java - Android开发(Java)-崩溃

Question

我正在尝试学习有关Java的更多信息。我对此一无所知。人们说，如果我懂PHP，我就会懂Java。我不这么认为。 Java太多了点打磨，并且不允许任何异常。

我的应用程序启动时立即崩溃。我已将“FINE_LOCATION”和“COARSE_LOCATION”添加到应用程序的权限。

package either.no.me.myapplication2;

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends AppCompatActivity {

    TextView textLat;
    TextView textLon;
    Timer timer1 = new Timer();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textLat = (TextView) findViewById(R.id.textLat);
        textLon = (TextView) findViewById(R.id.textLon);
        GPSFinder gpsFinder = new GPSFinder();
        gpsFinder.GetLocation();
    }
}

class GPSFinder extends MainActivity {
    public void GetLocation() {
        LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

        // Define a listener that responds to location updates
        LocationListener locationListener = new LocationListener() {
            public void onLocationChanged(Location location) {
                // Called when a new location is found by the network location provider.
                textLat.setText(Double.toString(location.getLatitude()));
                textLon.setText(Double.toString(location.getLongitude()));
            }

            public void onStatusChanged(String provider, int status, Bundle extras) {
            }

            public void onProviderEnabled(String provider) {
            }

            public void onProviderDisabled(String provider) {
            }
        };

        // Register the listener with the Location Manager to receive location updates
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
    }
}

我在logcat中遇到的错误:

07-31 01:36:45.611 1703-1703/either.no.me.myapplication2 E/AndroidRuntime: FATAL EXCEPTION: main
                                                                           Process: either.no.me.myapplication2, PID: 1703
                                                                           java.lang.RuntimeException: Unable to start activity ComponentInfo{either.no.me.myapplication2/either.no.me.myapplication2.MainActivity}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2219)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
                                                                               at android.app.ActivityThread.access$800(ActivityThread.java:135)
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                               at android.os.Looper.loop(Looper.java:136)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5045)
                                                                               at java.lang.reflect.Method.invokeNative(Native Method)
                                                                               at java.lang.reflect.Method.invoke(Method.java:515)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
                                                                               at dalvik.system.NativeStart.main(Native Method)
                                                                            Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
                                                                               at android.app.Activity.getSystemService(Activity.java:4532)
                                                                               at either.no.me.myapplication2.GPSFinder.GetLocation(MainActivity.java:37)
                                                                               at either.no.me.myapplication2.MainActivity.onCreate(MainActivity.java:31)
                                                                               at android.app.Activity.performCreate(Activity.java:5231)
                                                                               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2163)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269) 
                                                                               at android.app.ActivityThread.access$800(ActivityThread.java:135) 
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                               at android.os.Looper.loop(Looper.java:136) 
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5045) 
                                                                               at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                               at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
                                                                               at dalvik.system.NativeStart.main(Native Method) 
07-31 01:36:48.875 1703-1703/either.no.me.myapplication2 I/Process: Sending signal. PID: 1703 SIG: 9

Answer 1

删除GPSFinder类，并在MainActivity中使用GetLocation方法的代码
像下面

<pre>
package either.no.me.myapplication2;

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends AppCompatActivity {

    TextView textLat;
    TextView textLon;
    Timer timer1 = new Timer();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textLat = (TextView) findViewById(R.id.textLat);
        textLon = (TextView) findViewById(R.id.textLon);
        getLocation();
    }

public void getLocation() {
        LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

        // Define a listener that responds to location updates
        LocationListener locationListener = new LocationListener() {
            public void onLocationChanged(Location location) {
                // Called when a new location is found by the network location provider.
                textLat.setText(Double.toString(location.getLatitude()));
                textLon.setText(Double.toString(location.getLongitude()));
            }

            public void onStatusChanged(String provider, int status, Bundle extras) {
            }

            public void onProviderEnabled(String provider) {
            }

            public void onProviderDisabled(String provider) {
            }
        };

        // Register the listener with the Location Manager to receive location updates
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
    }  }