What is Data Binding?
It is a technique to connect Data with your views.
How it works?
It generates a java file that connects your views with the data.
Setting up project for Data Binding
build.gradle(:app)
plugins {
...
id 'kotlin-kapt'
}
android {
...
buildFeatures{
dataBinding = true
}
}
...
Getting Started with the code
To add data binding wrap your parent view/view group with the <layout> tag
<layout> tag contains 2 sections <data> and your parent view group.
<data> tag can contain 2 more tags, <import> & <variable>, as the name shows import is used to import the dependencies like class, interface, etc. And variable used to declare variables that we can use in our layout file (later in this post).
Our hierarchy looks like this.
activity_main.xml
<layout>
<data>
<import name="com.sample.MyViewModel" />
<variable
name="mViewModel"
type="MyViewModel" />
</data>
<FrameLayout>
..............
</FrameLayout>
</layout>
Setup binding in Activity
class MainActivity: AppCompatActivity() {
private lateinit var binding : ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
// start using the binding
}
}
Note: **ActivityMainBinding* is an auto-generated file, the file name will be based on your XML file, (not the activity or fragment file) *
Setup binding in Fragment
class SampleFragment : Fragment() {
private lateinit var binding: FragmentSampleBinding
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
binding = FragmentSampleBinding.inflate(inflater, container, false)
return binding.root
}
}
Assign value to XML variables
binding.mViewModel = mViewModel
// adding lifecycler owner to binding to use live data inside your XML
// this refer to lifecycler owner in Activity
binding.lifecycleOwner = this
// use viewLifecycleOwner to get lifecyclerOwner for Fragment, Bottomsheet, Dialog, etc.
binding.lifecycleOwner = viewLifecycleOwner
// this will do the pending binding things
binding.executePendingBindings()
Handle Variable inside the Data Binding
To use variables in XML you have to wrap your value inside @{YOUR-VALUE}
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@{mViewModel.username}" />
Handle interface inside the Data Binding
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@{()->mViewModel.yourFunction()}" />
Note: you can also get the reference of current view by
(view) -> mViewModel.yourFunction(view)
Default values and Null safety
Default value is used to show in the preview
android:text="@{mViewModel.name, default =`Default Value` }"
Handle null variables ??
android:text="@{mViewModel.name ?? `Nullable Value`}"
If mViewModel or name is null or not assigned then TextView will show 'Nullable Value'
Resource Reference
Dimen
android:padding="@{large? @dimen/largePadding : @dimen/smallPadding}"
String & plurals
android:text="@{@string/nameFormat(firstName, etFirstName.text)}"
android:text="@{@plurals/banana(bananaCount)}"
etFirstName is an edit text in the same layout file
Passing variables to included layout
sample_layout.xml
<layout>
<data>
<variable
name="customTitle"
type="String" />
</data>
....
</layout>
main_layout.xml
<include
app:customTitle="@{`Test Title`}"
...
/>
Note: You must provide value in @{} if you want to send the value as a variable
Thank you, guys.
Keep learning, Keep Sharing ❤️
Original post on yogeshpaliyal.com
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