下载任务在没有internet的情况下引发异常

Question

我有一个从互联网下载当前unix时间戳的应用程序。下载任务的代码如下。

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

        @Override
        protected String doInBackground(String... urls) {
            String result = "";
            URL url;
            HttpURLConnection urlConnection = null;
            try {
                url = new URL(urls[0]);
                urlConnection = (HttpURLConnection) url.openConnection();
                InputStream in = urlConnection.getInputStream();
                InputStreamReader reader = new InputStreamReader(in);
                int data = reader.read();
                while (data != -1) {
                    char current = (char) data;
                    result += current;
                    data = reader.read();
                }
                return result;
            } catch (Exception e) {
                e.printStackTrace();
                Toast.makeText(SplashActivity.this, "you aint got no internet man", Toast.LENGTH_SHORT).show();
            }
            return null;
        }

我在onCreate 中运行此代码

DownloadTask task = new DownloadTask();
        String result = null;
        try {
            result = task.execute("http://www.currenttimestamp.com/").get();
            Pattern p = Pattern.compile("current_time = (.*?);");
            Matcher m = p.matcher(result);
            m.find();
            String unixTime = (m.group(1));
            timeStamp = Integer.parseInt(unixTime);
            endTimeMaths = endTime/1000;
        } catch (InterruptedException e) {
            e.printStackTrace();
            Toast.makeText(SplashActivity.this, "you aint got no internet man", Toast.LENGTH_SHORT).show();
        } catch (ExecutionException e) {
            e.printStackTrace();
            Toast.makeText(SplashActivity.this, "you aint got no internet man", Toast.LENGTH_SHORT).show();
        }
        timeDelta = timeStamp-endTimeMaths;
        Log.i("TimeDelta", timeDelta+"");

        //If dem boys cheatin
        if (timeDelta < 1){
            Toast.makeText(SplashActivity.this, "You cheatin boi?", Toast.LENGTH_SHORT).show();
            reward=false;
        } else if (timeDelta >= 300){
            reward = true;
            Toast.makeText(SplashActivity.this, "Here is your reward for being gone", Toast.LENGTH_SHORT).show();
        }
    }

异常情况如下

09-04 21:26:42.853 8459-8493/com.firefluxentertainment.retroclicker         E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
        Process: com.firefluxentertainment.retroclicker, PID: 8459
        java.lang.RuntimeException: An error occurred while executing     doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:318)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
        at java.util.concurrent.FutureTask.run(FutureTask.java:242)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
        at java.lang.Thread.run(Thread.java:761)
        Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
        at android.os.Handler.<init>(Handler.java:200)
        at android.os.Handler.<init>(Handler.java:114)
        at android.widget.Toast$TN.<init>(Toast.java:346)
        at android.widget.Toast.<init>(Toast.java:101)
        at android.widget.Toast.makeText(Toast.java:260)
        at com.firefluxentertainment.retroclicker.SplashActivity$DownloadTask.doInBackground(SplashActivity.java:155)
        at com.firefluxentertainment.retroclicker.SplashActivity$DownloadTask.doInBackground(SplashActivity.java:119)
        at android.os.AsyncTask$2.call(AsyncTask.java:304)
        at java.util.concurrent.FutureTask.run(FutureTask.java:237)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243) 
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133) 
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607) 
        at java.lang.Thread.run(Thread.java:761)

由于所有的代码都在try-catch大括号中，我不知道它为什么会崩溃。非常感谢您的帮助！

Answer 1

这是因为您试图在non-UI thread中显示toast。您的问题有多种解决方案：

• 在"活动"中创建一个处理程序，并将其传递给DownloadTask。只需在Handler中发送一条消息并显示祝酒词即可。

• 另一种解决方案是在DownloadTask中发送上下文，并将toast显示为

   context.runOnUIThread(new Runnable() {
      public void run(){
         Toast.showToast("your message here")
      }
   )
  

• 您可以在onPostExecute()中发送任务的结果，并在那里显示Toast。