AsyncTask（异步任务）讲解-android的学习之旅（四十六）

AsyncTask简介

Android的UI线程主要处理用户的按键，触屏和View的绘制等，不能在里面处理耗时的操作，否则会出现ANR，因此耗时的操作要单独开一个线程处理，但是新线程不能直接处理UI线程的View。

AsyncTask的使用方法

代码示例

本实例只有一个按钮和文本框，点击按钮从网络下载数据，然后又在文本框显示。

package peng.liu.test;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
public class MainActivity extends Activity{
    private TextView tvAsync;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvAsync = (TextView) findViewById(R.id.tvAsync);
    }
    public void download(View source) throws MalformedURLException {
        DownTask downTask = new DownTask(this);
        downTask.execute(new URL("http://www.carzyit.org/ethos.php"));
    }
    class DownTask extends AsyncTask<URL,Integer,String>{
        ProgressDialog dialog;
        int hasdata;
        Context context;
        public DownTask(Context ctx){
            this.context = ctx;
        }
        @Override
        protected String doInBackground(URL... urls) {
            StringBuilder sb = new StringBuilder();
            try {
                URLConnection conn = urls[0].openConnection();
                BufferedReader bf = new BufferedReader(new InputStreamReader(conn.getInputStream(),"utf-8"));
                String line = null;
                while ((line = bf.readLine()) != null){
                    sb.append(line);
                    hasdata++;
                    publishProgress(hasdata);
                }
                return sb.toString();
            }
            catch (Exception e){
                e.printStackTrace();
            }
            return null;
        }
        @Override
        protected void onPostExecute(String s) {
            tvAsync.setText(s);
            dialog.dismiss();
        }
        @Override
        protected void onPreExecute() {
            dialog = new ProgressDialog(context);
            dialog.setTitle("hello");
            dialog.setCancelable(false);
            dialog.setMessage("world");
            dialog.setMax(202);
            dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            dialog.setIndeterminate(false);
            dialog.show();
        }
        @Override
        protected void onProgressUpdate(Integer... values) {
            tvAsync.setText(hasdata+"");
            dialog.setProgress(values[0]);
        }
    }
}