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我想了解更多關於Java的知識。我對這件事一無所知。人們在說，如果我知道PHP，我就會認識Java。我不這麼認爲。 Java太多了，並且不允許任何例外。Android開發（Java） - 崩潰
我的應用程序在啓動時立即崩潰。我已經爲應用程序的權限添加了「FINE_LOCATION」和「COARSE_LOCATION」。
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);
}
}
我得到的logcat的錯誤：
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
現在我刪除了類，並使用了MainActivity中的代碼，就像我可以像這樣使用void：GetLocation（）;但現在的錯誤看起來是這樣的：https://i.gyazo.com/35af174610f8c1e73f230c4c92207c0c.png –
我同意這種做法，他應該採取修復。但是ID說他的代碼崩潰的原因是因爲他擴展了一個Activity類，並且在其onCreate（）之前調用了一個需要上下文的方法，因此被稱爲 –
因此，我該怎麼做。我是Android開發人員的超級新手，我還沒有弄明白。我可以在onCreate完成初始化後使用void來調用它嗎？編輯：我把getLocation替換爲getLocation，它開始工作，但我使用Nox作爲模擬器進行調試，但它不包含「網絡」，所以我得到這個：「java.lang.IllegalArgumentException：提供者不存在：網絡「我必須解決它才能繼續。謝謝你的朋友。 –