首先检查是否是主线程

在Kotlin

fun isRunningOnMainThread(): Boolean {
    return Thread.currentThread() == Looper.getMainLooper().thread
}

在Java中

static boolean isRunningOnMainThread() {
  return Thread.currentThread().equals(Looper.getMainLooper().getThread());
}

一种基于协程的、与android无关的方法:

val onMainThread: Boolean
    get() = Thread.currentThread() === try {
        runBlocking(Dispatchers.Main.immediate) {
            Thread.currentThread()
        }
    } catch (e: IllegalStateException) {
        // No main dispatcher has been registered; not in an Android context?
        null
    }

Looper.myLooper() == Looper.getMainLooper()

如果返回true，那么你在UI线程上!

首先检查是否是主线程

在Kotlin

fun isRunningOnMainThread(): Boolean {
    return Thread.currentThread() == Looper.getMainLooper().thread
}

在Java中

static boolean isRunningOnMainThread() {
  return Thread.currentThread().equals(Looper.getMainLooper().getThread());
}

总结解决方案，我认为这是最好的一个:

boolean isUiThread = VERSION.SDK_INT >= VERSION_CODES.M 
    ? Looper.getMainLooper().isCurrentThread()
    : Thread.currentThread() == Looper.getMainLooper().getThread();

并且，如果你想在UI线程上运行一些东西，你可以使用这个:

new Handler(Looper.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
       //this runs on the UI thread
    }
});

你可以检查一下

if(Looper.myLooper() == Looper.getMainLooper()) {
   // You are on mainThread 
}else{
// you are on non-ui thread
}