Android 多线程注意事项

package com.example.MyStarRss;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class MyStarRssActivity extends Activity {
    /**
     * Called when the activity is first created.
     */

    private TextView showTextView;
    private String data = "";
    private Handler handler;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button startDownload_button = (Button)findViewById(R.id.start_download);
        showTextView = (TextView)findViewById(R.id.showdata_textview);
        startDownload_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 启动下载任务
                new Thread(downtask).start();

            }
        });
        handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                switch(msg.what){
                    case 0:
                        showTextView.setText(msg.obj.toString());
                }
            }
        };

    }

    Runnable downtask = new Runnable() {
        @Override
        public void run() {
            MyHttpDownLoader myHttpDownLoader = new MyHttpDownLoader("http://rss.sina.com.cn/ent/hot_roll.xml");
            String mydata = myHttpDownLoader.starDownload_Text();
            Message msg = new Message();
            msg.obj = mydata;
            msg.what = 0;
            handler.sendMessage(msg);
        }
    };


}