在 Firebase 侦听器中设置单例属性值
2022-09-01 15:49:38
我目前正在测试Firebase以及我计划在整个应用的生命周期内访问的单例模型。我现在被困在一些看起来微不足道的事情上，但我无法为我的生活弄清楚。我有一个我使用的模型示例：firebase中的书签。
public class BookSingleton {
private static BookSingleton model;
private ArrayList<BookMark> bookmarks = new ArrayList<BookMark>();
public static BookSingleton getModel()
{
if (model == null)
{
throw new IllegalStateException("The model has not been initialised yet.");
}
return model;
}
public ArrayList<Bookmark> theBookmarkList()
{
return this.bookmarks;
}
public void setBookmarks(ArrayList<Bookmark> bookmarks){
this.bookmarks = bookmarks;
}
public void loadModelWithDataFromFirebase(){
Firebase db = new Firebase(//url);
Firebase bookmarksRef = fb.child(//access correct child);
final ArrayList<Bookmark> loadedBookmarks = new ArrayList<Bookmark>();
bookmarksRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//getting all properties from firebase...
Bookmark bookmark = new Bookmark(//properties here);
loadedBookmarks.add(bookmark);
}
}
//bookmarks still exist here at this point
setBookmarks(loadedBookmarks);
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});
//by now loadedBookmarks is empty
//this is probably the issue?
//even without this line bookmarks is still not set in mainactivity
setBookmarks(loadedBookmarks);
}
现在，当我使用 Singleton 集的实例启动 mainActivity 时，我得到一个 null 错误，因为显然我编写的用于从 firebase 加载模型数据的函数没有设置任何内容。
像这样：MainActivity
public class MainActivity extends AppCompatActivity {
private BookSingleton theModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Load the model
theModel = BookSingleton.getModel(this);
//manually setting this works
// ArrayList<Book> bookSamples = new ArrayList<Book>;
// bookSamples.add(aBookSample);
theModel.loadModelWithSampleData(bookSamples);
//should have set the singleton model property Bookmarks to the results from firebase
theModel.loadModelWithDataFromFirebase();
//returns 0
Log.d(TAG, "" + theModel.theBookmarkList().size());
setContentView(R.layout.activity_main);
//......rest of code
我怎样才能做到这一点？
