我不知道为什么我的应用程序不会停止崩溃

Question

我正在编写一个需要位置信息的应用程序。 Logcat 告诉我我的代码很清楚，没有错误。但是当我启动应用程序（模拟或在我的 phone 上）时，它崩溃了。

这是我的代码：

package com.example.a291019;


import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;
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.os.Bundle;
import android.util.Log;
import android.widget.TextView;


public class MainActivity extends AppCompatActivity {

    TextView txtLocation = findViewById(R.id.txtLocation);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_DENIED || ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_DENIED) {

            assert locationManager != null;
            locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 500, 10, new LocationListener() {
                @Override
                public void onLocationChanged(Location location) {
                    Log.d("GPS", "Latitude" + location.getLatitude() + " et longitude " + location.getLongitude());
                    txtLocation.setText(Log.d("GPS", String.format("Latitude%s et longitude %s", location.getLatitude(), location.getLongitude())));
                }

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

                }

                @Override
                public void onProviderEnabled(String provider) {

                }

                @Override
                public void onProviderDisabled(String provider) {

                }

            });
        }


    }
}

Answer 1

从我的角度来看，那条线在那个位置的初始化是错误的：

public class MainActivity extends AppCompatActivity {
    TextView txtLocation = findViewById(R.id.txtLocation);

必须放在这一行之后：

setContentView(R.layout.activity_main);

这是您定义负责布局的位置 activity。

所以为 class 成员调用 findViewById 是行不通的。

Answer 2

1) 将此行移动到 onCreate 并使其成为 final:

final TextView txtLocation = findViewById(R.id.txtLocation);

2) Log.d() returns 整数，不应该是 setText 方法的参数，做这个而不是那个：

txtLocation.setText(String.format("Latitude%s et longitude %s", 
    location.getLatitude(), location.getLongitude()));

固定代码：

package com.example.a291019;

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.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;


public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    final TextView txtLocation = findViewById(R.id.txtLocation);

    LocationManager locationManager = (LocationManager) 
 getSystemService(Context.LOCATION_SERVICE);
    if (ContextCompat.checkSelfPermission(this, 
 Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_DENIED || 
 ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) 
 != PackageManager.PERMISSION_DENIED) {

        assert locationManager != null;
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 500, 10, 
          new LocationListener() {
            @Override
            public void onLocationChanged(Location location) {
                Log.d("GPS", "Latitude" + location.getLatitude() + " et longitude " + 
                    location.getLongitude());
                txtLocation.setText(String.format("Latitude%s et longitude %s", 
                    location.getLatitude(), location.getLongitude()));
            }

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

            }

            @Override
            public void onProviderEnabled(String provider) {

            }

            @Override
            public void onProviderDisabled(String provider) {

            }

        });
    }

  }
}

我不知道为什么我的应用程序不会停止崩溃

I don't know why my app don't stop crashing

java

android

location

geolocation