java - 应用程序在调用谷歌地图 Activity 后终止

Question

我在手机上构建 Google map Activity 时遇到问题。我创建的程序如下:

package com.example.calvin.navigation2;
import android.app.Activity;
import android.content.Context;
import android.support.v4.app.FragmentActivity;
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;

public class MapActivity extends FragmentActivity implements OnMapReadyCallback{
    private GoogleMap mMap;
    private final Context con;

    public MapActivity(Context context) {
        this.con = context;
        SupportMapFragment mapFragment = (SupportMapFragment) ((FragmentActivity)con).getSupportFragmentManager()
                .findFragmentById(R.id.mapView);
        mapFragment.getMapAsync(this);
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        // Add a marker in Sydney, Australia, and move the camera.
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    }
}

然后我调用本类(class)中的上一个类(class):

package com.example.calvin.navigation2;

import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Window;

public class Page2Activity extends AppCompatActivity {

    LocationTracker tracker;
    MapActivity myMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
        super.onCreate(savedInstanceState);
        ActionBar actionBar = getSupportActionBar();
        actionBar.hide();
        setContentView(R.layout.activity_page2);

        myMap = new MapActivity(Page2Activity.this);
    }
}

当编译它构建的程序时，但是当从我手机上的应用程序调用时，它总是会终止。

更新: 这是我的错误:

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.calvin.navigation2, PID: 29478
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.calvin.navigation2/com.example.calvin.navigation2.Page2Activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.SupportMapFragment.getMapAsync(com.google.android.gms.maps.OnMapReadyCallback)' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2594)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2685)
                      at android.app.ActivityThread.access$900(ActivityThread.java:188)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1530)
                      at android.os.Handler.dispatchMessage(Handler.java:111)
                      at android.os.Looper.loop(Looper.java:210)
                      at android.app.ActivityThread.main(ActivityThread.java:5839)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1113)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:879)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.SupportMapFragment.getMapAsync(com.google.android.gms.maps.OnMapReadyCallback)' on a null object reference
                      at com.example.calvin.navigation2.MapActivity.<init>(MapActivity.java:20)
                      at com.example.calvin.navigation2.Page2Activity.onCreate(Page2Activity.java:22)
                      at android.app.Activity.performCreate(Activity.java:6177)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1112)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2541)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2685) 
                      at android.app.ActivityThread.access$900(ActivityThread.java:188) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1530) 
                      at android.os.Handler.dispatchMessage(Handler.java:111) 
                      at android.os.Looper.loop(Looper.java:210) 
                      at android.app.ActivityThread.main(ActivityThread.java:5839) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:372) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1113) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:879) 
I/Process: Sending signal. PID: 29478 SIG: 9
Application terminated.

是什么意思？我不明白这个错误。有人可以给我这个错误的详细信息吗？

Answer 1

您需要在布局目录中创建一个 xml 文件

像map.xml

将以下代码放入该文件中:

               <fragment
                    android:id="@+id/mapView"
                    android:name="com.google.android.gms.maps.SupportMapFragment"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    tools:context=".MapActivity" />

之后将此代码添加到您的mapactivity.java 文件中:

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

    SupportMapFragment fragment = (SupportMapFragment) 
    getSupportFragmentManager().findFragmentById(mapView);
    fragment.getMapAsync(this);
   }

将以下代码更改为:

   public MapActivity(Context context) {
    this.con = context;
     }