因此，我正在Udemy的教程“完整的Android N開發人員課程”中學習，并試圖制作關于天氣應用程序的第86講。我從這里使用API https://openweathermap.org/current#cityid 并使用JSON來獲取所需的數據。當我輸入正確的城市名稱時，該應用程序工作正常，但是當輸入錯誤或清空時，應用程序崩潰而沒有捕獲任何異常。我不知道為什么它會崩潰，不知道在哪里看。所以我給你我寫的所有代碼。我試圖在這里和那里實現if語句，試圖找到它，但沒有任何運氣。我想知道問題出在哪里以及如何解決它，以便應用程序不再崩潰。提前致謝。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); }
1 回答
白衣染霜花
TA貢獻1796條經驗 獲得超10個贊
這是因為您正在嘗試使用以下行在異步任務的 doInBackground（Params...） 方法內使用后臺線程更改 UI：
try {
... return result;
} catch (MalformedURLException e1) {
Toast.makeText(MainActivity.this, "MalformedURLException", Toast.LENGTH_SHORT).show();
} catch (IOException e2) {
Toast.makeText(MainActivity.this, "IOException", Toast.LENGTH_SHORT).show();
} catch (Exception e) {
Toast.makeText(MainActivity.this, "General exception (doInBackground)", Toast.LENGTH_SHORT).show();
}你不應該在doInBackground（Params...）內調用Toast。在 onPostExecute（Result） 中執行此操作。
您可以通過忽略錯誤或在doInBackground中返回特定文本來避免這種情況。像這樣：
public class DownloadTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... urls) {
String result = "";
...
try {
...
return result;
} catch (MalformedURLException e1) {
result= "MalformedURLException";
} catch (IOException e2) {
result= "IOException";
} catch (Exception e) {
// do nothing and returning empty
result= "Exception";
}
return result;
}
@Override
protected void onPostExecute(String result) {
// check if there is an error
String errorMessage = "";
switch(result) {
case "MalformedURLException":
errorMessage = "MalformedURLException";
break;
case ""IOException":
errorMessage = "IOException";
break;
case "Exception":
errorMessage = "Exception";
break;
}
// there is an error, show a message.
if(!errorMessage.isEmpty()) {
Toast.makeText(MainActivity.this, "Could not find weather: " + errorMessage, Toast.LENGTH_SHORT).show();
return; // stop the process.
}
// do something when no error found.
}
}
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