/ Theme Object / Collections

Layers

This collection contains Layer objects that represent map layers upon which the theme has been created or/and own work layers of the theme. The order of layers in the collection corresponds to the order of displaying layers in the theme. The collection Layers is the default one. To access layers in the collection, use the Item method. The argument of the method can be a string (the layer name) or an integer (the layer internal number).

The work layers give an opportunity to organize the own set of features for a theme. The feature types of work layers cannot be linked with tables of GDB or external databases.

Taking into account peculiarities of implementation for work layers in the given version of GIS kernel, it is not recommended to create work layers with the number of features comparable with the number of features in map layers. Because it may cause the GIS kernel to reduce performance. In the given version of GIS kernel, it is assumed that features of work layers are mainly used to implement spatial filter conditions in a theme.

Modification of work layer features as well as the structure of work layers is performed beyond GDB transactions. All changes made to features of a work layer and its structure are saved to GDB while a theme is cataloged in GDB by adding to the GeoDatabase::Themes collection or by updating the cataloged theme using the Theme::Update method.

User permissions on changing both features of work layer and the structure of work layer correspond to permissions on changing the theme structure (see the gdbPermThemeChangeStructure constant in the "Permission Constants for Themes" table).

After completing the work with the theme, you should close it by the Theme::Close method if it contains work layers.