Question

我有一堆代码，应该从特定的网站获得特定的价值。显然我需要在AsyncTask中执行它，但是我对此一无所知。有人可以帮助我如何“正确”地做到这一点吗？如何执行我编写的AsyncTask代码块？

这里是我目前的状态：

public class BackgroundTask extends AsyncTask<String, Void, String> {

        String value = "presetvalue";

        @Override
        protected String doInBackground(String... urls) {

            class NamespaceResolver implements NamespaceContext {
                private Document document;

                public NamespaceResolver(Document doc) {
                    document = doc;
                }

                public String getNamespaceURI(String prefix) {
                    if (prefix.equals("")) {
                        return document.lookupNamespaceURI(null);
                    } else {
                        return document.lookupNamespaceURI(prefix);
                    }
                }

                public String getPrefix(String namespaceURI) {
                    return document.lookupPrefix(namespaceURI);
                }

                public Iterator<String> getPrefixes(String namespaceURI) {
                    return null;
                }
            }


            try {
                String url = "http://opendata.fmi.fi/wfs/fin?service=WFS&version=2.0.0&request=GetFeature&storedquery_id=fmi::observations::mareograph::timevaluepair&fmisid=134223&";

                StringBuilder sb = new StringBuilder();
                try (BufferedReader r = new BufferedReader(new InputStreamReader(new URL(url).openStream(), "UTF-8"))) {
                    String line;
                    while ((line = r.readLine()) != null) {
                        sb.append(line + "\n");
                    }
                }
                String xml = sb.toString();

                DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
                factory.setNamespaceAware(true);
                Document document = factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));

                XPath xpath = XPathFactory.newInstance().newXPath();

                xpath.setNamespaceContext(new NamespaceResolver(document));

                String time = xpath.evaluate("//wml2:MeasurementTimeseries[@gml:id='obs-obs-1-1-WATLEV']/wml2:point[last()]//wml2:time", document);
                value = xpath.evaluate("//wml2:MeasurementTimeseries[@gml:id='obs-obs-1-1-WATLEV']/wml2:point[last()]//wml2:value", document);
                System.out.format("time = %s; value = %s\n", time, value);
                return value;
            } catch (Exception e) {
                Log.d("EXCEPTIONFAIL", e.toString());
                return "FAIL: " + e.toString();
            }
        }
        @Override
        protected void onPostExecute(String feed) {

            MerenpintaWidget.eeee = feed;


        }
    }

这基本上是我需要在AsyncTask中执行的唯一部分：

try {
                String url = "http://opendata.fmi.fi/wfs/fin?service=WFS&version=2.0.0&request=GetFeature&storedquery_id=fmi::observations::mareograph::timevaluepair&fmisid=134223&";

                StringBuilder sb = new StringBuilder();
                try (BufferedReader r = new BufferedReader(new InputStreamReader(new URL(url).openStream(), "UTF-8"))) {
                    String line;
                    while ((line = r.readLine()) != null) {
                        sb.append(line + "\n");
                    }
                }
                String xml = sb.toString();

                DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
                factory.setNamespaceAware(true);
                Document document = factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));

                XPath xpath = XPathFactory.newInstance().newXPath();

                xpath.setNamespaceContext(new NamespaceResolver(document));

                String time = xpath.evaluate("//wml2:MeasurementTimeseries[@gml:id='obs-obs-1-1-WATLEV']/wml2:point[last()]//wml2:time", document);
                value = xpath.evaluate("//wml2:MeasurementTimeseries[@gml:id='obs-obs-1-1-WATLEV']/wml2:point[last()]//wml2:value", document);
                System.out.format("time = %s; value = %s\n", time, value);
                return value;
            } catch (Exception e) {
                Log.d("EXCEPTIONFAIL", e.toString());
                return "FAIL: " + e.toString();
            }

如果此代码正确编写，有人可以告诉我如何调用它吗？我真的不知道如何解决这个问题，我现在只是在闲逛。

Answer 1

您无需在doInBackground()方法中放入必须使用的url。如果要运行asyncTask类

String url = "http://opendata.fmi.fi/wfs/fin?service=WFS&version=2.0.0&request=GetFeature&storedquery_id=fmi::observations::mareograph::timevaluepair&fmisid=134223&";
public BackgroundTask  myTask = new BackgroundTask();
myTask.execute(url)

并在您的doInBackground()

中

 StringBuilder sb = new StringBuilder();
            try (BufferedReader r = new BufferedReader(new InputStreamReader(new URL(urls[0]).openStream(), "UTF-8"))) {
                String line;
                while ((line = r.readLine()) != null) {
                    sb.append(line + "\n");
                }
            }
            String xml = sb.toString();

如何在AsyncTask上调用execute？

1 个答案: