buildWhen property
An optional buildWhen can be implemented for more granular control over
how often BlocBuilder rebuilds.
buildWhen should only be used for performance optimizations as it
provides no security about the state passed to the builder
function.
buildWhen will be invoked on each bloc state
change.
buildWhen takes the previous state
and current state
and must
return a bool which determines whether or not the builder
function will
be invoked.
The previous state
will be initialized to the state
of the bloc when
the BlocBuilder is initialized.
buildWhen is optional and if omitted, it will default to true
.
BlocBuilder<BlocA, BlocAState>(
buildWhen: (previous, current) {
// return true/false to determine whether or not
// to rebuild the widget with state
},
builder: (context, state) {
// return widget here based on BlocA's state
}
)
Implementation
final BlocBuilderCondition<S>? buildWhen;