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FlowBinding
Kotlin Flow binding APIs for Android's platform and unbundled UI widgets, inspired by RxBinding.
Flow is (conceptually) a reactive streams implementation provided by the kotlinx-coroutines-core artifact.
FlowBinding offers an extensive set of extension functions that turn traditional callbacks / listeners on Android UI widgets into the Flow
type.
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Dependencies are hosted on Maven Central.
Latest version:
def flowbinding_version = "1.2.0"
Platform Bindings
implementation "io.github.reactivecircus.flowbinding:flowbinding-android:${flowbinding_version}"
AndroidX Bindings
implementation "io.github.reactivecircus.flowbinding:flowbinding-activity:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-appcompat:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-core:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-drawerlayout:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-lifecycle:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-navigation:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-preference:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-recyclerview:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-swiperefreshlayout:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-viewpager:${flowbinding_version}"
implementation "io.github.reactivecircus.flowbinding:flowbinding-viewpager2:${flowbinding_version}"
Material Components Bindings
implementation "io.github.reactivecircus.flowbinding:flowbinding-material:${flowbinding_version}"
Snapshots of the development version are available in Sonatype's snapshots
repository.
Usage
Binding UI Events
To observe click events on an Android View
:
findViewById<Button>(R.id.button)
.clicks() // binding API available in flowbinding-android
.onEach {
// handle button clicked
}
.launchIn(uiScope)
Binding Scope
launchIn(scope)
is a shorthand for scope.launch { flow.collect() }
provided by the kotlinx-coroutines-core library.
This uiScope
in the example above is a CoroutineScope
that defines the lifecycle of this Flow
. The binding implementation will respect this scope by unregistering the callback / listener automatically when the scope is cancelled.
In the context of Android lifecycle this means the uiScope
passed in here should be a scope that's bound to the Lifecycle
of the view the widget lives in.
androidx.lifecycle:lifecycle-runtime-ktx:2.2.0
introduced an extension property LifecycleOwner.lifecycleScope: LifecycleCoroutineScope
which will be cancelled when the Lifecycle
is destroyed.
In an Activity
it might look something like this:
class ExampleActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_example)
findViewById<ViewPager2>(R.id.viewPager)
.pageSelections() // binding API available in flowbinding-viewpager2
.onEach { pagePosition ->
// handle pagePosition
}
.launchIn(lifecycleScope) // provided by lifecycle-runtime-ktx
}
}
In a Fragment
:
class ExampleFragment : Fragment(R.layout.example_fragment_layout) {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
val binding = ExampleFragmentLayoutBinding.bind(view)
binding.viewPager
.pageSelections() // binding API available in flowbinding-viewpager2
.onEach { pagePosition ->
// handle pagePosition
}
.launchIn(viewLifecycleOwner.lifecycleScope) // provided by lifecycle-runtime-ktx
}
}
Note that with FlowBinding you no longer need to unregister / remove listeners or callbacks in onDestroy()
as this is done automatically for you.
Binding UI Events with Additional Information
Some UI widgets might hold a state internally which you might want to observe with a Flow
.
For example with a TabLayout
you might want to observe and react to the Tab selection events. In this case the binding API returns a Flow
of custom TabLayoutSelectionEvent
type which contains the currently selected Tab
:
tabLayout.tabSelectionEvents()
.filterIsInstance<TabLayoutSelectionEvent.TabSelected>() // only care about TabSelected events
.onEach { event ->
// sync selected tab title to some other UI element
selectedTabTitle.text = event.tab.text
}
.launchIn(uiScope)
Skipping Initial Value
Bindings which emit a stream of state changes return the InitialValueFlow
.
An InitialValueFlow
emits the current value (state) of the widget immediately upon collection of the Flow
.
In some cases you might want to skip the initial emission of the current value. This can be done by calling the skipInitialValue()
on the InitialValueFlow
:
slider.valueChanges()
.skipInitialValue()
.onEach { value ->
// handle value
}
.launchIn(uiScope) // current value won't be emitted immediately
Additional Samples
All binding APIs are documented with Example of usage.
All bindings are covered by instrumented tests which you may want to refer to.
Roadmap
Our goal is to provide most of the bindings provided by RxBinding, while shifting our focus to supporting more modern AndroidX APIs such as ViewPager2 and the new components in Material Components as they become available.
List of all bindings available:
- Platform bindings
- AndroidX Activity bindings
- AndroidX AppCompat bindings
- AndroidX Core bindings
- AndroidX DrawerLayout bindings
- AndroidX Lifecycle bindings
- AndroidX Navigation Component bindings
- AndroidX Preference bindings
- AndroidX RecyclerView bindings
- AndroidX SwipeRefreshLayout bindings
- AndroidX ViewPager bindings
- AndroidX ViewPager2 bindings
- Material Components bindings
Please feel free to create an issue if you think a useful binding is missing or you want a new binding added to the library.
Credits
This library is inspired by RxBinding which provides RxJava binding APIs for Android's UI widgets.
Many thanks to RxBinding's author Jake Wharton and its contributors.
License
Copyright 2019 Yang Chen
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.