android studio, kotlin
app keeps stopping after I try convert string to int. I need int to get random number.
New to kotlin so any help pls?
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val goButton = findViewById<Button>(R.id.goButton)
val textViewResult = findViewById<TextView>(R.id.textViewResult)
val editText = findViewById<EditText>(R.id.editTexts)
val txt = editText.text.toString().toInt()
goButton.setOnClickListener {
val rand = java.util.Random().nextInt(txt)
textViewResult.text=rand.toString()
}
}
Related
When the Icon clicked, viewModel.onLockIconClicked(it) is called to reverse the value of isLock in db.
The Icon is expected to be updated according based on the value of isLock.
I've checked the value did reversed in db table. But LazyColumn not update accordingly.
What did I miss? Thanks a lot!
Ex, initially, Screen: icon = lock and Db: isLock = true,
when Icon clicked, Screen: icon = lock and Db: isLock = false,
while expected is Screen: icon = lock_open and Db: isLock = false.
ListScreen:
#Composable
fun ListScreen(context: Context) {
val viewModel: ListViewModel =
viewModel(factory = ListViewModelFactory(Db.getInstance(context)))
val list by viewModel.list.collectAsState(initial = emptyList())
Scaffold() {
SwipeRefresh(
state = rememberSwipeRefreshState(viewModel.isRefreshing),
onRefresh = { }
) {
LazyColumn(
state = rememberLazyListState(),
) {
items(list) {
Row() {
Icon(
painter = painterResource(if (it.isLock) R.drawable.ic_baseline_lock_24 else R.drawable.ic_baseline_lock_open_24),
contentDescription = null,
modifier = Modifier.clickable() { viewModel.onLockIconClicked(it) }
)
Text(it.code)
}
}
}
}
}
}
ListViewModel:
class ListViewModel(db: Db) : ViewModel() {
private val sumDao = db.sumDao()
val list = sumDao.getAllRows()
var isRefreshing by mutableStateOf(false)
private set
//init
init {
viewModelScope.launch(Dispatchers.IO) {
val initialCodeList = listOf("aaa", "bbb")
for (code in initialCodeList) {
val sum = Sum()
sum.code = code
sumDao.insert(sum)
}
}
}
fun onLockIconClicked(sum: Sum) {
sum.isLock = !sum.isLock
viewModelScope.launch(Dispatchers.IO) {
sumDao.update(sum)
}
}
}
class ListViewModelFactory(private val db: Db) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(ListViewModel::class.java)) {
#Suppress("UNCHECKED_CAST")
return ListViewModel(db) as T
}
throw IllegalArgumentException("Unknown ViewModel class")
}
}
Sum:
#Entity(tableName = "sum", primaryKeys = ["code"])
data class Sum(
#ColumnInfo(name = "code")
var code: String = "",
#ColumnInfo(name = "is_lock")
var isLock: Boolean = true
)
SumDao:
#Dao
interface SumDao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(sum: Sum): Long
#Update(onConflict = OnConflictStrategy.REPLACE)
suspend fun update(sum: Sum): Int
#Delete
suspend fun delete(sum: Sum): Int
#Query("select * from sum")
fun getAllRows(): Flow<List<Sum>>
}
Db:
#Database(entities = [Sum::class], version = 1, exportSchema = false)
abstract class Db : RoomDatabase() {
abstract fun sumDao(): SumDao
companion object {
#Volatile
private var INSTANCE: Db? = null
fun getInstance(context: Context): Db {
return INSTANCE ?: synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
Db::class.java,
"db"
)
.fallbackToDestructiveMigration()
.build()
INSTANCE = instance
return instance
}
}
}
}
Consider taking the State-in-Compose for a better understanding of the concepts of state-handling in Compose.
I'm sorry but the information that you have provided is massive, so I can't pinpoint the source of the bug, but here's what you can do for now:
In your Dao class, just replace the words Flow<List<Sum>> with LiveData<List<Sum>>
In your ViewModel, you can get access to the LiveData inside the init like so
var list by mutableStateListOf<Sum>()
init{
sumDao.getAllRows().observeForever{
list = it
}
}
Now, list would ideally be updated every time the value in the databse changes, which infact would trigger recompositions since I am using a direct mutableStateListOf object here.
The problem may lie anywhere:
Since the class Sum is a custom-made class, it may have been experiencing issues triggering recompositions, which is a common problem among new developers, and even some experienced ones nowadays.
Since you are declaring the viewModel inside the Composable, wrong instances of ViewModels may have been passed around, leading to state-inconsistency - always try to declare your viewModels in the top-most layer possibly, i.e., somewhere like the onCreate method of the activity. Fragments are discourages so you should not face any problems over there.
Since you were not actively observing the Flow anywhere, that could have lead to the variable not being updated at all in the ViewModel, which would again lead to UI-inconsistency.
I am using Room to save objects in the database. and any time I perform an operation like insert or get all my application restarts.
this is my entity class:
#Entity
class Task(
#PrimaryKey val id: Int,
#ColumnInfo(name = "title") val title : String,
#ColumnInfo(name = "detail") val detail : String
)
this is my database class:
#Database(entities = [Task::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun taskDao() : TaskDao
companion object{
var INSTANCE: AppDatabase? = null
fun getAppDatabase(context: Context): AppDatabase? {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(
context,
AppDatabase::class.java,
"task-database"
)
.build()
}
return INSTANCE
}
}
}
I try calling it from my AndroidViewModel class like this:
class AddTaskViewModel(application: Application) : AndroidViewModel(application) {
private val context = application
var title : MutableLiveData<String> = MutableLiveData("")
var detail : MutableLiveData<String> = MutableLiveData("")
fun saveTask(){
val task = Task(id = 1, title = title.value!!, detail = detail.value!! )
val taskDao : TaskDao? = AppDatabase.getAppDatabase(context)?.taskDao()
taskDao!!.insertAll(task)
Toast.makeText(context, "it is done", Toast.LENGTH_LONG).show()
}
fun changeTitle(text: String){
title.value = text
}
fun changeDetail(text: String){
detail.value = text
}
}
and at the point where taskDao!!.insertAll(task) is called the app restarts.
I think the issue might be that when you are inserting tasks into your database the id which is supposed to be the primary key is violated, in the sense that it's not unique, so the unique constraints fail
val task = Task(id = 1, title = title.value!!, detail = detail.value!!)
Try incrementing the id for example or letting room do that for you
I had to run the function in a coroutine because it was locking the UI processas seen in this post
How can I convert io.ktor.utils.io.ByteReadChannel into kotlinx.coroutines.flow.Flow<java.nio.ByteBuffer>?
I use Ktor with this routing:
post("/upload") {
val channel: ByteReadChannel = call.receiveChannel()
val flow: Flow<ByteBuffer> = channel.asByteBufferFlow() // my custom extension method
transaction.execute {
testDao.saveFile(flow)
}
call.respond("OK")
}
The DAO uses R2DBC and Blob like this:
override suspend fun saveFile(input: Flow<ByteBuffer>) {
val connection = requireR2DBCTransactionConnection()
val publisher: Publisher<ByteBuffer> = input.asPublisher()
val statement: Statement = connection.createStatement("insert into bindata (data) values ($1)")
statement.bind(0, Blob.from(publisher))
val count: Int = statement.execute().awaitFirst().rowsUpdated.awaitFirst()
if (count != 1) {
throw IllegalStateException()
}
}
I tried to write this extension method but I failed:
fun ByteReadChannel.asByteBufferFlow(): Flow<ByteBuffer> = object : AbstractFlow<ByteBuffer>() {
override suspend fun collectSafely(collector: FlowCollector<ByteBuffer>) {
/* I have no idea */
}
}
My main problem is that I have not found any similar sample and both ByteBuffer and ByteReadChannel is new for me.
I'm trying to do a task with an Asynctask in kotlin. I want to show a dialog message to user In the case that user has a very slow or spotty data connection at the time of use, I'd like to make the AsyncTask timeout after a period of time 5 second .My point is where should l put dialog ? after finally in doInBackground ?
inner class Arr : AsyncTask<String, String, String>() {
val progressDialog = AlertDialog.Builder(this#MainActivity)
val dialogView = layoutInflater.inflate(R.layout.progress_dialog, null)
val message = dialogView.findViewById<TextView>(R.id.message_id)
val dialog = progressDialog.create()
override fun onPreExecute() {
super.onPreExecute()
dialog.setMessage("please wait")
dialog.setCancelable(false)
dialog.show()
}
// for build connection
override fun doInBackground(vararg url: String?): String {
var text: String
val connection = URL(url[0]).openConnection() as HttpURLConnection
connection.connectTimeout = 300
try {
connection.connect()
text = connection.inputStream.use { it.reader().use { reader -> reader.readText() } }
} finally {
dialog.setMessage("Sorry you dont have proper net connectivity..!\nCheck your internet settings or retry.")
dialog.setCancelable(false)
dialog.show()
}
return text
}
override fun onPostExecute(result: String?) {
super.onPostExecute(result)
handleJson(result)
dialog.dismiss();
}
override fun onProgressUpdate(vararg text: String?) {
}
}
I'd like to initialize my class's properties.
Because I'm using heavily the functional elements of Kotlin, I'd like to put these initializations to well named functions, to increase readability of my code.
The problem is that I cannot assign a val property, if the code is not in the init block, but in function which is called from the init block.
Is it possible to take apart initialization of a class, to different functions, if the properties are vals?
Here is the code:
val socket: DatagramSocket = DatagramSocket()
val data: ByteArray = "Cassiopeiae server discovery packet".toByteArray()
val broadcastAddresses: List<InetAddress>
init {
socket.broadcast = true
val interfaceAddresses = ArrayList<InterfaceAddress>()
collectValidNetworkInterfaces(interfaceAddresses)
collectBroadcastAddresses(interfaceAddresses)
}
private fun collectValidNetworkInterfaces(interfaceAddresses: ArrayList<InterfaceAddress>) {
NetworkInterface.getNetworkInterfaces().toList()
.filter { validInterface(it) }
.forEach { nInterface -> nInterface.interfaceAddresses.toCollection(interfaceAddresses) }
}
private fun collectBroadcastAddresses(interfaceAddresses: ArrayList<InterfaceAddress>) {
broadcastAddresses = interfaceAddresses
.filter { address -> address.broadcast != null }
.map { it.broadcast }
}
Of course it's not compiling, because collectBroadcastAddresses function tries to reassign the broadcastAddresses val. Although I don't want to put the code of this function to the init block, because it's not obvious what the code is doing, and the function name tells it very nicely.
What can I do in such cases? I'd like to keep my code clean, this is the most important point!
One way of approaching the problem is to use pure functions to initialize fields:
class Operation {
val socket = DatagramSocket().apply { broadcast = true }
val data: ByteArray = "Cassiopeiae server discovery packet".toByteArray()
val broadcastAddresses = collectBroadcastAddresses(collectValidNetworkInterfaces())
private fun collectValidNetworkInterfaces() =
NetworkInterface.getNetworkInterfaces().toList()
.filter { validInterface(it) }
.flatMap { nInterface -> nInterface.interfaceAddresses }
private fun validInterface(it: NetworkInterface?) = true
private fun collectBroadcastAddresses(interfaceAddresses: List<InterfaceAddress>) {
interfaceAddresses
.filter { address -> address.broadcast != null }
.map { it.broadcast }
}
}
Notice how the socket field initialization uses apply extension.
I often find it useful to extract collection manipulation routines into extension methods:
class Operation {
val socket = DatagramSocket().apply { broadcast = true }
val data: ByteArray = "Cassiopeiae server discovery packet".toByteArray()
val broadcastAddresses = NetworkInterface.getNetworkInterfaces()
.collectValidNetworkInterfaces { validInterface(it) }
.collectBroadcastAddresses()
private fun validInterface(it: NetworkInterface?) = true
}
fun Iterable<InterfaceAddress>.collectBroadcastAddresses(): List<InetAddress> =
filter { address -> address.broadcast != null }.map { it.broadcast }
fun Enumeration<NetworkInterface>.collectValidNetworkInterfaces(isValid: (NetworkInterface) -> Boolean = { true }) =
toList()
.filter { isValid(it) }
.flatMap { nInterface -> nInterface.interfaceAddresses }