指紋服務是Android系統中一個較為簡單的服務（相比于AMS，WMS等），也比較獨立，功能上包括幾點
和其他的system service 一樣，應用程序通過FingerprintManager實現與FingerprintService的通信，除了上面所說的功能之外，FingerprintManager提供了一些別的的接口，重要的接口都會要求系統級別的權限，并且也不是公開的api（指紋的錄入，刪除，重命名，重置錯誤計數等）
/** * Obtain the list of enrolled fingerprints templates. * @return list of current fingerprint items * * @hide */ @RequiresPermission(USE_FINGERPRINT) public List<Fingerprint> getEnrolledFingerprints(int userId) { if (mService != null) try { return mService.getEnrolledFingerprints(userId, mContext.getOpPackageName()); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); } return null; } /** * @hide */ @RequiresPermission(allOf = { USE_FINGERPRINT, INTERACT_ACROSS_USERS}) public boolean hasEnrolledFingerprints(int userId) { if (mService != null) try { return mService.hasEnrolledFingerprints(userId, mContext.getOpPackageName()); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); } return false; } /** * Determine if fingerprint hardware is present and functional. * * @return true if hardware is present and functional, false otherwise. */ @RequiresPermission(USE_FINGERPRINT) public boolean isHardwareDetected() { if (mService != null) { try { long deviceId = 0; /* TODO: plumb hardware id to FPMS */ return mService.isHardwareDetected(deviceId, mContext.getOpPackageName()); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); } } else { Log.w(TAG, "isFingerprintHardwareDetected(): Service not connected!"); } return false; }FingerprintService的啟動過程
FingerprintService在system server中創建并初始化，當檢測到手機支持指紋功能的時候就會啟動這個service
...if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)) { mSystemServiceManager.startService(FingerprintService.class); }...FingerprintService在初始化后會建立和HAL層的通信，即連接到fingerprintd，拿到用于通信的IFingerprintDaemon對象（binder）
public void onStart() { publishBinderService(Context.FINGERPRINT_SERVICE, new FingerprintServiceWrapper()); IFingerprintDaemon daemon = getFingerprintDaemon(); listenForUserSwitches(); }public IFingerprintDaemon getFingerprintDaemon() { if (mDaemon == null) { mDaemon = IFingerprintDaemon.Stub.asInterface(ServiceManager.getService(FINGERPRINTD)); if (mDaemon != null) { try { mDaemon.asBinder().linkToDeath(this, 0); mDaemon.init(mDaemonCallback); mHalDeviceId = mDaemon.openHal(); if (mHalDeviceId != 0) { updateActiveGroup(ActivityManager.getCurrentUser(), null); } else { Slog.w(TAG, "Failed to open Fingerprint HAL!"); MetricsLogger.count(mContext, "fingerprintd_openhal_error", 1); mDaemon = null; } } catch (RemoteException e) { Slog.e(TAG, "Failed to open fingeprintd HAL", e); mDaemon = null; // try again later! } } else { Slog.w(TAG, "fingerprint service not available"); } } return mDaemon; }本質上來說，除去安全相關的策略外，指紋的功能是依賴硬件實現的，FingerprintService也只是充當了framework java層與native層的消息傳遞者罷了，所以指紋的識別，錄入和監聽都是向fingerprintd發送命令和獲取相應的結果
指紋監聽認證過程
以指紋認證為例，介紹這一過程，錄入和刪除的過程和認證類似，不重復描述
FingerprintManager
public void authenticate(@Nullable CryptoObject crypto, @Nullable CancellationSignal cancel, int flags, @NonNull AuthenticationCallback callback, Handler handler, int userId) { if (callback == null) { throw new IllegalArgumentException("Must supply an authentication callback"); } if (cancel != null) { if (cancel.isCanceled()) { Log.w(TAG, "authentication already canceled"); return; } else { cancel.setOnCancelListener(new OnAuthenticationCancelListener(crypto)); } } if (mService != null) try { useHandler(handler); mAuthenticationCallback = callback; mCryptoObject = crypto; long sessionId = crypto != null ? crypto.getOpId() : 0; mService.authenticate(mToken, sessionId, userId, mServiceReceiver, flags, mContext.getOpPackageName()); } catch (RemoteException e) { Log.w(TAG, "Remote exception while authenticating: ", e); if (callback != null) { // Though this may not be a hardware issue, it will cause apps to give up or try // again later. callback.onAuthenticationError(FINGERPRINT_ERROR_HW_UNAVAILABLE, getErrorString(FINGERPRINT_ERROR_HW_UNAVAILABLE)); } } }可以看到，最終仍然是向FingerprintService發送消息，但是開啟指紋認證的函數傳入了兩個比較重要的參數，一個是CancellationSignal對象，用于取消指紋認證，另一個是指紋認證的回調對象AuthenticationCallback
public static abstract class AuthenticationCallback { public void onAuthenticationError(int errorCode, CharSequence errString) { } public void onAuthenticationHelp(int helpCode, CharSequence helpString) { } public void onAuthenticationSucceeded(AuthenticationResult result) { } public void onAuthenticationFailed() { } public void onAuthenticationAcquired(int acquireInfo) {} };看函數名稱也能知道其功能，他們分別代表了指紋認證時的回調結果（成功，失敗，檢測到指紋，認證異常等），參數包含了具體的信息，這些信息在FingerprintManager中都有對應的常量定義，有興趣可以查看代碼
FingerprintService
public void authenticate(final IBinder token, final long opId, final int groupId, final IFingerprintServiceReceiver receiver, final int flags, final String opPackageName) { final int callingUid = Binder.getCallingUid(); final int callingUserId = UserHandle.getCallingUserId(); final int pid = Binder.getCallingPid(); final boolean restricted = isRestricted(); mHandler.post(new Runnable() { @Override public void run() { if (!canUseFingerprint(opPackageName, true /* foregroundOnly */, callingUid, pid)) { if (DEBUG) Slog.v(TAG, "authenticate(): reject " + opPackageName); return; } MetricsLogger.histogram(mContext, "fingerprint_token", opId != 0L ? 1 : 0); // Get performance stats object for this user. HashMap<Integer, PerformanceStats> pmap = (opId == 0) ? mPerformanceMap : mCryptoPerformanceMap; PerformanceStats stats = pmap.get(mCurrentUserId); if (stats == null) { stats = new PerformanceStats(); pmap.put(mCurrentUserId, stats); } mPerformanceStats = stats; startAuthentication(token, opId, callingUserId, groupId, receiver, flags, restricted, opPackageName); } }); }前面會有對包名，userid以及應用進程是否在在前臺的檢查，繼續看
private void startAuthentication(IBinder token, long opId, int callingUserId, int groupId, IFingerprintServiceReceiver receiver, int flags, boolean restricted, String opPackageName) { updateActiveGroup(groupId, opPackageName); if (DEBUG) Slog.v(TAG, "startAuthentication(" + opPackageName + ")"); AuthenticationClient client = new AuthenticationClient(getContext(), mHalDeviceId, token, receiver, mCurrentUserId, groupId, opId, restricted, opPackageName) { @Override public boolean handleFailedAttempt() { mFailedAttempts++; if (mFailedAttempts == MAX_FAILED_ATTEMPTS) { mPerformanceStats.lockout++; } if (inLockoutMode()) { // Failing multiple times will continue to push out the lockout time. scheduleLockoutReset(); return true; } return false; } @Override public void resetFailedAttempts() { FingerprintService.this.resetFailedAttempts(); } @Override public void notifyUserActivity() { FingerprintService.this.userActivity(); } @Override public IFingerprintDaemon getFingerprintDaemon() { return FingerprintService.this.getFingerprintDaemon(); } }; if (inLockoutMode()) { Slog.v(TAG, "In lockout mode; disallowing authentication"); // Don't bother starting the client. Just send the error message. if (!client.onError(FingerprintManager.FINGERPRINT_ERROR_LOCKOUT)) { Slog.w(TAG, "Cannot send timeout message to client"); } return; } startClient(client, true /* initiatedByClient */); } AuthenticationClient繼承自ClientMonitor，用于處理指紋認證相關的功能事務，ClientMonitor的其他子類如RemovalMonior，EnrollMonitor也是如此，ClientMonitor會直接與fingerprintd通信，其核心是調用其start()或stop()方法，
對于AuthenticationClient而言
private void startClient(ClientMonitor newClient, boolean initiatedByClient) { ClientMonitor currentClient = mCurrentClient; if (currentClient != null) { if (DEBUG) Slog.v(TAG, "request stop current client " + currentClient.getOwnerString()); currentClient.stop(initiatedByClient); mPendingClient = newClient; mHandler.removeCallbacks(mResetClientState); mHandler.postDelayed(mResetClientState, CANCEL_TIMEOUT_LIMIT); } else if (newClient != null) { mCurrentClient = newClient; if (DEBUG) Slog.v(TAG, "starting client " + newClient.getClass().getSuperclass().getSimpleName() + "(" + newClient.getOwnerString() + ")" + ", initiatedByClient = " + initiatedByClient + ")"); newClient.start(); } }public int start() { IFingerprintDaemon daemon = getFingerprintDaemon(); if (daemon == null) { Slog.w(TAG, "start authentication: no fingeprintd!"); return ERROR_ESRCH; } try { final int result = daemon.authenticate(mOpId, getGroupId()); if (result != 0) { Slog.w(TAG, "startAuthentication failed, result=" + result); MetricsLogger.histogram(getContext(), "fingeprintd_auth_start_error", result); onError(FingerprintManager.FINGERPRINT_ERROR_HW_UNAVAILABLE); return result; } if (DEBUG) Slog.w(TAG, "client " + getOwnerString() + " is authenticating..."); } catch (RemoteException e) { Slog.e(TAG, "startAuthentication failed", e); return ERROR_ESRCH; } return 0; // success }向底層發送認證命令后就只需要等待認證結果就可以了，前面我們說到在初始化的時候會建立與fingerprintd的通信，其核心是下面這行代碼
mDaemon.init(mDaemonCallback);
mDaemonCallback是一個binder對象，接受來自底層的結果，然后通過FingerprintService和FingerManager一層層把結果發送到應用程序中去。
8.0的一些變化
8.0上的fingerprintd變化很大，甚至都不叫fingerprintd了，當然這是native層的東西，這里不討論，對于FingerprintService而言，一個顯著的變化是安全策略的調整
private static final int MAX_FAILED_ATTEMPTS_LOCKOUT_TIMED = 5;private static final int MAX_FAILED_ATTEMPTS_LOCKOUT_PERMANENT = 20;private int getLockoutMode() { if (mFailedAttempts >= MAX_FAILED_ATTEMPTS_LOCKOUT_PERMANENT) { return AuthenticationClient.LOCKOUT_PERMANENT; } else if (mFailedAttempts > 0 && mTimedLockoutCleared == false && (mFailedAttempts % MAX_FAILED_ATTEMPTS_LOCKOUT_TIMED == 0)) { return AuthenticationClient.LOCKOUT_TIMED; } return AuthenticationClient.LOCKOUT_NONE; }總結
以上所述是小編給大家介紹的Android7.0指紋服務FingerprintService實例介紹，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對VEVB武林網網站的支持！
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