Add method to retrieve dependent layers for map renderer cached images

nyalldawson · nyalldawson · commit aa392dc23a39 · 2017-02-06T11:27:42.000+10:00
diff --git a/python/core/qgsmaprenderercache.sip b/python/core/qgsmaprenderercache.sip
@@ -18,6 +18,8 @@ class QgsMapRendererCache : QObject
 
     QImage cacheImage( const QString& cacheKey ) const;
 
+    QList< QgsMapLayer* > dependentLayers( const QString& cacheKey ) const;
+
     void clearCacheImage( const QString& cacheKey );
 
 };
diff --git a/src/core/qgsmaprenderercache.cpp b/src/core/qgsmaprenderercache.cpp
@@ -129,6 +129,15 @@ QImage QgsMapRendererCache::cacheImage( const QString& cacheKey ) const
   return mCachedImages.value( cacheKey ).cachedImage;
 }
 
+QList< QgsMapLayer* > QgsMapRendererCache::dependentLayers( const QString& cacheKey ) const
+{
+  if ( mCachedImages.contains( cacheKey ) )
+  {
+    return _qgis_listQPointerToRaw( mCachedImages.value( cacheKey ).dependentLayers );
+  }
+  return QList< QgsMapLayer* >();
+}
+
 void QgsMapRendererCache::layerRequestedRepaint()
 {
   QgsMapLayer* layer = qobject_cast<QgsMapLayer*>( sender() );
diff --git a/src/core/qgsmaprenderercache.h b/src/core/qgsmaprenderercache.h
@@ -84,6 +84,12 @@ class CORE_EXPORT QgsMapRendererCache : public QObject
      */
     QImage cacheImage( const QString& cacheKey ) const;
 
+    /**
+     * Returns a list of map layers on which an image in the cache depends.
+     * @note added in QGIS 3.0
+     */
+    QList< QgsMapLayer* > dependentLayers( const QString& cacheKey ) const;
+
     /**
      * Removes an image from the cache with matching \a cacheKey.
      * @see clear()
diff --git a/tests/src/python/test_qgsmaprenderercache.py b/tests/src/python/test_qgsmaprenderercache.py
@@ -192,6 +192,26 @@ def testRequestRepaintMultiple(self):
             self.assertFalse(cache.cacheImage('nolayer').isNull())
             self.assertEqual(cache.cacheImage('nolayer'), im1)
 
+    def testDependentLayers(self):
+        # bad layer tests
+        cache = QgsMapRendererCache()
+        self.assertEqual(cache.dependentLayers('not a layer'), [])
+
+        layer1 = QgsVectorLayer("Point?field=fldtxt:string",
+                                "layer1", "memory")
+        layer2 = QgsVectorLayer("Point?field=fldtxt:string",
+                                "layer2", "memory")
+
+        im = QImage(200, 200, QImage.Format_RGB32)
+        cache.setCacheImage('no depends', im, [])
+        self.assertEqual(cache.dependentLayers('no depends'), [])
+        cache.setCacheImage('depends', im, [layer1, layer2])
+        self.assertEqual(set(cache.dependentLayers('depends')), set([layer1, layer2]))
+
+        # try deleting a layer in the meantime..
+        layer2 = None
+        self.assertEqual(set(cache.dependentLayers('depends')), set([layer1]))
+
 
 if __name__ == '__main__':
     unittest.main()
