我开发了一个应用程序，在Android模拟器屏幕上以指定的间隔显示一些文本。我正在使用Handler类。下面是我的代码片段:
handler = new Handler();
Runnable r = new Runnable() {
public void run() {
tv.append("Hello World");
}
};
handler.postDelayed(r, 1000);
当我运行这个应用程序时，文本只显示一次。为什么?
当前回答
Handler handler=new Handler();
Runnable r = new Runnable(){
public void run() {
tv.append("Hello World");
handler.postDelayed(r, 1000);
}
};
handler.post(r);
其他回答
科特林
private lateinit var runnable: Runnable
override fun onCreate(savedInstanceState: Bundle?) {
val handler = Handler()
runnable = Runnable {
// do your work
handler.postDelayed(runnable, 2000)
}
handler.postDelayed(runnable, 2000)
}
Java
Runnable runnable;
Handler handler;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
handler = new Handler();
runnable = new Runnable() {
@Override
public void run() {
// do your work
handler.postDelayed(this, 1000);
}
};
handler.postDelayed(runnable, 1000);
}
Handler handler=new Handler();
Runnable r = new Runnable(){
public void run() {
tv.append("Hello World");
handler.postDelayed(r, 1000);
}
};
handler.post(r);
带有协程的Kotlin
在Kotlin中，使用协程你可以做以下事情:
CoroutineScope(Dispatchers.Main).launch { // Main, because UI is changed
ticker(delayMillis = 1000, initialDelayMillis = 1000).consumeEach {
tv.append("Hello World")
}
}
在这里试试吧!
对于重复任务，您可以使用
new Timer().scheduleAtFixedRate(task, runAfterADelayForFirstTime, repeaingTimeInterval);
就像这样
new Timer().scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
}
},500,1000);
上面的代码将在半秒后(500)第一次运行，并在每一秒后重复运行(1000)
在哪里
任务是要执行的方法
之后时间到初始执行
(重复执行的时间间隔)
其次
如果你想要执行Task的次数，你也可以使用CountDownTimer。
new CountDownTimer(40000, 1000) { //40000 milli seconds is total time, 1000 milli seconds is time interval
public void onTick(long millisUntilFinished) {
}
public void onFinish() {
}
}.start();
//Above codes run 40 times after each second
你也可以用runnable来做。创建一个可运行的方法
Runnable runnable = new Runnable()
{
@Override
public void run()
{
}
};
用这两种方式来称呼它
new Handler().postDelayed(runnable, 500 );//where 500 is delayMillis // to work on mainThread
OR
new Thread(runnable).start();//to work in Background
现在在Kotlin中，你可以这样运行线程:
class SimpleRunnable: Runnable {
public override fun run() {
println("${Thread.currentThread()} has run.")
}
}
fun main(args: Array<String>) {
val thread = SimpleThread()
thread.start() // Will output: Thread[Thread-0,5,main] has run.
val runnable = SimpleRunnable()
val thread1 = Thread(runnable)
thread1.start() // Will output: Thread[Thread-1,5,main] has run
}
