從Android的官方API可以查到，向上層提供接口的是FingerprintManager，它的代碼在路徑frameworks/base/core/java/android/hardware/fingerprint下。
/**
* A class that coordinates access to the fingerprint hardware.
* @deprecated See {@link BiometricPrompt} which shows a system-provided dialog upon starting
* authentication. In a world where devices may have different types of biometric authentication,
* it's much more realistic to have a system-provided authentication dialog since the method may
* vary by vendor/device.
*/
@Deprecated
@SystemService(Context.FINGERPRINT_SERVICE)
@RequiresFeature(PackageManager.FEATURE_FINGERPRINT)
public class FingerprintManager implements BiometricFingerprintConstants
frameworks/base/core/java/android/hardware/fingerprint目錄下内容其實很少，一共隻有幾個檔案。
這裡除了FingerprintManager之外，就隻有Fingerprint一個類了，其他都是aidl檔案。
粗略的看了下Fingerprint類，它裡面的内容超級少，主要是包含了幾個成員變量，用來記錄指紋的資訊。
/**
* Container for fingerprint metadata.
* @hide
*/
public final class Fingerprint extends BiometricAuthenticator.BiometricIdentifier {
private CharSequence mName;
private int mGroupId;
private int mFingerId;
private long mDeviceId; // physical device this is associated with
public Fingerprint(CharSequence name, int groupId, int fingerId, long deviceId) {
mName = name;
mGroupId = groupId;
mFingerId = fingerId;
mDeviceId = deviceId;
}
//...
}
如果仔細看代碼的話，可以發現一個很神奇的東西，那個就Fingerprint類的所有成員都是private的，并且沒有提供任何public的set方法！
這個就厲害了，因為有做過指紋部分的朋友一定記得指紋提供一個rename的接口。沒有public的set方法，那它又是怎麼實作rename接口的呢？
帶着問題看源碼！
rename方法在Manager中的實作如下：
/**
* Renames the given fingerprint template
* @param fpId the fingerprint id
* @param userId the user who this fingerprint belongs to
* @param newName the new name
*
* @hide
*/
@RequiresPermission(MANAGE_FINGERPRINT)
public void rename(int fpId, int userId, String newName) {
// Renames the given fpId
if (mService != null) {
try {
mService.rename(fpId, userId, newName);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} else {
Slog.w(TAG, "rename(): Service not connected!");
}
}
這裡先直接找到Manager的服務類：FingerprintService
指紋服務的相關代碼在frameworks\base\services\core\java\com\android\server\fingerprint下。
/**
* A service to manage multiple clients that want to access the fingerprint HAL API.
* The service is responsible for maintaining a list of clients and dispatching all
* fingerprint-related events.
*
* @hide
*/
public class FingerprintService extends SystemService implements IHwBinder.DeathRecipient
看一下它裡面的rename是在内部類FingerprintServiceWrapper中實作的，具體如下：
@Override // Binder call
public void rename(final int fingerId, final int groupId, final String name) {
checkPermission(MANAGE_FINGERPRINT);
if (!isCurrentUserOrProfile(groupId)) {
return;
}
mHandler.post(new Runnable() {
@Override
public void run() {
mFingerprintUtils.renameFingerprintForUser(mContext, fingerId,
groupId, name);
}
}
}
找到同檔案夾下FingerprintUtils類，這個是工具類，裡面維護了一組FingerprintsUserState，具體得繼續看FingerprintsUserState；
FingerprintsUserState中維護了一組Fingerprint，下面具體看下rename操作：
@GuardedBy("this")
private final ArrayList<Fingerprint> mFingerprints = new ArrayList<Fingerprint>();
//...
public void renameFingerprint(int fingerId, CharSequence name) {
synchronized (this) {
for (int i = 0; i < mFingerprints.size(); i++) {
if (mFingerprints.get(i).getFingerId() == fingerId) {
Fingerprint old = mFingerprints.get(i);
mFingerprints.set(i, new Fingerprint(name, old.getGroupId(),
old.getFingerId(), old.getDeviceId()));
scheduleWriteStateLocked();
break;
}
}
}
}
這裡可以看到，在rename的實作時，代碼直接霸氣的new一個Fingerprint對象，然後覆寫List中對應id的對象。
OK，以上隻是一個小小的流程。
下面看下FingerprintManager的主要API：
public void enroll(byte [] token, CancellationSignal cancel, int flags,
int userId, EnrollmentCallback callback);
public void remove(Fingerprint fp, int userId, RemovalCallback callback);
public void rename(int fpId, int userId, String newName);
public List<Fingerprint> getEnrolledFingerprints()；
//不是hide的方法
public void authenticate(@Nullable CryptoObject crypto, @Nullable CancellationSignal cancel,int flags, @NonNull AuthenticationCallback callback, @Nullable Handler handler);
public boolean hasEnrolledFingerprints();
public boolean isHardwareDetected()
真正對三方開放的API隻有最下面的三個，分别用來授權、判斷是否錄入過指紋、判斷裝置是否支援指紋器件。
這裡面要特别提一下authenicate方法；
/**
* Request authentication of a crypto object. This call warms up the fingerprint hardware
* and starts scanning for a fingerprint. It terminates when
* {@link AuthenticationCallback#onAuthenticationError(int, CharSequence)} or
* {@link AuthenticationCallback#onAuthenticationSucceeded(AuthenticationResult)} is called, at
* which point the object is no longer valid. The operation can be canceled by using the
* provided cancel object.
*
* @param crypto object associated with the call or null if none required.
* @param cancel an object that can be used to cancel authentication
* @param flags optional flags; should be 0
* @param callback an object to receive authentication events
* @param handler an optional handler to handle callback events
*
* @throws IllegalArgumentException if the crypto operation is not supported or is not backed
* by <a href="{@docRoot}training/articles/keystore.html" target="_blank" rel="external nofollow" >Android Keystore
* facility</a>.
* @throws IllegalStateException if the crypto primitive is not initialized.
* @deprecated See {@link BiometricPrompt#authenticate(CancellationSignal, Executor,
* BiometricPrompt.AuthenticationCallback)} and {@link BiometricPrompt#authenticate(
* BiometricPrompt.CryptoObject, CancellationSignal, Executor,
* BiometricPrompt.AuthenticationCallback)}
*/
@Deprecated
@RequiresPermission(anyOf = {USE_BIOMETRIC, USE_FINGERPRINT})
public void authenticate(@Nullable CryptoObject crypto, @Nullable CancellationSignal cancel,
int flags, @NonNull AuthenticationCallback callback, @Nullable Handler handler) {
authenticate(crypto, cancel, flags, callback, handler, mContext.getUserId());
}
其中flags暫時沒用起來，直接設定為0。
這裡稍微講下crypto objiect。它是的一個内部類。暫時支援三種類型對象。如下：
/**
* A wrapper class for the crypto objects supported by FingerprintManager. Currently the
* framework supports {@link Signature}, {@link Cipher} and {@link Mac} objects.
* @deprecated See {@link android.hardware.biometrics.BiometricPrompt.CryptoObject}
*/
這個參數用于加密，保護指紋在使用過程中不被惡意軟體截獲和篡改。
Google的示例中用的是Cipher的加密對象。
需要結束監聽的話，使用CancellationSignal對象的cancel方法即可。
上面提到過Manager裡面的API具體實作都是Service中。
Manager中儲存有Service的對象private IFingerprintService mService;
這對象看命名方式就可以大概猜到是個AIDL了；
/**
* Communication channel from client to the fingerprint service.
* @hide
*/
interface IFingerprintService
它是在Manager的構造函數作為參數傳入的，找到建立Manager的地方：
frameworks/base/core/java/android/app/SystemServiceRegistry.java
registerService(Context.FINGERPRINT_SERVICE, FingerprintManager.class,
new CachedServiceFetcher<FingerprintManager>() {
@Override
public FingerprintManager createService(ContextImpl ctx) throws ServiceNotFoundException {
final IBinder binder;
if (ctx.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.O) {
binder = ServiceManager.getServiceOrThrow(Context.FINGERPRINT_SERVICE);
} else {
binder = ServiceManager.getService(Context.FINGERPRINT_SERVICE);
}
IFingerprintService service = IFingerprintService.Stub.asInterface(binder);
return new FingerprintManager(ctx.getOuterContext(), service);
}});
從這裡看，關鍵字是Context.FINGERPRINT_SERVICE這個服務！
這時候，靈機一動看一眼FingerprintService（通過搜尋可以搜到FingerprintService），它的onStart方法中有釋出這個服務，釋出的是它的内部類FingerprintServiceWrapper，這裡就解釋了為什麼之前Manager裡面的rename方法最後會在FingerprintServiceWrapper被搜尋到。
@Override
public void onStart() {
publishBinderService(Context.FINGERPRINT_SERVICE, new FingerprintServiceWrapper());
SystemServerInitThreadPool.get().submit(this::getFingerprintDaemon, TAG + ".onStart");
listenForUserSwitches();
}
而FingerprintService本身是在frameworks/base/services/java/com/android/server/SystemServer.java中啟動的；
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)) {
traceBeginAndSlog("StartFingerprintSensor");
mSystemServiceManager.startService(FingerprintService.class);
traceEnd();
}
下面來看一下一個消息回報的AIDL：IFingerprintServiceReceiver；
/**
* Communication channel from the FingerprintService back to FingerprintManager.
* @hide
*/
oneway interface IFingerprintServiceReceiver {
void onEnrollResult(long deviceId, int fingerId, int groupId, int remaining);
void onAcquired(long deviceId, int acquiredInfo, int vendorCode);
void onAuthenticationSucceeded(long deviceId, in Fingerprint fp, int userId);
void onAuthenticationFailed(long deviceId);
void onError(long deviceId, int error, int vendorCode);
void onRemoved(long deviceId, int fingerId, int groupId, int remaining);
void onEnumerated(long deviceId, int fingerId, int groupId, int remaining);
}
它的執行個體在Manager中；
private IFingerprintServiceReceiver mServiceReceiver = new IFingerprintServiceReceiver.Stub
作為參數被傳遞給Service，實作消息回報機制。
如果仔細看下FingerprintService所在的檔案夾，除了之前提到過的FingerprintService、FingerprintUtils和FingerprintsUserState以外就隻剩下大量和ClientMonitor 相關的類了；
/**
* Abstract base class for keeping track and dispatching events from fingerprint HAL to the
* the current client. Subclasses are responsible for coordinating the interaction with
* fingerprint HAL for the specific action (e.g. authenticate, enroll, enumerate, etc.).
*/
public abstract class ClientMonitor implements IBinder.DeathRecipient
它的子類包括AuthenticationClient、EnrollClient、EnumerateClient、InternalEnumerateClient、InternalRemovalClient和RemovalClient。
它們是真正負責和更下層的HAL層互動的類。
HAL層有關的内容這裡暫不讨論。
這樣的話，大概的一組流程被整理出來，FingerprintManager内部持有FingerprintService内部類FingerprintServiceWrapper的AIDL，FingerprintManager的API都是調用FingerprintServiceWrapper提供的接口實作的，同時通過參數實作IFingerprintServiceReceiver消息回傳。
這裡還有一點可以提一下，那就是指紋授權時的震動；
- frameworks/base/services/core/java/com/android/server/fingerprint/AuthenticationClient.java中會在授權成功或失敗後調用vibrateSuccess()和vibrateError()方法實作不同的震動效果
- frameworks/base/services/core/java/com/android/server/fingerprint/ClientMonitor.java有vibrateSuccess()和vibrateError()兩個方法的具體實作
- 在ClientMonitor中可以看到frameworks\base\core\java\android\os\VibrationEffect.java是真正實作震動的類
- 可以通過用VibrationEffect的createOneShot或createWaveform方法建立想要的震動效果