Android Wear应用程式已停止在Android Studio模拟器中运作

Question

I'm trying to run a code in my android studio emulator but after I run it, the emulator keeps showing "(App name) has stopped. Open app again".

This is an app to get accelerometer and gyro sensor data from Android wear.

I've checked the logcat and found this error in the process.

03-06 04:18:57.364 3189-3189/com.drejkim.androidwearmotionsensors E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                Process: com.drejkim.androidwearmotionsensors, PID: 3189
                                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.hardware.Sensor.getStringType()' on a null object reference
                                                                                    at com.drejkim.androidwearmotionsensors.SensorFragment.onCreateView(SensorFragment.java:63)
                                                                                    at android.app.Fragment.performCreateView(Fragment.java:2353)
                                                                                    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:995)
                                                                                    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1171)
                                                                                    at android.app.BackStackRecord.run(BackStackRecord.java:816)
                                                                                    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578)
                                                                                    at android.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:563)
                                                                                    at android.support.wearable.view.FragmentGridPagerAdapter.finishUpdate(FragmentGridPagerAdapter.java:196)
                                                                                    at android.support.wearable.view.GridViewPager.populate(GridViewPager.java:1161)
                                                                                    at android.support.wearable.view.GridViewPager.populate(GridViewPager.java:1008)
                                                                                    at android.support.wearable.view.GridViewPager.onMeasure(GridViewPager.java:1322)
                                                                                    at android.view.View.measure(View.java:19857)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                    at android.view.View.measure(View.java:19857)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                    at android.support.wearable.view.WatchViewStub.onMeasure(WatchViewStub.java:136)
                                                                                    at android.view.View.measure(View.java:19857)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                    at android.view.View.measure(View.java:19857)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                    at com.android.internal.policy.DecorView.onMeasure(DecorView.java:690)
                                                                                    at android.view.View.measure(View.java:19857)
                                                                                    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2275)
                                                                                    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1366)
                                                                                    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1675)
                                                                                    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
                                                                                    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6338)
                                                                                    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
                                                                                    at android.view.Choreographer.doCallbacks(Choreographer.java:686)
                                                                                    at android.view.Choreographer.doFrame(Choreographer.java:621)
                                                                                    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
                                                                                    at android.os.Handler.handleCallback(Handler.java:751)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                    at android.os.Looper.loop(Looper.java:154)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

And here're three of my java codes:

SensorFragments.java:

package com.drejkim.androidwearmotionsensors;

import android.app.Fragment;
import android.content.Context;
import android.graphics.Color;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.util.FloatMath;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class SensorFragment extends Fragment implements SensorEventListener {

    private static final float SHAKE_THRESHOLD = 1.1f;
    private static final int SHAKE_WAIT_TIME_MS = 250;
    private static final float ROTATION_THRESHOLD = 2.0f;
    private static final int ROTATION_WAIT_TIME_MS = 100;

    private View mView;
    private TextView mTextTitle;
    private TextView mTextValues;
    private SensorManager mSensorManager;
    private Sensor mSensor;
    private int mSensorType;
    private long mShakeTime = 0;
    private long mRotationTime = 0;

    public static SensorFragment newInstance(int sensorType) {
        SensorFragment f = new SensorFragment();

        // Supply sensorType as an argument
        Bundle args = new Bundle();
        args.putInt("sensorType", sensorType);
        f.setArguments(args);

        return f;
    }

    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Bundle args = getArguments();
        if(args != null) {
            mSensorType = args.getInt("sensorType");
        }

        mSensorManager = (SensorManager) getActivity().getSystemService(Context.SENSOR_SERVICE);
        mSensor = mSensorManager.getDefaultSensor(mSensorType);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        mView = inflater.inflate(R.layout.sensor, container, false);

        mTextTitle = (TextView) mView.findViewById(R.id.text_title);
        mTextTitle.setText(mSensor.getStringType());
        mTextValues = (TextView) mView.findViewById(R.id.text_values);

        return mView;
    }

    @Override
    public void onResume() {
        super.onResume();
        mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_NORMAL);
    }

    @Override
    public void onPause() {
        super.onPause();
        mSensorManager.unregisterListener(this);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // If sensor is unreliable, then just return
        if (event.accuracy == SensorManager.SENSOR_STATUS_UNRELIABLE)
        {
            return;
        }

        mTextValues.setText(
                "x = " + Float.toString(event.values[0]) + "\n" +
                "y = " + Float.toString(event.values[1]) + "\n" +
                "z = " + Float.toString(event.values[2]) + "\n"
        );

        if(event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
            detectShake(event);
        }
        else if(event.sensor.getType() == Sensor.TYPE_GYROSCOPE) {
            detectRotation(event);
        }
    }

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

    }


    // References:
    //  - http://jasonmcreynolds.com/?p=388
    //  - http://code.tutsplus.com/tutorials/using-the-accelerometer-on-android--mobile-22125
    private void detectShake(SensorEvent event) {
        long now = System.currentTimeMillis();

        if((now - mShakeTime) > SHAKE_WAIT_TIME_MS) {
            mShakeTime = now;

            float gX = event.values[0] / SensorManager.GRAVITY_EARTH;
            float gY = event.values[1] / SensorManager.GRAVITY_EARTH;
            float gZ = event.values[2] / SensorManager.GRAVITY_EARTH;

            // gForce will be close to 1 when there is no movement
            float gForce = FloatMath.sqrt(gX*gX + gY*gY + gZ*gZ);

            // Change background color if gForce exceeds threshold;
            // otherwise, reset the color
            if(gForce > SHAKE_THRESHOLD) {
                mView.setBackgroundColor(Color.rgb(0, 100, 0));
            }
            else {
                mView.setBackgroundColor(Color.BLACK);
            }
        }
    }

    private void detectRotation(SensorEvent event) {
        long now = System.currentTimeMillis();

        if((now - mRotationTime) > ROTATION_WAIT_TIME_MS) {
            mRotationTime = now;

            // Change background color if rate of rotation around any
            // axis and in any direction exceeds threshold;
            // otherwise, reset the color
            if(Math.abs(event.values[0]) > ROTATION_THRESHOLD ||
               Math.abs(event.values[1]) > ROTATION_THRESHOLD ||
               Math.abs(event.values[2]) > ROTATION_THRESHOLD) {
                mView.setBackgroundColor(Color.rgb(0, 100, 0));
            }
            else {
                mView.setBackgroundColor(Color.BLACK);
            }
        }
    }
}

MainActivity.Java:

package com.drejkim.androidwearmotionsensors;

import android.app.Activity;
import android.os.Bundle;
import android.support.wearable.view.DotsPageIndicator;
import android.support.wearable.view.GridViewPager;
import android.support.wearable.view.WatchViewStub;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);


        WatchViewStub stub = (WatchViewStub) findViewById(R.id.watch_view_stub);
        stub.setOnLayoutInflatedListener(new WatchViewStub.OnLayoutInflatedListener() {
            @Override public void onLayoutInflated(WatchViewStub stub) {
                final GridViewPager pager = (GridViewPager) findViewById(R.id.pager);
                pager.setAdapter(new SensorFragmentPagerAdapter(getFragmentManager()));

                DotsPageIndicator indicator = (DotsPageIndicator) findViewById(R.id.page_indicator);
                indicator.setPager(pager);
            }
        });
    }
}

SensorFragmentPagerAdapter.java:

package com.drejkim.androidwearmotionsensors;

import android.app.Fragment;
import android.app.FragmentManager;
import android.hardware.Sensor;
import android.support.wearable.view.FragmentGridPagerAdapter;

public class SensorFragmentPagerAdapter extends FragmentGridPagerAdapter {

    private int[] sensorTypes = {
            Sensor.TYPE_ACCELEROMETER,
            Sensor.TYPE_GYROSCOPE
    };

    public SensorFragmentPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getFragment(int row, int column) {
        return SensorFragment.newInstance(sensorTypes[column]);
    }

    @Override
    public int getRowCount() {
        return 1; // fix to 1 row
    }

    @Override
    public int getColumnCount(int row) {
        return sensorTypes.length;
    }
}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.drejkim.androidwearmotionsensors" >

    <uses-feature android:name="android.hardware.type.watch" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.DeviceDefault" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Can someone help me out? I got this code from some source and I don't know how to fix it since the logcat is showing a long fatal exception script highlighted in red. Thank you, I'll really appreciate it if someone can help.

Answer 1

From the error message in LogCat you can read that mSensor is null when you try to execute

mTextTitle.setText(mSensor.getStringType());

This means that the your sensor manager is unable to find a default sensor that matches the requested type

mSensor = mSensorManager.getDefaultSensor(mSensorType);

as stated in the documentation .