Retrieve data from Firebase on Android Studio - android

Can someone help me fix it?
Following code works without any error, however, it does not retrieve data from Firebase and show in the TextView.
private fun viewData() {
val postReference = FirebaseDatabase.getInstance().getReference("dataID")
val dbView= findViewById<TextView>(R.id.txtFdbData)
val postListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val post = dataSnapshot.getValue(Post::class.java)
dbView.text=post?.postName
}
override fun onCancelled(databaseError: DatabaseError) {
}
}
postReference.addValueEventListener(postListener)
Toast.makeText(this,"Retrieved",Toast.LENGTH_LONG).show()
}
Above code is called when I tap the button 'btnView'
viewButton = findViewById(R.id.btnView)
viewButton.setOnClickListener {
viewData()
}
When I hit the button it shows the toast message 'Retrieved' and the default value given in the TextView (txtFdbData) is deleted (or may be replaced with an empty string?, I do not know).
Following is the post Class
data class Post (
val postName: String="",
val postDescription:String="")
I am working on Android Studio, using Kotlin and Firebase Realtime Database.

You query to database return list of items. So loop through it and try to get Post. Check below:
override fun onDataChange(dataSnapshot: DataSnapshot) {
dataSnapshot.children.forEach {childSnapshot ->
val post = childSnapshot.getValue(Post::class.java)
dbView.text=post?.postName
}
}

getReference("dataID") is not your data node it is your parent node.
Then you have to access their children using getChildren() method.
Change you on data change method with this.
override fun onDataChange(dataSnapshot: DataSnapshot) {
for (postSnapshot : dataSnapshot.getChildren()) {
val post = postSnapshot .getValue(Post::class.java)
dbView.text=post?.postName
}
}

Related

Firebase to Kotlin Fragment

Is there any way to retrieved selected data in Firebase to a fragment in Kotlin? Not all data only selected row.
I'm new to Kotlin. Please help me.
firstly user login to the system. for this I checked the user name from Firebase. it works properly. But after that, I want to retrieve data of that username into a fragment. In one activity I add five fragments. I need to load all data of that user into one Fragment.
for example in this abi is a username and I need to load all data of only that username into one fragment.
Firebase data
Inside of abi
here's what I added.
val rootRef = FirebaseDatabase.getInstance().reference
val userRef = rootRef.child("User").child(sessionId)
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val name = dataSnapshot.child("fullName").getValue(String::class.java)
val age = dataSnapshot.child("age").getValue(String::class.java)
val phone = dataSnapshot.child("phoneNo").getValue(String::class.java)
val bank = dataSnapshot.child("bankAccNo").getValue(String::class.java)
val password = dataSnapshot.child("passwordRegister").getValue(String::class.java)
nameText.setText(name)
ageText.setText(age)
phoneText.setText(phone)
bankText.setText(bank)
passwordText.setText(password)
}
override fun onCancelled(error: DatabaseError) {
Log.d("TAG", error.getMessage())
}
}
userRef.addListenerForSingleValueEvent(valueEventListener)
To get the data from the Firebase Realtime Database that corresponds only to the abi user, please use the following lines of code:
val rootRef = FirebaseDatabase.getInstance().reference
val userRef = rootRef.child("User").child("abi")
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val name = dataSnapshot.child("fullName").getValue(String::class.java)
Log.d("TAG", name)
}
override fun onCancelled(databaseError: error) {
Log.d("TAG", error.getMessage()) //Don't ignore potential errors!
}
}
userRef.addListenerForSingleValueEvent(valueEventListener)
In the same way, you can also get the values of the other fields. The result in the logcat will be:
Abilashini

Get firebase snapshot data in Kotlin Android

I'm new to Android & I don't know how to get all the firebase snapshot data at once inside the UID in the single data class.
val usersPrivateRef = Constants.FIREBASE_RESIDENT_PRIVATE
usersPrivateRef?.child("Fs0qczU3GsfJuGDGAeEN7bIgfjD3")
?.addListenerForSingleValueEvent(object : ValueEventListener{
override fun onDataChange(snapshot: DataSnapshot) {
if (snapshot.exists()) {
println(snapshot)
} else {
showLongToast("Snapshot not exists")
}
}
override fun onCancelled(error: DatabaseError) {}
})
To get a value from the DataSnapshot you can use its child() and getValue calls. For example, to print Krishna's email, you'd do:
println(snapshot.child("personalDetails/email").getValue(String::class.java)
I have found a solution for my above question
With the help of Gson library & also I have created the Kotlin data classes same as my snapshot data.
private var residentDATA : ArrayList<MineUserInfo> = ArrayList<MineUserInfo>()
var gson = Gson()
val json = Gson().toJson(snapshot.value)
var data = gson?.fromJson(json, MineUserInfo::class.java)
residentDATA.add(data)

Display data from Firebase Realtime Database

Created next structure in my database, and now want to display data in my list
Tried to add next code in onViewCreated:
databaseReference = FirebaseDatabase.getInstance().reference
val wordsRef = databaseReference?.child("talk-6e3c0")?.child("words")
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
topWordsList.clear()
for (wordsSnapshot in dataSnapshot.children) {
val topWord = wordsSnapshot.getValue(TopWord::class.java)
topWord?.let { topWordsList.add(it) }
}
}
override fun onCancelled(databaseError: DatabaseError) {
Log.d("some", "Error trying to get targets for ${databaseError.message}")
}
}
wordsRef?.addListenerForSingleValueEvent(valueEventListener)
Method onDataChanged was called, but i can't get name for example.
My model:
data class TopWord(
val name: String = "",
val description: String = ""
)
You aren't getting something because you are adding the name of your project as a child in the reference and there is no need for that. So please change the following line of code:
val wordsRef = databaseReference?.child("talk-6e3c0")?.child("words")
to
val wordsRef = databaseReference?.child("words")
I just removed the call to .child("talk-6e3c0")?.

Populating Data Class via Simple Firebase Calls

Running into an error I have been researching and attempting to fix for the past couple weeks. There are tons of suggestions out there and I've tried at least half a dozen with the same result each time.
How does Kotlin access Firebase data and populate a very simple data class?
Error: com.google.firebase.database.DatabaseException:
Can't convert object of type java.lang.String to type com.touchtapapp.handsofhope.LandingTextTitles
Read about suggestions to first convert to a Map and then to my custom data class... attempted this, successfully created the Mapped values w/ correct data... but ran into the exact same error when sending the Mapped values to the customs data class (LandingTextTitles).
Current code:
Data Model Class
data class LandingTextTitles(
val subTitle: String,
val title: String
)
Method to retrieve data from firebase
private fun initTitles() {
val ref = FirebaseDatabase.getInstance().getReference("/landing")
ref.addListenerForSingleValueEvent(object: ValueEventListener {
override fun onDataChange(p0: DataSnapshot) {
p0.children.forEach {
val titles = it.getValue(LandingTextTitles::class.java)
}
}
override fun onCancelled(p0: DatabaseError) {
// Handle Cancelled Data
}
})
// Log the titles value to see if data passed correctly
Log.d("Titles", titles.toString())
}
When I log out something like Log.d(it.toString()), I see the keys and values just fine. What am I doing wrong here?
EDIT:
Firebase data snapshot
EDIT 2:
If we use Log.d("Titles", it.toString()), we get the following:
D/Titles: DataSnapshot { key = subTitle, value = Start Here. }
D/Titles: DataSnapshot { key = title, value = Facing unexpected problems? }
If you have the following database:
landing
randomId
subTitle : "Awesome"
title : "Developer Team"
Then you can retrieve title and subTitle by doing the following:
private fun initTitles() {
val ref = FirebaseDatabase.getInstance().getReference("/landing")
ref.addListenerForSingleValueEvent(object: ValueEventListener {
override fun onDataChange(p0: DataSnapshot) {
p0.children.forEach {
val title = it.child("title").getValue(String::class.java)
val subTitle = it.child("subTitle").getValue(String::class.java)
}
}
override fun onCancelled(p0: DatabaseError) {
// Handle Cancelled Data
}
})
// Log the titles value to see if data passed correctly
Log.d("Titles", titles.toString())
}
If you want to use the data class, then change this:
override fun onDataChange(p0: DataSnapshot) {
p0.children.forEach {
val titles = it.getValue(LandingTextTitles::class.java)
}
into this:
override fun onDataChange(p0: DataSnapshot) {
val titles = p0.getValue(LandingTextTitles::class.java)
}

Android App Development - Firebase Database

I'm building an activity in an app where users can upload a post, and other users in the app can view the post.
I built a function called loadPost()
This function will take what's there in the database and load it in my View.
Unfortunately, I'm facing an error with the
.addValueEventListener(ValueEventListener{
It's telling me that the interface needs a constructor.
here's the function:
//*******************************************************
//Load posts to the screen from the database
//****************************************************
fun loadPost(){
myRef.child("posts")
.addValueEventListener(ValueEventListener{
override fun onDataChange(#NonNull dataSnapshot: DataSnapshot?) {
try {
postElements.clear()
postElements.add(Post("0","him","url","add"))
postElements.add(Post("0","him","url","ads"))
//Hashmap : Key and value (represents the post and node)
var td= dataSnapshot!!.value as HashMap<String,Any>
for(key in td.keys){
var post= td[key] as HashMap<String,Any>
postElements.add(Post(key,
post["text"] as String,
post["postImage"] as String
,post["userUID"] as String))
}
adpater!!.notifyDataSetChanged() //notify when there's an update in the adapter
}catch (ex:Exception){}
}
override fun onCancelled(p0: DatabaseError?) {
}
})
}
this is how the constructor of a ValueEventListener should look alike:
object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
}
}
which means, that you have to replace this one line
.addValueEventListener(ValueEventListener {
with:
.addValueEventListener(object : ValueEventListener {
see https://youtrack.jetbrains.com/issue/KT-7770 (concerning the code-converter)

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