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How to start another activity in function? Kotlin

class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
val navigate = Intent(this,Activity2::class.java)
startActivity(navigate)
}
}
}
fun switchActivity(){
val navigate = Intent(this,Activity2::class.java)
startActivity(navigate)
}
I want to start an activity from a function and not from the main activity..
I can start an activity from main class but in function, the code doesnt work..
Please help.. I'm new to kotlin android programming..

You can also try like this
class MainActivity : AppCompatActivity() {
#SuppressLint("MissingInflatedId")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
nextActivity(this, MainActivity2())
}
private fun nextActivity(context: Context, activity: Activity) {
startActivity(Intent(context, activity::class.java))
}
}

Just use it
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
switchActivity()
}
}
fun switchActivity(){
val navigate = Intent(this#MainActivity, Activity2::class.java)
startActivity(navigate)
}

Actually i don't get your question clearly. But i'll try to answer your question based on my understanding of yours.
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
switchActivity()
// if you want to pass the class through the paramater,
// can try this
// TODO: Another Way
// switchActivityCustom(Activity2::class.java)
}
}
fun switchActivity(){
val navigate = Intent(this, Activity2::class.java)
startActivity(navigate)
}
// TODO: Another Function
// fun switchActivityCustom(destination: Class<*>,){
// val navigate = Intent(this, destination)
// startActivity(navigate)
// }
}
And the last one is, put your function inside the class (in this case: MainActivity Class)

If your function is declared at the top level, without a reference to this, you'd need to pass an instance of Activity to your function:
fun switchActivity(activity: Activity) {
val navigate = Intent(activity, Activity2::class.java)
activity.startActivity(navigate)
}

When to call livedata observer?

On a button click i have to get some value from API call and then launch one screen. I have two options:
Call the observer each time when user will click on button.
Call the observer on fragment onActivityCreated() and store the value in variable and act accordingly on button click.
So which approach I should follow?

Actually it's up to you. But i always prefer to call it in Activity's onCreate() function, so activity only has 1 observer. If you call it in button click, it will give you multiple observers as much as button clicking
Here is some example :
class HomeProfileActivity: BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
initObserver()
initView()
}
private fun initObserver() {
viewModel.profileWorkProccess.observe(this, {
swipeRefreshLayout.isRefreshing = it
})
viewModel.isLoadingJobs.observe(this, {
layoutProgressBarJobs.visibility = View.VISIBLE
recyclerViewJobs.visibility = View.GONE
dotsJobs.visibility = View.GONE
})
//other viewmodel observing ......
}
private fun initView() {
imageProfile.loadUrl(user.image, R.drawable.ic_user)
textName.text = identity.user?.fullName
textAddress.text = identity.user?.city
buttonGetData.setOnClickListener { viewModel.getData(this) }
}
}

If the button is placed on the Activity, and data is displayed in the Fragment, you need to store variable in Activity ViewModel and observe it in Fragment
You only need to call observe one time when fragment is created.
For example:
class MyActivity : AppCompatActivity() {
val viewModel: MyActViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
myButton.setOnClickListener { view ->
viewModel.getData()
}
}
}
class MyActViewModel: ViewModel {
val data: LiveData<String> = MutableLiveData()
fun getData() {}
}
class MyFragment: Fragment {
val actViewModel: MyActViewModel by activityViewModels()
override fun onActivityCreated(...) {
....
actViewModel.data.observe(viewLifecycleOwner, Observer { data ->
...
}
}
}

How to use interface in Android

I know the concept of "Interfaces" but I've hard time to understand how to use them in android development.
Let's say I created an interface to decide if to show progress bar or not -
interface ProgressBarInterface {
fun showProgressBar()
fun hideProgressBar()
}
And I implement this inside BaseActivity/MainActivity in single Activity app:
class BaseActivity : AppCompatActivity() , ProgressBarInterface {
private val TAG = "MainActivity"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
override fun showProgressBar() {
}
override fun hideProgressBar() {
}
}
And inside my other activity I've a button, that when I click on it, I want to trigger showProgressBar in the base activity:
button.setOnClickListener {
//Show progress bar
}
How can I interact with the interface to trigger the function inside base activity?

Since you already are implementing the interface in your BaseActivity, you can then just add what you need to do inside the interface methods, and then call them up in any point in your activity, if what you are looking for is to extend this BaseActiviy into more activities you will need to make this BaseActivity abstract then you can extend in each activity this BaseClass and just use the interface methods
abstract class BaseActivity : AppCompatActivity() , ProgressBarInterface {
private val TAG = "MainActivity"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
override fun showProgressBar() {
progressBar.visibility = View.VISIBLE
}
override fun hideProgressBar() {
progressBar.visibility = View.GONE
}
}
and then in your Activities you can extend from BaseActivity() and just use your interface methods as you have defined in that BaseActivity() to prevent coding them again, you can do
class FirstActivity : BaseActivity() {
...
button.setOnClickListener {
showProgressBar()
}
An easier way to show and hide the views? Use extension functions
fun View.show() {
this.visibility = View.VISIBLE
}
fun View.hide() {
this.visibility = View.GONE
}
you can define that extensions in any class, for example ViewUtils.kt and then just call
button.setOnClickListener {
progressBar.show()
}
or
button.setOnClickListener {
progressBar.hide()
}

Why my ViewModel is still alive after I replaced current fragment in Android?

Example, If I replaced 'fragmentA' with 'fragmentB', the 'viewModelA' of fragmentA is still live. why ?
onCreate() of Fragment
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel = ViewModelProvider.NewInstanceFactory().create(InvoicesViewModel::class.java)
}
ViewModel
class InvoicesViewModel : ViewModel() {
init {
getInvoices()
}
private fun getInvoices() {
viewModelScope.launch {
val response = safeApiCall() {
// Call API here
}
while (true) {
delay(1000)
println("Still printing although the fragment of this viewModel destroied")
}
if (response is ResultWrapper.Success) {
// Do work here
}
}
}
}
This method used to replace fragment
fun replaceFragment(activity: Context, fragment: Fragment, TAG: String) {
val myContext = activity as AppCompatActivity
val transaction = myContext.supportFragmentManager.beginTransaction()
transaction.replace(R.id.content_frame, fragment, TAG)
transaction.commitNow()
}
You will note the while loop inside the Coroutine still work although after replace fragment to another fragment.

this is about your implementation of ViewModelProvider.
use this way for creating your viewModel.
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel = ViewModelProvider(this).get(InvoicesViewModel::class.java)
}
in this way you give your fragment as live scope of view model.

Check, if you have created the ViewModel in Activity passing the context of activity or fragment.

Pass click event on a view in a Fragment to the Activity

I am trying to pass click event on a view in a Fragment to the Activity. I was following documentation guide from here.
As I understand it and I could be wrong but we need to create an interface, add a method declaration to it and trigger the method from when the click event is received on the Fragment. The Activity should then implement the interface defined in the fragment, so that the activity receives that event.
I have my Fragment:
class MoreFragment : Fragment() {
internal var callback: OnMoreItemClickedListener
fun setOnMoreItemClickedListener(callback: OnMoreItemClickedListener) {
this.callback = callback
}
interface OnMoreItemClickedListener {
fun onAddClothClicked()
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_more, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
}
override fun onStart() {
super.onStart()
btn_add_clothes.setOnClickListener {
callback.onAddClothClicked()
}
}
}
And I have my Activity:
class MainActivity : AppCompatActivity(), MoreFragment.OnMoreItemClickedListener {
override fun onAddClothClicked() {
Log.d("MainActivity", "HERE")
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val navView: BottomNavigationView = findViewById(R.id.nav_view)
val navController = findNavController(R.id.nav_host_fragment)
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
val appBarConfiguration = AppBarConfiguration(
setOf(
R.id.navigation_clothes,
R.id.navigation_seasons,
R.id.navigation_notifications,
R.id.navigation_more
)
)
setupActionBarWithNavController(navController, appBarConfiguration)
navView.setupWithNavController(navController)
}
override fun onAttachFragment(fragment: Fragment) {
super.onAttachFragment(fragment)
if(fragment is MoreFragment){
fragment.setOnMoreItemClickedListener(this)
}
}
}
Now the error that I am getting is:
MoreFragment.kt: (16, 5): Property must be initialized or be abstract
MoreFragment.kt: (16, 5) is internal var callback: OnMoreItemClickedListener.The doc link above does suggest the same/ similar code but it does not work.
Things that I have tried
I have tried putting a lateinit var for the callback: OnMoreItemClickedListener variable there but no luck. As it never gets initialized.
I put internal var callback: OnMoreItemClickedListener? = null and referenced callback using the null safe operator ?. but was not able to get the click event.
I am fairly new to Kotlin and Fragments too so please help me figure how to do this. Thanks

In Fragment override onAttach method
private lateinit var callback: OnMoreItemClickedListener
override onAttach(context : Context){
callback = context as OnMoreItemClickedListener
}
then your callback will be init. as onAttach will be first. so no Property must be initialized or be abstract errror will occur.
also in Activity implement your interface(OnMoreItemClickedListener) and override its method. You will get callback

Your both way is looks OK
I have tried putting a lateinit var for the callback:
I put internal var callback: OnMoreItemClickedListener? =
null
I guess issue is here just debug below code. is it going inside if
if(fragment is MoreFragment){
fragment.setOnMoreItemClickedListener(this)
}