Android 能够更新UI窗体线程。为什么？

根据文档，我们无法从后台线程更新UI。但在我的情况下，我能够更新用户界面没有任何问题。检查螺纹3。我还打印了线程名称，结果是线程4

为什么从后台线程访问主线程时不会引发异常

fun threadsWithThreadPoolExecutor(v: View) {
    val startTime = System.currentTimeMillis()
    var endTime: Long = startTime
    val threadPoolExecutor = Executors.newFixedThreadPool(3)
    val thread1 = Thread(Runnable {
        Thread.sleep(7000)
        endTime = System.currentTimeMillis()
    })
    val thread2 = Thread(Runnable {
        Thread.sleep(10000)
        endTime = System.currentTimeMillis()
    })
    val thread3 = Thread(Runnable {
        Thread.sleep(3000)
        endTime = System.currentTimeMillis()
        tv_result.text = "This is from thread"
    })

    showProcessRunning()
    threadPoolExecutor.submit(thread1)
    threadPoolExecutor.submit(thread2)
    threadPoolExecutor.submit(thread3)

    Log.d("MyLog", thread3.name)

    Handler().postDelayed(Runnable {
        showTotalTime(startTime, endTime)
    }, 20000)
}

更新 正如有人在评论中提到的，为什么我要在ThreadPoolExecutor#submit（）中传递线程，因为它实现了Runnable。另外，如果我不使用ThreadPool，那么问题仍然存在

fun threadsWithoutExecutor(v: View) {
    val startTime = System.currentTimeMillis()
    var endTime: Long = startTime
    val thread1 = Thread(Runnable {
        Thread.sleep(7000)
        endTime = System.currentTimeMillis()
    })
    val thread2 = Thread(Runnable {
        Thread.sleep(10000)
        endTime = System.currentTimeMillis()
    })
    val thread3 = Thread(Runnable {
        tv_result.text = "sdadadasda"
        Thread.sleep(3000)
        endTime = System.currentTimeMillis()
    })

    thread3.priority = Thread.MIN_PRIORITY
    showProcessRunning()
    thread1.start()
    thread2.start()
    thread3.start()

    Thread(Runnable {
        thread1.join()
        thread2.join()
        thread3.join()
        showTotalTime(startTime, endTime)
    }).start()
}

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你在使用Android Kotlin扩展吗？你能分享完整的代码吗？你等了20秒了吗？当你到达

tv\u结果时，它一定会崩溃。text

你在哪个设备和操作系统上运行，因为当我尝试上述代码时，应用程序会在3秒钟后崩溃。我没有使用任何kotlin扩展是的，我等待了1分钟，没有出现异常情况