Develop Reference

Correct way to parse eterogeneous arrays of data

I have this model that I would like to parse from JSON:
class CFInsertedValuesStructure {
#SerializedName("id")
val id : Int? = null
#SerializedName("value")
val value : List<String> = listOf();
#SerializedName("field_id")
val field_id : String? = null
}
There is a problem with the parameter "value" because it isn't always an array of String, sometimes it could be just a String type.
So when happens I would like to recognise it and create an array of just one String.

depending on what library you use the json parsing it may require a custom parsing type e.g. for kotlinx.serialization you might need to do something like a custom serializer
https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md#specifying-serializer-on-a-property
better still : tell you server-side developer it should always be an array!

How to covert the $document.data details to useful format so that I could use it in listviews

I would like to convert $document.data details to useful format so that I could use it for further applications. This is data from firestore documents.
private val mFireStore = FirebaseFirestore.getInstance()
mFireStore.collection("Users").whereEqualTo("lastName","H").whereEqualTo("firstName", "Uc").get()
.addOnSuccessListener{ documents ->
for(document in documents){
Log.d("TAG","${document.id}=>${document.data}")
Toast.makeText(applicationContext, "${document.id} => ${document.data}",
Toast.LENGTH_LONG).show()
}
}
.addOnFailureListener{exception ->
Log.w("TAG","Error getting documents:",exception)
Toast.makeText(applicationContext, "Failed",
Toast.LENGTH_LONG).show()
}
This is my code. Now when I run the code get this in the logcat
OL0rD4UfgHSh2K8UoTMnX6Xea6P2=>{lastName=H, image=, firstName=Uc, B=L, gender=, organization=, profileCompleted=0, mobile=0, blood group=o+, id=OL0rD4UfgHSh2K8UoTMnX6Xea6P2, email=jojoy09#gmail.com}
Now I want to convert this result to a useful format so that I could use it later. I wpuld like to convert the data so that I could load it in listview.

In the following for-loop:
for(document in documents) { ... }
The "document" object is of type DocumentSnapshot. When you call getData() on such an object, the type of object that is returned is a Map<String, Object>.
In Kotlin, this object is represented by Map<String, Any>. In order to get the data, you can simply iterate over the Map and get the data accordingly, using the following lines of code:
val map = document.data
for ((key, value) in map) {
Log.d("TAG", "$key = $value")
}
Or even simpler, using:
map.forEach { (key, value) -> Log.d("TAG", "$key = $value") }
However, if you only need, the value of a particular property, for example, the value of the email address, you can simply get it by using DocumentSnapshot#getString(String field) method:
val email = document.getString("email")
Log.d("TAG", email)
The result in the logcat will be:
jojoy09#gmail.com
.................
As I see in your screenshot, almost all of the properties are of type String. However, you can find different flavors for each type of field, like getLong(String field), getDouble(String field), getDate(String field), getTimestamp(String field), and so on.
Furthermore, if you need to get the entire document, and you want to convert it into an object of a specific class, as also #mehulbisht mentioned in his answer, you should use DocumentSnapshot#toObject(Class valueType). So assuming that you have a data class that looks like this:
data class User(
var email: String? = null,
var firstName: String? = null,
var lastName: String? = null,
//Other necessary fields
)
To convert the "document" object into an object of the "User" class, please use the following line of code:
val user = document.toObject(User::class.java)
Log.d("TAG", user.email)
The result in the logcat will be the same as above.
If you want to display a list of "User" objects in a ListView, then please check my answer from the following post:
What miss, with connect Firestore and ListView for random results in sample?
It's really simple to convert the Java code into Kotlin.

The Model that you used to set this data will be used here. You can convert the documents to your Model class using the .toObjects() method on it. Just use:
val myObjs = documents.toObjects(Model::class.java)
EDIT
For displaying this as a Log in Logcat use:
Log.d("myObjs ","""
$myObjs
""".trimIndent())
Do tell if this doesn't work for you :)

Pass values as parameters if not null or empty Kotlin

I have text values I retrieve from text inputs. I want to allow the user to not fill in these inputs. But if the user has not filled one or more values I want to display default values for these inputs.
I have a data class that looks something like this:
#Parcelize
data class Profile(
val firstName: String = "",
val lastName: String = "",
val description: String = "",
val imageUri: String = ""
) : Parcelable
On click I call a method from my ViewModel class and pass it the current input values which is then persisted using a Repository class:
viewModel.createProfile(
etFirstName.text.toString(),
etLastName.text.toString(),
etProfileDescription.text.toString(),
profileImageUri.toString()
)
// The createProfile function itself
fun createProfile(
firstName: String = "John",
lastName: String = "Doe",
description: String = "Default Description",
imageUri: String = ""
) {
val profile = Profile(firstName, lastName, description, imageUri)
// Persist data
}
In a another fragment I set some UI data using this persisted data like this:
private fun observeProfile() {
viewModel.getProfile()
viewModel.profile.observe(viewLifecycleOwner, Observer {
val profile = it
tvName.text = getString(R.string.profile_name, profile.firstName, profile.lastName)
tvDescription.text = profile.description
ivProfileImage.setImageURI(Uri.parse(profile.imageUri))
})
}
So currently createProfile expects 4 arguments. I'm able to pass less because I have optional parameters, but how can I conditionally pass arguments to createProfile based on if the value is non null or empty. I can of course create checks for each value, but what is the best way to approach this?
Update
I don't think I was clear enough in my original question, because I don't only pass values from text inputs to createProfile. profileImageUri is a class variable of type Uri? and is initially set to null. The user can select an image and this variable is updated with the image data. The reason I'm passing and storing the image data as a String is because all the profile data also gets persisted to Firestore so Strings are easier to work with.

Compared to your own answer, I'd create a helper function
fun CharSequence?.ifNullOrEmpty(default: String) = if (this.isNullOrEmpty()) default else this.toString()
And use it as
viewModel.createProfile(
etFirstName.text.ifNullOrEmpty("John"),
etLastName.text.ifNullOrEmpty("Doe"),
etProfileDescription.text.ifNullOrEmpty("Default Description"),
profileImageUri.ifNullOrEmpty("Default Uri")
)
EDIT: given the update, I'd consider
fun Any?.ifNullOrEmpty(default: String) =
if (this == null || (this is CharSequence && this.isEmpty()))
default
else
this.toString()

I have found a workaround.
Turns out it's possible to pass if-else statements as parameters, because if statements are expressions in Kotlin:
viewModel.createProfile(
if (!etFirstName.text.isNullOrEmpty()) etFirstName.text.toString() else "John",
if (!etLastName.text.isNullOrEmpty()) etLastName.text.toString() else "Doe",
if (!etProfileDescription.text.isNullOrEmpty()) etProfileDescription.text.toString() else "Default Description",
if (profileImageUri != null) profileImageUri.toString() else ""
)
Using this approach I also don't have to set default values for my data class variables and for my createProfile function parameters.
I additionally added a check in my observeProfile function so if profileImageUri is null it won't try to set the image:
// ...
if (profile.imageUri.isNotEmpty()) {
ivProfileImage.setImageURI(Uri.parse(profile.imageUri))
}
// ...
My initial idea doesn't seem to be possible using a data class. It does seem to be possible using a regular class and varargsbut it has problems:
#Parcelize
class Profile(
vararg val params: String
) : Parcelable
...
val params = arrayOfValues.filter{ !it.isNullOrBlank() } // filter out all unwanted data
val profile = Profile(*params) // pass every param separately using spread operator
Main problem here is that the parameters themselves are obfuscated. I can still get the reference to individual parameters using an index and do stuff with them, but it doesn't work as nicely.

I think what you want to use is the Elvis Operator in Kotlin: ?:.
val test = exampleExpression ?: "alternative value"
If the expression to the left of ?: is not null, the elvis operator returns it, otherwise it returns the expression to the right. Note that the right-hand side expression is evaluated only if the left-hand side is null.
viewModel.createProfile(
etFirstName.text.toString() ?: "John",
etLastName.text.toString() ?: "Doe",
etProfileDescription.text.toString() ?: "Default Description",
profileImageUri.toString() ?: "Default Uri"
)

Default values from Retrofit Server response are being shown as null

I am calling an api which will gives me some values and some not. So i have given some variables default values. But even when i am not getting them from server , they are being shown as null in log and app is crashing.
Here is the model class:
data class FeedbackData(
var questionNumber: Int = 0,
var imageUri: Uri? = null,
#SerializedName("id") val id: Int,
#SerializedName("question") val question: String? = null,
#SerializedName("answer") var answer: Answer = Answer()
)
data class Answer(
#SerializedName("description") var description: String = "",
#SerializedName("image") var image: String = ""
)
if you see i have given answer a default object (default initialization) incase server doesnt send it. My requirement is that if server sends it i should have it,if not then i should be able to write that answer object. But i am getting null pointer exception when i am trying to access that answer object.
Here is the log
E/xoxo: received list: [FeedbackData(questionNumber=0, imageUri=null, id=1, question=How was the event?, answer=null), FeedbackData(questionNumber=0, imageUri=null, id=2, question=Did you face any issue?, answer=null)
And here is the server response:
{"id":1,"question":"How was the event?"},
{"id":2,"question":"Did you face any issue?"}

So for now i have given value to all the fields above, to id also which did not have default value and now it seems to work. It is seeming like a cheat solution but its working.

Based on the code you have shown, you are initializing
var answer: Answer = Answer()
But since server is returning null, it is replacing the default Answer with null value.
One possible solution could be to provide getter method, something on these lines
var name: answer : Answer
get() = field?:Answer()
Note: Verify syntax.

If you are using progaurd, keep your model classes away from obfuscation.
Use keepclassmembers in progaurd.

How to manage null value for android application while JSON parsing via GSON lib in kotlin

I am working on android application and want to manage null value that is comes from API.
I did not found the best solution.
I also try these methods
1. While generating getter in model class i give a conditional statement in getter like
if(value == null){
value = ""
}
but this is not a right way because of i have to write this code for each and every getter in whole application.
2. replace the string from 'null' to "" before JSON parsing.
this is replace all type of value (int/float etc) in to blank string that is invalid.

You can use JsonDeserializer to create your Gson.

You can create model class like this
class ExampleModel {
#SerializedName("id")
#Expose
val id: Int? = null
#SerializedName("category")
#Expose
val category: String? = null
}
This class will be able to handle null value and data as well.