java - 调用谷歌地图活动后应用程序终止
问题描述
在我的手机上构建谷歌地图活动时遇到问题。我创建了如下程序:
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));
}
}
然后我在这个类中调用上一个类:
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);
}
}
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.
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?
解决方案
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;
}
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