# BlocBuilder

### BlocBuilder with automatically retrieved Bloc

```kotlin
@Composable
inline fun <reified BlocA:BlocBase<BlocAState>,BlocAState:Any> 
BlocBuilder(
    blocTag:String?=null,
    noinline buildWhen:@DisallowComposableCalls ((previous:BlocAState?,current:BlocAState)->Boolean)?=null,
    content:@Composable (BlocAState)->Unit
    )
```

`BlocBuilder` handles retrieving a [Bloc](https://beyondeye.gitbook.io/compose-bloc/bloc-documentation/bloc-and-cubit-overview/bloc) of the specified type from the registered `Blocs` in the current composable subtree (see [BlocProvider](https://beyondeye.gitbook.io/compose-bloc/bloc-documentation/blocs-and-compose-overview/blocprovider)) and start listening to the associated stream of Bloc state updates, passing it to the `content` composable method.&#x20;

Each new value emitted in the `Bloc` stream of states will trigger recomposition.

&#x20;Please refer to [BlocListener ](https://beyondeye.gitbook.io/compose-bloc/bloc-documentation/blocs-and-compose-overview/bloclistener)if you instead want to "do" anything in response to `state` changes such as navigation, showing a dialog, etc...&#x20;

An optional `blocTag` parameter can be specified in order to identify a specific `Bloc` instance, in case there is more than one instance of a `Bloc` of  the same type registered for the current composable subtree (see [BlocProvider ](https://beyondeye.gitbook.io/compose-bloc/bloc-documentation/blocs-and-compose-overview/blocprovider)).&#x20;

The `blocTag` parameter is not present in the original `flutter_bloc` implementation&#x20;

An optional  `buildWhen` lambda can be provided for more granular control over what specific kind of state change should trigger recomposition

`buildWhen` will be invoked on each `Bloc state` change:  `buildWhen` takes the previous `state` and current `state` and must return a `Boolean` which determines whether or not the `content` composable function will be triggered with the new state

For  the first call to `buildWhen` the previous `state` will be initialized to the `state` of the `Bloc` when the `BlocBuilder` was initialized.

### BlocBuilder for externally provided Bloc

```kotlin
@Composable
inline fun <reified BlocA:BlocBase<BlocAState>,BlocAState:Any>
BlocBuilder(
    externallyProvidedBlock:BlocA,
    noinline buildWhen:@DisallowComposableCalls ((previous:BlocAState?,current:BlocAState)->Boolean)?=null,
    content:@Composable (BlocAState)->Unit)
```

This is the same as the previous method but with an explicitly specified Bloc instance `externallyProvidedBlock` , not retrieved implicitly from current registered blocs in the current composable subtree.

&#x20;Use this method if for example you have retrieved the Bloc already with [`rememberProvidedBlocOf` ](https://beyondeye.gitbook.io/compose-bloc/bloc-documentation/blocprovider#rememberprovidedblocof)


---

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