Android Studio-Code kompiliert, wird aber nicht ausgeführt

Question

Erstellen eines Schrittzählers mit dem Beschleunigungssensor. Code kompiliert ohne Fehler, aber wenn ich es auf dem Telefon (S5) ausführen, schlägt es fehl.

CODE IN zentral-

public class MainActivity extends Activity implements SensorEventListener{ 

     TextView display; 
     float g; 

    @Override 
    public void onCreate(Bundle savedInstanceState){ 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     display = (TextView) findViewById(R.id.testView); // Correction 
     SensorManager mgr = (SensorManager) getSystemService(SENSOR_SERVICE); 
     Sensor GSensor = mgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); 
     mgr.registerListener(this, GSensor, SensorManager.SENSOR_DELAY_NORMAL); 

     String mytext = Float.toString(g); 

     display.setText(mytext); 


    } 
    @Override 
    public void onSensorChanged(SensorEvent event){ 

     float x = event.values[0]; 
     float y = event.values[1]; 
     float z = event.values[2]; 

     g = (x * x + y * y + z *z)/(SensorManager.GRAVITY_EARTH *SensorManager.GRAVITY_EARTH); 



    } 



    @Override 
    public void onAccuracyChanged(Sensor sensor, int accuracy){ 
    } 
} 

FEHLER IN LOG ..

05-20 09:35:44.773 11142-11142/com.liamoc.stepcounteraccel1 E/Zygote: MountEmulatedStorage() 
05-20 09:35:44.773 11142-11142/com.liamoc.stepcounteraccel1 E/Zygote: v2 
05-20 09:35:44.773 11142-11142/com.liamoc.stepcounteraccel1 I/libpersona: KNOX_SDCARD checking this for 10199 
05-20 09:35:44.773 11142-11142/com.liamoc.stepcounteraccel1 I/libpersona: KNOX_SDCARD not a persona 
05-20 09:35:44.793 11142-11142/com.liamoc.stepcounteraccel1 I/SELinux: Function: selinux_compare_spd_ram , priority [2] , priority version is VE=SEPF_SM-G900F_5.0-1_0032 
05-20 09:35:44.793 11142-11142/com.liamoc.stepcounteraccel1 E/SELinux: [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL 
05-20 09:35:44.793 11142-11142/com.liamoc.stepcounteraccel1 I/art: Late-enabling -Xcheck:jni 
05-20 09:35:44.823 11142-11142/com.liamoc.stepcounteraccel1 D/TimaKeyStoreProvider: TimaSignature is unavailable 
05-20 09:35:44.823 11142-11142/com.liamoc.stepcounteraccel1 D/ActivityThread: Added TimaKeyStore provider 
05-20 09:35:44.863 11142-11142/com.liamoc.stepcounteraccel1 D/ResourcesManager: creating new AssetManager and set to /data/app/com.liamoc.stepcounteraccel1-2/base.apk 
05-20 09:35:44.883 11142-11142/com.liamoc.stepcounteraccel1 W/art: Failed to find OatDexFile for DexFile /data/data/com.liamoc.stepcounteraccel1/files/instant-run/dex/slice-slice_6-classes.dex (canonical path /data/data/com.liamoc.stepcounteraccel1/files/instant-run/dex/slice-slice_6-classes.dex) with checksum 0x1ff97ab0 in OatFile /data/data/com.liamoc.stepcounteraccel1/cache/slice-slice_6-classes.dex 
05-20 09:35:45.053 11142-11142/com.liamoc.stepcounteraccel1 D/AndroidRuntime: Shutting down VM 
05-20 09:35:45.053 11142-11142/com.liamoc.stepcounteraccel1 E/AndroidRuntime: FATAL EXCEPTION: main 
                       Process: com.liamoc.stepcounteraccel1, PID: 11142 
                       java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.liamoc.stepcounteraccel1/com.liamoc.stepcounteraccel1.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference 
                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2515) 
                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723) 
                        at android.app.ActivityThread.access$900(ActivityThread.java:172) 
                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422) 
                        at android.os.Handler.dispatchMessage(Handler.java:102) 
                        at android.os.Looper.loop(Looper.java:145) 
                        at android.app.ActivityThread.main(ActivityThread.java:5832) 
                        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:1399) 
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 
                       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference 
                        at android.app.Activity.findViewById(Activity.java:2168) 
                        at com.liamoc.stepcounteraccel1.MainActivity.<init>(MainActivity.java:29) 
                        at java.lang.reflect.Constructor.newInstance(Native Method) 
                        at java.lang.Class.newInstance(Class.java:1650) 
                        at android.app.Instrumentation.newActivity(Instrumentation.java:1079) 
                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2505) 
                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)  
                        at android.app.ActivityThread.access$900(ActivityThread.java:172)  
                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)  
                        at android.os.Handler.dispatchMessage(Handler.java:102)  
                        at android.os.Looper.loop(Looper.java:145)  
                        at android.app.ActivityThread.main(ActivityThread.java:5832)  
                        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:1399)  
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)  

Jede Hilfe ist wirklich einfach .. Dank

Answer 1

initialisieren, im ein Noob so sorry ifthe prob geschätzt Ihre Textansicht nach setContentView()

TextView display; 

    @Override 
     public void onCreate(Bundle savedInstanceState){ 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_main); 

      display = (TextView) findViewById(R.id.testView); 

      SensorManager mgr = (SensorManager) getSystemService(SENSOR_SERVICE); 
      Sensor GSensor = mgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); 
      mgr.registerListener(this, GSensor, SensorManager.SENSOR_DELAY_NORMAL); 

     } 

Wert von g ist initializating in onSensorChanged(), so ist es in diesem Verfahren festgelegt:

@Override 
    public void onSensorChanged(SensorEvent event){ 

     float x = event.values[0]; 
     float y = event.values[1]; 
     float z = event.values[2]; 

     g = (x * x + y * y + z *z)/(SensorManager.GRAVITY_EARTH *SensorManager.GRAVITY_EARTH); 

     String mytext = Float.toString(g); 
     display.setText(mytext); 

    }