使用 SupportMapFragment 时，我如何知道地图已准备好使用? [英] How do I know the map is ready to get used when using the SupportMapFragment?
问题描述
在 onCreate 方法中，我使用 SupportMapFragment 来显示地图.
In the onCreate method, I am making use of the SupportMapFragment to show a map.
SupportMapFragment fragment = new SupportMapFragment();
getSupportFragmentManager().beginTransaction()
.add(android.R.id.content, fragment).commit();
为此，我想添加一个标记.问题是当对 getMap 的调用为空时，我什么时候可以再试一次?是否有我可以注册的活动，或者我的方法本身是错误的?
In conjunction to this, I would like to add a marker. The problem is when the call to getMap is null, when can I try again? Is there an event I can register for or is my approach in and of itself wrong?
mMap = ((SupportMapFragment)(getSupportFragmentManager().findFragmentById(R.id.map))).getMap();
if(mMap == null)
//what do I do here?
地图实际上显示在手机上，但我似乎没有运气获得添加标记的参考.
The map is in fact displaying on the phone however I appear to be having no luck in obtaining the reference to add markers.
更新:
我通过构造函数创建 SupportMapFragment 的原因是典型的 setContentView 崩溃并且不起作用.这让我陷入了无法在 onCreate 方法中获取引用的困境，因为当时我实际上正在创建 SupportMapFragment.在进一步调查中，我的 setContentView 问题似乎是没有将 Google-play-services jar 和模块/src 设置为整个项目的一部分的副产品.完成这两项操作后，setContentView 现在可以工作，我可以通过 getMap() 获得参考.
The reason I was creating the SupportMapFragment via the constructor is because the typical setContentView was crashing and did not work. This put me in the predicament where I could not obtain my reference in the onCreate method since I was in fact creating the SupportMapFragment at that time. In further investigation, it appears my setContentView issue was a byproduct of not having both the Google-play-services jar AND the module/src set up as part of the overall project. Upon doing BOTH of these, setContentView now works and I can obtain the reference via getMap() as I would expect.
lots.xml...
lots.xml...
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent" />
LotsActivity.java...
LotsActivity.java...
public class LotsActivity extends FragmentActivity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.lots);
GoogleMap mMap;
mMap = ((SupportMapFragment)(getSupportFragmentManager().findFragmentById(R.id.map))).getMap();
if(mMap == null)
//this should not occur now
}
推荐答案
问题是当getMap的调用为null时，我什么时候可以再试一次?
The problem is when the call to getMap is null, when can I try again?
这取决于问题的性质.
如果通过布局中的SupportMapFragment，则可以在getMap()中成功调用getMap()代码>onCreate().但是，如果您通过构造函数创建 SupportMapFragment，那就太快了 -- GoogleMap 尚不存在.您可以扩展 SupportMapFragment 并覆盖 onActivityCreated()，因为届时 getMap() 已准备就绪.
If you set up the SupportMapFragment via the <fragment> element in the layout, you can call getMap() successfully in onCreate(). But, if you create the SupportMapFragment via the constructor, that's too soon -- the GoogleMap does not yet exist. You can extend SupportMapFragment and override onActivityCreated(), as getMap() is ready by then.
但是，getMap() 也可以返回null 来解决更大的问题，例如未安装 Google Play 服务.您需要使用诸如 GooglePlayServicesUtil.isGooglePlayServicesAvailable() 之类的东西来检测这种情况并按照您的意愿进行处理.
However, getMap() can also return null for a bigger problem, such as Google Play Services not being installed. You would need to use something like GooglePlayServicesUtil.isGooglePlayServicesAvailable() to detect this condition and deal with it however you wish.
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