```
public interface MpnSubscriptionListener
```
Interface to be implemented to receive MpnSubscription events including subscription/unsubscription, triggering and status change.
Events for these listeners are dispatched by a different thread than the one that generates them. This means that, upon reception of an event, it is possible that the internal state of the client has changed. On the other hand, all the notifications for a single LightstreamerClient, including notifications to ClientListener, SubscriptionListener, ClientMessageListener, MpnDeviceListener and MpnSubscriptionListener will be dispatched by the same thread.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`onListenEnd()`	Event handler called when the MpnSubscriptionListener instance is removed from an `MpnSubscription` through `MpnSubscription.removeListener(MpnSubscriptionListener)`. This is the last event to be fired on the listener.
`void`	`onListenStart()`	Event handler called when the MpnSubscriptionListener instance is added to an `MpnSubscription` through `MpnSubscription.addListener(MpnSubscriptionListener)`. This is the first event to be fired on the listener.
`void`	`onModificationError(int code, java.lang.String message, java.lang.String propertyName)`	Event handler called when the value of a property of `MpnSubscription` cannot be changed. Properties can be modified by direct calls to their setters.
`void`	`onPropertyChanged(java.lang.String propertyName)`	Event handler called each time the value of a property of `MpnSubscription` is changed. Properties can be modified by direct calls to their setter or by server sent events.
`void`	`onStatusChanged(java.lang.String status, long timestamp)`	Event handler called when the server notifies that an `MpnSubscription` changed its status. Note that in some server clustering configurations the status change for the MPN subscription's trigger event may not be called.
`void`	`onSubscription()`	Event handler called when an `MpnSubscription` has been successfully subscribed to on the server's MPN Module. This event handler is always called before other events related to the same subscription. Note that this event can be called multiple times in the life of an MpnSubscription instance only in case it is subscribed multiple times through `LightstreamerClient.unsubscribe(MpnSubscription)` and `LightstreamerClient.subscribe(MpnSubscription, boolean)`.
`void`	`onSubscriptionError(int code, java.lang.String message)`	Event handler called when the server notifies an error while subscribing to an `MpnSubscription`. By implementing this method it is possible to perform recovery actions.
`void`	`onTriggered()`	Event handler called when the server notifies that an `MpnSubscription` did trigger. For this event to be called the MpnSubscription must have a trigger expression set and it must have been evaluated to true at least once. Note that this event can be called multiple times in the life of an MpnSubscription instance only in case it is subscribed multiple times through `LightstreamerClient.unsubscribe(MpnSubscription)` and `LightstreamerClient.subscribe(MpnSubscription, boolean)`.
`void`	`onUnsubscription()`	Event handler called when an `MpnSubscription` has been successfully unsubscribed from on the server's MPN Module. After this call no more events can be received until a new `onSubscription()` event. Note that this event can be called multiple times in the life of an MpnSubscription instance only in case it is subscribed multiple times through `LightstreamerClient.unsubscribe(MpnSubscription)` and `LightstreamerClient.subscribe(MpnSubscription, boolean)`.
`void`	`onUnsubscriptionError(int code, java.lang.String message)`	Event handler called when the server notifies an error while unsubscribing from an `MpnSubscription`. By implementing this method it is possible to perform recovery actions.

- Method Detail
  - onListenStart
```
void onListenStart()
```
    Event handler called when the MpnSubscriptionListener instance is added to an MpnSubscription through MpnSubscription.addListener(MpnSubscriptionListener).
    This is the first event to be fired on the listener.
  - onListenEnd
```
void onListenEnd()
```
    Event handler called when the MpnSubscriptionListener instance is removed from an MpnSubscription through MpnSubscription.removeListener(MpnSubscriptionListener).
    This is the last event to be fired on the listener.
  - onSubscription
```
void onSubscription()
```
    Event handler called when an MpnSubscription has been successfully subscribed to on the server's MPN Module.
    This event handler is always called before other events related to the same subscription.
    Note that this event can be called multiple times in the life of an MpnSubscription instance only in case it is subscribed multiple times through LightstreamerClient.unsubscribe(MpnSubscription) and LightstreamerClient.subscribe(MpnSubscription, boolean). Two consecutive calls to this method are not possible, as before a second onSubscription() event an onUnsubscription() event is always fired.
  - onUnsubscription
```
void onUnsubscription()
```
    Event handler called when an MpnSubscription has been successfully unsubscribed from on the server's MPN Module.
    After this call no more events can be received until a new onSubscription() event.
    Note that this event can be called multiple times in the life of an MpnSubscription instance only in case it is subscribed multiple times through LightstreamerClient.unsubscribe(MpnSubscription) and LightstreamerClient.subscribe(MpnSubscription, boolean). Two consecutive calls to this method are not possible, as before a second onUnsubscription() event an onSubscription() event is always fired.
  - onSubscriptionError
```
void onSubscriptionError(int code,
                         @Nullable
                         java.lang.String message)
```
    Event handler called when the server notifies an error while subscribing to an MpnSubscription.
    By implementing this method it is possible to perform recovery actions.
    Parameters:
    
    code - The error code sent by the Server. It can be one of the following:
    
    17 - bad Data Adapter name or default Data Adapter not defined for the current Adapter Set.
    
    21 - bad Group name.
    
    22 - bad Group name for this Schema.
    
    23 - bad Schema name.
    
    24 - mode not allowed for an Item.
    
    30 - subscriptions are not allowed by the current license terms (for special licenses only).
    
    40 - the MPN Module is disabled, either by configuration or by license restrictions.
    
    41 - the request failed because of some internal resource error (e.g. database connection, timeout, etc.).
    
    43 - invalid or unknown application ID.
    
    44 - invalid syntax in trigger expression.
    
    45 - invalid or unknown MPN device ID.
    
    46 - invalid or unknown MPN subscription ID (for MPN subscription modifications).
    
    47 - invalid argument name in notification format or trigger expression.
    
    48 - MPN device suspended.
    
    49 - one or more subscription properties exceed maximum size.
    
    50 - no items or fields have been specified.
    
    52 - the notification format is not a valid JSON structure.
    
    53 - the notification format is empty.
    
    66 - an unexpected exception was thrown by the Metadata Adapter while authorizing the connection.
    
    68 - the Server could not fulfill the request because of an internal error.
    
    <= 0 - the Metadata Adapter has refused the subscription request; the code value is dependent on the specific Metadata Adapter implementation.
    
    message - The description of the error sent by the Server; it can be null.
  - onUnsubscriptionError
```
void onUnsubscriptionError(int code,
                           @Nullable
                           java.lang.String message)
```
    Event handler called when the server notifies an error while unsubscribing from an MpnSubscription.
    By implementing this method it is possible to perform recovery actions.
    Parameters:
    
    code - The error code sent by the Server. It can be one of the following:
    
    30 - subscriptions are not allowed by the current license terms (for special licenses only).
    
    40 - the MPN Module is disabled, either by configuration or by license restrictions.
    
    41 - the request failed because of some internal resource error (e.g. database connection, timeout, etc.).
    
    43 - invalid or unknown application ID.
    
    45 - invalid or unknown MPN device ID.
    
    46 - invalid or unknown MPN subscription ID.
    
    48 - MPN device suspended.
    
    66 - an unexpected exception was thrown by the Metadata Adapter while authorizing the connection.
    
    68 - the Server could not fulfill the request because of an internal error.
    
    <= 0 - the Metadata Adapter has refused the unsubscription request; the code value is dependent on the specific Metadata Adapter implementation.
    
    message - The description of the error sent by the Server; it can be null.
  - onTriggered
```
void onTriggered()
```
    Event handler called when the server notifies that an MpnSubscription did trigger.
    For this event to be called the MpnSubscription must have a trigger expression set and it must have been evaluated to true at least once.
    Note that this event can be called multiple times in the life of an MpnSubscription instance only in case it is subscribed multiple times through LightstreamerClient.unsubscribe(MpnSubscription) and LightstreamerClient.subscribe(MpnSubscription, boolean). Two consecutive calls to this method are not possible.
    Note also that in some server clustering configurations this event may not be called. The corrisponding push notification is always sent, though.
    
    See Also:
    
    MpnSubscription.setTriggerExpression(String)
  - onStatusChanged
```
void onStatusChanged(@Nonnull
                     java.lang.String status,
                     long timestamp)
```
    Event handler called when the server notifies that an MpnSubscription changed its status.
    Note that in some server clustering configurations the status change for the MPN subscription's trigger event may not be called. The corresponding push notification is always sent, though.
    Parameters:
    
    status - The new status of the MPN subscription. It can be one of the following:
    
    UNKNOWN
    
    ACTIVE
    
    SUBSCRIBED
    
    TRIGGERED
    
    timestamp - The server-side timestamp of the new subscription status.
    
    See Also:
    
    MpnSubscription.getStatus(), MpnSubscription.getStatusTimestamp()
  - onPropertyChanged
```
void onPropertyChanged(@Nonnull
                       java.lang.String propertyName)
```
    Event handler called each time the value of a property of MpnSubscription is changed.
    Properties can be modified by direct calls to their setter or by server sent events. A propery may be changed by a server sent event when the MPN subscription is modified, or when two MPN subscriptions coalesce (see LightstreamerClient.subscribe(MpnSubscription, boolean)).
    Parameters:
    
    propertyName - The name of the changed property. It can be one of the following:
    
    mode
    
    group
    
    schema
    
    adapter
    
    notification_format
    
    trigger
    
    requested_buffer_size
    
    requested_max_frequency
    
    status_timestamp
  - onModificationError
```
void onModificationError(int code,
                         java.lang.String message,
                         java.lang.String propertyName)
```
    Event handler called when the value of a property of MpnSubscription cannot be changed.
    Properties can be modified by direct calls to their setters. See MpnSubscription.setNotificationFormat(String) and MpnSubscription.setTriggerExpression(String).
    Parameters:
    
    code - The error code sent by the Server.
    
    message - The description of the error sent by the Server.
    
    propertyName - The name of the changed property. It can be one of the following:
    
    notification_format
    
    trigger

Interface MpnSubscriptionListener

Method Summary

Method Detail

onListenStart

onListenEnd

onSubscription

onUnsubscription

onSubscriptionError

onUnsubscriptionError

onTriggered

onStatusChanged

onPropertyChanged

onModificationError