andriod 动态显示当前时间

<?xml version="1.0" encoding="UTF-8"?>

<LinearLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical">

    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="New Text"

        android:id="@+id/time"

        android:layout_gravity="center_horizontal" />

</LinearLayout>

package com.example.yanlei.mytk;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.support.v7.app.AppCompatActivity;

import android.widget.TextView;

import java.text.SimpleDateFormat;

import java.util.Date;

public class MainActivity extends AppCompatActivity  implements Runnable {

    private Handler handler;

    private TextView textView;

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        textView=(TextView) findViewById(R.id.time);

        handler = new Handler() {

            public void handleMessage(Message msg) {

                textView.setText((String)msg.obj);

            }

        };

        new Thread(this).start();

    }

    @Override

    public void run() {

        // TODO Auto-generated method stub

        try {

            while(true){

                SimpleDateFormat sdf=new SimpleDateFormat("yyyy年MM月dd日   HH:mm:ss");

                String str=sdf.format(new Date());

                handler.sendMessage(handler.obtainMessage(100,str));

                Thread.sleep(1000);

            }

        } catch (InterruptedException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

}