在 Android 中等待 Firebase 异步检索数据 [英] Wait Firebase async retrieve data in Android

问题描述

我需要存储他自己异步的 FireBase getValue 方法的结果.我不能使用诸如onPostExecute()"之类的东西，而且出于我的目的，我无法将所有操作执行到 onDataChange()"中，因为我将来需要在其他活动中引用一些参考资料.

I need to store the result of FireBase getValue method that is async by his own. I can't use something like "onPostExecute()" and, for my purpose, i can't execute all my operation "into onDataChange()" because i need some references in future time in other activities.

这是我检索数据的片段:

Here my snippet to retrieve data:

    List<Village> villages = new LinkedList<>();
    Firebase ref = new Firebase("MYFIREBASEURL").child("village");
    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            spinnerArray.clear();
            for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                Village v = postSnapshot.getValue(Village.class);
                villages.add(v);
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            System.out.println("The read failed: " + firebaseError.getMessage());
        }
    });

如果我尝试从onDataChange"中读取村庄，那么对于他的异步生活来说，自然是空值.有没有办法确保调用了 onDataChange?.

If i try to read villages out of "onDataChange" i have, naturally for his async life, null value. There is a way to ensure that onDataChange was called?.

推荐答案

对不起，如果这不是你想要的，因为我的英语太糟糕了.您可以定义一个侦听器接口来处理它.示例:

Sorry if it's not what you want because my English too bad. You can define a listener interface to handle it. Example:

 public interface OnGetDataListener {
    public void onStart();
    public void onSuccess(DataSnapshot data);
    public void onFailed(DatabaseError databaseError);
}

我创建了一个自定义函数来获取 Database.class 中的数据:

And I create a custom function to get data in Database.class:

  public void mReadDataOnce(String child, final OnGetDataListener listener) {
    listener.onStart();
   FirebaseDatabase.getInstance().getReference().child(child).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            listener.onSuccess(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            listener.onFailed(databaseError);
        }
    });
}

当我想从 Main.class 获取数据时，我这样做:

When I want to get data from Main.class, I do:

private void mCheckInforInServer(String child) {
    new Database().mReadDataOnce(child, new OnGetDataListener() {
        @Override
        public void onStart() {
            //DO SOME THING WHEN START GET DATA HERE
        }

        @Override
        public void onSuccess(DataSnapshot data) {
           //DO SOME THING WHEN GET DATA SUCCESS HERE
        }

        @Override
        public void onFailed(DatabaseError databaseError) {
           //DO SOME THING WHEN GET DATA FAILED HERE
        }
    });

}

通过这种方式，您可以重用您的方法并处理数据.

By this way, you can reuse your method and handle data.

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