尝试在后台使用 AsyncTask 解析 JSON 时强制关闭 [英] Force close when trying to parse JSON with AsyncTask in the background

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问题描述

我是 android 开发的新手，我正在处理 json 数据.我设法让解析工作.我想显示一个 ProgressDialog 并且我读到我需要使用 AsyncTask .但是出于某种原因，我将相同的工作代码放入 doInBackground() 后立即强制关闭，尽管 eclipse 表示一切正常.

i'm new to android development and i'm playing around with json data. I managed to get the parsing to work. I want to show a ProgressDialog and i read that i need to use AsyncTask that. But for some reason i get a force close as soon as i put the same working code inside doInBackground() eventhough eclipse says everything is fine.

这是源代码:

public class HomeActivity extends Activity {


  public class BackgroundAsyncTask extends AsyncTask<Void, Integer, Void> {

      ProgressDialog dialog = new ProgressDialog (HomeActivity.this);


      @Override
      protected void onPreExecute() {
        dialog.setMessage("Loading...please wait");
        dialog.setIndeterminate(true);
        dialog.setCancelable(false);
        dialog.show();
      }

      protected void onPostExecute() {
             dialog.dismiss();
          }

      @Override
      protected Void doInBackground(Void... params) {         
            try {
                URL json = new URL("http://www.corps-marchia.de/jsontest.php");
                URLConnection tc = json.openConnection();
                BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream()));

                String line;
                while ((line = in.readLine()) != null) {
                    JSONArray ja = new JSONArray(line);
                    JSONObject jo = (JSONObject) ja.get(0);
                    TextView txtView = (TextView)findViewById(R.id.TextView01);
                    txtView.setText(jo.getString("text"));
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            }

       return null;
       }
     }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        new BackgroundAsyncTask().execute();
    }

}

错误日志如下:

01-08 12:33:48.225: ERROR/AndroidRuntime(815): FATAL EXCEPTION: AsyncTask #1
01-08 12:33:48.225: ERROR/AndroidRuntime(815): java.lang.RuntimeException: An error occured while executing doInBackground()
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.lang.Thread.run(Thread.java:1019)
01-08 12:33:48.225: ERROR/AndroidRuntime(815): Caused by: android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.ViewRoot.checkThread(ViewRoot.java:2932)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.ViewRoot.requestLayout(ViewRoot.java:629)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.View.requestLayout(View.java:8267)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.View.requestLayout(View.java:8267)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.View.requestLayout(View.java:8267)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.View.requestLayout(View.java:8267)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.view.View.requestLayout(View.java:8267)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.widget.TextView.checkForRelayout(TextView.java:5521)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.widget.TextView.setText(TextView.java:2724)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.widget.TextView.setText(TextView.java:2592)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.widget.TextView.setText(TextView.java:2567)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at net.ajzele.demo.andy1.HomeActivity$BackgroundAsyncTask.doInBackground(HomeActivity.java:52)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at net.ajzele.demo.andy1.HomeActivity$BackgroundAsyncTask.doInBackground(HomeActivity.java:1)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
01-08 12:33:48.225: ERROR/AndroidRuntime(815):     ... 4 more
01-08 12:33:51.605: ERROR/WindowManager(815): Activity net.ajzele.demo.andy1.HomeActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@4051d0c0 that was originally added here
01-08 12:33:51.605: ERROR/WindowManager(815): android.view.WindowLeaked: Activity net.ajzele.demo.andy1.HomeActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@4051d0c0 that was originally added here
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.view.ViewRoot.<init>(ViewRoot.java:258)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.view.Window$LocalWindowManager.addView(Window.java:424)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.Dialog.show(Dialog.java:241)
01-08 12:33:51.605: ERROR/WindowManager(815):     at net.ajzele.demo.andy1.HomeActivity$BackgroundAsyncTask.onPreExecute(HomeActivity.java:33)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.os.AsyncTask.execute(AsyncTask.java:391)
01-08 12:33:51.605: ERROR/WindowManager(815):     at net.ajzele.demo.andy1.HomeActivity.onCreate(HomeActivity.java:72)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1586)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1638)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:928)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.os.Looper.loop(Looper.java:123)
01-08 12:33:51.605: ERROR/WindowManager(815):     at android.app.ActivityThread.main(ActivityThread.java:3647)
01-08 12:33:51.605: ERROR/WindowManager(815):     at java.lang.reflect.Method.invokeNative(Native Method)
01-08 12:33:51.605: ERROR/WindowManager(815):     at java.lang.reflect.Method.invoke(Method.java:507)
01-08 12:33:51.605: ERROR/WindowManager(815):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-08 12:33:51.605: ERROR/WindowManager(815):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-08 12:33:51.605: ERROR/WindowManager(815):     at dalvik.system.NativeStart.main(Native Method)

有什么提示吗?我希望你能帮助我我在网上搜索并没有找到任何可行的解决方案......提前致谢

Any hints? I hope you can help me out ive searched the net and didnt find any working solution...Thanks in advance

推荐答案

检查 AsyncTask 的文档.您不能从 doInBackground 中直接操作 UI.为了进行 UI 更新，您需要调用 publishProgress.您还需要更改 AsyncTask 的签名以传递 String.所以是这样的:

Check the docs for AsyncTask. You can't directly manipulate the UI from within doInBackground. In order to make UI updates, you need to call publishProgress. You will also need to change the signature of your AsyncTask to pass a String. So something like this:

public class BackgroundAsyncTask extends AsyncTask<Void, String, Void> {
    TextView txtView = (TextView)findViewById(R.id.TextView01);
    ...
    protected void onProgressUpdate(String... message) {
        txtView.setText(message[0]);
    }
    ...
    @Override
    protected Void doInBackground(Void... params) {
         try {
             URL json = new URL("http://www.corps-marchia.de/jsontest.php");
             URLConnection tc = json.openConnection();
             BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream()));

             String line;
             while ((line = in.readLine()) != null) {
                 JSONArray ja = new JSONArray(line);
                 JSONObject jo = (JSONObject) ja.get(0);
                 publishProgress(jo.getString("text"));
             }
         } catch (MalformedURLException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         } catch (JSONException e) {
             e.printStackTrace();
         }

    return null;
    }

这篇关于尝试在后台使用 AsyncTask 解析 JSON 时强制关闭的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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