Question

尝试获取设备的最后位置

public class MainActivity extends AppCompatActivity implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener {

GoogleApiClient mGoogleApiClient;
TextView textView;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    textView = (TextView) findViewById(R.id.text_view);
    setContentView(R.layout.activity_main);
    if (mGoogleApiClient == null) {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
    }


}

@Override
protected void onStart() {
    mGoogleApiClient.connect();
    super.onStart();
}

@Override
protected void onStop() {
    mGoogleApiClient.disconnect();
    super.onStop();
}

@Override
public void onConnected(@Nullable Bundle bundle) {
    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;
    }
    Location mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
    if (mLastLocation != null) {
        double lat = mLastLocation.getLatitude();

        textView.setText(String.valueOf(lat));          
    }
}

@Override
public void onConnectionSuspended(int i) {

}

@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {

}
}

这些是错误

09-01 12：16：06.385 24018-24018 / mzkhan.assignmenttask E / AndroidRuntime：FATAL EXCEPTION：main 过程：mzkhan.assignmenttask，PID：24018 java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget.TextView.setText（java.lang.CharSequence）＆＃39;在null对象引用上 at mzkhan.assignmenttask.MainActivity.onConnected（MainActivity.java:70）在com.google.android.gms.common.internal.zzl.zzo（未知来源）在com.google.android.gms.internal.zzpy.zzm（未知来源）在com.google.android.gms.internal.zzpw.zzapp（未知来源）在com.google.android.gms.internal.zzpw.onConnected（未知来源）在com.google.android.gms.internal.zzqa.onConnected（未知来源）在com.google.android.gms.internal.zzpp.onConnected（未知来源）在com.google.android.gms.common.internal.zzk $ 1.onConnected（未知来源）在com.google.android.gms.common.internal.zzd $ zzj.zzasd（未知来源）在com.google.android.gms.common.internal.zzd $ zza.zzc（未知来源）在com.google.android.gms.common.internal.zzd $ zza.zzv（未知来源）在com.google.android.gms.common.internal.zzd $ zze.zzasf（未知来源）在com.google.android.gms.common.internal.zzd $ zzd.handleMessage（未知来源）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:145）在android.app.ActivityThread.main（ActivityThread.java:5938） at java.lang.reflect.Method.invoke（Native Method）在java.lang.reflect.Method.invoke（Method.java:372）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1400）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1195）

Answer 1

在textView方法下方定义setContentView()。

像这样......

setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text_view);

Answer 2

请查看下面的代码更改。您在onCreate中设置上下文视图之前已启动textview，因此在访问文本视图时它将返回NPE。

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView) findViewById(R.id.text_view); // swapped this line
    if (mGoogleApiClient == null) {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this)
            .addApi(LocationServices.API)
            .build();
    }
}

Erron使用Android中的GoogleApiClient获取最后一个已知位置

尝试获取设备的最后位置

2 个答案: