如何使用结果从火力地堡查询最终填充的Android Studio的一个ListView [英] How to use results from a Firebase query to ultimately populate a ListView in Android Studio
问题描述
我发现当运行应用程序,因为火力地堡查询时之前将适配器设置没有更新我的ListView中。
第一个问题:反正是有设定查询完成一个监听器?这样我可以设置适配器
有来代替。我知道有些火力地堡方法自动生成的onComplete()
/ 的onSuccess()
听众。
有关调试目的,我可以通过重新输入触发更新到ListView onResume()
。这是我收到一条错误消息:
适配器的内容发生了变化,但ListView控件没有收到通知。确保您的适配器的内容不是从后台线程修改,但只能从UI线程。确保您的适配器调用notifyDataSetChanged()时,其含量的变化。 [中的ListView(16908298,类android.widget.ListView)与适配器(类android.widget.ArrayAdapter)
据我了解这个错误意味着我不能将项目添加到我的的ArrayList
用户名
如果我使用用户名
在我的 ArrayAdapter $的
onChildAdded()
方法中C $ C>。
第二个问题:如何我还可以存储值从我的火力地堡查询返回,并使用这些最终填充一个ListView没有从后台线程直接改变它的内容是什么?
我的尝试:
公共类EditFriendsActivity扩展AppCompatActivity { 保护的ArrayList<串GT;用户名=新的ArrayList<>(); @覆盖
保护无效onResume(){
super.onResume(); 火力地堡usernameRef = ref.child(用户);
查询queryRef = usernameRef.orderByKey(); queryRef.addChildEventListener(新ChildEventListener(){
@覆盖
公共无效onChildAdded(DataSnapshot dataSnapshot,一个String){
字符串username =(字符串)dataSnapshot.child(用户名)的getValue()。
usernames.add(用户名);
Log.v(TAG,用户名+);
}
@覆盖
公共无效onChildChanged(DataSnapshot dataSnapshot,一个String){
Log.v(TAG,内部ChildChanged);
} @覆盖
公共无效onChildRemoved(DataSnapshot dataSnapshot){
Log.v(TAG,内部ChildRemoved);
} @覆盖
公共无效onChildMoved(DataSnapshot dataSnapshot,一个String){
Log.v(TAG,内部ChildMoved);
} @覆盖
公共无效onCancelled(FirebaseError firebaseError){ Log.e(TAG,firebaseError.getMessage()); AlertDialog.Builder建设者=新AlertDialog.Builder(EditFriendsActivity.this);
builder.setTitle(R.string.error_title)
.setMessage(firebaseError.getMessage())
.setPositiveButton(android.R.string.ok,NULL); AlertDialog对话框= builder.create();
dialog.show();
}
}); //阵列适配器
ArrayAdapter<串GT;适配器=新ArrayAdapter<>(
EditFriendsActivity.this,
android.R.layout.simple_list_item_multiple_choice,
用户名); mFriendsList.setAdapter(适配器);
}
}
更新code:从显着回答听众固定错字和清除列表中的每个时间
火力地堡userRef = ref.child(用户);
userRef.addListenerForSingleValueEvent(新ValueEventListener(){ @覆盖
公共无效onDataChange(DataSnapshot dataSnapshot){
usernames.clear(); //清除列表更新前
对于(DataSnapshot孩子:dataSnapshot.getChildren()){
字符串username =(字符串)child.child(用户名)的getValue()。
usernames.add(用户名);
Log.v(TAG,用户名+);
}
跟进质询,<一个href=\"http://stackoverflow.com/questions/32530957/retrieving-data-in-alphabetical-order-using-firebase-in-android-studio\">Here
反正是有设定查询完成一个监听器?这样我可以设置适配器,而不是那里。我知道有些火力地堡方法自动生成
的onComplete()
/的onSuccess()
听众。
块引用>重火力从后端到您的应用程序进行同步数据。因此,不同于具有请求/响应流程传统的数据库,查询火力地堡真的不完整的。这就是为什么在我们保持开放的监听器,并通知任何变化ListView中 FirebaseUI库。
这是说:如果你只是想一次加载从位置的数据,你可以使用
addSingleValueEventListener
:queryRef.addListenerForSingleValueEvent(新ValueEventListener(){
@覆盖
公共无效onDataChange(DataSnapshot快照){
对于(DataSnapshot孩子:snapshot.getChildren()){
字符串username =(字符串)child.child(用户名)的getValue()。
usernames.add(用户名);
}
ArrayAdapter&LT;串GT;适配器=新ArrayAdapter&LT;&GT;(
EditFriendsActivity.this,
android.R.layout.simple_list_item_multiple_choice,
用户名); mFriendsList.setAdapter(适配器);
} @覆盖
公共无效onCancelled(FirebaseError firebaseError){
Log.e(TAG,firebaseError.getMessage());
}
});有可能在上面的错别字,但这是它的一般要点。
I found that my ListView is not updated when the app is run because the adapter is set before the Firebase query occurs.
First Question: Is there anyway to set a listener for query completion? This way I can set the
adapter
there instead. I know some Firebase methods auto-generateonComplete()
/onSuccess()
listeners.For debugging purposes I can trigger an update to the ListView by re-entering
onResume()
. This is where I receive an error message:The content of the adapter has changed but ListView did not receive a notification. Make sure the content of your adapter is not modified from a background thread, but only from the UI thread. Make sure your adapter calls notifyDataSetChanged() when its content changes. [in ListView(16908298, class android.widget.ListView) with Adapter(class android.widget.ArrayAdapter)]
To my understanding this error means I cannot add items to my
ArrayList
"usernames
" inside theonChildAdded()
method if I useusernames
in myArrayAdapter
.Second Question: How else can I store the values returned from my Firebase query and use those to ultimately populate a ListView without directly changing its contents from a "background thread"?
My attempt:
public class EditFriendsActivity extends AppCompatActivity { protected ArrayList<String> usernames = new ArrayList<>(); @Override protected void onResume() { super.onResume(); Firebase usernameRef = ref.child("users"); Query queryRef = usernameRef.orderByKey(); queryRef.addChildEventListener(new ChildEventListener() { @Override public void onChildAdded(DataSnapshot dataSnapshot, String s) { String username = (String) dataSnapshot.child("username").getValue(); usernames.add(username); Log.v(TAG, usernames + ""); } @Override public void onChildChanged(DataSnapshot dataSnapshot, String s) { Log.v(TAG, "Inside ChildChanged"); } @Override public void onChildRemoved(DataSnapshot dataSnapshot) { Log.v(TAG, "Inside ChildRemoved"); } @Override public void onChildMoved(DataSnapshot dataSnapshot, String s) { Log.v(TAG, "Inside ChildMoved"); } @Override public void onCancelled(FirebaseError firebaseError) { Log.e(TAG, firebaseError.getMessage()); AlertDialog.Builder builder = new AlertDialog.Builder(EditFriendsActivity.this); builder.setTitle(R.string.error_title) .setMessage(firebaseError.getMessage()) .setPositiveButton(android.R.string.ok, null); AlertDialog dialog = builder.create(); dialog.show(); } }); // Array adapter ArrayAdapter<String> adapter = new ArrayAdapter<>( EditFriendsActivity.this, android.R.layout.simple_list_item_multiple_choice, usernames); mFriendsList.setAdapter(adapter); } }
Updated Code: Fixed typo in listener from marked answer and cleared list each time.
Firebase userRef = ref.child("users"); userRef.addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { usernames.clear(); // Clear list before updating for (DataSnapshot child : dataSnapshot.getChildren()) { String username = (String) child.child("username").getValue(); usernames.add(username); Log.v(TAG, usernames + ""); }
Follow Up Question Here
解决方案Is there anyway to set a listener for query completion? This way I can set the adapter there instead. I know some Firebase methods auto-generate
onComplete()
/onSuccess()
listeners.Firebases synchronizes data from a backend to your application. So unlike a traditional database that has a request/response flow, Firebase queries don't really complete. That's why in the FirebaseUI library we keep an open listener and notify the ListView of any changes.
That said: if you just want to load the data from a location once, you can use
addSingleValueEventListener
:queryRef.addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(DataSnapshot snapshot) { for (DataSnapshot child: snapshot.getChildren()) { String username = (String) child.child("username").getValue(); usernames.add(username); } ArrayAdapter<String> adapter = new ArrayAdapter<>( EditFriendsActivity.this, android.R.layout.simple_list_item_multiple_choice, usernames); mFriendsList.setAdapter(adapter); } @Override public void onCancelled(FirebaseError firebaseError) { Log.e(TAG, firebaseError.getMessage()); } });
There are probably typos in the above, but this is the general gist of it.
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