android - 卫星 map 类型不工作

Question

尊敬的成员(member)，我正在开发一个基本的 Google map 应用程序。我已经为这个应用程序实现了一些功能，如 GPS 检查、互联网检查、工作互联网检查等。我刚刚在顶部添加了一个选项菜单，其中包含一个 SATELLITE TYPE map 。我已经编写了正确的代码，但每当我单击 SATELLITE 选项以更改我的 map View 时，该应用程序都会自行关闭。终端中没有显示错误。应用程序在所有其他方面都运行良好。我不知道我哪里做错了，这是关闭我的应用程序而不是加载特定的 map 类型。以下是我的 main_menu XML 资源文件:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/SatelliteType"
    android:title="@string/satellite"/>
</menu>

以下是 Java 代码。如果我需要更清楚地阐述这些内容以了解我在这种编码实践中的错误/缺点，请告诉我:

package com.example.Test;
//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.LocationManager;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GoogleApiAvailability;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import java.net.InetAddress;

//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
public class MapsActivity extends AppCompatActivity implements OnMapReadyCallback {
    GoogleMap googleMap;
    private static final int ERROR_DIALOG_REQUEST = 9901;

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


        //****************************Checking the GPS at start*******************
        final LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {

            Toast.makeText(this, "GPS is Enabled in your device", Toast.LENGTH_SHORT).show();
        } else {
            showGPSDisabledAlertToUser();
        }

        //********Checking the Google Play Services at start*********
        if (ServicesOK()) {
            Toast.makeText(this, "CONNECTED to Google Play Services", Toast.LENGTH_SHORT).show();
        }
        //****************************Checking the NETWORKING DEVICE at start*******************
        if (isConnected()) {
            Toast.makeText(this, "CONNECTED to NETWORKING DEVICE", Toast.LENGTH_SHORT).show();
        }
        //****************************Checking the INTERNET SERVICE at Start*******************
        if (isInternetAvailable()) {
            Toast.makeText(this, "CONNECTED to INTERNET", Toast.LENGTH_SHORT).show();
        }

        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

    }

    //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    //****************************When MAP is perfectly LOADED*******************
    @Override
    public void onMapReady(GoogleMap googleMap) {
        // Add a marker in CIITLAHORE and move the camera
        LatLng ciitlahore = new LatLng(31.400693, 74.210941);
        googleMap.addMarker(new MarkerOptions().position(ciitlahore).title("Marker in CIIT LAHORE"));
        googleMap.moveCamera(CameraUpdateFactory.newLatLng(ciitlahore));
        googleMap.animateCamera(CameraUpdateFactory.zoomTo(17.0f));
    }

    //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    //****************************Making MENU Option******************

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        //Add menu handling code
        switch (id) {
            case R.id.SatelliteType:
                googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
                return (true);
            default :
                return super.onOptionsItemSelected(item);
        }
    }
    //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    //****************************METHOD for checking GOOGLE PLAY SERVICES*************************
    public boolean ServicesOK() {
        int resultCode = GoogleApiAvailability.getInstance().isGooglePlayServicesAvailable(this);

        if (resultCode == ConnectionResult.SUCCESS) {
            return true;
        } else {
            GoogleApiAvailability.getInstance().getErrorDialog(this, resultCode, ERROR_DIALOG_REQUEST).show();
            Toast.makeText(this, "Can't connect to mapping services", Toast.LENGTH_SHORT).show();
        }
        return false;
    }

//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    //****************************METHOD for checking INTERNET AVAILABLE*************************
    public boolean isInternetAvailable() {
        try {
            InetAddress ipAddr = InetAddress.getByName("google.com");
            return !ipAddr.equals("");
        } catch (Exception e) {
            return false;
        }
    }

    //****************************METHOD for checking INTERNET CONNECTIVITY*************************

    public boolean isConnected() {
        ConnectivityManager cm = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        if (activeNetwork != null) {
            // connected to the internet
            if (activeNetwork.getType() == ConnectivityManager.TYPE_WIFI) {
                // connected to wifi
                Toast.makeText(this, "WIFI CONNECTION AVAILABLE", Toast.LENGTH_SHORT).show();
            } else if (activeNetwork.getType() == ConnectivityManager.TYPE_MOBILE) {
                // connected to the mobile provider's data plan
                Toast.makeText(this, "CELLULAR CONNECTION AVAILABLE", Toast.LENGTH_SHORT).show();
            }
        } else {
            // not connected to the internet
            Toast.makeText(this, "NOT CONNECTED to any working INTERNET service", Toast.LENGTH_SHORT).show();
        }
        return false;
    }

    //****************************GPS DIALOGUE BOX*************************
    private void showGPSDisabledAlertToUser() {
        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
        alertDialogBuilder.setMessage("GPS is disabled in your device. Would you like to enable it?")
                .setCancelable(false)
                .setPositiveButton("YES",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                Intent callGPSSettingIntent = new Intent(
                                        android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                                startActivity(callGPSSettingIntent);
                            }
                        });

        alertDialogBuilder.setNegativeButton("NO",
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        dialog.cancel();
                        finishAffinity();
                    }
                });
        AlertDialog alert = alertDialogBuilder.create();
        alert.show();
    }
    //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//+++++++++++++++++++++++++++++++++++++++++++  END   +++++++++++++++++++++++++++++++++++++++++++++++
}

Answer 1

您的 googleMap 对象是 null。您需要将其添加到您的 onMapReady 方法中:

this.googleMap = googleMap;

此外，当您选择菜单时，您的 googleMap 对象可能为 null，因此您需要检查它:

if (googleMap != null) {
    googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
}