Transaction.Handler

interface Transaction.Handler


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

Summary

Public functions

Transaction.Result
doTransaction(currentData: MutableData)

This method will be called, possibly multiple times, with the current data at this location.

Unit
onComplete(
    error: DatabaseError?,
    committed: Boolean,
    currentData: DataSnapshot?
)

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

Public functions

doTransaction

fun doTransaction(currentData: MutableData): Transaction.Result

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 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: MutableData

The current data at the location. Update this to the desired data at the location

Returns
Transaction.Result

Either the new data, or an indication to abort the transaction

onComplete

fun onComplete(
    error: DatabaseError?,
    committed: Boolean,
    currentData: DataSnapshot?
): Unit

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

Parameters
error: DatabaseError?

null if no errors occurred, otherwise it contains a description of the error

committed: Boolean

True if the transaction successfully completed, false if it was aborted or an error occurred

currentData: DataSnapshot?

The current data at the location or null if an error occurred