I'm trying to call my database (made with Room) from an activity on Android, but it needs the application context, and if I passed "application : Application" in the constructor of my Activity, the build crash and tell me :
java.lang.Class<com.exemple.instabus.PhotoActivity> has no zero argument constructor
Here is my code :
class PhotoActivity(application: Application) : AppCompatActivity() {
private val pictureDao = PictureDatabase.getDatabase(app)
//Some code ....
I need a context, i've tried to pass "this" but i got another error
Can someone give me some help please, I'm a beginner in this technology
EDIT:
Here is my database class, just to show you why I need an Application Context
#Database(entities = [Picture::class], version = 1, exportSchema = false)
abstract class PictureDatabase : RoomDatabase(){
abstract fun pictureDao() : PictureDao
companion object{
#Volatile
private var INSTANCE : PictureDatabase? = null
fun getDatabase(context: Context): PictureDatabase {
if(INSTANCE == null){
synchronized(this){
INSTANCE = Room.databaseBuilder(
context.applicationContext,
PictureDatabase::class.java,
"pictures.db"
).build()
}
}
return INSTANCE!!
}
}
}
Activity is something we do declare in the manifest and then start them using intent, However, the creation of an instance of an activity is done by the system and not by us. An instance is created using constructor, but if it is us then we can have any number of overloaded constructors. But the system needs only one constructor which should be a zero parameter constructor and it should be public.
So your activity signature
class PhotoActivity(application: Application) : AppCompatActivity() {
should be changed to
class PhotoActivity() : AppCompatActivity() {
To call the fun getDatabase(context: Context): PictureDatabase you can pass this from the activity. Activity is an indirect child of Context.
You can do it in the following ways,
private val pictureDao by lazy{ PictureDatabase.getDatabase(this) }
private lateinit var pictureDao:PictureDatabase
then in onCreate() initialize it
final override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.your_layout)
PictureDatabase.getDatabase(this)
//your logic goes here
}
First create a ViewModel, and inside the ViewModel you can access the your Dao, pictureDao.
class PictureViewModel(application: Application) :
AndroidViewModel(application) {
val pictureDao: PictureDao
init {
pictureDao =
PictureDatabase.getDatabase(application).pictureDao()
}
}
Then in your activity, initialize the ViewModel. And access your Dao.
class PhotoActivity : AppCompatActivity() {
private lateinit var pictureViewModel: PictureViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_photo)
pictureViewModel =
ViewModelProviders.of(this).get(PictureViewModel::class.java)
//You can now access your Dao class here:
val pictureDao = pictureViewModel.pictureDao
}
}
You should not pass Application to the constructor. You should pass applicationContext to getDatabase(), like private val pictureDao = PictureDatabase.getDatabase(applicationContext)
Related
In my activity, I have multiple variables being initiated from Intent Extras. As of now I am using ViewModelFactory to pass these variables as arguments to my viewModel.
How do I eliminate the need for ViewModelFacotory with hilt
Here are two variables in my Activity class
class CommentsActivity : AppCompatActivity() {
private lateinit var viewModel: CommentsViewModel
override fun onCreate(savedInstanceState: Bundle?) {
val contentId = intent.getStringExtra(CONTENT_ID_FIELD) //nullable strings
val highlightedCommentId = intent.getStringExtra(HIGHLIGHTED_COMMENT_ID_RF) //nullable strings
val commentsViewModelFactory = CommentsViewModelFactory(
contentId,
highlightedCommentId
)
viewModel = ViewModelProvider(this, commentsViewModelFactory[CommentsViewModel::class.java]
}
}
Here is my viewModel
class CommentsViewMode(
contentId : String?,
highlightedCo;mmentId : String?,
) : ViewModel() {
//logic code here
}
My app is already set up to use hilt but in this case How can I pass these 2 variables and eliminate the viewModelFactory entirely
The trick is to initialize those variables only once, while the activity can be created multiple times. In my apps, I use a flag.
View model:
class CommentsViewModel : ViewModel() {
private var initialized = false
private var contentId : String? = null
private var highlightedCommentId : String? = null
fun initialize(contentId : String?, highlightedCommentId : String?) {
if (!initialized) {
initialized = true
this.contentId = contentId
this.highlightedCommentId = highlightedCommentId
}
}
//logic code here
}
Also, you should know that there is an open issue in dagger project exactly for this capability:
https://github.com/google/dagger/issues/2287
You're welcome to follow the progress.
If you want to use hilt effectively u can follow this steps
Use #HiltViewModel in your view model
#HiltViewModel
class MyViewModel #inject constructor(private val yrParameter): ViewModel {}
Also you no longer need any ViewModelFactory! All is done for you! In your activity or fragment, you can now just use KTX viewModels() directly.
private val viewModel: MyViewModel by viewModels()
Or if you want to use base classes for fragment and activity you can use this code to pass viewModel class
abstract class BaseFragment<V: ViewModel, T: ViewDataBinding>(#LayoutRes val layout: Int, viewModelClass: Class<V>) : Fragment() {
private val mViewModel by lazy {
ViewModelProvider(this).get(viewModelClass)
}
}
I am currently building an app and I have added Dagger Hilt in order to define a single class to access data. the injection seems working fine but I am not able to store a value in the data class I use.
I have created a Singleton first, which is used by the code to set/get value from a data structure.
#Singleton
class CarListMemorySource #Inject constructor() : CarListInterface {
private var extendedCarList: ExtendedCarList? = null
override fun setListOfVehicles(listOfVehicles: List<item>)
{
extendedCarList?.listOfVehicles = listOfVehicles
}
}
When I am calling setListOfVehicles the listOfVehicules contains 10 items but
The data structure ExtendedCarList is defined as below:
data class ExtendedCarList(
var listOfVehicles: List<item>
)
The Singleton in passed using Hilt like for example in the viewModel below:
#HiltViewModel
class HomeScreenViewModel #Inject constructor(
private val carList: CarListMemorySource
): ViewModel() {
fun getList() {
--> DO SOMETHING TO Get A ListA
carList.setListOfVehicles(ListA)
}
}
And in the activity, using the viewModel, I am just doing this:
#AndroidEntryPoint
class HomeScreenActivity: AppCompatActivity() {
private val viewModel: HomeScreenViewModel by viewModels()
....
viewModel.getList()
....
}
Any idea why and how to fix it ?
Thanks
you never initialize extendedCarList.
extendedCarList?.listOfVehicles = listOfVehicles
above line is exactly the same as
if (extendedCarList != null) extendedCarList.listOfVehicles = listOfVehicles
But it never passes the null check.
I think just changing
private var extendedCarList: ExtendedCarList? = null
to
private val extendedCarList = ExtendedCarList()
might solve it
I am writing an android application following the Android Architectural Components design.
This is the database class:
#Database(entities = [Authentication::class],version = 1, exportSchema = false)
abstract class AuthDB: RoomDatabase(){
abstract val authenticationDao :AuthenticationAccessObject
companion object{
#Volatile
private var INSTANCE: AuthDB? = null
fun getInstance(context: Context): AuthDB {
synchronized(this){
var instance = INSTANCE
if(instance == null){
instance = Room.databaseBuilder(
context.applicationContext,
AuthDB::class.java,
"authentication_database"
)
.fallbackToDestructiveMigration()
.build()
INSTANCE = instance
}
return instance
}
}
}
}
This is the Repository class:
class Repository2() {
private val database: AuthDB = AuthDB.getInstance(context = getContext())
private val daoA = database.authenticationDao
//Function to register a new user to system
fun insertAuth(userData: Any){
if (userData is Authentication){
daoA.insertAuth(userData)
} else {
throw IllegalArgumentException()
}
}
My target is that when I write the ViewModel, I want to create instance of Repository2 and call functions for example as follows:
var repo = Repository2()
repo.insertAuth(authenticationObject)
I am having problem giving context to getInstance in the Repository. The context should be such that when I instantiate the repository, it should automatically get the application context and instantiate the AuthDB database.
Until now,
I have tried to create Application class that extends Application and tried to get application context from there as suggested in another stackoverflow solution
Instantiated database with following code and failed:
private val database: AuthDB = AuthDB.getInstance(context = getContext())
Instantiated database with following code and failed:
private val database: AuthDB = AuthDB.getInstance(Application.getApplicationContext())
I have been trying for about two days now and nothing is working, I believe I am missing a major concept here. I hope someone can nudge me in the right direction?
Kind regards,
Salik
try this solution
EDIT:-
use this way to your RoomDatabase
#Database(
entities = [CompaniesModel::class, CompaniesHomeModel::class, UserPoint::class, Image::class, Offer::class, Rewords::class, BranchModel::class, PointsModel::class, RedeemModel::class, MainData::class, SubData::class],
version = 15)
abstract class DataBase : RoomDatabase() {
abstract fun homeDao(): HomeDao
abstract fun menuDao(): MenuDao
abstract fun companiesDao(): CompaniesListDao
abstract fun branchesDao(): BranchesDao
companion object {
#Volatile
private var databaseInstance: DataBase? = null
fun getDatabaseInstance(mContext: Context): DataBase =
databaseInstance ?: synchronized(this) {
databaseInstance ?: buildDatabaseInstance(mContext).also {
databaseInstance = it
}
}
private fun buildDatabaseInstance(mContext: Context) =
Room.databaseBuilder(mContext, DataBase::class.java, "crm")
.fallbackToDestructiveMigration()
.allowMainThreadQueries()
.build()
}
}
and for the getContext(), use Application() class like this:
class App : Application() {
override fun onCreate() {
super.onCreate()
instance = this
}
companion object {
lateinit var instance: App
}
}
and pass it like this
private val database: AuthDB = AuthDB.getInstance(app.instance)
I have created an application class in Kotlin. I need to access a method that returns a variable from anywhere in my application. The problem is I am not able to access that method from other parts of the program. I am able to access when code is written in Java , but when code is written in Kotlin,then the method in Application class is not accessible. Please find below code for reference:
class MyRetroApplication : Application() {
lateinit var apiComponent:APIComponent
companion object {
var ctx: Context? = null
}
override fun onCreate() {
super.onCreate()
ctx = applicationContext
apiComponent = initDaggerComponent()
}
fun getMyComponent(): APIComponent {
return apiComponent
}
fun initDaggerComponent():APIComponent{
apiComponent = DaggerAPIComponent
.builder()
.aPIModule(APIModule(APIURL.BASE_URL))
.build()
return apiComponent
} }
In the above code how to access the function getMyComponent() globally in Kotlin.
Put getMyComponen() inside companion like #Md. Asaduzzaman answer or use applicationContext to access it like -
(application as MyRetroApplication).getMyComponent()
or
(applicationContext as MyRetroApplication).getMyComponent()
or
MyRetroApplication.ctx?.let{
(it as MyRetroApplication).getMyComponent() //by your companion app context
}
Approach-1:
Put getMyComponent() inside companion
companion object {
var ctx: Context? = null
private lateinit var apiComponent: APIComponent
fun getMyComponent(): APIComponent = apiComponent
}
And then from anywhere:
MyRetroApplication.getMyComponent()
Approach-2:
Change the type of ctx to MyRetroApplication instead of Context and then from anywhere:
MyRetroApplication.ctx.getMyComponent()
Approach-3:
Same as approach 2 but in a formal way. Create getInstance() inside companion and pass ctx (private)
companion object {
private lateinit var ctx: MyRetroApplication
fun getInstance(): MyRetroApplication {
return ctx
}
}
And then from anywhere:
MyRetroApplication.getInstance().getMyComponent()
How can we access application context inside companion object in Android kotlin?
I have a companion object inside an abstract class and I want to access context to read Shared Preferences, but I'm not able to get the context.
UPDATE: I'm working with this stuff in an Android library and also the class that I'm working in is abstract
please see this go to link
class MainApplication : Application() {
init {
instance = this
}
companion object {
private var instance: MainApplication? = null
fun applicationContext() : Context {
return instance!!.applicationContext
}
}
override fun onCreate() {
super.onCreate()
// initialize for any
// Use ApplicationContext.
// example: SharedPreferences etc...
val context: Context = MainApplication.applicationContext()
}
}
Extends Application class like this
import android.app.Application
import android.content.Context
class MyApplication : Application() {
override fun onCreate() {
super.onCreate()
MyApplication.appContext = applicationContext
}
companion object {
lateinit var appContext: Context
}
}
then get context like this
val context = MyApplication.appContext
Actually I'm working inside an Android library and the class is abstract, so can't go with the already suggested solutions. However, I found way to do that.
Creat a lateinit Context field inside companion object.
abstract class MyClass {
companion object {
private lateinit var context: Context
fun setContext(con: Context) {
context=con
}
}
}
And then set it after the app has started
public class WelcomeActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_welcome);
MyClass.Companion.setContext(this);
}
}
There is a super cool article from the guys from Firebase explaining how their SDK gets hold of the context.
Basically my contentprovider looks like this:
/**
* This content provider is only responsible to inject the application context into the common module.
*/
class ContextProvider : ContentProvider() {
companion object {
private val TAG = ContextProvider::class.java.simpleName
}
override fun onCreate(): Boolean {
context?.let {
Common.setContext(it)
return true
}
Logger.e(TAG, "Context injection to common failed. Context is null! Check ContextProvider registration in the Manifest!")
return false
}
override fun query(uri: Uri, projection: Array<String>?, selection: String?, selectionArgs: Array<String>?, sortOrder: String?): Cursor? = null
override fun getType(uri: Uri): String? = null
override fun insert(uri: Uri, values: ContentValues?): Uri? = null
override fun delete(uri: Uri, selection: String?, selectionArgs: Array<String>?): Int = 0
override fun update(uri: Uri, values: ContentValues?, selection: String?, selectionArgs: Array<String>?): Int = 0
}
And the Common object, which I treat like an sibling of any Application class looks like this:
/**
* Partially working like an Application class by holding the appContext which makes it accessible inside this module.
*/
#SuppressLint("StaticFieldLeak")
object Common {
/**
* App appContext
*/
#Volatile
lateinit var appContext: Context
var isStoreVersion: Boolean = false
fun setContext(context: Context) {
appContext = context
}
}
As you can see I also enriched the Common object with a flag to store if the current build is a store version or not. Mainly because the BuildConfig of the app module is also not available in a module or library.
Don't forget to add the ContentProvider to the AndroidManifest of your library within the <application> tag
<provider android:name=".util.ContextProvider"
android:authorities="${applicationId}.common.util.contextprovider"
android:exported="false" />
You can save the instance directly inside a companion object and accessing it outside without problems, I think this approach is the simplest.
IMPORTANT: change the visibility of the instance property to private to ensure no one but Application has write access.
class App : Application() {
override fun onCreate() {
super.onCreate()
instance = this
}
companion object {
lateinit var instance: App
private set
}
}
class Test {
companion object {
lateinit var sharedPreferences: SharedPreferences
fun init(context: Context) {
// to prevent multiple initialization
if (!Companion::sharedPreferences.isInitialized) {
sharedPreferences = context.getSharedPreferences("preference_name", Context.MODE_PRIVATE)
}
}
}
}