我知道如何用 Java 创建一个简单的倒计时器。但我想用 Kotlin 创建这个。
package android.os;
new CountDownTimer(20000, 1000) {
public void onTick(long millisUntilFinished) {
txtField.setText("seconds remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
txtField.setText("Time's finished!");
}
}.start();
如何使用 Kotlin 做到这一点？
您可以使用 Kotlin 对象：
val timer = object: CountDownTimer(20000, 1000) {
override fun onTick(millisUntilFinished: Long) {...}
override fun onFinish() {...}
}
timer.start()
我已经用 Kotlin 中的计时器解决了我的问题，如下所示：
class Timer {
private val job = SupervisorJob()
private val scope = CoroutineScope(Dispatchers.Default + job)
private fun startCoroutineTimer(delayMillis: Long = 0, repeatMillis: Long = 0, action: () -> Unit) = scope.launch(Dispatchers.IO) {
delay(delayMillis)
if (repeatMillis > 0) {
while (true) {
action()
delay(repeatMillis)
}
} else {
action()
}
}
private val timer: Job = startCoroutineTimer(delayMillis = 0, repeatMillis = 20000) {
Log.d(TAG, "Background - tick")
doSomethingBackground()
scope.launch(Dispatchers.Main) {
Log.d(TAG, "Main thread - tick")
doSomethingMainThread()
}
}
fun startTimer() {
timer.start()
}
fun cancelTimer() {
timer.cancel()
}
//...
}
我使用协程作为计时器。
计时器可以设置倒计时，在我看来这是最简单的方法。
在布局 xml 中添加 Chronometer 视图，例如
<Chronometer
android:id="@+id/view_timer"
tools:targetApi="24"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
然后在您的活动或片段中：
view_timer.isCountDown = true
view_timer.base = SystemClock.elapsedRealtime() + 20000
view_timer.start()
如果你想显示倒计时，包括天、小时、分钟和秒
private lateinit var countDownTimer:CountDownTimer
.
.
.
fun printDifferenceDateForHours() {
val currentTime = Calendar.getInstance().time
val endDateDay = "03/02/2020 21:00:00"
val format1 = SimpleDateFormat("dd/MM/yyyy hh:mm:ss",Locale.getDefault())
val endDate = format1.parse(endDateDay)
//milliseconds
var different = endDate.time - currentTime.time
countDownTimer = object : CountDownTimer(different, 1000) {
override fun onTick(millisUntilFinished: Long) {
var diff = millisUntilFinished
val secondsInMilli: Long = 1000
val minutesInMilli = secondsInMilli * 60
val hoursInMilli = minutesInMilli * 60
val daysInMilli = hoursInMilli * 24
val elapsedDays = diff / daysInMilli
diff %= daysInMilli
val elapsedHours = diff / hoursInMilli
diff %= hoursInMilli
val elapsedMinutes = diff / minutesInMilli
diff %= minutesInMilli
val elapsedSeconds = diff / secondsInMilli
txt_timeleft.text = "$elapsedDays days $elapsedHours hs $elapsedMinutes min $elapsedSeconds sec"
}
override fun onFinish() {
txt_timeleft.text = "done!"
}
}.start()
}
如果您正在导航到另一个活动/片段，请务必取消倒计时
countDownTimer.cancel()
代码输出
51天17小时56分5秒
对于未来的读者，您可以使用timer
内置
Kotlin内联函数。
示例：
import kotlin.concurrent.timer
....
....
timer(initialDelay = 1000L, period = 1000L ) {
launch {
executeTask()
}
}
object: CountDownTimer(3000, 1000){
override fun onTick(p0: Long) {}
override fun onFinish() {
//add your code here
}
}.start()
尝试使用对象，如下所示：
var countDownTimer = object : CountDownTimer(2000, 1000) {
// override object functions here, do it quicker by setting cursor on object, then type alt + enter ; implement members
}
试试这个网站：https://try.kotlinlang.org/#/Kotlin%20Koans/Introduction/Java%20to%20Kotlin%20conversion/Task.kt
右上角有一个小按钮“从 Java 转换”，可能对您有用。
编辑：
不要忘记在需要时启动此对象，方法是在声明末尾或活动/片段中的任何位置添加
.start()countDownTimer.start()
class CustomCountDownTimer(var mutableLiveData: MutableLiveData<String>) {
lateinit var timer: CountDownTimer
val zone = ZoneId.systemDefault()
val startDateTime: ZonedDateTime = LocalDateTime.now().atZone(zone)
fun start(endOn: Long) {
if (this::timer.isInitialized) {
return
}
timer = object : CountDownTimer(endOn * 1000, 1000) {
override fun onTick(millisUntilFinished: Long) {
val stringBuilder = StringBuilder()
val endDateTime: ZonedDateTime =
Instant.ofEpochMilli(millisUntilFinished).atZone(ZoneId.systemDefault())
.toLocalDateTime().atZone(zone)
var diff: Duration = Duration.between(startDateTime, endDateTime)
if (diff.isZero() || diff.isNegative) {
stringBuilder.append("Already ended!")
} else {
val days: Long = diff.toDays()
if (days != 0L) {
stringBuilder.append("${days}day : ")
diff = diff.minusDays(days)
}
val hours: Long = diff.toHours()
stringBuilder.append("${hours}hr : ")
diff = diff.minusHours(hours)
val minutes: Long = diff.toMinutes()
stringBuilder.append("${minutes}min : ")
diff = diff.minusMinutes(minutes)
val seconds: Long = diff.getSeconds()
stringBuilder.append("${seconds}sec")
}
mutableLiveData.postValue(stringBuilder.toString())
//Log.d("CustomCountDownTimer", stringBuilder.toString())
}
override fun onFinish() {
}
}
timer.start()
}
fun getTimerState(): LiveData<String> {
return mutableLiveData
}
}
使用方法：
val liveData: MutableLiveData<String> = MutableLiveData()
val customCountDownTimer = CustomCountDownTimer(liveData)
customCountDownTimer.start(1631638786) //Epoch timestamp
customCountDownTimer.mutableLiveData.observe(this, Observer { counterState ->
counterState?.let {
println(counterState)
}
})
输出：
22hr : 42min : 51sec1day : 23hr : 52min : 44sec我知道我已经很晚了，但这可能会对想要构建倒计时器应用程序的人有所帮助。
xml文件：
<?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"
tools:context=".MainActivity">
<TextView
android:id="@+id/tv_timer"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="60"
android:textSize="30dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:padding="20dp"
/>
<TextView
android:id="@+id/startBtn"
android:layout_width="160dp"
android:layout_height="50dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@id/tv_timer"
android:text="START"
android:gravity="center"
android:background="@color/grey"
android:textColor="@color/black"
android:textStyle="bold"
android:layout_margin="12dp"
/>
<TextView
android:id="@+id/pauseBtn"
android:layout_width="160dp"
android:layout_height="50dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@id/startBtn"
android:text="PAUSE"
android:gravity="center"
android:background="@color/grey"
android:textColor="@color/black"
android:textStyle="bold"
android:layout_margin="12dp"
/>
<TextView
android:id="@+id/resetBtn"
android:layout_width="160dp"
android:layout_height="50dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@id/pauseBtn"
android:text="RESET"
android:gravity="center"
android:background="@color/grey"
android:textColor="@color/black"
android:textStyle="bold"
android:layout_margin="12dp"
/>
</androidx.constraintlayout.widget.ConstraintLayout><br/>
MainActivity.kt 文件：
package com.example.countdownapp
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.os.CountDownTimer
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
private var countdown_timer: CountDownTimer? = null
private var time_in_milliseconds = 60000L
private var pauseOffSet = 0L
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
tv_timer.text= "${(time_in_milliseconds/1000).toString()}"
startBtn.setOnClickListener{
starTimer(pauseOffSet)
}
pauseBtn.setOnClickListener{
pauseTimer()
}
resetBtn.setOnClickListener{
resetTimer()
}
}
private fun starTimer(pauseOffSetL : Long){
countdown_timer = object : CountDownTimer(time_in_milliseconds - pauseOffSetL, 1000){
override fun onTick(millisUntilFinished: Long) {
pauseOffSet = time_in_milliseconds - millisUntilFinished
tv_timer.text= (millisUntilFinished/1000).toString()
}
override fun onFinish() {
Toast.makeText(this@MainActivity, "Timer finished", Toast.LENGTH_LONG).show()
}
}.start()
}
private fun pauseTimer(){
if (countdown_timer!= null){
countdown_timer!!.cancel()
}
}
private fun resetTimer(){
if (countdown_timer!= null){
countdown_timer!!.cancel()
tv_timer.text = " ${(time_in_milliseconds/1000).toString()}"
countdown_timer = null
pauseOffSet =0
}
}
}
使用天文台来
minapi=24 <Chronometer
android:id="@+id/timer_expire_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="@dimen/spacing_m"
android:countDown="true"
android:textColor="@color/white"
android:textSize="@dimen/text_size_huge"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
tools:targetApi="24" />
在 kotlin 中：
binding.timerExpireTime.apply {
base = SystemClock.elapsedRealtime()
start()
}