带有 AsyncTask 的 HttpURLConnection 太慢（Android）

Question

我尝试从互联网上获取数据并将它们保存在变量中，但是这个过程太慢了......这是我的代码：

`public class CurrConvert extends AsyncTask {

    boolean connection = true;

    float exchangeRate(final String currencyFrom, final String currencyTo) throws IOException {
        URL url = new URL("http://quote.yahoo.com/d/quotes.csv?s=" + currencyFrom + currencyTo + "=X&f=l1&e=.csv");
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
        urlConnection.setUseCaches(false);
        InputStream inputStream = urlConnection.getInputStream();
        String result = IOUtils.toString(inputStream);
        return Float.parseFloat(result);
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(getActivity());
        pDialog.setMessage(getContext().getString(R.string.updating));
        pDialog.setCancelable(false);
        pDialog.show();
    }

    @Override
    protected Object doInBackground(Object[] objects) {
        try {
            USD_AUD = exchangeRate("USD", "AUD");
            USD_CAD = exchangeRate("USD", "CAD");
            USD_EUR = exchangeRate("USD", "EUR");
            USD_GBP = exchangeRate("USD", "GBP");
            USD_INR = exchangeRate("USD", "INR");
            USD_JPY = exchangeRate("USD", "JPY");
            USD_SGD = exchangeRate("USD", "SGD");

            EUR_AUD = exchangeRate("EUR", "AUD");
            EUR_CAD = exchangeRate("EUR", "CAD");
            EUR_GBP = exchangeRate("EUR", "GBP");
            EUR_INR = exchangeRate("EUR", "INR");
            EUR_JPY = exchangeRate("EUR", "JPY");
            EUR_SGD = exchangeRate("EUR", "SGD");
            EUR_USD = exchangeRate("EUR", "USD");

            AUD_CAD = exchangeRate("AUD", "CAD");
            AUD_EUR = exchangeRate("AUD", "EUR");
            AUD_GBP = exchangeRate("AUD", "GBP");
            AUD_INR = exchangeRate("AUD", "INR");
            AUD_JPY = exchangeRate("AUD", "JPY");
            AUD_SGD = exchangeRate("AUD", "SGD");
            AUD_USD = exchangeRate("AUD", "USD");

            CAD_AUD = exchangeRate("CAD", "AUD");
            CAD_EUR = exchangeRate("CAD", "EUR");
            CAD_GBP = exchangeRate("CAD", "GBP");
            CAD_INR = exchangeRate("CAD", "INR");
            CAD_JPY = exchangeRate("CAD", "JPY");
            CAD_SGD = exchangeRate("CAD", "SGD");
            CAD_USD = exchangeRate("CAD", "USD");

            SGD_AUD = exchangeRate("SGD", "AUD");
            SGD_CAD = exchangeRate("SGD", "CAD");
            SGD_EUR = exchangeRate("SGD", "EUR");
            SGD_GBP = exchangeRate("SGD", "GBP");
            SGD_INR = exchangeRate("SGD", "INR");
            SGD_JPY = exchangeRate("SGD", "JPY");
            SGD_USD = exchangeRate("SGD", "USD");

            GBP_AUD = exchangeRate("GBP", "AUD");
            GBP_CAD = exchangeRate("GBP", "CAD");
            GBP_EUR = exchangeRate("GBP", "EUR");
            GBP_INR = exchangeRate("GBP", "INR");
            GBP_JPY = exchangeRate("GBP", "JPY");
            GBP_SGD = exchangeRate("GBP", "SGD");
            GBP_USD = exchangeRate("GBP", "USD");

            JPY_AUD = exchangeRate("JPY", "AUD");
            JPY_CAD = exchangeRate("JPY", "CAD");
            JPY_EUR = exchangeRate("JPY", "EUR");
            JPY_GBP = exchangeRate("JPY", "GBP");
            JPY_INR = exchangeRate("JPY", "INR");
            JPY_SGD = exchangeRate("JPY", "SGD");
            JPY_USD = exchangeRate("JPY", "USD");

            INR_AUD = exchangeRate("INR", "AUD");
            INR_CAD = exchangeRate("INR", "CAD");
            INR_EUR = exchangeRate("INR", "EUR");
            INR_GBP = exchangeRate("INR", "GBP");
            INR_JPY = exchangeRate("INR", "JPY");
            INR_SGD = exchangeRate("INR", "SGD");
            INR_USD = exchangeRate("INR", "USD");

        } catch (IOException e) {
            connection = false;
        }
        return 0;
    }

    @Override
    protected void onPostExecute(Object o) {
        super.onPostExecute(o);
        pDialog.dismiss();
        if (connection) {
            Toast.makeText(getContext(), "Done", Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(getContext(), R.string.no_connection, Toast.LENGTH_LONG).show();
        }
    }
}`

doInBackground 方法需要将近 30 秒才能完成该过程...有没有办法保持同步？

Answer 1

每次调用exchangeRate 方法时，都必须下载一个 csv 文件来提取汇率值。您总共有 56 个请求，这就是您的 AsyncTask 太慢的原因。

我的建议是使用这个链接：all currencies in JSON format。

现在，很简单！只需解码 JSON 响应，您可以参考此链接：How to parse the Json response in android?。

获取responses JSON Array，每个 JSON Object 的结构如下（示例）：

{
"resource" : { 
"classname" : "Quote",
"fields" : { 
"change" : "-0.006400",
"chg_percent" : "-0.481094",
"name" : "USD/AUD",
"price" : "1.323900",
"symbol" : "AUD=X",
"ts" : "1472750677",
"type" : "currency",
"utctime" : "2016-09-01T17:24:37+0000",
"volume" : "0"
}
}
}

您现在要做的就是获取pricevalue，在您的情况下是汇率。

希望这会有所帮助:)

Answer 2

AsyncTask 默认以较低的优先级运行，以帮助确保 UI 线程保持响应，但您可以更改它：

protected Void doInBackground() {
    Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    // do your work
}