问题
I have a variable in my code say it is \"status\".
I want to display some text in the application depending on this variable value. This has to be done with a specific time delay.
It\'s like,
Check status variable value
Display some text
Wait for 10 seconds
Check status variable value
Display some text
Wait for 15 seconds
and so on. The time delay may vary and it is set once the text is displayed.
I have tried Thread.sleep(time delay) and it failed. Any better way to get this done?
回答1:
You should use Handler's postDelayed function for this purpose. It will run your code with specified delay on the main UI thread, so you will be able to update UI controls.
private int mInterval = 5000; // 5 seconds by default, can be changed later
private Handler mHandler;
@Override
protected void onCreate(Bundle bundle) {
// your code here
mHandler = new Handler();
startRepeatingTask();
}
@Override
public void onDestroy() {
super.onDestroy();
stopRepeatingTask();
}
Runnable mStatusChecker = new Runnable() {
@Override
public void run() {
try {
updateStatus(); //this function can change value of mInterval.
} finally {
// 100% guarantee that this always happens, even if
// your update method throws an exception
mHandler.postDelayed(mStatusChecker, mInterval);
}
}
};
void startRepeatingTask() {
mStatusChecker.run();
}
void stopRepeatingTask() {
mHandler.removeCallbacks(mStatusChecker);
}
回答2:
To anyone interested, here's a class I created using inazaruk's code that creates everything needed (I called it UIUpdater because I use it to periodically update the UI, but you can call it anything you like):
import android.os.Handler;
/**
* A class used to perform periodical updates,
* specified inside a runnable object. An update interval
* may be specified (otherwise, the class will perform the
* update every 2 seconds).
*
* @author Carlos Simões
*/
public class UIUpdater {
// Create a Handler that uses the Main Looper to run in
private Handler mHandler = new Handler(Looper.getMainLooper());
private Runnable mStatusChecker;
private int UPDATE_INTERVAL = 2000;
/**
* Creates an UIUpdater object, that can be used to
* perform UIUpdates on a specified time interval.
*
* @param uiUpdater A runnable containing the update routine.
*/
public UIUpdater(final Runnable uiUpdater) {
mStatusChecker = new Runnable() {
@Override
public void run() {
// Run the passed runnable
uiUpdater.run();
// Re-run it after the update interval
mHandler.postDelayed(this, UPDATE_INTERVAL);
}
};
}
/**
* The same as the default constructor, but specifying the
* intended update interval.
*
* @param uiUpdater A runnable containing the update routine.
* @param interval The interval over which the routine
* should run (milliseconds).
*/
public UIUpdater(Runnable uiUpdater, int interval){
UPDATE_INTERVAL = interval;
this(uiUpdater);
}
/**
* Starts the periodical update routine (mStatusChecker
* adds the callback to the handler).
*/
public synchronized void startUpdates(){
mStatusChecker.run();
}
/**
* Stops the periodical update routine from running,
* by removing the callback.
*/
public synchronized void stopUpdates(){
mHandler.removeCallbacks(mStatusChecker);
}
}
You can then create a UIUpdater object inside your class and use it like so:
...
mUIUpdater = new UIUpdater(new Runnable() {
@Override
public void run() {
// do stuff ...
}
});
// Start updates
mUIUpdater.startUpdates();
// Stop updates
mUIUpdater.stopUpdates();
...
If you want to use this as an activity updater, put the start call inside the onResume() method and the stop call inside the onPause(), so the updates start and stop according to the activity visibility.
回答3:
I think the new hotness is to use a ScheduledThreadPoolExecutor. Like so:
private final ScheduledThreadPoolExecutor executor_ =
new ScheduledThreadPoolExecutor(1);
this.executor_.scheduleWithFixedDelay(new Runnable() {
@Override
public void run() {
update();
}
}, 0L, kPeriod, kTimeUnit);
回答4:
Timer works fine. Here, I use Timer to search text after 1.5s and update UI. Hope that helps.
private Timer _timer = new Timer();
_timer.schedule(new TimerTask() {
@Override
public void run() {
// use runOnUiThread(Runnable action)
runOnUiThread(new Runnable() {
@Override
public void run() {
search();
}
});
}
}, timeInterval);
回答5:
Timer is another way to do your work but be quiet sure to add runOnUiThread if you are working with UI.
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.TextView;
import android.app.Activity;
public class MainActivity extends Activity {
CheckBox optSingleShot;
Button btnStart, btnCancel;
TextView textCounter;
Timer timer;
MyTimerTask myTimerTask;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
optSingleShot = (CheckBox)findViewById(R.id.singleshot);
btnStart = (Button)findViewById(R.id.start);
btnCancel = (Button)findViewById(R.id.cancel);
textCounter = (TextView)findViewById(R.id.counter);
btnStart.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View arg0) {
if(timer != null){
timer.cancel();
}
//re-schedule timer here
//otherwise, IllegalStateException of
//"TimerTask is scheduled already"
//will be thrown
timer = new Timer();
myTimerTask = new MyTimerTask();
if(optSingleShot.isChecked()){
//singleshot delay 1000 ms
timer.schedule(myTimerTask, 1000);
}else{
//delay 1000ms, repeat in 5000ms
timer.schedule(myTimerTask, 1000, 5000);
}
}});
btnCancel.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
if (timer!=null){
timer.cancel();
timer = null;
}
}
});
}
class MyTimerTask extends TimerTask {
@Override
public void run() {
Calendar calendar = Calendar.getInstance();
SimpleDateFormat simpleDateFormat =
new SimpleDateFormat("dd:MMMM:yyyy HH:mm:ss a");
final String strDate = simpleDateFormat.format(calendar.getTime());
runOnUiThread(new Runnable(){
@Override
public void run() {
textCounter.setText(strDate);
}});
}
}
}
and xml is...
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="vertical"
tools:context=".MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:autoLink="web"
android:text="http://android-er.blogspot.com/"
android:textStyle="bold" />
<CheckBox
android:id="@+id/singleshot"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Single Shot"/>
Another Way to use CountDownTimer
new CountDownTimer(30000, 1000) {
public void onTick(long millisUntilFinished) {
mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
mTextField.setText("done!");
}
}.start();
Schedule a countdown until a time in the future, with regular notifications on intervals along the way. Example of showing a 30 second countdown in a text field:
For Details
回答6:
Do it in Android's way with the help of Handler.
Declare a inner Handler class which does not leak Memory in your Activity/Fragment class
/**
* Instances of static inner classes do not hold an implicit
* reference to their outer class.
*/
private static class NonLeakyHandler extends Handler {
private final WeakReference<FlashActivity> mActivity;
public NonLeakyHandler(FlashActivity activity) {
mActivity = new WeakReference<FlashActivity>(activity);
}
@Override
public void handleMessage(Message msg) {
FlashActivity activity = mActivity.get();
if (activity != null) {
// ...
}
}
}
Declare a runnable which will perform your repetitive task in your Activity/Fragment class
private Runnable repeatativeTaskRunnable = new Runnable() {
public void run() {
new Handler(getMainLooper()).post(new Runnable() {
@Override
public void run() {
//DO YOUR THINGS
}
};
Initialize Handler object in your Activity/Fragment (here FlashActivity is my activity class)
//Task Handler
private Handler taskHandler = new NonLeakyHandler(FlashActivity.this);
To repeat a task after fix time interval
taskHandler.postDelayed(repeatativeTaskRunnable , DELAY_MILLIS);
To stop the repetition of task
taskHandler .removeCallbacks(repeatativeTaskRunnable );
UPDATE: In Kotlin:
//update interval for widget
override val UPDATE_INTERVAL = 1000L
//Handler to repeat update
private val updateWidgetHandler = Handler()
//runnable to update widget
private var updateWidgetRunnable: Runnable = Runnable {
run {
//Update UI
updateWidget()
// Re-run it after the update interval
updateWidgetHandler.postDelayed(updateWidgetRunnable, UPDATE_INTERVAL)
}
}
// SATART updating in foreground
override fun onResume() {
super.onResume()
updateWidgetHandler.postDelayed(updateWidgetRunnable, UPDATE_INTERVAL)
}
// REMOVE callback if app in background
override fun onPause() {
super.onPause()
updateWidgetHandler.removeCallbacks(updateWidgetRunnable);
}
回答7:
Try following example it works !!!
Use [Handler] in onCreate() method which makes use of postDelayed() method that Causes the Runnable to be added to the message queue, to be run after the specified amount of time elapses that is 0 in given example. 1
Refer this code :
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//------------------
//------------------
android.os.Handler customHandler = new android.os.Handler();
customHandler.postDelayed(updateTimerThread, 0);
}
private Runnable updateTimerThread = new Runnable()
{
public void run()
{
//write here whaterver you want to repeat
customHandler.postDelayed(this, 1000);
}
};
回答8:
You can use a Handler to post runnable code. This technique is outlined very nicely here: https://guides.codepath.com/android/Repeating-Periodic-Tasks
回答9:
Based on the above post concerning the ScheduledThreadPoolExecutor, I came up with a utility that suited my needs (wanted to fire a method every 3 seconds):
class MyActivity {
private ScheduledThreadPoolExecutor mDialogDaemon;
private void initDebugButtons() {
Button btnSpawnDialogs = (Button)findViewById(R.id.btn_spawn_dialogs);
btnSpawnDialogs.setVisibility(View.VISIBLE);
btnSpawnDialogs.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
spawnDialogs();
}
});
}
private void spawnDialogs() {
if (mDialogDaemon != null) {
mDialogDaemon.shutdown();
mDialogDaemon = null;
}
mDialogDaemon = new ScheduledThreadPoolExecutor(1);
// This process will execute immediately, then execute every 3 seconds.
mDialogDaemon.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
runOnUiThread(new Runnable() {
@Override
public void run() {
// Do something worthwhile
}
});
}
}, 0L, 3000L, TimeUnit.MILLISECONDS);
}
}
回答10:
In my case, I had to execute a process if one of these conditions were true: if a previous process was completed or if 5 seconds had already passed. So, I did the following and worked pretty well:
private Runnable mStatusChecker;
private Handler mHandler;
class {
method() {
mStatusChecker = new Runnable() {
int times = 0;
@Override
public void run() {
if (times < 5) {
if (process1.isRead()) {
executeProcess2();
} else {
times++;
mHandler.postDelayed(mStatusChecker, 1000);
}
} else {
executeProcess2();
}
}
};
mHandler = new Handler();
startRepeatingTask();
}
void startRepeatingTask() {
mStatusChecker.run();
}
void stopRepeatingTask() {
mHandler.removeCallbacks(mStatusChecker);
}
}
If process1 is read, it executes process2. If not, it increments the variable times, and make the Handler be executed after one second. It maintains a loop until process1 is read or times is 5. When times is 5, it means that 5 seconds passed and in each second, the if clause of process1.isRead() is executed.
回答11:
For people using Kotlin, inazaruk's answer will not work, the IDE will require the variable to be initialized, so instead of using the postDelayed inside the Runnable, we'll use it in an separate method.
Initialize your
Runnablelike this :private var myRunnable = Runnable { //Do some work //Magic happens here ↓ runDelayedHandler(1000) }Initialize your
runDelayedHandlermethod like this :private fun runDelayedHandler(timeToWait : Long) { if (!keepRunning) { //Stop your handler handler.removeCallbacksAndMessages(null) //Do something here, this acts like onHandlerStop } else { //Keep it running handler.postDelayed(myRunnable, timeToWait) } }As you can see, this approach will make you able to control the lifetime of the task, keeping track of
keepRunningand changing it during the lifetime of the application will do the job for you.
来源：https://stackoverflow.com/questions/6242268/repeat-a-task-with-a-time-delay