无法在未调用Looper.prepare（）Android的线程内创建处理程序

Question

我正在使用AsyncTask来调用yahooweather API。 以下是代码：

public class myactivity extends Activity {
    final String yahooapisBase = "http://query.yahooapis.com/v1/public/yql?q=select*from%20geo.places%20where%20text=";
    final String yahooapisFormat = "&format=xml";
    String yahooAPIsQuery;


EditText input_city; EditText input_zip; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.myactivity); Button btn_findout = (Button) findViewById(R.id.btn_findout); input_city = (EditText) findViewById(R.id.input_cityOrcountry); input_zip = (EditText) findViewById(R.id.input_zip); // when Zip textbox has focus input_zip.setOnFocusChangeListener(new View.OnFocusChangeListener() { @Override public void onFocusChange(View v, boolean hasFocus) { if (hasFocus) { String string = ""; input_city.setText(string); } } }); // when city/country textbox has focus input_city.setOnFocusChangeListener(new View.OnFocusChangeListener() { @Override public void onFocusChange(View v, boolean hasFocus) { if (hasFocus) { String string = ""; input_zip.setText(string); } } }); // when findout button is clicked btn_findout.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { // Perform action on click String uriPlace = Uri.encode(input_city.getText().toString()); yahooAPIsQuery = yahooapisBase + "%22" + uriPlace + "%22" + yahooapisFormat; Toast.makeText(getBaseContext(), "Before entering into sub thread", Toast.LENGTH_LONG) .show(); new WeatherAPITask().execute(yahooAPIsQuery); Toast.makeText(getBaseContext(), "After sub thread", Toast.LENGTH_LONG).show(); Log.i("my label", "back in main thread..."); // String woeidString = QueryYahooWeather(yahooAPIsQuery); // input_city.setText(woeidString); } }); } private String QueryYahooWeather(String queryString) { String qResult = ""; HttpClient httpClient = new DefaultHttpClient(); HttpGet httpGet = new HttpGet(queryString); try { Log.i("WeatherApp", "digging into try block..."); Log.i("queryString", queryString); HttpEntity httpEntity = httpClient.execute(httpGet).getEntity(); if (httpEntity != null) { InputStream inputStream = httpEntity.getContent(); Reader in = new InputStreamReader(inputStream); BufferedReader bufferedreader = new BufferedReader(in); StringBuilder stringBuilder = new StringBuilder(); String stringReadLine = null; while ((stringReadLine = bufferedreader.readLine()) != null) { stringBuilder.append(stringReadLine + "\n"); } qResult = stringBuilder.toString(); } } catch (ClientProtocolException e) { e.printStackTrace(); Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG) .show(); } catch (IOException e) { e.printStackTrace(); Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG) .show(); } catch (Exception e) { e.printStackTrace(); Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG) .show(); } Toast.makeText(getBaseContext(), "Returning from function", Toast.LENGTH_LONG).show(); return qResult; } private class WeatherAPITask extends AsyncTask { protected void onPostExecute(String result) { Log.i("my label", "entering in onPostExecute"); Log.i("result", result); input_city.setText("result"); } @Override protected Object doInBackground(Object... params) { // TODO Auto-generated method stub try { Log.i("my label", "entering in doInBackground"); Log.i("params[0]", params[0].toString()); return QueryYahooWeather(params[0].toString()); } catch (Exception e) { Log.i("my label", e.toString()); return null; } } } 

}

调试代码后，我发现yahooAPI调用是成功的，我可以在QueryYahooWeather函数中看到XML响应。 但是，只要执行此函数，就会抛出异常： Can't create handler inside thread that has not called Looper.prepare()

请帮帮我。

Answer 1

从QueryYahooWeather方法中删除所有Toast，因为此方法是从AsyncTask doInBackground(Object... params)调用的，并且您无法从后台Thread访问Uast元素，如Toast（也是一个Ui元素）。

注意：如果你想知道背景中发生了什么，那么使用Log而不是Toast

编辑：

将doInBackground更改为：

@Override
protected String doInBackground(Object... params) {
    // TODO Auto-generated method stub
    String strresult="";
    try {
        Log.i("my label", "entering in doInBackground");
        Log.i("params[0]", params[0].toString());
         strresult= QueryYahooWeather(params[0].toString());
         Log.i("strresult result ::: ", strresult);

    } catch (Exception e) {
        Log.i("my label", e.toString());
        return null;
    }
 return strresult;
}

Answer 2

你在打电话

Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG)
            .show();

在QueryYahooWeather ，在QueryYahooWeather中doInBackground 。

您无法从后台线程调用UI调用。