Qt 5.11 | Qt Location | Places (C++)

Qt 5.11.3 Reference Documentation

# Places (C++)

## Overview

The Places API allows users to discover places/points of interest and view details about them such as address and contact information; some places may even have rich content such as images and reviews. The Places API also facilitates management of places and categories, allowing users to save and remove them.

## Place Definition

A place is a point of interest, it could be a favorite restaurant, a park or someone's home. A QPlace object represents a place by acting as a container for various information about that place.

This information can be divided into 2 broad classifications

- Details
- Rich content

The place details consist of properties of the place, such as the name, location, contact information and so on. When a place is returned during a search, these details are filled in. Sometimes in order to save bandwidth, there are further details about the place that can be retrieved on an individual place by place basis, if the user is interested. The QPlace::detailsFetched() function can be queried to see if all available details have been fetched, and if not, QPlaceManager::getPlaceDetails() can be used to retrieve them. Precisely which details are populated during a search and which need to be fetched individually may vary from provider to provider. See plugin documentation for more details.

The rich content of a place consists of items such as images, reviews and editorials. Potentially there may be many rich content items, so they are treated separately from the place details. They can be retrieved in a paged fashion via QPlaceManager::getPlaceContent(). If necessary, the content may be assigned to a place so it can act as a convenient container.

## Common Operations

### Initializing a Manager

All places functionality is facilitated by a QPlaceManager instance. One must specify a QGeoServiceProvider in order to create the QPlaceManager

      //The "provider name" is used to select a particular provider
      QGeoServiceProvider *provider = new QGeoServiceProvider("provider name");
      QPlaceManager *manager = provider->placeManager();

### Discovery/Search

In order to perform a search operation we simply create a QPlaceSearchRequest and set the desired search parameters, such as a search term and search center.

      //instantiate request and set parameters
      QPlaceSearchRequest searchRequest;
      searchRequest.setSearchTerm("ice cream");
      searchRequest.setSearchArea(QGeoCircle(QGeoCoordinate(12.34, 56.78)));

      //send off a search request
      /*QPlaceSearchReply * */ searchReply = manager->search(searchRequest);

      //connect a slot to handle the reply
      connect(searchReply, SIGNAL(finished()), this, SLOT(handleSearchReply()));

The request is an asynchronous operation so we need a slot to handle the completion of the request. In the handler we check that there are no errors and that our search result type is a place. If so we can then retrieve some of the core details of the place. At the end of the slot, we delete the reply since they are for single use only.

      void handleSearchReply() {
          if (searchReply->error() == QPlaceReply::NoError) {
              foreach (const QPlaceSearchResult &result, searchReply->results()) {
                  if (result.type() == QPlaceSearchResult::PlaceResult) {
                      QPlaceResult placeResult = result;
                      qDebug() << "Name: " << placeResult.place().name();
                      qDebug() << "Coordinate " << placeResult.place().location().coordinate().toString();
                      qDebug() << "Street: " << placeResult.place().location().address().street();
                      qDebug() << "Distance: " << placeResult.distance();
                  }
              }
          }
          searchReply->deleteLater();  //discard reply
          searchReply = 0;
      }

Note: Depending upon the plugin backend that was chosen, the search results may contain places which have further details that can be fetched on a place by place basis. To fetch these other details see Fetching Place Details.

#### Recommendations

Recommendations can be retrieved by supplying a place id via QPlaceSearchRequest::setRecommendationId(). Any places similar to the given place are retrieved.

#### Paging

If the plugin supports paging, the limit parameter may be provided to the search request.

      QPlaceSearchRequest searchRequest;
      searchRequest.setLimit(15); //specify how many results are to be retrieved.

### Fetching Place Details

A place that has been returned from a search request may have more details that can be fetched. The following demonstrates how to check if there are further details and if so how to request them.

      if (!place.detailsFetched()) {
          /*QPlaceDetailsReply * */ detailsReply = manager->getPlaceDetails(place.placeId());
          connect(detailsReply, SIGNAL(finished()), this, SLOT(handleDetailsReply()));
      }
          ...
          ...
      void handleDetailsReply() {
          QPlace place;
          if (detailsReply->error() == QPlaceReply::NoError)
              place = detailsReply->place();

          detailsReply->deleteLater(); //discard reply
          detailsReply = 0;
      }

### Fetching Rich Content

Rich content such as images and reviews is retrieved through the manager and then if required assigned to a place.

      QPlaceContentRequest request;
      request.setContentType(QPlaceContent::ImageType);
      request.setPlaceId(place.placeId());
      request.setLimit(5);
      /*QPlaceContentReply * */ contentReply = manager->getPlaceContent(request);
      connect(contentReply, SIGNAL(finished()), this, SLOT(handleImagesReply()));

We can handle the content request as shown below.

      void handleImagesReply() {
          if (contentReply->error() == QPlaceReply::NoError) {
              QMapIterator<int, QPlaceContent> iter(contentReply->content());
              while (iter.hasNext()) {
                  qDebug() << "Index: " << iter.key();
                  QPlaceImage image = iter.value();
                  qDebug() << image.url();
                  qDebug() << image.mimeType();
              }

              //alternatively if indexes are irrelevant
              foreach (const QPlaceImage &image, contentReply->content()) {
                  qDebug() << image.url();
                  qDebug() << image.mimeType();
              }

              //we can assign content to the place that it belongs to.
              //the place object serves as a container where we can retrieve
              //content that has already been fetched
              place.insertContent(contentReply->request().contentType(), contentReply->content());
              place.setTotalContentCount(contentReply->request().contentType(), contentReply->totalCount());
          }

          contentReply->deleteLater();
          contentReply = 0;
      }

It is important to note that the results in the QPlaceContentReply, is a QPlaceContent::Collection which is essentially a QMap<int, QPlaceContent>. The key `int` in this case is the index of the content, and the value is the content itself. Due to the way Content is implemented it is possible to convert a content type as follows

      QPlaceImage image = content; //provided that 'content' has a type QPlace::ImageType

The usage of the QPlaceContent::Collection and the conversion between content and its subtypes means that code for handling the mechanics of paging reviews, images and editorials can be easily shared.

### Search Suggestions

The retrieval of search term suggestions is very similar to performing a place search. A QPlaceSearchRequest is used just like a place search, the only difference being that the search term is set to a partially completed string.

      QPlaceSearchRequest request;
      request.setSearchTerm("piz");
      request.setSearchArea(QGeoCircle(QGeoCoordinate(12.34, 56.78)));
      /* QPlaceSearchSuggestion * */suggestionReply = manager->searchSuggestions(request);
      connect(suggestionReply, SIGNAL(finished()), this, SLOT(handleSuggestionReply()));

And when the request is done, we can use the reply to show the suggestions.

      void handleSuggestionReply() {
          if (suggestionReply->error() == QPlaceReply::NoError) {
              foreach (const QString &suggestion, suggestionReply->suggestions())
                  qDebug() << suggestion;
          }

          suggestionReply->deleteLater(); //discard reply
          suggestionReply = 0;
      }

### Saving a Place

The saving of a new place is performed as follows, we create a QPlace instance and populate it with information such as a name, address and coordinate. Once done we can invoke QPlaceManager::savePlace() to begin a save operation.

      QPlace  place;
      place.setName( "Fred's Ice Cream Parlor" );

      QGeoLocation location;
      location.setCoordinate(QGeoCoordinate(12.34, 56.78));

      QGeoAddress address;
      address.setStreet("111 Nother Street");
          ...
      location.setAddress(address);
      place.setLocation(location);

      /* QPlaceIdReply * */savePlaceReply = manager->savePlace(place);
      connect(savePlaceReply, SIGNAL(finished()), this, SLOT(handleSavePlaceReply()));

Once a place is saved the reply contains the new identifier for that place.

      void handleSavePlaceReply() {
          if (savePlaceReply->error() == QPlaceReply::NoError)
              qDebug() << savePlaceReply->id();

          savePlaceReply->deleteLater(); //discard reply
          savePlaceReply = 0;
      }

Note that to save an already existing place, the QPlace::placeId() must be filled in with the correct identifier. Otherwise a new place will be created if empty or the wrong place overwritten if the identifier is incorrect.

When a place is saved, the QPlaceManager may emit QPlaceManager::placedAdded() or QPlaceManager::placeUpdated() signals. However whether a manager does so or not is provider specific, managers accessing places from a web service will typically not emit these signals while managers accessing places locally stored generally will.

#### Caveats

The Places API is currently designed for only saving core details. Saving rich content like images and reviews or details like supplier and rating is not a supported use case. Typically a manager will generally ignore these fields upon save and may produce a warning message if they are populated.

The Places API only supports saving of the following core details:

- name
- place id
- location
- contact details
- icon
- categories (tag-like names to describe a place)
- visibility scope

It is possible that providers may only support a subset of these. See the plugin documentation for more details.

Saving of properties such as the rating, extended attributes, images, reviews, editorials and supplier is explicitly not supported by the Places API.

#### Saving Between Managers

When saving places between managers, there are a few things to be aware of. Some fields of a place such as the id, categories and icons are manager specific entities for example the categories in one manager may not be recognized in another. Therefore trying to save a place directly from one manager to another is not possible.

The typical approach is to use the QPlaceManager::compatiblePlace() function, it creates a copy of a place, but only copies data that the manager supports. Manager specific data such as the place identifier is not copied over. The new copy is now suitable for saving into the manager. If the manager supports matching by alternative identifiers, an alternative identifier attribute is assigned to the copy (see Matching places between managers)

      //result retrieved from a different manager)
      QPlace place = manager->compatiblePlace(result.place());
      saveReply = manager->savePlace(place);

### Removing a Place

The removal of a place is performed as follows:

      /* QPlaceIdReply * */removePlaceReply = manager->removePlace(place.placeId());
      connect(removePlaceReply, SIGNAL(finished()), this, SLOT(handleRemovePlaceReply()));
          ...
          ...
      void handleRemovePlaceReply() {
          if (removePlaceReply->error() == QPlaceReply::NoError)
              qDebug() << "Removal of place identified by"
                       << removePlaceReply->id() << "was successful";

          removePlaceReply->deleteLater(); //discard reply
          removePlaceReply = 0;
      }

When a place is removed, the QPlaceManager may emit the QPlaceManager::placeRemoved() signal. Whether a manager does so is provider specific. Managers accessing places from a web service will typically not emit these signals, while managers accessing places stored locally generally will.

### Using Categories

Categories are keywords that can describe a place. For example, 'park', 'theater', 'restaurant'. A place could be described by many categories, it could be a park and a music venue and a ferry or bus stop.

To use categories they must first be initialized.

      /* QPlaceReply * */initCatReply = manager->initializeCategories();
      connect(initCatReply, SIGNAL(finished()), this, SLOT(handleInitCatReply()));
          ...
          ...
      void handleInitCatReply() {
          if (initCatReply->error() == QPlaceReply::NoError)
              qDebug() << "Categories initialized";
          else
              qDebug() << "Failed to initialize categories";

          initCatReply->deleteLater();
          initCatReply = 0;
      }

After the categories have been initialized we can then use these category functions.

- QPlaceManager::childCategories()
- QPlaceManager::category()
- QPlaceManager::parentCategoryId()
- QPlaceManager::childCategoryIds();

To retrieve the top level categories we use the QPlaceManager::childCategories() function but do not provide a category identifier.

      QList<QPlaceCategory> topLevelCategories = manager->childCategories();
      foreach (const QPlaceCategory &category, topLevelCategories)
          qDebug() << category.name();

If we did provide an identifier then we could retrieve a category's children.

      QList<QPlaceCategory> childCategories = manager->childCategories(pizza.categoryId());

### Saving a Category

The following shows how to save a category

      QPlaceCategory fastFood;

      QPlaceCategory category;
      category.setName("pizza");
      /*QPlaceIdReply */ saveCategoryReply = manager->saveCategory(category);
      connect(saveCategoryReply, SIGNAL(finished()), this, SLOT(handleSaveCategoryReply()));

      //we could have saved a category as a child by supplying a parent identifier.
      saveCategoryReply = manager->saveCategory(category, fastFood.categoryId());
          ...
          ...
      void handleSaveCategoryReply() {
          if (saveCategoryReply->error() == QPlaceReply::NoError) {
              qDebug() << "Saved category id =" << saveCategoryReply->id();
          }

          saveCategoryReply->deleteLater();
          saveCategoryReply = 0;
      }

When a category is saved, the QPlaceManager may emit QPlaceManager::categoryAdded() or QPlaceManager::categoryUpdated() signals. However whether a manager does so or not is provider specific, managers accessing places from a web service will typically not emit these signals while managers accessing places locally stored generally will.

### Removing a Category

Category removal is very similar to removing a place

      /* QPlaceIdReply * */removeCategoryReply = manager->removeCategory(place.placeId());
      connect(removeCategoryReply, SIGNAL(finished()), this, SLOT(handleRemoveCategoryReply()));
          ...
          ...
      void handleRemoveCategoryReply() {
          if (removeCategoryReply->error() == QPlaceReply::NoError)
              qDebug() << "Removal of category identified by"
                       << removeCategoryReply->id() << "was successful";

          removeCategoryReply->deleteLater(); //discard reply
          removeCategoryReply = 0;
      }

When a category is removed, the QPlaceManager may emit the QPlaceManager::categoryRemoved() signal. Whether a manager does so is provider specific. Managers accessing places from a web service will typically not emit these signals, while managers accessing places stored locally generally will.

### Matching Places Between Managers

Sometimes you may want to cross reference whether places from one manager match those from another manager. Such a situation may arise where one manager provides read-only access to places (origin manager) while another second r/w manager (destination manager) is used to save selected favorites from the first. During a search of the origin manager we may want to know which ones have been 'favorited' into the destination manager and perhaps display a customized favorite name rather than the original name.

The matching mechanism can vary between managers, but is typically accomplished through an alternative identifier. As part of the save process, the place identifier from the origin manager is saved as an alternative identifier attribute in the destination manager (which can have its own place identifier scheme). In the following example, the origin manager is from the 'here' QGeoServiceProider, therefore as part of the saving process an alternative identifier attribute, x_id_here, is set for the place saved into the destination manager (when QPlaceManager::compatiblePlace() is called)

      origin R/O manager(here)       destination R/W manager (places_jsondb)
                              Save
      Place id: ae246         --->    Place id: 0001
      Attribute type: x_provider      Attribute type: x_id_here
      Attribute value: here           Attribute text value: ae246

In order to perform the matching, we create a QPlaceMatchRequest and assign it the search results from the origin manager. The QPlaceMatchRequest will be used on the destination manager to return corresponding places. We also specify matching parameters which are key value pairs. As mentioned previously, this can vary depending on the manager but typically the key is QPlaceMatchRequest::AlternativeId to indicate we are matching by alternative id, the value in this case would be x_id_here which specifies which alternative identifier attribute we are using to do the matching.

      QPlaceMatchRequest request;
      request.setResults(results);
      QVariantMap parameters;
      parameters.insert(QPlaceMatchRequest::AlternativeId, "x_id_here");
      request.setParameters(parameters);
      matchReply = manager->matchingPlaces(request);
          ...
          ...
      void matchHandler() {
          if (matchReply->error() == QPlaceReply::NoError) {
              foreach (const QPlace place, matchReply->places()) {
                  if (place != QPlace())
                      qDebug() << "Place is a favorite with name" << place.name();
                  else
                      qDebug() << "Place is not a favorite";
              }
          }

          matchReply->deleteLater();
          matchReply = 0;
      }

## Classes in Places

### Data Classes

QPlace | Represents a set of data about a place
QPlaceAttribute | Represents generic attribute information about a place
QPlaceCategory | Represents a category that a QPlace can be associated with
QPlaceContactDetail | Represents a contact detail such as a phone number or website url
QPlaceContent | Serves as the base class for rich content types
QPlaceEditorial | Represents a publisher's article describing a place
QPlaceIcon | Represents an icon
QPlaceImage | Represents a reference to an image
QPlaceProposedSearchResult | Represents a search result containing a proposed search
QPlaceRatings | Holds rating information about a place
QPlaceResult | Represents a search result containing a place
QPlaceReview | Represents a review of a place
QPlaceSearchResult | The base class for search results
QPlaceSupplier | Represents a supplier of a place or content associated with a place
QPlaceUser | Represents an individual user

### Request Classes

QPlaceContentRequest | Represents the parameters of a content request
QPlaceMatchRequest | Used to find places from one manager that match those from another. It represents a set of request parameters
QPlaceSearchRequest | Represents the set of parameters for a search request

### Reply classes

QPlaceContentReply | Manages a content retrieval operation started by an instance of QPlaceManager
QPlaceDetailsReply | Manages a place details fetch operation started by an instance of QPlaceManager
QPlaceIdReply | Manages operations which return an identifier such as saving and removal operations of places and categories
QPlaceMatchReply | Manages a place matching operation started by an instance of QPlaceManager
QPlaceReply | Manages an operation started by an instance of QPlaceManager and serves as a base class for more specialized replies
QPlaceSearchReply | Manages a place search operation started by an instance of QPlaceManager
QPlaceSearchSuggestionReply | Manages a search suggestion operation started by an instance of QPlaceManager

### Manager Classes

QPlaceManager | The interface which allows clients to access places stored in a particular backend
QPlaceManagerEngine | Interface for implementers of QGeoServiceProvider plugins who want to provide access to place functionality