android - 如何在android asynctask中使用输入流作为参数？

Question

我正在制作一个 android 应用程序来跟踪股票详细信息，我将通过 csv(yahoo finance)检索数据。据我所知，在android 4.0中，网络连接不能在主线程上完成。因此，我将使用 asynctask 来建立连接。但是，我在参数方面遇到了一些问题。请问inputstream类型可以作为参数吗？

public class StockDetails extends Activity {
    private InputStream is = null;
    private BufferedReader reader = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.stock_details);
        Intent i = getIntent();
        String stockNo = i.getStringExtra(MainActivity.STOCK_NO).toString();
        Log.i("Stock No", stockNo);
        String strURL = "http://download.finance.yahoo.com/d/quotes.csv?s="+ stockNo +".HK&f=nsl1opc1";
        Log.i("URL", strURL);
        class HostConnection extends AsyncTask<String, Void, InputStream> {
            private Exception ex;

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
            }

            protected InputStream doInBackground(String... urls) {
                try {
                    // defaultHttpClient
                    DefaultHttpClient httpClient = new DefaultHttpClient();
                    HttpGet httpGet = new HttpGet(urls[0]);
                    HttpContext localContext = new BasicHttpContext();
                    HttpResponse httpResponse = httpClient.execute(httpGet, localContext);
                    HttpEntity httpEntity = httpResponse.getEntity();
                    return httpEntity.getContent();
                } catch (Exception e) {
                    this.ex = e;
                    return null;
                } 
            }
            @Override
            protected void onPostExecute(InputStream is) {
                super.onPostExecute(is);
                reader = new BufferedReader(new InputStreamReader(is));
            }
        }
        new HostConnection().execute(strURL);
        try {
            String line;
            while ((line = reader.readLine()) != null){
                String[] RowData = line.split(",");
                String name = RowData[0];
                String symbol = RowData[1];
                String currPrice = RowData[2];
                String open = RowData[3];
                String prevClose = RowData[4];
                String change = RowData[5];

                TextView stockName = (TextView)findViewById(R.id.stockName);
                stockName.setText(name);
                TextView stockSymbol = (TextView)findViewById(R.id.stockSym);
                stockSymbol.setText(symbol);
                TextView stockCurrPrice = (TextView)findViewById(R.id.currPrice);
                stockCurrPrice.setText(currPrice);
                TextView stockOpen = (TextView)findViewById(R.id.open);
                stockOpen.setText(open);
                TextView stockPrevClose = (TextView)findViewById(R.id.prevClose);
                stockPrevClose.setText(prevClose);
                TextView stockChange = (TextView)findViewById(R.id.change);
                stockChange.setText(change);
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        ...
    }

}

以上是我的代码，无法执行return httpEntity.getContent();语句，跳转到异常部分。请帮忙。谢谢!

Answer 1

使用 InputStream 作为 Result 值类型是完全合法的，任何其他类也是如此。但是您必须知道 AsyncTask 是异步执行的，因此如果您调用 new HostConnection().execute(strURL); 然后立即尝试使用正在初始化的变量在 AsyncTask 中，您会遇到麻烦。你应该等待 AsyncTask 通过定义某种回调机制来完成它的执行，或者在你的情况下，因为 AsyncTask 是一个内部类，你可以只推送所有BufferedReader相关的代码到onPostExecute()。