android–Google Vision API– 关于空对象引用的Face方法

概述我正在尝试更改Google提供的示例应用,以便在Android上进行面部检测.FaceDetectordetector=newFaceDetector.Builder(getApplicationContext()).setTrackingEnabled(false).setMode(FaceDetector.ACCURATE_MODE)//Accuratemodeallowst

我正在尝试更改Google提供的示例应用,以便在Android上进行面部检测.

FaceDetector detector = new FaceDetector.Builder(getApplicationContext())                .setTrackingEnabled(false)                .setMode(FaceDetector.ACCURATE_MODE) // Accurate mode allows to get better face detection and better position (but the detection will be slower)                .setLandmarkType(FaceDetector.ALL_LANDMARKS)                .build();        // This is a temporary workaround for a BUG in the face detector with respect to operating        // on very small images.  This will be fixed in a future release.  But in the near term, use        // of the SafeFaceDetector class will patch the issue.        Detector<Face> safeDetector = new SafeFaceDetector(detector);        // Create a frame from the bitmap and run face detection on the frame.        Bitmap bitmap = ((BitmapDrawable)ivPhoto.getDrawable()).getBitmap();        Frame frame = new Frame.Builder().setBitmap(bitmap).build();        SparseArray<Face> faces = safeDetector.detect(frame);        if (!safeDetector.isOperational()) {            Log.w(TAG, "Face detector dependencIEs are not yet available.");            // Check for low storage.  If there is low storage, the library will not be            // downloaded, so detection will not become operational.            IntentFilter lowStorageFilter = new IntentFilter(Intent.ACTION_DEVICE_STORAGE_LOW);            boolean hasLowStorage = registerReceiver(null, lowStorageFilter) != null;            if (hasLowStorage) {                Toast.makeText(this, R.string.low_storage_error, Toast.LENGTH_LONG).show();                Log.w(TAG, getString(R.string.low_storage_error));            }        }

我的问题是,当我尝试在检测到的面上调用方法时,例如：

for(int i = 0; i < faces.size(); i++) {            Face face = faces.get(i);                float x = face.getposition().x + (face.getWIDth() / 2);            float y = face.getposition().y + (face.getHeight() / 2);}

然后有时我在应用程序崩溃时遇到此异常：

04-01 09:07:23.154 30199-30199/ch.epfl.proshare E/AndroIDRuntime: FATAL EXCEPTION: main                                                                  Process: ch.epfl.proshare, PID: 30199                                                                  java.lang.RuntimeException: Unable to start activity ComponentInfo{ch.epfl.proshare/ch.epfl.proshare.main.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'voID androID.support.v7.app.AppCompatActivity.setSupportActionbar(androID.support.v7.Widget.Toolbar)' on a null object reference                                                                      at androID.app.ActivityThread.performlaunchActivity(ActivityThread.java:2306)                                                                      at androID.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366)                                                                      at androID.app.ActivityThread.access0(ActivityThread.java:149)                                                                      at androID.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)                                                                      at androID.os.Handler.dispatchMessage(Handler.java:102)                                                                      at androID.os.Looper.loop(Looper.java:135)                                                                      at androID.app.ActivityThread.main(ActivityThread.java:5297)                                                                      at java.lang.reflect.Method.invoke(Native Method)                                                                      at java.lang.reflect.Method.invoke(Method.java:372)                                                                      at com.androID.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)                                                                      at com.androID.internal.os.ZygoteInit.main(ZygoteInit.java:703)                                                                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'voID androID.support.v7.app.AppCompatActivity.setSupportActionbar(androID.support.v7.Widget.Toolbar)' on a null object reference                                                                      at ch.epfl.proshare.main.MainFragment.onCreateVIEw(MainFragment.java:169)                                                                      at androID.support.v4.app.Fragment.performCreateVIEw(Fragment.java:1962)                                                                      at androID.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:1067)                                                                      at androID.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:1248)                                                                      at androID.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:1230)                                                                      at androID.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:2042)                                                                      at androID.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:165)                                                                      at androID.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:543)                                                                      at androID.app.Instrumentation.callActivityOnStart(Instrumentation.java:1220)                                                                      at androID.app.Activity.performStart(Activity.java:6036)                                                                      at androID.app.ActivityThread.performlaunchActivity(ActivityThread.java:2269)                                                                      at androID.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366)                                                                       at androID.app.ActivityThread.access0(ActivityThread.java:149)                                                                       at androID.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)                                                                       at androID.os.Handler.dispatchMessage(Handler.java:102)                                                                       at androID.os.Looper.loop(Looper.java:135)                                                                       at androID.app.ActivityThread.main(ActivityThread.java:5297)                                                                       at java.lang.reflect.Method.invoke(Native Method)                                                                       at java.lang.reflect.Method.invoke(Method.java:372)                                                                       at com.androID.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)                                                                       at com.androID.internal.os.ZygoteInit.main(ZygoteInit.java:703) 

我真的不明白为什么SafeDetector会返回带有空面的面的SparseArray.有谁遇到过这个问题？

解决方法:

我实际上刚刚找到了解决问题的方法.
面存储在SparseArray中,实际上类似于从整数(IDs)到面的映射.因此,获得一张脸应该通过以下方式完成：

Face face = faces.valueAt(i);

代替

Face face = faces.get(i);

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