FATAL EXCEPTION Android佩戴心率App

Question

我正在尝试在Android上制作心率监测应用程序，当我尝试在我的设备上运行应用程序（LG G手表R）时，我有

  

“不幸的是，应用停止了”

在Android工作室上我看到了这个错误：

package com.example.ryuu.appka;

import android.app.Activity;
import android.os.Bundle;
import android.support.wearable.view.WatchViewStub;
import android.widget.TextView;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.util.Log;
import android.view.WindowManager;

import java.text.SimpleDateFormat;
import java.util.Calendar;

public class activity_wear extends Activity implements SensorEventListener {

private TextView mTextView;
private static final String TAG = "MainActivity";
private TextView mTextViewStepCount;
private TextView mTextViewStepDetect;
private TextView mTextViewHeart;


@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_activity_wear);

    final WatchViewStub stub = (WatchViewStub) findViewById(R.id.watch_view_stub);
    stub.setOnLayoutInflatedListener(new WatchViewStub.OnLayoutInflatedListener() {

        @Override
        public void onLayoutInflated(WatchViewStub stub) {
            mTextView = (TextView) stub.findViewById(R.id.text);
            mTextViewStepCount = (TextView) stub.findViewById(R.id.step_count);
            mTextViewStepDetect = (TextView) stub.findViewById(R.id.step_detect);
            mTextViewHeart = (TextView) stub.findViewById(R.id.heart);
            getStepCount();
        }
    });
}

private void getStepCount() {
    SensorManager mSensorManager = ((SensorManager)getSystemService(SENSOR_SERVICE));
    Sensor mHeartRateSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_HEART_RATE);
    Sensor mStepCountSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_STEP_COUNTER);
    Sensor mStepDetectSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_STEP_DETECTOR);

    mSensorManager.registerListener(this, mHeartRateSensor, SensorManager.SENSOR_DELAY_NORMAL);
    mSensorManager.registerListener(this, mStepCountSensor, SensorManager.SENSOR_DELAY_NORMAL);
    mSensorManager.registerListener(this, mStepDetectSensor, SensorManager.SENSOR_DELAY_NORMAL);
}

private String currentTimeStr() {
    Calendar c = Calendar.getInstance();
    SimpleDateFormat df = new SimpleDateFormat("HH:mm:ss");
    return df.format(c.getTime());
}

@Override
public void onSensorChanged(SensorEvent event) {
    if (event.sensor.getType() == Sensor.TYPE_HEART_RATE) {
        String msg = "" + (int)event.values[0];
        mTextViewHeart.setText(msg);
        Log.d(TAG, msg);
    }
    else if (event.sensor.getType() == Sensor.TYPE_STEP_COUNTER) {
        String msg = "Count: " + (int)event.values[0];
        mTextViewStepCount.setText(msg);
        Log.d(TAG, msg);
    }
    else if (event.sensor.getType() == Sensor.TYPE_STEP_DETECTOR) {
        String msg = "Detected at " + currentTimeStr();
        mTextViewStepDetect.setText(msg);
        Log.d(TAG, msg);
    }
    else
        Log.d(TAG, "Unknown sensor type");
}


@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
    Log.d(TAG, "onAccuracyChanged - accuracy: " + accuracy);
}

}

整个源代码位于Google Drive

Answer 1

您的mTextViewHeart似乎是null。显然，在调用onSensorChanged()方法时，mTextViewHeart尚未初始化。

在尝试调用方法之前，可以通过检查它是否为null来阻止它。

另请阅读What is a Null Pointer Exception, and how do I fix it?以帮助您更好地了解问题。