androidkotlinandroid-mvvmandroid-viewbinding

BaseFragment with viewbinding


To use viewbinding in an android app I am basically creating base classes for Activity & Fragment to remove boilerplate of everytime writing inflating code.

ACTIVITY:

BaseActivity with viewbinding:

abstract class BaseActivity<VB : ViewBinding> : AppCompatActivity() {
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = getViewBinding()
    }

    abstract fun getViewBinding(): VB

}

MainActivity:

class MainActivity : BaseActivity<ActivityMainBinding>() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(binding.root)
        //we can directly use binding now and it works fine inside activity
        //binding.view.doSomething() 
    }

 override fun getViewBinding(): ActivityMainBinding = ActivityMainBinding.inflate(layoutInflater)
}

FRAGMENTS :

BaseFragment:

abstract class BaseFragment<VB : ViewBinding> : Fragment() {

    var binding: VB? = null

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding = getViewBinding(view)
    }

    abstract fun getViewBinding(view: View): VB
}

DemoFragment:

class DemoFragment : BaseFragment<DemoFragmentBinding>() {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        //problem is here
        binding.txtData.text="Something"
    }

    override fun getViewBinding(view: View): DemoFragmentBinding = DemoFragmentBinding.bind(view)

}

demo_fragment.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.fragments.DemoFragment">

    <TextView
        android:id="@+id/txt_data"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Hello" />

</FrameLayout>

Problem : Unable to access views using binding inside Demofragment. I don't know why it works with activity and not with fragment.

2nd way that I don't want todo:

implementation 'androidx.fragment:fragment-ktx:1.3.1'

class DemoFragment : Fragment(R.layout.demo_fragment) {

    lateinit var binding: DemoFragmentBinding

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding = DemoFragmentBinding.bind(view).apply {
            txtData.text = "Hello World"
        }
    }
}

Solution

  • You need to override onCreateView in BaseFragment and initialize the viewbinding

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        _binding = getViewBinding()
        return binding.root
    }
    

    Then change this line

    override fun getViewBinding(view: View): DemoFragmentBinding = DemoFragmentBinding.bind(view)
    

    with

    override fun getViewBinding() = DemoFragmentBinding.inflate(layoutInflater)
    

    BaseFragment:

    abstract class BaseFragment<VB : ViewBinding> : Fragment() {
        private var _binding: VB? = null
        val binding get() = _binding!!
    
        override fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
            savedInstanceState: Bundle?
        ): View? {
            _binding = getViewBinding()
            return binding.root
        }
    
        abstract fun getViewBinding(): VB
    }
    

    DemoFragment:

    class DemoFragment : BaseFragment<DemoFragmentBinding>() {
    
        override fun getViewBinding() = DemoFragmentBinding.inflate(layoutInflater)
    
        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            super.onViewCreated(view, savedInstanceState)
    
            binding.apply {
                txtData.text = "Something"
            }
        }
    }