等待Firebase异步在Android中检索数据 [英] Wait Firebase async retrieve data in Android
问题描述
我需要存储由他自己异步生成的FireBase getValue方法的结果.我不能使用诸如"onPostExecute()"之类的东西,并且出于我的目的,我无法执行所有的操作"into onDataChange()",因为在将来的其他活动中我需要一些引用.
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.
这是我的代码段以检索数据:
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,我自然会得到null值.有一种方法可以确保调用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
抱歉,这不是您想要的,因为我的英语太差了. 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);
}
然后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,我做了:
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,您可以重用方法并处理数据.
By this way, you can reuse your method and handle data.
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