Android-practice-5-DataBinding

Replacement of findViewById() with data binding object

When app has complex view hierarchies, findViewById() would slow down the app since it traverses them to find the desired view during the runtime. And this happens whenever the view is recreated, while user is interacting with the application.

Through a Binding object, we get a reference to the view and can access them directly. The traversing happens only once at compile time to get the view.

Set up for data binding

• Data binding has to be explicitly enabled in the Gradle file becuase it increases the compile time. Inside the android section we need to add the following :

  buildFeatures {
     dataBinding true
  }
  

• The XML layout has to be wrapped by <layout> tag. Upon compiler seeing this tag, it will auto-generate the binding class whose name is derived as PascalCase from that of layout file. In this case, the binding class name will be ActivityMainBinding from activity_name.xml. The namespace declarations must also be in the <layout> tag.

Creating a data binding object

• Use setContentView(..) in DataBindingUtil class instead of auto-generated setContentView(..) method. This will set the activity's content view and also return the binding object to the given layout.

• Upon creation of binding object, compiler generates the names of the views into the binding object as camelCase from IDs of the views in the layout.

  private lateinit var binding: ActivityMainBinding
  
  override fun onCreate(savedInstanceState: Bundle?) {
      binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main)
      binding.doneButton.setOnClickListener { onButtonClicked() }
      ...
  }
  
  private fun onButtonClicked() {
      binding.apply {
          nicknameText.visibility = View.VISIBLE
          nicknameEdit.visibility = View.GONE
          doneButton.visibility = View.GONE
      }
      ...
  }
  

Making data class available to a view

• Using data binding, we can make a data class directly available to the layout file and don't need to use the string resources.

  data class MyName(var name: String = "", var nickName: String = "")
  

• Add the data class reference to the layout with <data> and <variable> tag as below. The type parameter should be the name of the data class with package name. Now we can reference the userName variable to set the text of view.

  <data>
      <variable
          name = "userName"
          type = "com.example.myapplication.MyName"/>
  <data/>
  ..
  <TextView
      ..
      android:text="@={userName.name}" />
  

• In the activity after instantiation of a data class object, we assign it to userName through binding object.

  binding.userName = MyName("Robin", "Robinku")
  

  To have the updated UI make effect, call binding.invalidateAll()