如何解决在 android 上获取位置时应用程序崩溃的错误？

Question

这是我编写的完整代码。该代码旨在获取设备的位置，然后按下按钮。有 2 个文本字段，其中将显示纬度和经度。这是我的 MainActivity.java 文件

package com.example.shankhanilghosh.test;

import android.content.Context;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    final TextView tLat=(TextView)findViewById(R.id.latitude),
            tLong=(TextView)findViewById(R.id.longitude);

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

        Button b=findViewById(R.id.button1);
        final LocationListener l=new MyLocationListener();
        b.setOnClickListener(new View.OnClickListener(){
            public void onClick(View v) throws SecurityException
            {
                locM.requestLocationUpdates(LocationManager.GPS_PROVIDER,30000,50,l);
                Location loc=locM.getLastKnownLocation(LocationManager.GPS_PROVIDER);
            }
        });
    }
    public class MyLocationListener implements LocationListener{

        @Override
        public void onLocationChanged(Location location) {
            tLat.setText(Double.toString(location.getLatitude()));
            tLong.setText(Double.toString(location.getLongitude()));
        }

        @Override
        public void onStatusChanged(String s, int i, Bundle bundle) {

        }

        @Override
        public void onProviderEnabled(String s) {

        }

        @Override
        public void onProviderDisabled(String s) {

        }
    }
}

我还在 AndroidManifest.xml 文件中添加了必要的权限。这是权限页面

<uses-permission
    android:name="android.permission.ACCESS_FINE_LOCATION" />

我正在使用 android 工作室。每当我构建代码并执行 APK 时，应用程序都会崩溃。请说明导致我的代码崩溃的原因，以及我该如何解决它。

这里是 logcat.

01-19 07:52:24.042 21131-21131/com.example.shankhanilghosh.test E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                  Process: com.example.shankhanilghosh.test, PID: 21131
                                                                                  java.lang.NullPointerException: Attempt to invoke virtual method 'void android.location.LocationManager.requestLocationUpdates(java.lang.String, long, float, android.location.LocationListener)' on a null object reference
                                                                                      at com.example.shankhanilghosh.test.MainActivity.onClick(MainActivity.java:29)
                                                                                      at android.view.View.performClick(View.java:5269)
                                                                                      at android.view.View$PerformClick.run(View.java:21556)
                                                                                      at android.os.Handler.handleCallback(Handler.java:815)
                                                                                      at android.os.Handler.dispatchMessage(Handler.java:104)
                                                                                      at android.os.Looper.loop(Looper.java:207)
                                                                                      at android.app.ActivityThread.main(ActivityThread.java:5769)
                                                                                      at java.lang.reflect.Method.invoke(Native Method)
                                                                                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
                                                                                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)

Answer 1

我认为你还没有初始化你的 LocationManager 在按钮 OnClickListner 之前添加此行

locM=(LocationManager)this.getSystemService(Context.LOCATION_SERVICE);

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