Toast in loop is not displaying properly

Question

I have the following code in my main activity (Note: GPSTracker in this application works):

    double latitude, longitude;
    gps = new GPSTracker(MainActivity.this);
    if(gps.canGetLocation()){
         latitude = gps.getLatitude();
         longitude = gps.getLongitude();
         Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
    }
    else{
         gps.showSettingsAlert();
    }

I want to create a loop, which would display in some time intervals Toast with my current position. I´ve tried this:

    double latitude, longitude;
    long currentTime = System.currentTimeMillis();
    long myTimestamp = currentTime;
    int i = 0;
    gps = new GPSTracker(MainActivity.this);
    while(i < 5)
    {
        myTimestamp = System.currentTimeMillis();
        if((myTimestamp - currentTime) > 5000)
        {
            i++;
            currentTime = System.currentTimeMillis();
            if(gps.canGetLocation()){
                latitude = gps.getLatitude();
                longitude = gps.getLongitude();
                Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();  
            }else{
                gps.showSettingsAlert();
            }
        }
    }

With this code, Toast is shown only one time (the last iteration). Could you help me with this? Thanks in advance.

Like I said, toast is displayed during the last iteration (i = 5) — Tom11, Feb 24 '13 at 18:08
Is Toast.makeText called 5 times? Or only once on the last iteration? — Simon, Feb 24 '13 at 18:11
I want it to be shown every iteration (for example every 5 seconds). Now, it seems to be called only on the last iteration — Tom11, Feb 24 '13 at 18:14
update 'currentTime = System.currentTimeMillis();' in 'if' after toast — nayab, Feb 24 '13 at 18:14
Why don't you debug your code to see what is the flow of the code? That way you'll see what's happening.... Also, read about threading, because this way you're blocking your UI thread, which is not a good idea (check this one out: www.edumobile.org/android/android-development/timer-thread-example-in-android-programming/). — Nuno Gonçalves, Feb 24 '13 at 18:16

score 1 · Accepted Answer · edited May 23 '17 at 11:56

I want it to be shown every iteration (for example every 5 seconds).

The code above doesn't loop every five seconds, it loops continuously but only increments your counter every five seconds... This is a very inefficient way of creating a time delay because nothing else can happen while the loop runs. (Even if you run this on a separate thread it is still not good tactic.)

Instead use LocationManager's requestLocationUpdates which will use callbacks so your app can do things between updates. A couple quick notes:

Understand that the GPS may not be able to get a fix every five seconds and that this interval is really short so use it sparingly or you'll run the battery down.
Some pre-Jelly Bean devices may not observe the minTime parameter, but you can enforce your time parameter yourself as I describe in Android Location Listener call very often.

All that aside, you use your existing code but I recommend a Handler and Runnable, like this:

handler.postDelayed(new Runnable() {
    @Override
    public void run() {
        // Fetch your location here

        // Run the code again in about 5 seconds
        handler.postDelayed(this, 5000);
    }
}, 5000);

score 0 · Answer 2 · answered Feb 24 '13 at 18:20

One problem is that this method does a 'busy-wait', which, I suspect, prevents the toast from being displayed. Try doing a sleep() to wait until it's time for the next Toast:

public void sleepForMs(long sleepTimeMs) {
    Date now = new Date();
    Date wakeAt = new Date(now.getTime() + sleepTimeMs);
    while (now.before(wakeAt)) {
        try {
            long msToSleep = wakeAt.getTime() - now.getTime();
            Thread.sleep(msToSleep);
        } catch (InterruptedException e) {
        }

        now = new Date();
    }

}

You are still blocking the UI thread. You should put the code in a separate thread. — Nuno Gonçalves, Feb 24 '13 at 18:23

Toast in loop is not displaying properly

2 Answers2

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