java - 如何修复 android.os.NetworkOnMainThread

Question

这个问题已经有答案了:

How can I fix 'android.os.NetworkOnMainThreadException'? (65 个回答)

已关闭 4 年前。

我收到"android.os.NetworkOnMainThreadException"即使我没有在主线程中运行任何与网络相关的内容。我该如何解决这个问题？

我实际上在 Eclipse 中尝试了代码，它运行得很好，但在我正在开发应用程序本身的 Android Studio 中却不行。

测试类.java:

package com.*****.*****;



        import android.graphics.Bitmap;
        import android.os.AsyncTask;
        import android.view.View;

        import java.io.*;
        import java.net.*;
        import java.util.*;
        import javax.xml.xpath.*;
        import javax.xml.namespace.*;
        import org.xml.sax.InputSource;
        import javax.xml.parsers.DocumentBuilderFactory;
        import org.w3c.dom.Document;

abstract class Testclass {


    public static 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;
        }
    }

    public static String downloadString(String url) throws Exception {
        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");
            }
        }
        return sb.toString();
    }

    public static Document createDocumentFromString(String xml) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
        return factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
    }

    static String value;

    public static String result() {

        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&";

            String xml = downloadString(url);
            Document document = createDocumentFromString(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) {
            return "FAIL: " + e.toString();
        }
    }

}

在 android studio 中运行时输出:"null"并且还抛出 "android.os.NetworkOnMainThreadException"

在 Eclipse 中运行时的输出:"-97.0" (正确输出)

Answer 1

您需要在另一个线程上运行网络相关任务，如下所示:

Thread mThread = new Thread(new Runnable() {
@Override
public void run() {
    try  {
        //Put your code that you want to run in here
    } catch (Exception e) {
        e.printStackTrace();
    }
  }

现在，如果您不确定导致此问题的原因，您可以检查错误日志，它会引导您找到导致此问题的行。

您可以做的另一件事是添加带有错误描述的自定义日志/打印，稍后，您可以检查这些日志以查看是否调用了其中的任何一个(如果是，则意味着您收到了错误)