android - 使用 Android AsyncTask 下载 html 文件

Question

我刚开始使用 android，我正在开发一个应该下载 html 文件内容的简单应用程序。我正在按照建议使用 AsyncTask，但我遇到了一个问题。在下面的代码中(我遵循了教程代码)，我得到 tv cannot be resolved 用于 onPostExecute 方法。如何访问下载的文件？谢谢:

public class FlashResults extends Activity {
  @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView tv = new TextView(this);
        setContentView(tv);
        readWebpage(tv);                
  }


  protected class DownloadPage extends AsyncTask<String, Void, String> {
          protected String doInBackground(String... urls) {

          String responseStr = null;

          try {
              for (String url : urls) {   
              DefaultHttpClient httpClient = new DefaultHttpClient();
              HttpGet get = new HttpGet(url);
              HttpResponse httpResponse = httpClient.execute(get);
              HttpEntity httpEntity = httpResponse.getEntity();
              responseStr = EntityUtils.toString(httpEntity);
              } 
          } catch (UnsupportedEncodingException e) {

          } catch (ClientProtocolException e) {

          } catch (IOException e) {

          }
          return responseStr;
      }

      protected void onPostExecute(String result) {           
          tv.setText(result);
      }
  }

  public void readWebpage(View v) {
        DownloadPage task = new DownloadPage();
        task.execute(new String[] { "http://seznam.cz" });
      }

Answer 1

到目前为止建议的所有其他答案都可以。但是，我会添加一些其他注释:

1. 如果您只访问 TextView tv在此 onCreate 和 DownloadPage Activity 中，您可以限制对 tv 的访问通过直接将其提供给 DownloadPage 的构造函数
2. 对于像 DownloadPage AsyncTask 这样有用的东西，我通常将它从任何 Activity 的内部类中删除，而是将其放在一个名为“Utils”的公共(public)类中，许多其他 Activity 可以根据需要使用它。 (代码模块化)
3. 如果你打算使用一个内部类(完全合法)，那么做它总是好的做法private和 static对于你正在做的事情。

像这样:

public class FlashResults extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView tv = new TextView(this);
        setContentView(tv);
        readWebpage(tv);
    }

    public void readWebpage(View v) {
        DownloadPage task = new DownloadPage(tv);
        task.execute(new String[] { "http://seznam.cz" });
    }

    private static class DownloadPage extends AsyncTask<String, Void, String> {

        private TextView textView;
        public DownloadPage(TextView tv){
            textView = tv;
        }

        protected String doInBackground(String... urls) {

         String responseStr = null;

          try {
              for (String url : urls) {   
              DefaultHttpClient httpClient = new DefaultHttpClient();
              HttpGet get = new HttpGet(url);
              HttpResponse httpResponse = httpClient.execute(get);
              HttpEntity httpEntity = httpResponse.getEntity();
              responseStr = EntityUtils.toString(httpEntity);
              } 
          } catch (UnsupportedEncodingException e) {

          } catch (ClientProtocolException e) {

          } catch (IOException e) {

          }
            return responseStr;
        }

        protected void onPostExecute(String result) {           
            if (textView != null) {
                textView.setText(result);
            }
        }
    }
}