这段代码有啥问题？应用程序应该获取位置

Posted 2023-04-15

【中文标题】这段代码有啥问题？应用程序应该获取位置

【英文标题】：What is wrong with this code? App should get the location这段代码有什么问题？应用程序应该获取位置

【发布时间】：2017-11-07 07:43:32

【问题描述】：

应用程序（它应该读取我的位置）在我尝试启动时崩溃：

我已尽一切努力修复它，但在我看来，我已经监督了一些基本问题。

主要活动：

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;
import android.support.v4.content.LocalBroadcastManager;
import java.util.Locale;

public class MainActivity extends Activity 
    public static final String TAG = "MainActivity";
    private LocalBroadcastManager mLocalBroadcastManager;
    private BroadcastReceiver mBroadcastReceiver;
    private Intent mServiceIntent;
    private TextView mLatitude;
    private TextView mLongitude;

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

        mLatitude = (TextView) findViewById(R.id.latitude);
        mLongitude = (TextView) findViewById(R.id.longitude);

        mServiceIntent = new Intent(this, LocationService.class);

        mLocalBroadcastManager = LocalBroadcastManager.getInstance(this);
        mBroadcastReceiver = new BroadcastReceiver() 
        @Override
        public void onReceive(Context context, Intent intent) 
            Log.d(TAG, "onReceive()");
            mLatitude.setText(String.format(Locale.getDefault(), "%.6f", intent.getDoubleExtra(LocationService.EXTRA_LATITUDE, 0.0)));
            mLongitude.setText(String.format(Locale.getDefault(), "%.6f", intent.getDoubleExtra(LocationService.EXTRA_LONGITUDE, 0.0)));
        
    ;

    mLocalBroadcastManager.registerReceiver(mBroadcastReceiver, new IntentFilter(LocationService.INTENT_NAME));

    mLatitude.setText(savedInstanceState.getString(LocationService.EXTRA_LATITUDE, "0.0"));
    mLongitude.setText(savedInstanceState.getString(LocationService.EXTRA_LONGITUDE, "0.0"));


@Override
protected void onSaveInstanceState(Bundle bundle)
    super.onSaveInstanceState(bundle);
    bundle.putString(LocationService.EXTRA_LONGITUDE, mLatitude.getText().toString());
    bundle.putString(LocationService.EXTRA_LATITUDE, mLongitude.getText().toString());
    Log.d(TAG, bundle.toString());


@Override
protected void onDestroy()
    mLocalBroadcastManager.unregisterReceiver(mBroadcastReceiver);


public void startGps()
    startService(mServiceIntent);


public void stopGps()
    stopService(mServiceIntent);

定位服务：

import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.support.v4.content.LocalBroadcastManager;
import android.util.Log;

public class LocationService extends Service 
    public static final String TAG = "LocationService";
    public static final String INTENT_NAME = "location_changed";
    public static final String EXTRA_LATITUDE = "latitude";
    public static final String EXTRA_LONGITUDE = "longitude";
    private LocationManager mLocationManager;
    private LocationListener mLocationListener;
    private LocalBroadcastManager mLocalBroadcastManager;

    public void onCreate(Bundle bundle)
        mLocalBroadcastManager = LocalBroadcastManager.getInstance(this);

        mLocationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
        mLocationListener = new LocationListener() 
            @Override
            public void onLocationChanged(final Location location) 
                Log.d(TAG, "onLocationChanged()");

                Intent intent = new Intent(INTENT_NAME);
                intent.putExtra("Latitude", location.getLatitude());
                intent.putExtra("Longitude", location.getLongitude());

                mLocalBroadcastManager.sendBroadcast(intent);
            

            // we do not need the following function, but they have to be implemented (even if they are just empty)
            @Override
            public void onStatusChanged(String provider, int status, Bundle extras) 
            @Override
            public void onProviderEnabled(String provider) 
            @Override
            public void onProviderDisabled(String provider) 
        ;
    

    @Override
    public void onDestroy() throws SecurityException
        mLocationManager.removeUpdates(mLocationListener);
    

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) throws SecurityException
        super.onStartCommand(intent, flags, startId);
        mLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, mLocationListener);
        return Service.START_NOT_STICKY;
    

    @Override
    public IBinder onBind(Intent intent)
        return null;
    

【问题讨论】：

你能发布崩溃日志（logcat）

引起：java.lang.NullPointerException：尝试调用虚拟方法'java.lang.String android.os.Bundle.getString(java.lang.String, java.lang.String)' on空对象引用

java.lang.RuntimeException：无法启动活动 ComponentInfoat.klex.damagedapplication/at.klex.damagedapplication.MainActivity：java.lang.NullPointerException：尝试调用虚拟方法 'java.lang .String android.os.Bundle.getString(java.lang.String, java.lang.String)' 在空对象引用上

你应该edit你的帖子添加额外的信息。

【参考方案1】：

onCreate(savedInstanceState) 的 javadoc 声明：

savedInstanceState Bundle：如果活动在之前关闭后重新初始化，则此Bundle 包含它最近在onSaveInstanceState(Bundle) 中提供的数据。 注意：否则为空。

当您致电 savedInstanceState.getString 时，您会收到一个 NPE，并带有一条消息告诉您 savedInstanceState。

解决方法：修改你的onCreate方法，以应对还没有保存实例的情况；即当savedInstanceState 是null。