of triggering the UI timeout and scheduling recognitions on the
* background thread.
*
* @return whether the touch event was handled.
*/
public boolean addNewTouchEvent(MotionEvent event)
int action = event.getActionMasked();
float x = event.getX();
float y = event.getY();
long t = System.currentTimeMillis();
// A new event happened -> clear all pending timeout messages.
uiHandler.removeMessages(TIMEOUT_TRIGGER);
switch (action)
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_MOVE:
strokeBuilder.addPoint(Ink.Point.create(x, y, t));
break;
case MotionEvent.ACTION_UP:
strokeBuilder.addPoint(Ink.Point.create(x, y, t));
inkBuilder.addStroke(strokeBuilder.build());
strokeBuilder = Ink.Stroke.builder();
stateChangedSinceLastRequest = true;
recognize();
/* if (triggerRecognitionAfterInput)
recognize();
*/
break;
default:
// Indicate touch event wasn't handled.
return false;
return true;
// Listeners to update the drawing and status.
public void setContentChangedListener(ContentChangedListener contentChangedListener)
this.contentChangedListener = contentChangedListener;
public void setStatusChangedListener(StatusChangedListener statusChangedListener)
this.statusChangedListener = statusChangedListener;
public void setDownloadedModelsChangedListener(
DownloadedModelsChangedListener downloadedModelsChangedListener)
this.downloadedModelsChangedListener = downloadedModelsChangedListener;
public List<RecognitionTask.RecognizedInk> getContent()
return content;
public String getStatus()
return status;
// Model downloading / deleting / setting.
public void setActiveModel(String languageTag)
setStatus(modelManager.setModel(languageTag));
public Task<Void> deleteActiveModel()
return modelManager
.deleteActiveModel()
.addOnSuccessListener(unused -> refreshDownloadedModelsStatus())
.onSuccessTask(
status ->
setStatus(status);
return Tasks.forResult(null);
);
public Task<Void> download()
setStatus("Download started.");
return modelManager
.download()
.addOnSuccessListener(unused -> refreshDownloadedModelsStatus())
.onSuccessTask(
status ->
setStatus(status);
return Tasks.forResult(null);
);
// Recognition-related.
public Task<String> recognize()
if (!stateChangedSinceLastRequest || inkBuilder.isEmpty())
setStatus("No recognition, ink unchanged or empty");
return Tasks.forResult(null);
if (modelManager.getRecognizer() == null)
setStatus("Recognizer not set");
return Tasks.forResult(null);
return modelManager
.checkIsModelDownloaded()
.onSuccessTask(
result ->
if (!result)
setStatus("Model not downloaded yet");
return Tasks.forResult(null);
stateChangedSinceLastRequest = false;
recognitionTask =
new RecognitionTask(modelManager.getRecognizer(), inkBuilder.build());
uiHandler.sendMessageDelayed(
uiHandler.obtainMessage(TIMEOUT_TRIGGER), CONVERSION_TIMEOUT_MS);
return recognitionTask.run();
);
public void refreshDownloadedModelsStatus()
modelManager
.getDownloadedModelLanguages()
.addOnSuccessListener(
downloadedLanguageTags ->
if (downloadedModelsChangedListener != null)
downloadedModelsChangedListener.onDownloadedModelsChanged(downloadedLanguageTags);
);
3. 创建 ModelManager.java
/**
* author: Kevin-Dev
* date: 2023/2/2
* desc:
*/
public class ModelManager
private static final String TAG = "MLKD.ModelManager";
private DigitalInkRecognitionModel model;
private DigitalInkRecognizer recognizer;
final RemoteModelManager remoteModelManager = RemoteModelManager.getInstance();
public String setModel(String languageTag)
// Clear the old model and recognizer.
model = null;
if (recognizer != null)
recognizer.close();
recognizer = null;
// Try to parse the languageTag and get a model from it.
DigitalInkRecognitionModelIdentifier modelIdentifier;
try
modelIdentifier = DigitalInkRecognitionModelIdentifier.fromLanguageTag(languageTag);
catch (MlKitException e)
Log.e(TAG, "Failed to parse language '" + languageTag + "'");
return "";
if (modelIdentifier == null)
return "No model for language: " + languageTag;
// Initialize the model and recognizer.
model = DigitalInkRecognitionModel.builder(modelIdentifier).build();
recognizer =
DigitalInkRecognition.getClient(DigitalInkRecognizerOptions.builder(model).build());
Log.i(
TAG,
"Model set for language '"
+ languageTag
+ "' ('"
+ modelIdentifier.getLanguageTag()
+ "').");
return "Model set for language: " + languageTag;
public DigitalInkRecognizer getRecognizer()
return recognizer;
public Task<Boolean> checkIsModelDownloaded()
return remoteModelManager.isModelDownloaded(model);
public Task<String> deleteActiveModel()
if (model == null)
Log.i(TAG, "Model not set");
return Tasks.forResult("Model not set");
return checkIsModelDownloaded()
.onSuccessTask(
result ->
if (!result)
return Tasks.forResult("Model not downloaded yet");
return remoteModelManager
.deleteDownloadedModel(model)
.onSuccessTask(
aVoid ->
Log.i(TAG, "Model successfully deleted");
return Tasks.forResult("Model successfully deleted");
);
)
.addOnFailureListener(e -> Log.e(TAG, "Error while model deletion: " + e));
public Task<Set<String>> getDownloadedModelLanguages()
return remoteModelManager
.getDownloadedModels(DigitalInkRecognitionModel.class)
.onSuccessTask(
(remoteModels) ->
Set<String> result = new HashSet<>();
for (DigitalInkRecognitionModel model : remoteModels)
result.add(model.getModelIdentifier().getLanguageTag());
Log.i(TAG, "Downloaded models for languages:" + result);
return Tasks.forResult(result);
);
public Task<String> download()
if (model == null)
return Tasks.forResult("Model not selected.");
return remoteModelManager
.download(model, new DownloadConditions.Builder().build())
.onSuccessTask(
aVoid ->
Log.i(TAG, "Model download succeeded.");
return Tasks.forResult("Downloaded model successfully");
)
.addOnFailureListener(e -> Log.e(TAG, "Error while downloading the model: " + e));
- 创建 RecognitionTask.java
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