在TextView上显示的消息有些能显示，有些不能显示

Question

 package com.example.theadtest;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener {
    private TextView tv;
    private Button mButton;
    private Handler handler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv=(TextView)findViewById(R.id.tv);
        mButton=(Button)findViewById(R.id.bt);
        mButton.setOnClickListener(this);
        handler=new Handler()
        {
            public void handleMessage(Message msg)
            {
                tv.setText(msg.obj.toString());
            }
        };
        Message messagef=Message.obtain();
        messagef.obj="我在主";
        handler.sendMessage(messagef);
        tv.setText("我是main");
    }
    @Override
    public void onClick(View v)
    {
        switch (v.getId())
        {
        case R.id.bt:
            new MyThread("MyThread").start();
            break;
        }
    }
    class MyThread extends Thread
    {
        String name;
        public MyThread(String name)
        {
            this.name=name;
        }
        public void run()
        {
            Log.e("MainActivity", "外---当前线程为:"+Thread.currentThread().getName());
            Message messag=Message.obtain();
            messag.obj="I love you";
            handler.sendMessage(messag);
            handler.post(new Runnable()
            {
                public void run()
                {
                    Message message=Message.obtain();
                    message.obj="Hello Worldbbb";
                    handler.sendMessage(message);
                    tv.setText("我是post");
                    Log.e("MainActivity", "内---当前线程为:"+Thread.currentThread().getName());
                }
            });
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

Answer 1

这sendMessage之后在handleMessage方法里面对textView的字体重新设置了，覆盖了前面设置的。并不是“不显示”。
另外不要子线程中操作ui