我是 Android 开发的新手，我正在尝试编写一个小应用程序，它允许我获取外部 JSON 文件并解析它。我让它工作了，但是如果我尝试在后台将它作为 AsyncTask 执行，它就不会工作。 Eclipse 给我错误

The method findViewById(int) is undefined for the type LongOperation

在这一行中:

TextView txtView1 = (TextView)findViewById(R.id.TextView01);

这是我的代码:

public class Main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        new LongOperation().execute();
    }
}


class LongOperation extends AsyncTask<String, Void, String> {
    private final Context LongOperation = null;


    @Override
    protected String doInBackground(String... 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 txtView1 = (TextView)findViewById(R.id.TextView01);
                    txtView1.setText(jo.getString("text") + " - " + jo.getString("secondtest"));
            }
        } catch (MalformedURLException e) {
            Toast.makeText(this.LongOperation, "Malformed URL Exception: " + e, Toast.LENGTH_LONG).show();
        } catch (IOException e) {
            Toast.makeText(this.LongOperation, "IO Exception: " + e, Toast.LENGTH_LONG).show();
        } catch (JSONException e) {
            Toast.makeText(this.LongOperation, "JSON Exception: " + e, Toast.LENGTH_LONG).show();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
    }
    protected void onPreExecute() {
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        ProgressDialog pd = new ProgressDialog(LongOperation);
        pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        pd.setMessage("Working...");
        pd.setIndeterminate(true);
        pd.setCancelable(false);
    }    

}

关于如何解决这个问题有什么想法吗？

最佳答案

这里是你应该做的让它按照你想要的方式工作。使用 onPostExecute()

public class Main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        new LongOperation(this).execute();
    }
}


class LongOperation extends AsyncTask<String, Void, String> {
    private Main longOperationContext = null;

    public LongOperation(Main context) {
        longOperationContext = context;
        Log.v("LongOper", "Konstuktor");
    }

    @Override
    protected String doInBackground(String... params) {
        Log.v("doInBackground", "inside");
        StringBuilder sb = new StringBuilder();

        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);
                    Log.v("line = ", "jo.getString() ="+jo.getString("text"));
                    sb.append(jo.getString("text") + " - " + jo.getString("secondtest")).append("\n");
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
            Log.v("Error", "URL exc");
        } catch (IOException e) {
            e.printStackTrace();
            Log.v("ERROR", "IOEXECPTOIn");
        } catch (JSONException e) {
            e.printStackTrace();
            Log.v("Error", "JsonException");
        }
        String result = sb.toString();
        return result;
    }

    @Override
    protected void onPostExecute(String result) {
        Log.v("onPostExe", "result = "+result);
      TextView txtView1 = (TextView)longOperationContext.findViewById(R.id.textView01);
      txtView1.setText(result);


    }
    protected void onPreExecute() {
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        ProgressDialog pd = new ProgressDialog(longOperationContext);
        pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        pd.setMessage("Working...");
        pd.setIndeterminate(true);
        pd.setCancelable(false);
    }    

}

关于android - 方法 findViewById(int) 未定义，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/4979454/