Question

我试图了解AsyncTask的工作原理。我有以下代码，但是我收到以下错误：Class＆＃39; AsyncTask＆＃39;必须被宣布为抽象的或实现抽象方法＆＃39; doInBackground（Params ...）＆＃39;

private class WeatherDataTask extends AsyncTask<Void, Void, String> {

        protected String doInBackgrond() throws Exception{
            HttpURLConnection connection = null;
            BufferedReader reader = null;
            String data = null;
            try{
                URL url = new URL("http://api.openweathermap.org/data/2.5/weather?zip=90210,us&units=imperial");
                connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.connect();

                InputStream stream = connection.getInputStream();
                StringBuffer buffer = new StringBuffer();

                reader = new BufferedReader(new InputStreamReader(stream));

                String line;
                while ((line = reader.readLine()) != null) {
                    buffer.append(line + "\n");
                }

                if (buffer.length() == 0) {
                    data = null;
                }
                return data = buffer.toString();
            } catch (IOException e) {
                Log.e("PlaceholderFragment", "Error ", e);
                data = null;
                return data;
            } finally{
                if (connection != null) {
                    connection.disconnect();
                }
                if (reader != null) {
                    try {
                        reader.close();
                    } catch (final IOException e) {
                        Log.e("PlaceholderFragment", "Error closing stream", e);
                    }
                }
            }
        }

        protected void onPostExecute(String jsonParse){
            if(jsonParse == null){
                TextView progress = (TextView) findViewById(R.id.container);
                progress.setText("Unable to get weather");
            }
            else {
                try {
                    JSONObject jsonRootObject = new JSONObject(jsonParse);
                    int temp = Integer.parseInt(jsonRootObject.getJSONObject("main").getString("temp"));
                    TextView displayTemp = (TextView) findViewById(R.id.container);
                    displayTemp.setText(temp);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }
    }

我只想尝试获取温度并更新textview。感谢

Answer 1

检查出来

private class TestTask extends AsyncTask<String,Integer,Boolean>{

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Boolean aBoolean) {
        super.onPostExecute(aBoolean);
    }

    @Override
    protected Boolean doInBackground(String... params) throws Exception{
        return null;
    }
}

这是AsyncTask源中的方法

 /**
 * Override this method to perform a computation on a background thread. The
 * specified parameters are the parameters passed to {@link #execute}
 * by the caller of this task.
 *
 * This method can call {@link #publishProgress} to publish updates
 * on the UI thread.
 *
 * @param params The parameters of the task.
 *
 * @return A result, defined by the subclass of this task.
 *
 * @see #onPreExecute()
 * @see #onPostExecute
 * @see #publishProgress
 */
protected abstract Result doInBackground(Params... params);

注意它不会抛出异常，因此在那里使用“throws Exception”意味着你没有覆盖超类方法并与之发生冲突。

Answer 2

您只需将doInBackgrond() throws Exception更改为doInBackground(Void... params)

即可

Answer 3

将@Override添加到doInBackground方法，当您扩展AsyncTask时，至少必须覆盖doInBackground方法。删除投掷。
据说doInBackground不是你的“doInBackgrond”错字

Android AsyncTask错误实现摘要

3 个答案: