我正在努力解决与 openFileOutput() 关联的“无法解析方法”。我怀疑我的问题与上下文有关，但不知道如何解决。我有一个文件处理类 (FileHelper.java)，它是从从网站读取数据的异步任务 (AirLineListRetriever.java) 调用的。 AsynchTask 是从 Activity 调用的。
FileHelper.java 提取
public static boolean saveToFile(String data){
try {
FileOutputStream fileOutputStream = openFileOutput("airlinedata.txt", MODE_PRIVATE);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream);
outputStreamWriter.write(data);
outputStreamWriter.close();
Log.d (TAG, "Airline List written to file");
return true;
} catch(FileNotFoundException ex) {
Log.d(TAG, ex.getMessage());
} catch(IOException ex) {
Log.d(TAG, ex.getMessage());
}
return false;
}
doInBackground摘录
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
StringBuilder stringBuilder = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line).append("\n");
}
bufferedReader.close();
FileHelper.saveToFile(stringBuilder.toString());
完整的异步类
class AirLineListRetriever extends AsyncTask<Void, Void, List<Airline>> {
private String FSAPIid = "appId=xxxxx";
public interface AirLineListResponse{
void processFinish(List<Airline> airlines);
}
AirLineListResponse delegate;
public AirLineListRetriever(AirLineListResponse delegate){
this.delegate = delegate;
}
@Override
protected List<Airline> doInBackground(Void... params) {
JSONObject JSONAirlines;
JSONObject JSONAirline;
JSONArray JSONAirlinesList;
Airline airline;
List<Airline> airlineList;
try {
Log.d("ALPrint", "In Retrieve Airline List");
URL url = new URL("https://api.flightstats.com/flex/airlines/rest/v1/json/active?" + FSAPIid);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
StringBuilder stringBuilder = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line).append("\n");
}
bufferedReader.close();
FileHelper.saveToFile(stringBuilder.toString());
JSONAirlines = new JSONObject(stringBuilder.toString());
JSONAirlinesList = JSONAirlines.getJSONArray("airlines");
airlineList = new ArrayList<Airline>();
for (int i = 0; i < JSONAirlinesList.length(); i++) {
JSONAirline = JSONAirlinesList.getJSONObject(i);
String airlineName = JSONAirline.has("name") ? JSONAirline.getString("name") : null;
String fsCode = JSONAirline.has("fs") ? JSONAirline.getString("fs") : null;
String iataCode = JSONAirline.has("iata") ? JSONAirline.getString("iata") : null;
String icaoCode = JSONAirline.has("icao") ? JSONAirline.getString("icao") : null;
airline = new Airline(
airlineName,
fsCode,
iataCode,
icaoCode
);
airlineList.add(airline);
}
return airlineList;
} finally {
urlConnection.disconnect();
}
} catch (Exception e) {
Log.e("ERROR", e.getMessage(), e);
return null;
}
}
protected void onPostExecute(List<Airline> airlineList){
this.delegate.processFinish(airlineList);
}
}
调用异步类的 Activity 摘录
new AirLineListRetriever(
new AirLineListRetriever.AirLineListResponse() {
@Override
public void processFinish(List<Airline> airlines) {
String selectedAirLine = null;
airlineList = airlines;
Log.d("EndRetrieve", "Completed the retrieve");
// sort the airline list
Collections.sort(airlineList, new Comparator<Airline>() {
@Override
public int compare(Airline airline, Airline t1)
{
Airline airline1 = (Airline) airline;
Airline airline2 = (Airline) t1;
return airline1.airlineName.compareToIgnoreCase(airline2.airlineName);
}
});
final ArrayList airlineArrayList = new ArrayList();
//copy the airline list to an array to populate the autoCompleteTextView
for (int i=0; i < airlineList.size(); i++){
airlineArrayList.add(airlineList.get(i).airlineName);
}
progressDialog.dismiss();
acAirlines = (AutoCompleteTextView) findViewById(R.id.autoCompleteAirLines);
acAirlines.setVisibility(View.VISIBLE);
//acAirlines.setThreshold(4);
final ArrayAdapter<String> adapter = new ArrayAdapter<String> (AddFlightActivity.this, android.R.layout.simple_list_item_1, airlineArrayList);
acAirlines.setThreshold(2);
acAirlines.setAdapter(adapter);
acAirlines.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int index, long id) {
String selectedAirLine = adapter.getItem(index);
int position = airlineArrayList.indexOf(selectedAirLine);
String alIataCode = airlineList.get(position).iataCode;
Log.d("ALCodePrint", selectedAirLine + " " + alIataCode);
alCode.setText(alIataCode);
alCode_Set = true;
extFunctions.hideKeyboard(AddFlightActivity.this);
}
});
}
}
).execute();
最佳答案
要将上下文传递给异步任务，请更改其构造函数以接收上下文，如下所示，并将其传递给 saveToFile 方法。
class AirLineListRetriever extends AsyncTask<Void, Void, List<Airline>> {
private String FSAPIid = "appId=xxxxx";
private Context mContext;
public interface AirLineListResponse{
void processFinish(List<Airline> airlines);
}
AirLineListResponse delegate;
public AirLineListRetriever(AirLineListResponse delegate, Context context){
this.delegate = delegate;
this.mContext = context;
}
@Override
protected List<Airline> doInBackground(Void... params) {
JSONObject JSONAirlines;
JSONObject JSONAirline;
JSONArray JSONAirlinesList;
Airline airline;
List<Airline> airlineList;
try {
Log.d("ALPrint", "In Retrieve Airline List");
URL url = new URL("https://api.flightstats.com/flex/airlines/rest/v1/json/active?" + FSAPIid);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
StringBuilder stringBuilder = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line).append("\n");
}
bufferedReader.close();
FileHelper.saveToFile(stringBuilder.toString(), mContext);
JSONAirlines = new JSONObject(stringBuilder.toString());
JSONAirlinesList = JSONAirlines.getJSONArray("airlines");
airlineList = new ArrayList<Airline>();
for (int i = 0; i < JSONAirlinesList.length(); i++) {
JSONAirline = JSONAirlinesList.getJSONObject(i);
String airlineName = JSONAirline.has("name") ? JSONAirline.getString("name") : null;
String fsCode = JSONAirline.has("fs") ? JSONAirline.getString("fs") : null;
String iataCode = JSONAirline.has("iata") ? JSONAirline.getString("iata") : null;
String icaoCode = JSONAirline.has("icao") ? JSONAirline.getString("icao") : null;
airline = new Airline(
airlineName,
fsCode,
iataCode,
icaoCode
);
airlineList.add(airline);
}
return airlineList;
} finally {
urlConnection.disconnect();
}
} catch (Exception e) {
Log.e("ERROR", e.getMessage(), e);
return null;
}
}
protected void onPostExecute(List<Airline> airlineList){
this.delegate.processFinish(airlineList);
}
}
在 activty 中创建异步任务时，将上下文作为第二个参数传递给其构造函数，
new AirLineListRetriever(
new AirLineListRetriever.AirLineListResponse() {
@Override
public void processFinish(List<Airline> airlines) {
String selectedAirLine = null;
airlineList = airlines;
Log.d("EndRetrieve", "Completed the retrieve");
// sort the airline list
Collections.sort(airlineList, new Comparator<Airline>() {
@Override
public int compare(Airline airline, Airline t1)
{
Airline airline1 = (Airline) airline;
Airline airline2 = (Airline) t1;
return airline1.airlineName.compareToIgnoreCase(airline2.airlineName);
}
});
final ArrayList airlineArrayList = new ArrayList();
//copy the airline list to an array to populate the autoCompleteTextView
for (int i=0; i < airlineList.size(); i++){
airlineArrayList.add(airlineList.get(i).airlineName);
}
progressDialog.dismiss();
acAirlines = (AutoCompleteTextView) findViewById(R.id.autoCompleteAirLines);
acAirlines.setVisibility(View.VISIBLE);
//acAirlines.setThreshold(4);
final ArrayAdapter<String> adapter = new ArrayAdapter<String> (AddFlightActivity.this, android.R.layout.simple_list_item_1, airlineArrayList);
acAirlines.setThreshold(2);
acAirlines.setAdapter(adapter);
acAirlines.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int index, long id) {
String selectedAirLine = adapter.getItem(index);
int position = airlineArrayList.indexOf(selectedAirLine);
String alIataCode = airlineList.get(position).iataCode;
Log.d("ALCodePrint", selectedAirLine + " " + alIataCode);
alCode.setText(alIataCode);
alCode_Set = true;
extFunctions.hideKeyboard(AddFlightActivity.this);
}
});
}
}, this.getApplicationContext()
).execute();
更改 saveToFile 签名以接收上下文，
public static boolean saveToFile(String data, Context ctxt){..
然后使用该上下文打开文件流，
FileOutputStream fileOutputStream = ctxt.openFileOutput("airlinedata.txt", MODE_PRIVATE);
关于java - Android 从类中读/写，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45529492/