httpurlConnection.getInputStream() 给出致命错误

Question

我正在开发一个用于预订的 Android 应用。这是我关于stackoverflow的第一个问题。如果我没有完全遵守规则，请原谅我。我被这个致命错误困住了：

FATAL EXCEPTION: main


 Process: com.connectandroiddb.myapplication, PID: 26440
    android.os.NetworkOnMainThreadException
        at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1147)
        at java.net.InetAddress.lookupHostByName(InetAddress.java:418)
        at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)
        at java.net.InetAddress.getAllByName(InetAddress.java:215)
        at com.android.okhttp.HostResolver$1.getAllByName(HostResolver.java:29)
        at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:232)
        at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:124)
        at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:272)
        at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:211)
        at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:382)
        at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:332)
        at com.android.okhttp.internal.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:199)
        at com.example.myapplication.JSONParser.makeHttpRequest(JSONParser.java:65)
        at com.example.myapplication.MainActivity$GetProductDetails$1.run(MainActivity.java:144)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

我借用了以下代码： https://androidhive.info/2012/05/how-to-connect-android-with-php-mysql/ 相关代码如下： 我正在调用 GetProductDetails() 如下

public void sendMessage(View view) {
.....
new GetProductDetails().execute(); 
......
}

在 MainActivity.java 中

/**
     * Background Async Task to Get complete product details
     * */
class GetProductDetails extends AsyncTask<String, String, String> { 
        protected void onPreExecute() {
            super.onPreExecute();
        }
        /**
         * Getting product details in background thread
         * */
        protected String doInBackground(String... params) {

            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {

                    JSONObject json = jsonParser.makeHttpRequest(
                            url_get_product_details, "GET");// Line 144

                }
            });
                     return null;
        }

                /**
         * After completing background task Dismiss the progress dialog
         * **/
                protected void onPostExecute(String file_url) {
                    }
    } 

这些是来自 JSONParser 的相关部分：

private String readStream(InputStream is) {
        try {
            ByteArrayOutputStream bo = new ByteArrayOutputStream();
            int i = is.read();
            while(i != -1) {
                bo.write(i);
                i = is.read();
            }
            return bo.toString();
        } catch (IOException e) {
            return "";
        }
    }

        public JSONObject makeHttpRequest(String url, String method)
    {
 HttpURLConnection urlConnection = null;

        // Making HTTP request
        try {

            // check for request method
            if(method == "POST"){
                // request method is POST  CHECK


            }else if(method == "GET"){
                // request method is GET

            URL u = new URL("http://example.com/");
            urlConnection = (HttpURLConnection) u.openConnection();
            InputStream in = new BufferedInputStream(urlConnection.getInputStream()); //JSONParser.java:65
            json=readStream(in);
            }    
        }   
        catch (MalformedURLException ex) {
            Logger.getLogger(getClass().getName()).log(Level.SEVERE, null, ex);
        } 
        catch (IOException ex) {
            Logger.getLogger(getClass().getName()).log(Level.SEVERE, null, ex);
        }
        finally {
            if (urlConnection != null) {
                try {
                    urlConnection.disconnect();
                } catch (Exception ex) {
                    Logger.getLogger(getClass().getName()).log(Level.SEVERE, null, ex);
                }       
        } 
        }
}

我在 AndroidManifest.xml 中添加了互联网权限。 请帮忙！！！。提前谢谢，

Answer 1

您的问题出在这部分代码中：

protected String doInBackground(String... params) {

    // updating UI from Background Thread
    runOnUiThread(new Runnable() {
        public void run() {

            JSONObject json = jsonParser.makeHttpRequest(url_get_product_details, "GET");   
        }
    });
    return null;
}

如您所见，在 doInBackground 方法中，您正在 UI 线程上执行某些操作。 Android 在同一个 UI 线程中运行所有 UI，您不能在该线程上执行任何长时间运行的任务（如网络请求），因为 UI 将保持冻结状态。

这就是人们使用异步任务或简单线程的原因。如果在doInBackground 方法中执行runOnUiThread，则您违反了该规则，并引发异常NetworkOnMainThreadException。

阅读教程 here，了解如何使用 AsyncTask 在后台和 UI 之间传递信息。提示，需要使用onPostExecute