AsyncTask（非同步任務）講解-android的學習之旅（四十六），asynctask-android

AsyncTask（非同步任務）講解-android的學習之旅（四十六），asynctask-android
AsyncTask簡介Android的UI線程主要處理使用者的按鍵，觸屏和View的繪製等，不能在裡面處理耗時的操作，否則會出現ANR，因此耗時的操作要單獨開一個線程處理，但是新線程不能直接處理UI線程的View。

AsyncTask的使用方法

程式碼範例

本執行個體只有一個按鈕和文字框，點擊按鈕從網路下載資料，然後又在文字框顯示。

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]);        }    }}