Transaction.Handler

public static interface Transaction.Handler

An object implementing this interface is used to run a transaction, and will be notified of the results of the transaction.

Public Method Summary

abstract Transaction.Result
doTransaction(MutableData currentData)
This method will be called, possibly multiple times, with the current data at this location.
abstract void
onComplete(DatabaseError error, boolean committed, DataSnapshot currentData)
This method will be called once with the results of the transaction.

Public Methods

public abstract Transaction.Result doTransaction (MutableData currentData)

This method will be called, possibly multiple times, with the current data at this location. It is responsible for inspecting that data and returning a Transaction.Result specifying either the desired new data at the location or that the transaction should be aborted.

Since this method may be called repeatedly for the same transaction, be extremely careful of any side effects that may be triggered by this method. In addition, this method is called from within the Firebase Database library's run loop, so care is also required when accessing data that may be in use by other threads in your application.

Best practices for this method are to rely only on the data that is passed in.

Parameters
currentData The current data at the location. Update this to the desired data at the location
Returns
  • Either the new data, or an indication to abort the transaction

public abstract void onComplete (DatabaseError error, boolean committed, DataSnapshot currentData)

This method will be called once with the results of the transaction.

Parameters
error null if no errors occurred, otherwise it contains a description of the error
committed True if the transaction successfully completed, false if it was aborted or an error occurred
currentData The current data at the location

Send feedback about...

Need help? Visit our support page.