我有一个关于执行顺序的问题。我从服务器（城市名称，LatLng）和onPostExecute获取一些数据我正在尝试计算城市之间的距离。在最后一次onPostExecute期间，有一些距离计算。问题在于
for(j=0;j<3;j++) {
or = markerPoints.get(j);
dest = markerPoints.get(j+1);
Log.d("or", or.toString());
Log.d("dest", dest.toString());
// Getting URL to the Google Directions API
String url = getDirectionsUrl(or, dest);
DownloadTask downloadTask = new DownloadTask();
// Start downloading json data from Google Directions API
downloadTask.execute(url);
}
downloadTask在循环“for”完成后第一次执行，这意味着当j等于2.为什么不是3次;这不奇怪;
我的整个代码
public class Check_Itineraries1 extends FragmentActivity {
private ProgressDialog pDialog;
String username , origin_lat ,origin_lng ,destination_lat ,destination_lng ,
waypoint1_lat ,waypoint1_lng ,waypoint2_lat ,waypoint2_lng ,waypoints ,
origin_lat_pro ,origin_lng_pro ,destination_lat_pro ,destination_lng_pro , start_pro , final_pro;
int i, j ,b ;
double x,z ,t ,s;
TextView v1 , v2;
ArrayList<Double> Array = new ArrayList<Double>();
ArrayList<Double> Array_add = new ArrayList<Double>();
ArrayList<Double> Array_dif = new ArrayList<Double>();
ListView list;
ArrayList<LatLng> markerPoints;
// URL to get contacts JSON
private static String LOGIN_URL = "http://**************************";
public static final String PREFS_NAME = "MyPreferencesFile";
// JSON Node names
JSONParser jsonParser = new JSONParser();
// contacts JSONArray
JSONArray contacts = null;
// Hashmap for ListView
ArrayList<HashMap<String, String>> itinList , final_itinList ;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.checkitineraries);
itinList = new ArrayList<HashMap<String, String>>();
new GetData().execute();
}
private class GetData extends AsyncTask<Void, Void, Void> {
public void onPreExecute() {
super.onPreExecute();
Log.d("meg", "meg");
pDialog = new ProgressDialog(Check_Itineraries1.this);
pDialog.setMessage("Επεξεργάζομαι τα δεδομένα...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
username = settings.getString("username", "nikos");
}
protected Void doInBackground(Void... args) {
// TODO Auto-generated method stub
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username", username));
JSONObject json = jsonParser.makeHttpRequest(LOGIN_URL, "POST",
params);
// JSONObject jObj = new JSONObject();
JSONArray itin_results = json.getJSONArray("itin_results");
for (int i = 0; i < itin_results.length(); i++) {
JSONObject c = itin_results.getJSONObject(i);
String username = c.getString("username");
String startPoliPro = c.getString("startPoliPro");
String start_lat_pro = c.getString("start_lat_pro");
String start_lng_pro = c.getString("start_lng_pro");
String finalPoliPro = c.getString("finalPoliPro");
String final_lat_pro = c.getString("final_lat_pro");
String final_lng_pro = c.getString("final_lng_pro");
LinkedHashMap<String, String> pinakas = new LinkedHashMap<String, String>();
// adding each child node to HashMap key => value
pinakas.put("username", username);
pinakas.put("startPoliPro", startPoliPro);
pinakas.put("start_lat_pro", start_lat_pro);
pinakas.put("start_lng_pro", start_lng_pro);
pinakas.put("finalPoliPro", finalPoliPro);
pinakas.put("final_lat_pro", final_lat_pro);
pinakas.put("final_lng_pro", final_lng_pro);
// Διαλέγω αφετηρία και προορισμό του δρομολογίου του επαγγελματία
Log.d("1", username);
Log.d("2", startPoliPro);
Log.d("3", start_lat_pro);
Log.d("4", start_lng_pro);
Log.d("5", finalPoliPro);
Log.d("6", final_lat_pro);
Log.d("7", final_lng_pro);
itinList.add(pinakas);
b = itin_results.length(); // Είναι τα δρομολόγια των πελατων που ταιριάζουν ΣΥΝ το δρομολόγιο του επαγγελματία
Log.d("b", String.valueOf(b));
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
origin_lat_pro = itinList.get(0).get("start_lat_pro").toString();
origin_lng_pro = itinList.get(0).get("start_lng_pro").toString();
destination_lat_pro = itinList.get(0).get("final_lat_pro").toString();
destination_lng_pro = itinList.get(0).get("final_lng_pro").toString();
start_pro = itinList.get(0).get("startPoliPro").toString();
final_pro = itinList.get(0).get("finalPoliPro").toString();
LatLng origin_pro = new LatLng(Double.parseDouble(origin_lat_pro),Double.parseDouble(origin_lng_pro));
LatLng destination_pro = new LatLng(Double.parseDouble(destination_lat_pro),Double.parseDouble(destination_lng_pro));
for (i = 0; i <b; i++) {
markerPoints = new ArrayList<LatLng>();
origin_lat = itinList.get(i).get("start_lat_pro").toString();
origin_lng = itinList.get(i).get("start_lng_pro").toString();
destination_lat = itinList.get(i).get("final_lat_pro").toString();
destination_lng = itinList.get(i).get("final_lng_pro").toString();
LatLng or = new LatLng(Double.parseDouble(origin_lat),Double.parseDouble(origin_lng));
LatLng dest = new LatLng(Double.parseDouble(destination_lat),Double.parseDouble(destination_lng));
markerPoints.add(origin_pro);
markerPoints.add(or);
markerPoints.add(dest);
markerPoints.add(destination_pro);
Log.d("a", markerPoints.get(0).toString());
Log.d("b", markerPoints.get(1).toString());
Log.d("c", markerPoints.get(2).toString());
Log.d("d", markerPoints.get(3).toString());
z = 0;
for(j=0;j<3;j++) {
or = markerPoints.get(j);
dest = markerPoints.get(j+1);
Log.d("or", or.toString());
Log.d("dest", dest.toString());
// Getting URL to the Google Directions API
String url = getDirectionsUrl(or, dest);
DownloadTask downloadTask = new DownloadTask();
// Start downloading json data from Google Directions API
downloadTask.execute(url);
}
}
}
}
//Αυτοτελές
private String getDirectionsUrl(LatLng or, LatLng dest) {
// Origin of route
String str_origin = "origin=" + or.latitude + ","+ or.longitude;
// Destination of route
String str_dest = "destination=" + dest.latitude + "," + dest.longitude;
// Sensor enabled
String sensor = "sensor=false";
Log.d("sos1", "sos1");
// Building the parameters to the web service
String parameters = str_origin + "&" + str_dest + "&" + sensor;
// Output format
String output = "json";
// Building the url to the web service
String url = "https://maps.googleapis.com/maps/api/directions/"
+ output + "?" + parameters;
return url;
}
//Αυτοτελές//
//Αυτοτελές
private String downloadUrl(String strUrl) throws IOException {
String data = "";
InputStream iStream = null;
HttpURLConnection urlConnection = null;
try {
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
Log.d("sos2", "sos2");
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(
iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while ((line = br.readLine()) != null) {
sb.append(line);
}
data = sb.toString();
br.close();
} catch (Exception e) {
Log.d("Exception while downloading url", e.toString());
} finally {
iStream.close();
urlConnection.disconnect();
}
return data;
}
//Αυτοτελές//
// Fetches data from url passed
//Αυτοτελές
private class DownloadTask extends AsyncTask<String, Void, String> {
// Downloading data in non-ui thread
@Override
protected String doInBackground(String... url) {
// For storing data from web service
String data = "";
try {
// Fetching the data from web service
data = downloadUrl(url[0]);
Log.d("sos3", "sos3");
} catch (Exception e) {
Log.d("Background Task", e.toString());
}
return data;
}
// Executes in UI thread, after the execution of
// doInBackground()
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
ParserTask parserTask = new ParserTask();
Log.d("sos4", "sos4");
// Invokes the thread for parsing the JSON data
parserTask.execute(result);
}
}
//Αυτοτελές//
public class ParserTask extends
AsyncTask<String, Integer, List<List<HashMap<String, String>>>> {
// Parsing the data in non-ui thread
@Override
protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) {
JSONObject jObject;
List<List<HashMap<String, String>>> routes = null;
try {
jObject = new JSONObject(jsonData[0]);
DirectionsJSONParser parser = new DirectionsJSONParser();
Log.d("sos5", "sos5");
// Starts parsing data
routes = parser.parse(jObject);
Log.d("json", jObject.toString());
} catch (Exception e) {
e.printStackTrace();
}
return routes;
}
// Executes in UI thread, after the parsing process
@Override
protected void onPostExecute(List<List<HashMap<String, String>>> result) {
ArrayList<LatLng> points = null;
String distance = "";
String duration = "";
Log.d("sos6", "sos6");
Log.d("result", String.valueOf(result.size()));
// Traversing through all the routes
for (int i = 0; i < result.size(); i++) {
points = new ArrayList<LatLng>();
// Fetching i-th route
List<HashMap<String, String>> path = result.get(i);
// Fetching all the points in i-th route
for(int j=0;j<path.size();j++){
HashMap<String,String> point = path.get(j);
if(j==0){ // Get distance from the list
distance = point.get("distance");
continue;
}else if(j==1){ // Get duration from the list
duration = point.get("duration");
continue;
}
double lat = Double.parseDouble(point.get("lat"));
double lng = Double.parseDouble(point.get("lng"));
LatLng position = new LatLng(lat, lng);
points.add(position);
//
//
}
}
Log.d("finito", distance);
String asd[] = distance.split(" ");
Log.d("ass", asd[0]);
Log.d("ass", asd[1]);
double x = Double.parseDouble(asd[0]);
if(asd[1].equals("m")){
x = x/1000;
}
Log.d("intValue", String.valueOf(x));
x = Math.round(x);
Array.add(x);
Log.d("Array", Array.toString());
if(Array.size()==3){
z = Array.get(0) + Array.get(1) + Array.get(2);
Array_add.add(z);
Array.clear();
}
Log.d("size", String.valueOf(Array_add.size()));
Log.d("Αθροισμα", String.valueOf(z));
}
}
//Αυτοτελές
}
答案 0 :(得分：1)
首次引入时，AsyncTasks在单个上串行执行 背景线程。从...开始
{android.os.Build.VERSION_CODES#DONUT}，这已更改为池 线程允许多个任务并行运行。开始 使用{ android.os.Build.VERSION_CODES#HONEYCOMB}，执行任务 在单个线程上避免由于引起的常见应用程序错误 并行执行。
此外，由于AsyncTask的执行程序是静态的，因此您可以获得应用程序的单个执行程序。
现在它已经运行了GetData asyncTask并且它以串行方式运行asynsTask，因此无法执行DownloadTask。它只能在GetDataTask完成后才能运行。
如果要并行运行多个asynctasks，可以查看Asynctask.executeOnExecutor()。