Create QgsProviderSublayerTask for retrieving sublayer details in a thread

This can sometimes take a looooong time, so it's worth doing in the
background

python/core/auto_generated/providers/qgsprovidersublayertask.sip.in

@@ -0,0 +1,53 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/providers/qgsprovidersublayertask.h                         *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+
+
+class QgsProviderSublayerTask : QgsTask
+{
+%Docstring(signature="appended")
+
+A :py:class:`QgsTask` which retrieves sublayer details for a URI.
+
+.. versionadded:: 3.22
+%End
+
+%TypeHeaderCode
+#include "qgsprovidersublayertask.h"
+%End
+  public:
+
+    QgsProviderSublayerTask( const QString &uri );
+%Docstring
+Constructor for QgsProviderSublayerTask, which retrieves sublayer details for the
+specified ``uri``.
+%End
+
+    ~QgsProviderSublayerTask();
+
+    QList<QgsProviderSublayerDetails> results() const;
+%Docstring
+Return the sublayer details as calculated by the task.
+%End
+
+    virtual bool run();
+
+    virtual void cancel();
+
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/providers/qgsprovidersublayertask.h                         *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/core/core_auto.sip

@@ -515,6 +515,7 @@
 %Include auto_generated/providers/qgsprovidermetadata.sip
 %Include auto_generated/providers/qgsproviderregistry.sip
 %Include auto_generated/providers/qgsprovidersublayerdetails.sip
+%Include auto_generated/providers/qgsprovidersublayertask.sip
 %Include auto_generated/providers/arcgis/qgsarcgisportalutils.sip
 %Include auto_generated/providers/arcgis/qgsarcgisrestutils.sip
 %Include auto_generated/providers/memory/qgsmemoryproviderutils.sip

src/core/CMakeLists.txt

@@ -233,6 +233,7 @@ set(QGIS_CORE_SRCS
   providers/qgsprovidermetadata.cpp
   providers/qgsproviderregistry.cpp
   providers/qgsprovidersublayerdetails.cpp
+  providers/qgsprovidersublayertask.cpp
 
   providers/arcgis/qgsarcgisportalutils.cpp
   providers/arcgis/qgsarcgisrestquery.cpp
@@ -1522,6 +1523,7 @@ set(QGIS_CORE_HDRS
   providers/qgsprovidermetadata.h
   providers/qgsproviderregistry.h
   providers/qgsprovidersublayerdetails.h
+  providers/qgsprovidersublayertask.h
 
   providers/arcgis/qgsarcgisportalutils.h
   providers/arcgis/qgsarcgisrestquery.h

src/core/providers/qgsprovidersublayertask.cpp

@@ -0,0 +1,50 @@
+/***************************************************************************
+                             qgsprovidersublayertask.cpp
+                             ----------------------
+    begin                : June 2021
+    copyright            : (C) 2021 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsprovidersublayertask.h"
+#include "qgsfeedback.h"
+#include "qgsproviderregistry.h"
+#include "qgsprovidersublayerdetails.h"
+
+QgsProviderSublayerTask::QgsProviderSublayerTask( const QString &uri )
+  : QgsTask( tr( "Retrieving layers" ), QgsTask::CanCancel | QgsTask::CancelWithoutPrompt )
+  , mUri( uri )
+{
+}
+
+QList<QgsProviderSublayerDetails> QgsProviderSublayerTask::results() const
+{
+  return mResults;
+}
+
+QgsProviderSublayerTask::~QgsProviderSublayerTask() = default;
+
+bool QgsProviderSublayerTask::run()
+{
+  mFeedback = std::make_unique< QgsFeedback >();
+
+  mResults = QgsProviderRegistry::instance()->querySublayers( mUri, Qgis::SublayerQueryFlag::ResolveGeometryType | Qgis::SublayerQueryFlag::CountFeatures, mFeedback.get() );
+  return true;
+}
+
+void QgsProviderSublayerTask::cancel()
+{
+  if ( mFeedback )
+    mFeedback->cancel();
+
+  QgsTask::cancel();
+}

src/core/providers/qgsprovidersublayertask.h

@@ -0,0 +1,66 @@
+/***************************************************************************
+                             qgsprovidersublayertask.h
+                             ----------------------
+    begin                : June 2021
+    copyright            : (C) 2021 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSPROVIDERSUBLAYERTASKTASK_H
+#define QGSPROVIDERSUBLAYERTASKTASK_H
+
+#include "qgstaskmanager.h"
+#include <memory>
+
+class QgsFeedback;
+class QgsProviderSublayerDetails;
+
+/**
+ * \ingroup core
+ *
+ * \brief A QgsTask which retrieves sublayer details for a URI.
+ *
+ * \since QGIS 3.22
+ */
+class CORE_EXPORT QgsProviderSublayerTask : public QgsTask
+{
+    Q_OBJECT
+
+  public:
+
+    /**
+     * Constructor for QgsProviderSublayerTask, which retrieves sublayer details for the
+     * specified \a uri.
+     */
+    QgsProviderSublayerTask( const QString &uri );
+
+    ~QgsProviderSublayerTask() override;
+
+    /**
+     * Return the sublayer details as calculated by the task.
+     */
+    QList<QgsProviderSublayerDetails> results() const;
+
+    bool run() override;
+    void cancel() override;
+
+  private:
+
+    QString mUri;
+
+    std::unique_ptr< QgsFeedback > mFeedback;
+
+    QList<QgsProviderSublayerDetails> mResults;
+
+};
+
+#endif // QGSPROVIDERSUBLAYERTASKTASK_H