Class CEnvironmentChangeNotifier

class CEnvironmentChangeNotifier : public CActive;

Description

Environment change notifier. This is an active object and can be used to handle environment change events.

Derivation

• CBase - Base class for all classes to be instantiated on the heap.

• CActive - The core class of the active object abstraction.

• CEnvironmentChangeNotifier - Environment change notifier. This is an active object and can be used to handle ...

Members

Defined in CEnvironmentChangeNotifier:

• Change()constReturns the last set of change events.
• DoCancel()Implements cancellation of an outstanding request.
• NewL(TInt,const TCallBack &)Constructs a new environment change notifier object with the specified active ob...
• RunL()Handles an active object's request completion event.
• Set(const TCallBack &)Sets the callback function.
• Start()Issues a request for change events.
• ~CEnvironmentChangeNotifier()Destructor. Frees all resources owned by the object, prior to its destruction.

Inherited from CActive:

• CActive(TInt)Constructs the active object with the specified priority.
• Cancel()Cancels the wait for completion of an outstanding request.
• Deque()Removes the active object from the active scheduler's list of active objects.
• EPriorityHighA priority higher than EPriorityUserInput.
• EPriorityIdleA low priority, useful for active objects representing background processing.
• EPriorityLowA priority higher than EPriorityIdle but lower than EPriorityStandard.
• EPriorityStandardMost active objects will have this priority.
• EPriorityUserInputA priority higher than EPriorityStandard; useful for active objects handling use...
• Extension_(TUint,TAny *&,TAny *)Extension function
• IsActive()constDetermines whether the active object has a request outstanding.
• IsAdded()constDetermines whether the active object has been added to the active scheduler's li...
• Priority()constGets the priority of the active object.
• RunError(TInt)Handles a leave occurring in the request completion event handler CActive::RunL(...
• SetActive()Indicates that the active object has issued a request and that it is now outstan...
• SetPriority(TInt)Sets the priority of the active object.
• TPriorityDefines standard priorities for active objects.
• iStatusThe request status associated with an asynchronous request.

Inherited from CBase:

• Delete(CBase *)Deletes the specified object.
• operator new(TUint)Allocates the object from the heap and then initialises its contents to binary z...
• operator new(TUint,TAny *)Initialises the object to binary zeroes.
• operator new(TUint,TLeave)Allocates the object from the heap and then initialises its contents to binary z...
• operator new(TUint,TLeave,TUint)Allocates the object from the heap and then initialises its contents to binary z...
• operator new(TUint,TUint)Allocates the object from the heap and then initialises its contents to binary z...

IMPORT_C static CEnvironmentChangeNotifier* NewL(TInt aPriority, const TCallBack &aCallBack);

Description

Constructs a new environment change notifier object with the specified active object priority and callback function.

The function requires a priority value for this active object and a reference to a TCallBack object encapsulating a pointer to the call back function which is to run when change events occur.

As part of its implementation, the function:

creates a Kernel side change notifier and opens a handle (an RChangeNotifier) to it.

adds this active object to the current active scheduler.

Note that construction of the environment change notifier does not issue any requests for change events.

Parameters

TInt aPriority The priority of this active object. Priority values determine the order in which an active scheduler handles completed active object requests. const TCallBack &aCallBack A reference to a callback object which the caller must construct to encapsulate the callback function.

Return value

CEnvironmentChangeNotifier * A pointer to the new environment change notifier object.

See also:

• CEnvironmentChangeNotifier::Start()Issues a request for change events.
• CActive::TPriorityDefines standard priorities for active objects.

IMPORT_C ~CEnvironmentChangeNotifier();

Description

Destructor. Frees all resources owned by the object, prior to its destruction.

In particular, it cancels any outstanding request to the Kernel side change notifier before closing the handle to it.

IMPORT_C void Start();

Description

Issues a request for change events.

The request completes when change events occur, as signalled by the Kernel side change notifier service. The request may also complete if it is cancelled by calling the CActive::Cancel() member function of this active object.

When change events occur, the callback function is called.

Note that after the first call to this function, the callback function is called immediately; this is because of the way the underlying change notifier is implemented. The changes reported are all those defined by the TChanges enum.

See also:

• CActive::Cancel()Cancels the wait for completion of an outstanding request.
• TChanges...

IMPORT_C TInt Set(const TCallBack &aCallBack);

Description

Sets the callback function.

A callback is normally set when this active object is constructed through the CEnvironmentChangeNotifier::NewL(TInt,const TCallBack &) function. This function replaces any existing callback object with the specified callback object.

Parameters

const TCallBack &aCallBack A reference to the call back object encapsulating the call back function.

Return value

TInt KErrNone if successful, KErrInUse if this active object currently has an outstanding request for change events, or another of the system-wide error-codes.

inline TInt Change() const;

Description

Returns the last set of change events.

If the last outstanding request completed normally, the function returns a bit pattern where each bit value corresponds to one of the enumerators defined by TChanges. A set bit indicates that the corresponding change event occurred.

For example, if the bit value EChangesMidnightCrossover is set, then the system time has passed midnight.

Return value

TInt A set of bits consisting of one or more of the values defined by TChanges, or KErrCancel if the last outstanding request was cancelled.

See also:

• TChanges...

private: virtual void RunL();

Description

Handles an active object's request completion event.

A derived class must provide an implementation to handle the completed request. If appropriate, it may issue another request.

The function is called by the active scheduler when a request completion event occurs, i.e. after the active scheduler's WaitForAnyRequest() function completes.

Before calling this active object's CEnvironmentChangeNotifier::RunL() function, the active scheduler has:

1. decided that this is the highest priority active object with a completed request

2. marked this active object's request as complete (i.e. the request is no longer outstanding)

CEnvironmentChangeNotifier::RunL() runs under a trap harness in the active scheduler. If it leaves, then the active scheduler calls CActive::RunError(TInt) to handle the leave.

Note that once the active scheduler's CEnvironmentChangeNotifier::Start() function has been called, all user code is run under one of the program's active object's CEnvironmentChangeNotifier::RunL() or CActive::RunError(TInt) functions.

See also:

• CActiveScheduler::Start()Starts a new wait loop under the control of the current active scheduler.
• CActiveScheduler::Error(TInt)constHandles the result of a leave occurring in an active object’s RunL() function.
• CActiveScheduler::WaitForAnyRequest()Wait for an asynchronous request to complete.

private: virtual void DoCancel();

Description

Implements cancellation of an outstanding request.

This function is called as part of the active object's CActive::Cancel().

It must call the appropriate cancel function offered by the active object's asynchronous service provider. The asynchronous service provider's cancel is expected to act immediately.

CEnvironmentChangeNotifier::DoCancel() must not wait for event completion; this is handled by CActive::Cancel().

See also:

• CActive::Cancel()Cancels the wait for completion of an outstanding request.