Handler -- Async Task

Handler: Async Task。
使用 Async Task (非同步任務）的方式下載網頁的內容。當背景下載完成時，才載入TextView 裡顯現出來。

參考：http://www.vogella.com/articles/AndroidPerformance/article.html

res/layout/main.xml:

<?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" >

    <Button

        android:id="@+id/button1"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="Load Webpage" />

     <ScrollView

        android:id="@+id/scrollView"

        android:layout_width="fill_parent"

        android:layout_height="fill_parent"

        android:fadingEdge="vertical"

        android:paddingTop="10dip"

        android:scrollbars="vertical" >

     <TextView

            android:id="@+id/textView01"

            android:layout_width="fill_parent"

            android:layout_height="wrap_content"

            android:paddingTop="10dip"

            android:text="Taipei Times (台北時報)"

            android:textColor="#00FF00"

           />

    </ScrollView>

      

</LinearLayout>

****************************************

main.java:

/**

 *  Async Task  using Android HttpClient

 * */

public class HandlerAsyncTaskActivity extends Activity {

    /** Called when the activity is first created. */

private TextView tv;

private Button btn;

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        tv = (TextView) findViewById(R.id.textView01);

      

        btn = (Button) findViewById(R.id.button1);

        btn.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

readWebpage(tv);

}

});

    }

    

    

    private class DownloadWebPageTask extends AsyncTask<String, Void, String>{

@Override

protected String doInBackground(String... urls) {

// TODO Auto-generated method stub

String response = "";

for (String url : urls) {

DefaultHttpClient client = new DefaultHttpClient();

HttpGet httpGet = new HttpGet(url);

try {

HttpResponse execute = client.execute(httpGet);

InputStream content = execute.getEntity().getContent();

BufferedReader buffer = new BufferedReader(new InputStreamReader(content));

String s = "";

while ((s = buffer.readLine()) != null) {

response += s;

}

}catch (Exception e) {

e.printStackTrace();

}

}

return response;

}

@Override

protected void onPostExecute(String result) {

// TODO Auto-generated method stub

//super.onPostExecute(result);

tv.setText(result);

}

    

    }

    

    public void readWebpage (View view) {

    DownloadWebPageTask task = new DownloadWebPageTask();

    task.execute(new String[] {"http://www.taipeitimes.com"});

    }

}