Unable to run OnSetClickLestiner
as I can see you cant find the button with the id. You have to options
1st option: go to ur code and use the line
val myButton: Button = findViewById(R.id.button)
myButton.setOnClickListener{
...
}
2nd option: go to gradle.app file and add into the plugins the line:
id 'kotlin-android-extensions'
and then keep the same code as you have
Follow this format when calling setOnClickListener
Always initialize your Button variables before calling them.
public class MyActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_layout_id);
Button button = findViewById(R.id.button_id);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Code here executes on main thread after user presses button
}
});
}
}
Related
I'm facing this issue where the data I'm retrieving from an API, https://randomuser.me/api/ at first compose it doesn't load.
But every time I rotate the screen the data updates.
First load
After screen rotation
View
class MainActivity : ComponentActivity() {
private val userViewModel : UserViewModel by viewModels()
private var userList: List<UserModel> = listOf()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
userViewModel.userModel.observe(this, Observer {
userList = it
})
userViewModel.onCreate()
setContent {
ListUsers(userList = userList)
}
}
}
ViewModel
class UserViewModel : ViewModel() {
val userModel = MutableLiveData<List<UserModel>>()
var getRandomUsersUseCase = RandomUsersUseCase()
fun onCreate() {
viewModelScope.launch {
val result = getRandomUsersUseCase()
if(!result.isNullOrEmpty()){
userModel.postValue(result)
}
}
}
}
Use State to ensure the data changes trigger recomposition of the Composable.
If you use another observable type such as LiveData in Compose, you
should convert it to State before reading it in a composable using
a composable extension function like LiveData.observeAsState().
Changes to your code would be,
val userListState by userViewModel.userModel.observeAsState()
setContent {
ListUsers(userList = userListState)
}
Why does it shows the data during rotation?
When rotating the screen or during any other configuration changes, the activity will be recreated.
More info on that here - Docs
In most cases, you would not require data to be changed when the screen rotates.
If you want to persist the data even after screen rotation, move the code inside onCreate() in your UserViewModel to the init block, like this.
init {
getData()
}
fun getData() {
viewModelScope.launch {
val result = getRandomUsersUseCase()
if(!result.isNullOrEmpty()){
userModel.postValue(result)
}
}
}
If you need to refresh the data on any other event like button click, swipe to refresh, etc, just call the getData() again on the event handler.
P.S: Check correct imports are added as required.
import androidx.compose.runtime.setValue
import androidx.compose.runtime.getValue
I'm trying to implement LayoutInflater for a button, but after doing it I'm getting this error. I'm not sure whether it has been implemented correctly or not. I tried different solutions available for the same question, but still, being new to Android, I'm finding it difficult to solve this issue.
https://www.dropbox.com/s/s2k92n6ss4mtztg/Screenrecorder-2020-11-23-00-34-16-139.mp4?dl=0 (I apologize for not able to explain the workflow but please refer this clip for better understanding, the first activity is IntroductoryActivity & the last one where start button is there is onboardingfragment3)
Please shed some light on this problem. Thank You!
IntroductoryActivity.java:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_introductory);
............
**//The button from fragment_on_boarding3**
start_l=findViewById(R.id.startb);
.............
**//Having issue with this part**
LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View layoutScreen = inflater.inflate(R.layout.fragment_on_boarding3,null);
start_l.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent mainActivity = new Intent(getApplicationContext(),MainActivity.class);
startActivity(mainActivity);
// I need to save a boolean value to storage so next time when the user runs the app,I could know that he has already checked the intro screen activity
// I'm going to use shared preferences forthat process
savePrefsData();
finish();
}
});
}
private boolean restorePrefData() {
SharedPreferences pref = getApplicationContext().getSharedPreferences("myPrefs",MODE_PRIVATE);
Boolean isIntroActivityOpnendBefore = pref.getBoolean("isIntroOpnend",false);
return isIntroActivityOpnendBefore;
}
private void savePrefsData() {
SharedPreferences pref = getApplicationContext().getSharedPreferences("myPrefs",MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit();
editor.putBoolean("isIntroOpnend",true);
editor.commit();
}
}
OnBoardingFragment3.java:
public class OnBoardingFragment3 extends Fragment {
Context mContext ;
Button start;
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
ViewGroup root=(ViewGroup) inflater.inflate(R.layout.fragment_on_boarding3,container,false);
return root;
}
fragment_on_boarding3.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button android:id="#+id/startb"
android:layout_width="157dp"
android:layout_height="59dp"
android:fontFamily="#font/bungee"
android:text="Let's Start"
android:textSize="15dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.498"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.754" />
</androidx.constraintlayout.widget.ConstraintLayout>
Error:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.liq/com.example.liq.IntroductoryActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946) at....................
findViewById is actually is called this:
this.findViewById(someId);
this refers to Activity (in your case IntroductoryActivity);
From the docs:
Finds a view that was identified by the android:id XML attribute that was processed in onCreate(Bundle).
This onCreate() method is onCreate method of Activity on which you are calling findViewById. In your case, that id (and View) belongs to fragment so Activity is unable to find view associated with that id and returns null and you get NPE when you want to setOnClickListener to start_l button.
You can set onClickListener to that button inside onViewCreated method of fragment:
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
start_l=view.findViewById(R.id.startb);
start_l.setOnClickListener.......
}
Edit: suggestion by Prince Ali is also a possible and maybe better way to do it. You can initialize views inside onCreateView:
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
ViewGroup root=(ViewGroup) inflater.inflate(R.layout.fragment_on_boarding3,container,false);
start_l=root.findViewById(R.id.startb);
start_l.setOnClickListener.......
return root;
}
I also recommend looking at this post
I want when I click on a notification to open a fragment and not recreate it. I am using navigation component and using NavDeepLinkBuilder
val pendingIntent = NavDeepLinkBuilder(this)
.setComponentName(MainActivity::class.java)
.setGraph(R.navigation.workouts_graph)
.setDestination(R.id.workoutFragment)
.createPendingIntent()
My case is I have a fragment and when you exit the app, there is a notification which when you click on it, it should return you to that same fragment. Problem is every time i click on it it's creating this fragment again, I don't want to be recreated.
I had the same issue. Looks like there is not an option to use the NavDeepLinkBuilder without clearing the stack according to the documentation
I'm not sure the exact nature of your action, but I'll make two assumptions:
You pass the destination id to your MainActivity to navigate.
Your MainActivity is using ViewBinding and has a NavHostFragment
You will have to create the pending intent like:
val intent = Intent(this, MainActivity::class.java).apply {
flags = Intent.FLAG_ACTIVITY_SINGLE_TOP
putExtra("destination", R.id.workoutFragment)
}
val pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
And in your MainActivity, you can handle both cases (app was already open, app was not already open)
override fun onStart() {
super.onStart()
// called when application was not open
intent?.let { processIntent(it) }
}
override fun onNewIntent(intent: Intent?) {
super.onNewIntent(intent)
// called when application was open
intent?.let { processIntent(it) }
}
private fun processIntent(intent: Intent) {
intent.extras?.getInt("destination")?.let {
intent.removeExtra("destination")
binding.navHostFragment.findNavController().navigate(it)
}
}
I'm trying to finish an activity from another (android) with kotlin. I know the wat to do it with java is with the following code (https://stackoverflow.com/a/10379275/7280257)
at the first activity:
BroadcastReceiver broadcast_reciever = new BroadcastReceiver() {
#Override
public void onReceive(Context arg0, Intent intent) {
String action = intent.getAction();
if (action.equals("finish_activity")) {
finish();
// DO WHATEVER YOU WANT.
}
}
};
registerReceiver(broadcast_reciever, new IntentFilter("finish_activity"));
On the other activity:
Intent intent = new Intent("finish_activity");
sendBroadcast(intent);
For some reason converting the java activity to kotlin doesn't give a valid output, if someone could give me the correct syntax to do it properly with kotlin I will appreciate it
kotlin output (first activity) [OK]:
val broadcast_reciever = object : BroadcastReceiver() {
override fun onReceive(arg0: Context, intent: Intent) {
val action = intent.action
if (action == "finish_activity") {
finish()
// DO WHATEVER YOU WANT.
}
}
}
registerReceiver(broadcast_reciever, IntentFilter("finish_activity"))
kotlin output (2nd activity) [OK]
val intent = Intent("finish_activity")
sendBroadcast(intent)
ERROR: http://i.imgur.com/qaQ2YHv.png
FIX: THE CODE SHOWN IS RIGHT, YOU JUST NEED TO PLACE IT INSIDE THE onCreate FUNCTION
Simple code to finish a particular activity from another:
class SplashActivity : AppCompatActivity(), NavigationListner {
class MyClass{
companion object{
var activity: Activity? = null
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
MyClass.activity = this#SplashActivity
}
override fun navigateFromScreen() {
val intent = Intent(this,LoginActivity::class.java)
startActivity(intent)
}
}
Now call SplashActivity.MyClass.activity?.finish() from another activity to finish above activity.
The error Expecting member declaration is there because you wrote a statement (the function call) inside a class. In that scope, declarations (functions, inner classes) are expected.
You have to place your statements inside functions (and then call those from somewhere) in order for them to be executed.
Follow this tutorial: Android - Start Another Activity if I made MainActivity.java button OnClick attribute has the sendMessage() method.
But if I made MainActivity.kt button OnClick attribute has nothing to show, just a none.
Is this an Android Studio 3 bug or I missed something for Kotlin?
Java mainActivity:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
/** Called when the user taps the Send button */
public void sendMessage(View view) {
// Do something in response to button
}
}
Kotlin mainActivity:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
/** Called when the user taps the Send button */
fun sendMessage(view: View) {
// Do something in response to button
}
}
XML layout (Java and Kotlin project are the same)
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="ir.bigbang.vahid.myapplication.MainActivity">
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button"
tools:layout_editor_absoluteX="148dp"
tools:layout_editor_absoluteY="81dp" />
</android.support.constraint.ConstraintLayout>
It seems like the designer does not support Kotlin yet. Here are some solution:
XML (Not Recommended)
Add the following line to your Button tag. This is exactly what the designer will do.
android:onClick="sendMessage"
Old Fashion
No need to add anything.
val button = findViewById<Button>(R.id.Button)
button.setOnClickListener {
}
kotlin-android-extensions (Recommended)
Add apply plugin: "kotlin-android-extensions" to your build.gradle
// button is the Button id
button.setOnClickListener {
}
Your code will like this:
button.setOnClickListener(){
Toast.makeText(this#MainActivity, "Its toast!", Toast.LENGTH_SHORT).show();
}
Here import will:
import kotlinx.android.synthetic.main. activity_main.*
Here "button" is the id of that Button in .xml file. Here the advantage is no need to create Button object in your java class.
Once defined the sendMessage class as :
/** Called when the user taps the Send button */
fun sendMessage(view: View) {
setContentView(R.layout.activity_second)
// Do something in response to button
}
And also defined a second activity as:
class SecondActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_second)
}
}
I added the SendMessage to the OnClick function:
And then it worked.
You can easily define this inside the XML itself. But using the android:onClick attribute is still a little expensive.
Instead you could consider using the Kotlin Android Extensions and synthetic properties:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
button.setOnClickListener {
// Do something in response to button
}
}
Button OnClick implementation it's can be done by some ways in Android
some of the possible ways are below in sample:
1>Using OnClickListener as a interface
Here we implement our main activity with OnClicklistener
and override the function onClick
override fun onClick(v: View?) {
when (v?.id){
(R.id.btn1) -> {
toastmsg("Button1");
}
R.id.btn2 -> {
toastmsg("Button2");
}
}
}
2>And create a function and pass the OnClickListener with
variable sample:
findViewById<Button>(R.id.btn3).setOnClickListener(btnClick);
var btnClick =
OnClickListener {
Toast.makeText(this, "BtnClick", Toast.LENGTH_SHORT).show() ;
}
3>Create OnClickListener in Oncreate()
btn1=findViewById(R.id.btn1);
btn1?.setOnClickListener {
toastmsg("test button1");
}
full sample Code of the example it contains all the possible implementation of the Button OnClickListener :
class MainActivity : AppCompatActivity() , OnClickListener{
lateinit var tv1:TextView;
lateinit var tv2:TextView;
lateinit var tv3:TextView;
var btn1: Button? =null;
var btn2: Button? =null;
var btn3: Button? =null;
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
btn1=findViewById(R.id.btn1);
btn1?.setOnClickListener {
toastmsg("test button1");
}
findViewById<Button>(R.id.btn2).setOnClickListener(this);
findViewById<Button>(R.id.btn3).setOnClickListener(btnClick);
}
var btnClick =
OnClickListener {
Toast.makeText(this, "BtnClick", Toast.LENGTH_SHORT).show() ;
}
override fun onClick(v: View?) {
when (v?.id){
(R.id.btn1) -> {
toastmsg("Button1");
}
R.id.btn2 -> {
toastmsg("Button2");
}
}
}
private fun toastmsg(msg: String){
Toast.makeText(this, "DaggerTest" + msg, Toast.LENGTH_SHORT).show();
}
}
Here's the solution I came up with in the MainActivity.kt file.
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val button = findViewById<Button>(R.id.button)
button.setOnClickListener {
sendMessage()
}
}
/** Called when the user taps the Send button */
private fun sendMessage() {
val editText = findViewById<EditText>(R.id.editText)
val message = editText.text.toString()
val intent = Intent(this, DisplayMessageActivity::class.java).apply
{
putExtra(EXTRA_MESSAGE, message)
}
startActivity(intent)
}