Accurate version of Android CountDownTimer

Usage

The same as Android CountDownTimer.

Download

Add it in your root build.gradle at the end of repositories:

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

Add the dependency:

dependencies {
    implementation 'com.github.cardinalby:accurate-count-down-timer:1.0'
}

Details

If you start default CountDownTimer (new CountDownTimer(10000, 1000)) and log millisUntilFinished in onTick you will observe something like this:

9999        // 1 ms lag
8997        // 3 ms lag
7995        // 5 ms lag
6993        // 7 ms lag
5991        // 9 ms lag
4987        // 13 ms lag
3985        // 15 ms lag
2979        // 21 ms lag
1975        // 25 ms lag
971         // 29 ms lag

As you can see it increases it's lag by 2-3 milliseconds each tick. The reason is that it's implementation doesn't take into account the time a message stays in thread's message queue and the time needed for synchronization.

Check out my fix and results of the same test after applying it:

9999        // 1 ms lag
8999        // 1 ms lag
7999        // 1 ms lag
6997        // 3 ms lag
5997        // 3 ms lag
4998        // 2 ms lag
3997        // 3 ms lag
2998        // 2 ms lag
1997        // 3 ms lag
997         // 3 ms lag

Now you can see that although delay is still here it doesn't increase. The delay is caused by the time message stays in message queue until it gets processed by Looper and can't be precisely predicted to be taken into account.