AsyncTask

来源：互联网发布：司马懿新旧知乎编辑：程序博客网时间：2024/06/15 05:03

public class MainActivity extends Activity {private static final String TAG = "ASYNC_TASK";private Button execute;private Button cancel;private ProgressBar progressBar;private TextView textView;private MyTask mTask;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                execute = (Button) findViewById(R.id.execute);        execute.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//注意每次需new一个实例,新建的任务只能执行一次,否则会出现异常mTask = new MyTask();mTask.execute("http://developers.douban.com");execute.setEnabled(false);cancel.setEnabled(true);}});        cancel = (Button) findViewById(R.id.cancel);        cancel.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//取消一个正在执行的任务,onCancelled方法将会被调用mTask.cancel(true);}});        progressBar = (ProgressBar) findViewById(R.id.progress_bar);        textView = (TextView) findViewById(R.id.text_view);            }        private class MyTask extends AsyncTask<String, Integer, String> {    //1 onPreExecute方法用于在执行后台任务前做一些UI操作    @Override    protected void onPreExecute() {    Log.i(TAG, "onPreExecute() called");    textView.setText("loading...");    }        //doInBackground方法内部执行后台任务,不可在此方法内修改UI@Overrideprotected String doInBackground(String... params) {Log.i(TAG, "doInBackground(Params... params) called");try {HttpClient client = new DefaultHttpClient();HttpGet get = new HttpGet(params[0]);HttpResponse response = client.execute(get);if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {HttpEntity entity = response.getEntity();InputStream is = entity.getContent();long total = entity.getContentLength();ByteArrayOutputStream baos = new ByteArrayOutputStream();byte[] buf = new byte[1024];int count = 0;int length = -1;while ((length = is.read(buf)) != -1) {baos.write(buf, 0, length);count += length;//调用publishProgress公布进度,最后onProgressUpdate方法将被执行publishProgress((int) ((count / (float) total) * 100));//为了演示进度,休眠500毫秒Thread.sleep(500);}return new String(baos.toByteArray(), "utf-8");}} catch (Exception e) {Log.e(TAG, e.getMessage());}return null;}//onProgressUpdate方法用于更新进度信息@Override    protected void onProgressUpdate(Integer... progresses) {Log.i(TAG, "onProgressUpdate(Progress... progresses) called");progressBar.setProgress(progresses[0]);textView.setText("loading..." + progresses[0] + "%");    }    //onPostExecute方法用于在执行完后台任务后更新UI,显示结果@Overrideprotected void onPostExecute(String result) {Log.i(TAG, "onPostExecute(Result result) called");textView.setText(result);execute.setEnabled(true);cancel.setEnabled(false);}//onCancelled方法用于在取消执行中的任务时更改UI@Overrideprotected void onCancelled() {Log.i(TAG, "onCancelled() called");textView.setText("cancelled");progressBar.setProgress(0);execute.setEnabled(true);cancel.setEnabled(false);}    }}

<?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/execute"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="execute" />    <Button        android:id="@+id/cancel"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:enabled="false"        android:text="cancel" />    <ProgressBar        android:id="@+id/progress_bar"        style="?android:attr/progressBarStyleHorizontal"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:max="100"        android:progress="0" />    <ScrollView        android:layout_width="fill_parent"        android:layout_height="wrap_content" >        <TextView            android:id="@+id/text_view"            android:layout_width="fill_parent"            android:layout_height="wrap_content" />    </ScrollView></LinearLayout>

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