So im trying to understand how data is saved on android. I am currently working on a simple notes app. How it currently works, is the user creates a new note, types whatever they want, and once they hit the back button that entry is saved in to a list. I am using compose viewmodel so the entries are saved up until the point the app is destroyed. what is the best way to save the list entries so they are pemenantly saved on the phone. This is also just a general question on how apps generally save user input data that is not saved in the cloud.
here is some example of the code.
data class NotesBlueprint(
val header: String,
val note: String,
val key: Int
)
data class NotesVars(
val header:String = "", <<<< instance of header and the note
val note: String = "" <<<<
var list: List<NotesBlueprint> = mutableListOf() <<< list that the Notes are saved in to
)
You can store the data on android via Shared Preference, Database, and Files. This storage overview guide gives the idea regarding different types of the storage system and how they are saved on android.
In your case, if you want to save notes which user has written, it would be better to go with the database.
Android provides the Room library for storing data in the local database. You can check out the guide here.
I am trying to push the form data to the firebase-firestore. And I also did it successfully. But, the problem is that whenever I am trying to submit the form data again and again it just updates the last data with the current data.
Actually, my requirement is that whenever the user hit the submit button. It creates a document with a random id and stores the all data into that specific id that is generated.
You are specifying the document ID in .document() so it'll overwrite the same document. If you want a document with a random ID on every click, try using add() instead as shown below:
val collectionRef = FirebaseFirestore.getInstance().collection("Maintainance")
collectionRef.add(user).addOnCompleteListener(...)
Alternatively, you can leave .document() empty to get a DocumentReference with a random ID:
val userDocument = FirebaseFirestore.getInstance().collection("Maintanance").document() // <-- don't pass an ID
In addition to #Dharmaraj answer:
CASE_1: In a case where you need to track each user's all submitted forms, probably from your explanation you may need to organize each user's form.
Therefore if you need to organize each user's form then create another sub-collection [example: document(userId).collection("USER_FORMS")] within userID document like this:
val documentRef = FirebaseFirestore.getInstance().collection("Maintainance").document(UserUtils.user?.id.toString()).collection("USER_FROMS").document();
CASE_2 : In a case where you need to make your own custom document ID:
1- make a random number or string or any other data type.
2- The random number/string variable must be local to the code block/method that will execute the form submision function.
3- use the number/string generated as the form document Id like this:
//This must be local so as user clicks submision button so as it generates new random number;
val randomFormId = "generateThenumberOrStringAndInitializeTheVariable";
Then use the random number as the form document Id like this:
val documentRef = FirebaseFirestore.getInstance().collection("Maintainance").document(UserUtils.user?.id.toString()).collection("USER_FROMS").document(randomFormId);
I am new to Firestore and I am developing an android app where I am loading comments in Recycler View.
Below is sample data class for comment.
data class Comment(
val id: String,
val text: String,
val user: DocumentReference
)
Currently I am using this below code in onBindViewHolder in adapter
comment.userId.get()
.addOnCompleteListener {
if (it.isSuccessful) {
val u = it.result.toObject(User::class.java)
user = u.name
binding.userTv.text = user
}
}
binding.commentTv.text = comment.text
I have to explicitally run Task<TResult> every time to fetch the user in adapter.
I am looking for a better way to retrieve user from comment to display username is a single query.
Typically when dealing with usernames that may update regularly, traditionally you would store the raw user name string in each document which requires heavy read/writes to keep it updated. Instead, it has been found better to store them in a master document/collection that assigns all user UID's with the display name as the value, allowing you to look up any user UID and know it from one source of truth.
This has been made easier with the new Bundle Feature which allows all apps to preload documents in your app to prevent the need to fetch them every time. The only catch is you will need to retrieve the data when a new user isn't in their cached data yet or have a dedicated source for all new users to reduce overhead in those situations.
Source: Data Bundles
I have a realtive simple Firebase database, in which i have 2 models. A ListModel and a UserModel. In my Lists, i'm using push() method to generate unique ids. Each unique id i want to be added as a key and "true" as it's value under Users/gmail#gmail,com/Lists.
When i add the first list, the database looks like this:
And everything works fine, but when i try to add another one, the database looks like this:
In Users/gmail#gmail,com/Lists, the first one is overwritten by the second insert. How can i add the specific id and the specific value, as a new item as shown below?
And this is my code:
final UserModel um = new UserModel();
um.setUserEmail("gmail#gmail,com");
userDatabaseReference.setValue(um);
ListModel lm = new ListModel();
lm.setListName(listName);
listKeyDatabaseReference = listDatabaseReference.push();
listKey = listKeyDatabaseReference.getKey();
listKeyDatabaseReference.setValue(lm);
listDatabaseReference.child(listKey).child("Users").child("gmail#gmail,com").setValue("true");
userDatabaseReference.child("gmail#gmail,com").child("Lists").child(listKey).setValue("true");
Thanks in advance!
Check the official doc:
For basic write operations, you can use setValue() to save data to a specified reference, replacing any existing data at that path.
Your problem is here:
userDatabaseReference.setValue(um);
In this way you are overriding all children in the userDatabaseReference path.
It means that the first record in Users/gmail#gmail,com/Lists is just deleted when you are adding the second one.
Before using the
userDatabaseReference.setValue(um);
you can check if the record exists.
If doesn't exist use the setValue to add the user-model with all its data.
If it exists, just skip this step and add the data in the lists path inside the same user.
I'm trying to test out Firebase to allow users to post comments using push. I want to display the data I retrieve with the following;
fbl.child('sell').limit(20).on("value", function(fbdata) {
// handle data display here
}
The problem is the data is returned in order of oldest to newest - I want it in reversed order. Can Firebase do this?
Since this answer was written, Firebase has added a feature that allows ordering by any child or by value. So there are now four ways to order data: by key, by value, by priority, or by the value of any named child. See this blog post that introduces the new ordering capabilities.
The basic approaches remain the same though:
1. Add a child property with the inverted timestamp and then order on that.
2. Read the children in ascending order and then invert them on the client.
Firebase supports retrieving child nodes of a collection in two ways:
by name
by priority
What you're getting now is by name, which happens to be chronological. That's no coincidence btw: when you push an item into a collection, the name is generated to ensure the children are ordered in this way. To quote the Firebase documentation for push:
The unique name generated by push() is prefixed with a client-generated timestamp so that the resulting list will be chronologically-sorted.
The Firebase guide on ordered data has this to say on the topic:
How Data is Ordered
By default, children at a Firebase node are sorted lexicographically by name. Using push() can generate child names that naturally sort chronologically, but many applications require their data to be sorted in other ways. Firebase lets developers specify the ordering of items in a list by specifying a custom priority for each item.
The simplest way to get the behavior you want is to also specify an always-decreasing priority when you add the item:
var ref = new Firebase('https://your.firebaseio.com/sell');
var item = ref.push();
item.setWithPriority(yourObject, 0 - Date.now());
Update
You'll also have to retrieve the children differently:
fbl.child('sell').startAt().limitToLast(20).on('child_added', function(fbdata) {
console.log(fbdata.exportVal());
})
In my test using on('child_added' ensures that the last few children added are returned in reverse chronological order. Using on('value' on the other hand, returns them in the order of their name.
Be sure to read the section "Reading ordered data", which explains the usage of the child_* events to retrieve (ordered) children.
A bin to demonstrate this: http://jsbin.com/nonawe/3/watch?js,console
Since firebase 2.0.x you can use limitLast() to achieve that:
fbl.child('sell').orderByValue().limitLast(20).on("value", function(fbdataSnapshot) {
// fbdataSnapshot is returned in the ascending order
// you will still need to order these 20 items in
// in a descending order
}
Here's a link to the announcement: More querying capabilities in Firebase
To augment Frank's answer, it's also possible to grab the most recent records--even if you haven't bothered to order them using priorities--by simply using endAt().limit(x) like this demo:
var fb = new Firebase(URL);
// listen for all changes and update
fb.endAt().limit(100).on('value', update);
// print the output of our array
function update(snap) {
var list = [];
snap.forEach(function(ss) {
var data = ss.val();
data['.priority'] = ss.getPriority();
data['.name'] = ss.name();
list.unshift(data);
});
// print/process the results...
}
Note that this is quite performant even up to perhaps a thousand records (assuming the payloads are small). For more robust usages, Frank's answer is authoritative and much more scalable.
This brute force can also be optimized to work with bigger data or more records by doing things like monitoring child_added/child_removed/child_moved events in lieu of value, and using a debounce to apply DOM updates in bulk instead of individually.
DOM updates, naturally, are a stinker regardless of the approach, once you get into the hundreds of elements, so the debounce approach (or a React.js solution, which is essentially an uber debounce) is a great tool to have.
There is really no way but seems we have the recyclerview we can have this
query=mCommentsReference.orderByChild("date_added");
query.keepSynced(true);
// Initialize Views
mRecyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
mManager = new LinearLayoutManager(getContext());
// mManager.setReverseLayout(false);
mManager.setReverseLayout(true);
mManager.setStackFromEnd(true);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(mManager);
I have a date variable (long) and wanted to keep the newest items on top of the list. So what I did was:
Add a new long field 'dateInverse'
Add a new method called 'getDateInverse', which just returns: Long.MAX_VALUE - date;
Create my query with: .orderByChild("dateInverse")
Presto! :p
You are searching limitTolast(Int x) .This will give you the last "x" higher elements of your database (they are in ascending order) but they are the "x" higher elements
if you got in your database {10,300,150,240,2,24,220}
this method:
myFirebaseRef.orderByChild("highScore").limitToLast(4)
will retrive you : {150,220,240,300}
In Android there is a way to actually reverse the data in an Arraylist of objects through the Adapter. In my case I could not use the LayoutManager to reverse the results in descending order since I was using a horizontal Recyclerview to display the data. Setting the following parameters to the recyclerview messed up my UI experience:
llManager.setReverseLayout(true);
llManager.setStackFromEnd(true);
The only working way I found around this was through the BindViewHolder method of the RecyclerView adapter:
#Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
final SuperPost superPost = superList.get(getItemCount() - position - 1);
}
Hope this answer will help all the devs out there who are struggling with this issue in Firebase.
Firebase: How to display a thread of items in reverse order with a limit for each request and an indicator for a "load more" button.
This will get the last 10 items of the list
FBRef.child("childName")
.limitToLast(loadMoreLimit) // loadMoreLimit = 10 for example
This will get the last 10 items. Grab the id of the last record in the list and save for the load more functionality. Next, convert the collection of objects into and an array and do a list.reverse().
LOAD MORE Functionality: The next call will do two things, it will get the next sequence of list items based on the reference id from the first request and give you an indicator if you need to display the "load more" button.
this.FBRef
.child("childName")
.endAt(null, lastThreadId) // Get this from the previous step
.limitToLast(loadMoreLimit+2)
You will need to strip the first and last item of this object collection. The first item is the reference to get this list. The last item is an indicator for the show more button.
I have a bunch of other logic that will keep everything clean. You will need to add this code only for the load more functionality.
list = snapObjectAsArray; // The list is an array from snapObject
lastItemId = key; // get the first key of the list
if (list.length < loadMoreLimit+1) {
lastItemId = false;
}
if (list.length > loadMoreLimit+1) {
list.pop();
}
if (list.length > loadMoreLimit) {
list.shift();
}
// Return the list.reverse() and lastItemId
// If lastItemId is an ID, it will be used for the next reference and a flag to show the "load more" button.
}
I'm using ReactFire for easy Firebase integration.
Basically, it helps me storing the datas into the component state, as an array. Then, all I have to use is the reverse() function (read more)
Here is how I achieve this :
import React, { Component, PropTypes } from 'react';
import ReactMixin from 'react-mixin';
import ReactFireMixin from 'reactfire';
import Firebase from '../../../utils/firebaseUtils'; // Firebase.initializeApp(config);
#ReactMixin.decorate(ReactFireMixin)
export default class Add extends Component {
constructor(args) {
super(args);
this.state = {
articles: []
};
}
componentWillMount() {
let ref = Firebase.database().ref('articles').orderByChild('insertDate').limitToLast(10);
this.bindAsArray(ref, 'articles'); // bind retrieved data to this.state.articles
}
render() {
return (
<div>
{
this.state.articles.reverse().map(function(article) {
return <div>{article.title}</div>
})
}
</div>
);
}
}
There is a better way. You should order by negative server timestamp. How to get negative server timestamp even offline? There is an hidden field which helps. Related snippet from documentation:
var offsetRef = new Firebase("https://<YOUR-FIREBASE-APP>.firebaseio.com/.info/serverTimeOffset");
offsetRef.on("value", function(snap) {
var offset = snap.val();
var estimatedServerTimeMs = new Date().getTime() + offset;
});
To add to Dave Vávra's answer, I use a negative timestamp as my sort_key like so
Setting
const timestamp = new Date().getTime();
const data = {
name: 'John Doe',
city: 'New York',
sort_key: timestamp * -1 // Gets the negative value of the timestamp
}
Getting
const ref = firebase.database().ref('business-images').child(id);
const query = ref.orderByChild('sort_key');
return $firebaseArray(query); // AngularFire function
This fetches all objects from newest to oldest. You can also $indexOn the sortKey to make it run even faster
I had this problem too, I found a very simple solution to this that doesn't involved manipulating the data in anyway. If you are rending the result to the DOM, in a list of some sort. You can use flexbox and setup a class to reverse the elements in their container.
.reverse {
display: flex;
flex-direction: column-reverse;
}
myarray.reverse(); or this.myitems = items.map(item => item).reverse();
I did this by prepend.
query.orderByChild('sell').limitToLast(4).on("value", function(snapshot){
snapshot.forEach(function (childSnapshot) {
// PREPEND
});
});
Someone has pointed out that there are 2 ways to do this:
Manipulate the data client-side
Make a query that will order the data
The easiest way that I have found to do this is to use option 1, but through a LinkedList. I just append each of the objects to the front of the stack. It is flexible enough to still allow the list to be used in a ListView or RecyclerView. This way even though they come in order oldest to newest, you can still view, or retrieve, newest to oldest.
You can add a column named orderColumn where you save time as
Long refrenceTime = "large future time";
Long currentTime = "currentTime";
Long order = refrenceTime - currentTime;
now save Long order in column named orderColumn and when you retrieve data
as orderBy(orderColumn) you will get what you need.
just use reverse() on the array , suppose if you are storing the values to an array items[] then do a this.items.reverse()
ref.subscribe(snapshots => {
this.loading.dismiss();
this.items = [];
snapshots.forEach(snapshot => {
this.items.push(snapshot);
});
**this.items.reverse();**
},
For me it was limitToLast that worked. I also found out that limitLast is NOT a function:)
const query = messagesRef.orderBy('createdAt', 'asc').limitToLast(25);
The above is what worked for me.
PRINT in reverse order
Let's think outside the box... If your information will be printed directly into user's screen (without any content that needs to be modified in a consecutive order, like a sum or something), simply print from bottom to top.
So, instead of inserting each new block of content to the end of the print space (A += B), add that block to the beginning (A = B+A).
If you'll include the elements as a consecutive ordered list, the DOM can put the numbers for you if you insert each element as a List Item (<li>) inside an Ordered Lists (<ol>).
This way you save space from your database, avoiding unnecesary reversed data.