The -control environment

The control environment packages the interface to the window server and -provides an environment for creating controls. It is implemented in a single -class, CCoeEnv, which encapsulates active objects and an -active scheduler for receiving events from the window server. Each application -has exactly one CCoeEnv object which is stored in Thread -Local Storage (TLS).

CCoeEnv also provides a number of utilities which are -useful to most applications. These utilities include:

creating a graphics -context, the system graphics context. This is the standard -graphics context which is normally used for drawing controls. It may be accessed -using CCoeEnv::SystemGc() but controls should get their -graphics context using CCoeControl::SystemGc() rather than -directly from the environment.
access to the window -server session
utilities for using -fonts
utilities for reading -resource values from resource files
Support for singleton -(static) objects

Resource readers and resource files

CCoeEnv maintains -a list of the resource files used by the application. Files may be added to -the list using AddResourceFileL() and removed using DeleteResourceFile().

The -utility functions provided by the control environment read resources and resource -data from the resource files in its list.

A resource file consists -of a list of resources, each identified by a resource ID. Each resource consists -of a list of resource values in the form of binary data. The order and lengths -of the values for each resource type are defined in a resource definition -(generally stored in a file with an .rh extension).

Reading -data from a resource file requires two stages:

read a resource from -the resource file into a buffer
read values from the -resource using a resource reader

CCoeEnv provides utility functions to perform the -first of these stages and functions to create resource readers.

An -application's default resource file, one which has the same name as the application, -is loaded automatically.

It should be noted that stage two can be -omitted if the resource contains only one value, or if it is read into a formatted -buffer. In both of these cases the resource data can be read straight from -the buffer.

Singletons - CCoeStatic

The CCoeStatic base -class is closely associated with CCoeEnv. Between them -they allow singleton objects to be created and stored in Thread Local Storage -(TLS). By doing so they provide an equivalent to writeable global static data.

Classes -derived from CCoeStatic are automatically added to the -environment when they are instantiated for the first time. Subsequent attempts -to instantiate an object of the same type will result in a panic (with error -code ECoePanicDuplicateObjectUid).

Each singleton -requires a UID and may be given a destruction priority (relative to other -singletons and the AppUi) and a scope (EThread or EApp).

Once -a singleton has been created it may be accessed through the CCoeEnv API.

// Singleton access -IMPORT_C static CCoeStatic* Static( TUid aUid ) ; -IMPORT_C CCoeStatic* FindStatic( TUid aUid ) ;

CCoeStatic has -no public functions.