应用崩溃，但未捕获任何异常

Question

因此，我正在Udemy的教程“完整的Android N开发人员课程”中学习，并试图制作关于天气应用程序的第86讲。

我从这里使用API https://openweathermap.org/current#cityid 并使用JSON来获取所需的数据。

当我输入正确的城市名称时，该应用程序工作正常，但是当输入错误或清空时，应用程序崩溃而没有捕获任何异常。

我不知道为什么它会崩溃，不知道在哪里看。所以我给你我写的所有代码。我试图在这里和那里实现if语句，试图找到它，但没有任何运气。

我想知道问题出在哪里以及如何解决它，以便应用程序不再崩溃。

提前致谢。

public class MainActivity extends AppCompatActivity {

    EditText editText;

    String city = "";

    TextView textView;

    public void getWeather (View view)  {

        try {

            city = URLEncoder.encode(editText.getText().toString(), "UTF-8");

            if (editText.getText().toString() == "") {

                Toast.makeText(MainActivity.this, "Could not find weather", Toast.LENGTH_SHORT).show();

                textView.setText("Please enter a city.");

            } else  {

                DownloadTask task = new DownloadTask();

                task.execute("http://api.openweathermap.org/data/2.5/weather?q=" + city + "&appid=c6ef169a79d84674ef7e1414301eb5c4");

            }

            InputMethodManager mgr = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);

            mgr.hideSoftInputFromWindow(editText.getWindowToken(), 0);

        } catch (UnsupportedEncodingException e1) {

            Toast.makeText(MainActivity.this, "UnsupportedEncodingException", Toast.LENGTH_SHORT).show();

        }catch (Exception e) {

            Toast.makeText(MainActivity.this, "General exception (getWeather)", Toast.LENGTH_SHORT).show();

        }

    }

    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 = null;

                in = urlConnection.getInputStream();

                InputStreamReader reader = new InputStreamReader(in);

       

        }

Answer 1

这是因为您正在尝试使用以下行在异步任务的&nbsp;doInBackground（Params...）&nbsp;方法内使用后台线程更改 UI：try&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;result; }&nbsp;catch&nbsp;(MalformedURLException&nbsp;e1)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;Toast.makeText(MainActivity.this,&nbsp;"MalformedURLException",&nbsp;Toast.LENGTH_SHORT).show(); }&nbsp;catch&nbsp;(IOException&nbsp;e2)&nbsp;{ Toast.makeText(MainActivity.this,&nbsp;"IOException",&nbsp;Toast.LENGTH_SHORT).show(); }&nbsp;catch&nbsp;(Exception&nbsp;e)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;Toast.makeText(MainActivity.this,&nbsp;"General&nbsp;exception&nbsp;(doInBackground)",&nbsp;Toast.LENGTH_SHORT).show(); }你不应该在doInBackground（Params...）内调用Toast。在&nbsp;onPostExecute（Result） 中执行此操作。您可以通过忽略错误或在doInBackground中返回特定文本来避免这种情况。像这样：public class DownloadTask extends AsyncTask<String, Void, String> {&nbsp; &nbsp; @Override&nbsp; &nbsp; protected String doInBackground(String... urls) {&nbsp; &nbsp; &nbsp; &nbsp; String result = "";&nbsp; &nbsp; &nbsp; &nbsp; ...&nbsp; &nbsp; &nbsp; &nbsp; try {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ...&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return result;&nbsp; &nbsp; &nbsp; &nbsp; } catch (MalformedURLException e1) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result= "MalformedURLException";&nbsp; &nbsp; &nbsp; &nbsp; } catch (IOException e2) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result= "IOException";&nbsp; &nbsp; &nbsp; &nbsp; } catch (Exception e) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // do nothing and returning empty&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result= "Exception";&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return result;&nbsp; &nbsp; }&nbsp; &nbsp; @Override&nbsp; &nbsp; protected void onPostExecute(String result) {&nbsp; &nbsp; &nbsp; &nbsp; // check if there is an error&nbsp; &nbsp; &nbsp; &nbsp; String errorMessage = "";&nbsp; &nbsp; &nbsp; &nbsp; switch(result) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case "MalformedURLException":&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; errorMessage = "MalformedURLException";&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case ""IOException":&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; errorMessage = "IOException";&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case "Exception":&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; errorMessage = "Exception";&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;// there is an error, show a message.&nbsp; &nbsp; &nbsp; &nbsp; if(!errorMessage.isEmpty()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Toast.makeText(MainActivity.this, "Could not find weather: " + errorMessage, Toast.LENGTH_SHORT).show();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return; // stop the process.&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;// do something when no error found.&nbsp; &nbsp; }}