了解Firebase何时完成API调用？ [英] Knowing when Firebase has completed API call?
问题描述
Firebase文档后，我发现以下内容： $ b
值事件总是最后触发，并保证包含在拍摄快照之前发生的任何其他事件的更新。
我明白这只是说在完成 onChildAdded 调用之后，调用 ValueEventListener 。因此，我认为可以在 onChildAdded 函数中填充我的 RecyclerView ，然后填充 onSingleValueListener 调用，我可以简单地完成动画我的加载屏幕（这已经开始动画在这个函数调用之前）并继续。然而，我遇到了一个问题，我把一些小心 System.out.println 语句，发现在我的情况下， Test 1 Test 2 之前调用c $ c>。这会导致问题，因为这实际上是我想要的相反的行为：我希望 onChildAdded 函数完成，然后调用 onSingleValueListener 函数打印出 Test 1 被调用。这有什么道理吗？有什么办法呢？我将不胜感激解释为什么发生这种情况。
preublic $ getComments（final String postId，final Activity activity，final View fragmentView，final View progressOverlay）{
最终Firebase commentsRef = firebaseRef.child（/ comments）;
Firebase linkRef = firebaseRef.child（/ posts /+ postId）;
linkRef.addListenerForSingleValueEvent（new ValueEventListener（）{
@Override $ b $ public void onDataChange（DataSnapshot dataSnapshot）{
System.out.println（Test 1）;
$ if（progressOverlay.getVisibility（）== View.VISIBLE）{
progressOverlay.setVisibility（View.GONE）;
AndroidUtils.animateView（progressOverlay，View.GONE，0，200）;
fragmentView.findViewById（R.id.rv_view_comments）.setVisibility（View.VISIBLE）;
}
}
$ b @Override
public void onCancelled（FirebaseError firebaseError） {
}
}）;
linkRef.addChildEventListener（new ChildEventListener（）{
@Override
public void onChildAdded（DataSnapshot dataSnapshot，String s）{
commentsRef.child（dataSnapshot.getKey（））。addListenerForSingleValueEvent （new ValueEventListener（）{
@Override
public void onDataChange（DataSnapshot dataSnapshot）{
Comment comment = dataSnapshot.getValue（Comment.class）;
System.out.println（ Test 2）;
application.getCommentsRecyclerViewAdapter（）。getCommentsList（）。add（comment）;
application.getCommentsRecyclerViewAdapter（）。notifyDataSetChanged（）;
}
@Override
public void onCancelled（FirebaseError firebaseError）{
}）
$ b @Override $ b $公共无效onChildChanged（DataSnapsh ot dataSnapshot，String s）{
}
$ b $ @覆盖
public void onChildRemoved（DataSnapshot dataSnapshot）{
}
@Override
public void onChildMoved（DataSnapshot dataSnapshot，String s）{
$ @覆盖
public void onCancelled（FirebaseError firebaseError）{
}
}）;
$解析方案 $ c>Firebase linkRef = firebaseRef.child（/ posts /+ postId）;我可以看到您使用的是旧版Firebase API。 现已弃用！
请将您的代码更新为新的Firebase 3.xx API。
下面两个是独立的异步调用;根据您的使用情况，您可以使用其中一个监听器来读取您的数据。
1。 linkRef.addListenerForSingleValueEvent（new ValueEventListener（）{}）;
2. linkRef.addChildEventListener（new ChildEventListener（）{}）;
您可以参考firebase文档以获取有关数据库侦听器的更多信息。
https://firebase.google.com/docs/database/android / retrieve-data
使用以下代码片段，您可以检索并填充您的评论列表。
public void getComments（final String postId，final Activity activity，final View fragmentView，final View progressOverlay）{
DatabaseReference commentsRef = firebaseRef.child（/ comments） ;
DatabaseReference linkRef = commentsRef.child（/ posts /+ postId）;
linkRef.addListenerForSingleValueEvent（new ValueEventListener（）{
@Override
public void onDataChange（DataSnapshot dataSnapshot）{
//遍历数据快照并更新Adapter数据集$ b （DataSnapshot snapshot：dataSnapshot.getChildren（））{
Comment comment = snapshot.getValue（Comment.class）;
application.getCommentsRecyclerViewAdapter（）。getCommentsList（）。add（comment）;
application.getCommentsRecyclerViewAdapter（）。notifyDataSetChanged（）;
//关闭加载进度条
if（progressOverlay.getVisibility（）== View.VISIBLE）{
progressOverlay.setVisibility（View.GONE）;
AndroidUtils.animateView（progressOverlay，View.GONE，0，200）;
fragmentView.findViewById（R.id.rv_view_comments）.setVisibility（View .VISIBLE）;
}
}
$ b @覆盖
public void onCancelled（DatabaseError databaseError）{
//处理失败事件在这里
}
}）;
希望这会对您有所帮助！
I am having some trouble knowing when my Firebase API call is finished. After reading the Firebase documentation I have found the following:
Value events are always triggered last and are guaranteed to contain updates from any other events which occurred before that snapshot was taken.
I understand this to mean that only after all the onChildAdded call is finished, then the ValueEventListener is called. As a result, I thought that I can populate my RecyclerView in the onChildAdded function and then the onSingleValueListener call, I can simply finish animating my loading screen (which has started animating before this function call) and proceed. However, I have run into an issue where I put some careful System.out.println statements and found that in my case, Test 1 is called before Test 2 is ever called. This causes problems because this is actually the opposite behavior of what I wanted: I wanted the onChildAdded function to finish and then call the onSingleValueListener function that prints out Test 1 to be called. Is there any reason why this is happening? Any way around this? I would appreciate an explanation on why this is happening. Thanks!
public void getComments(final String postId, final Activity activity, final View fragmentView, final View progressOverlay) {
final Firebase commentsRef = firebaseRef.child("/comments");
Firebase linkRef = firebaseRef.child("/posts/" + postId);
linkRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println("Test 1");
if (progressOverlay.getVisibility() == View.VISIBLE) {
progressOverlay.setVisibility(View.GONE);
AndroidUtils.animateView(progressOverlay, View.GONE, 0, 200);
fragmentView.findViewById(R.id.rv_view_comments).setVisibility(View.VISIBLE);
}
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});
linkRef.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
commentsRef.child(dataSnapshot.getKey()).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
Comment comment = dataSnapshot.getValue(Comment.class);
System.out.println("Test 2");
application.getCommentsRecyclerViewAdapter().getCommentsList().add(comment);
application.getCommentsRecyclerViewAdapter().notifyDataSetChanged();
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});
}
With this code "Firebase linkRef = firebaseRef.child("/posts/" + postId);" I could see that you're using legacy Firebase API. Its deprecated now!
Kindly update your code to new Firebase 3.x.x API.
Below two are independent async call; Based on your use-case, you can use either one of the listener to read your data.
1. linkRef.addListenerForSingleValueEvent(new ValueEventListener() {});
2. linkRef.addChildEventListener(new ChildEventListener() {});
You can refer the firebase document to get more information about database listeners. https://firebase.google.com/docs/database/android/retrieve-data
With the following code snippet, you can retrieve and populate your list of comments.
public void getComments(final String postId, final Activity activity, final View fragmentView, final View progressOverlay) {
DatabaseReference commentsRef = firebaseRef.child("/comments");
DatabaseReference linkRef = commentsRef.child("/posts/" + postId);
linkRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// Iterate through data-snapshot, and update your Adapter dataset
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Comment comment = snapshot.getValue(Comment.class);
application.getCommentsRecyclerViewAdapter().getCommentsList().add(comment);
}
application.getCommentsRecyclerViewAdapter().notifyDataSetChanged();
// Dismiss your loading progressbar
if (progressOverlay.getVisibility() == View.VISIBLE) {
progressOverlay.setVisibility(View.GONE);
AndroidUtils.animateView(progressOverlay, View.GONE, 0, 200);
fragmentView.findViewById(R.id.rv_view_comments).setVisibility(View.VISIBLE);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
// Handle fail case here
}
});
Hope this would help you!
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