如何使用kotlin更新线程中TextView文本

Question

我正在从服务器接收UDP数据，我想将UDP数据显示给TextView。但每次都会发生NullPointerException。我不知道为什么。

下面是我的代码：

open class MainActivity: AppCompatActivity() {

    companion object {
        lateinit var readSocket: DatagramSocket
        lateinit var readPacket: DatagramPacket
        val buffer = ByteArray(2048)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        println("Create Runnable example!")
        val threadWithRunnable = Thread(UdpDataArrival())
        threadWithRunnable.start()

        // Add text to textView1
        val textView = findViewById<TextView>(R.id.textView1)
        textView.setText("Hello World from main!\n")

        println("MainActivity onCreate success.")
    }

}

这个类是线程，用于继续接收UDP数据

class UdpDataArrival: Runnable, MainActivity() {

   override fun run() {
       println("${Thread.currentThread()} Runnable Thread Started.")
       readSocket = DatagramSocket(Settings.remotePort)
       readSocket.broadcast = true
       readPacket = DatagramPacket(buffer, buffer.size)
       while (true) {
           receiveUDP()
       }
   }

   open fun receiveUDP() {
       try {
            // Keep a socket open to listen to all the UDP traffic that is destined for this port
            readSocket.receive(readPacket)
            println("open fun receiveUDP packet received = " + readPacket.data)

            str = String(readPacket.data, 0, readPacket.length, Charsets.UTF_8)

            println(str)

            // I tried to update textview in here but the exception occurs
            //textView1.setText(str)

        } catch (e: Exception) {
           println("open fun receiveUDP catch exception.$e")
           e.printStackTrace()
        }
//        finally {
//           readSocket?.close()
//        }

    }
}

我应该做什么来向TextView显示'str'？

这是StackTrace：

java.lang.NullPoInterException：尝试在Android.Content.ContextWrapper.GetApplicationInfo（ContextWrapper.getApplicationInfo（））（ContextWrapper.java:173)（Android.View.ContextThemeWrapper.getTheme（ContextThemeWrapper.java:174)（Android.Content.Context.ObtainStyleDatTributes（Context.java:744)（AndroidX.AppCompat.AppCompatDelegateImpl.CreateSubdecor（roid.os.handler.dispatchMessage（handler.java：99）在android.os.looper.loop（looper.java：223）在android.app.activitythread.main（activitythread.java：7656）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.runtimeinit$methodandargscaller.run（runtimeinit.java:592)在com.android.internal.os.zygoteinit.main（

Answer 1

在settext周围添加UI线程或访问UI线程内的任何UI小部件

runOnUiThread {
   textView.setText(str)       
}