如何等待onPostExecute完成

Question

所以我是编程新手，我想做的是制作一个安卓应用程序，为客户提供去电影院/加油站/市场的最近、最快的方式。问题是，首先我需要通过谷歌api找到最近的地方，获取lats和lngs，然后使用它们来指导api。所以我所做的是：

GetNearbyPlaces.java

public class GetNearbyPlaces extends AsyncTask<Object, String, String>
{
private String googleplaceData, url;
private GoogleMap mMap;
@Override
protected String doInBackground(Object... objects)
{
mMap = (GoogleMap) objects[0];
url = (String) objects[1];
DownloadUrl downloadUrl = new DownloadUrl();
try
{
googleplaceData = downloadUrl.ReadTheURL(url);
}
catch (IOException e)
{
e.printStackTrace();
}
return googleplaceData;
}

@Override
protected void onPostExecute(String s)
{
List<HashMap<String, String>> nearbyPlacesList = null;
DataParser dataParser = new DataParser();
nearbyPlacesList = dataParser.parse(s);
DisplayNearbyPlaces(nearbyPlacesList);
super.onPostExecute(s);
Log.d("Message","telos execute ");
}
private void DisplayNearbyPlaces(List<HashMap<String, String>> nearbyPlacesList)
{
for (int i=0; i<nearbyPlacesList.size(); 
{
Log.d("Message","mesa stin for ");
MarkerOptions markerOptions = new MarkerOptions();
HashMap<String, String> googleNearbyPlace = nearbyPlacesList.get(i);
String nameOfPlace = googleNearbyPlace.get("place_name");
String vicinity = googleNearbyPlace.get("vicinity");
double lat = Double.parseDouble(googleNearbyPlace.get("lat"));
double lng = Double.parseDouble(googleNearbyPlace.get("lng"));
LatLng latLng = new LatLng(lat, lng);
markerOptions.position(latLng);
markerOptions.title(nameOfPlace + " : " + vicinity);
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_YELLOW));
mMap.addMarker(markerOptions);
mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
mMap.animateCamera(CameraUpdateFactory.zoomTo(10));
}
}

}

GoogleUserMaps.java

case R.id.gasstation_nearby:
mMap.clear();
mMap.addMarker(userLocMarkerOptions);
mMap.setTrafficEnabled(true);
url = getUrl(latitude,longitude,gasStation);
transferData[0] = mMap;
transferData[1] = url;
Log.d("Message","Prin kanei execute ");
getNearbyPlaces.execute(transferData);
Log.d("Message","afou kanei execute ");

Toast.makeText(this, "Searching for Nearby Gas Stations.", Toast.LENGTH_SHORT).show();
Toast.makeText(this, "Showing for Nearby Gas Stations.", Toast.LENGTH_SHORT).show();
break;

我想在DisplayNearbyPlaces中添加一些公共变量，以便获得lats和lngs，但当我在getNearbyPPlaces.execute(transferData(.get((之后使用它时；在GoogleUserMaps.java中，它给了我0的结果。我听不懂AsyncTask。有什么办法让我等到getNearbyPlaces.execute(transferData(.get((；完成执行以获得lats和lngs？

提前谢谢！

我的日志我想在执行完成后得到结果，正如我在下面的图像中所示

Answer 1

@Strack我正在发布界面的代码示例

`

public interface PlaceListener{
void searchStarted();
void searchEnded();
}

public class GetNearbyPlaces extends AsyncTask<Object, String, String>
{
private String googleplaceData, url;
private GoogleMap mMap;
private PlaceListener placeListener;
public GetNearbyPlaces(PlaceListener placeListener){
this.placeListner = placeListener;
}
//onPreExecute(){ placeListner.searchStarted();}
@Override
protected String doInBackground(Object... objects)
{
mMap = (GoogleMap) objects[0];
url = (String) objects[1];
DownloadUrl downloadUrl = new DownloadUrl();
try
{
googleplaceData = downloadUrl.ReadTheURL(url);
}
catch (IOException e)
{
e.printStackTrace();
}
return googleplaceData;
}

@Override
protected void onPostExecute(String s)
{
placeListner.serachEnded();
List<HashMap<String, String>> nearbyPlacesList = null;
DataParser dataParser = new DataParser();
nearbyPlacesList = dataParser.parse(s);
DisplayNearbyPlaces(nearbyPlacesList);
super.onPostExecute(s);
Log.d("Message","telos execute ");
}

}

`

在Caller Activity中实现PlaceListener，并在searchEnded中执行所需任务。您可以根据您想要通过的所需数据来设置接口方法的参数

Answer 2

好的。创建一个新的回调：

public interface MyCallBack {
void myTaskDone(List<HashMap<String, String>> nearbyPlacesList);
}

在您的活动中创建一个：

MyCallBack myCallBack = new MyCallBack() {
@Override
public void myTaskDone(List<HashMap<String, String>> nearbyPlacesList) {
DisplayNearbyPlaces(nearbyPlacesList);
}
};

向Aynctask:发送参考

getNearbyPlaces.execute(transferData, map, new MyCallBack() {
@Override
public void myTaskDone(List<HashMap<String, String>> nearbyPlacesList) {
DisplayNearbyPlaces(nearbyPlacesList);
}
});

完整代码：

public interface MyCallBack {
void myTaskDone(List<HashMap<String, String>> nearbyPlacesList);
}
public class GetNearbyPlaces extends AsyncTask<Object, String, String> {
private String googleplaceData;
private String url;
private GoogleMap mMap;
private MyCallBack myCallBack;
public GetNearbyPlaces(String url, GoogleMap mMap, MyCallBack myCallBack) {
this.url = url;
this.mMap = mMap;
this.myCallBack = myCallBack;
}
@Override
protected String doInBackground(Object... objects) {
DownloadUrl downloadUrl = new DownloadUrl();
try {
googleplaceData = downloadUrl.ReadTheURL(url);
} catch (IOException e) {
e.printStackTrace();
}
return googleplaceData;
}

@Override
protected void onPostExecute(String s) {
List<HashMap<String, String>> nearbyPlacesList = null;
DataParser dataParser = new DataParser();
nearbyPlacesList = dataParser.parse(s);
myCallBack.myTaskDone(nearbyPlacesList);
}
}
private void DisplayNearbyPlaces(List<HashMap<String, String>> nearbyPlacesList) {
/// your code
}
MyCallBack myCallBack = new MyCallBack() {
@Override
public void myTaskDone(List<HashMap<String, String>> nearbyPlacesList) {
DisplayNearbyPlaces(nearbyPlacesList); 
}
};

如何称呼它：

//.....
transferData[0] = mMap;
transferData[1] = url;
Log.d("Message","Prin kanei execute ");
GetNearbyPlaces getNearbyPlaces = new GetNearbyPlaces(transferData, map, myCallBack);
getNearbyPlaces.execute();
//or:
GetNearbyPlaces getNearbyPlaces = new GetNearbyPlaces(transferData, map, new MyCallBack() {
@Override
public void myTaskDone(List<HashMap<String, String>> nearbyPlacesList) {
DisplayNearbyPlaces(nearbyPlacesList);
}
});
getNearbyPlaces.execute();