ViewBindingDelegate

Author: Petrus Nguyễn Thái Học

• Simplify usage of Android View Binding with Kotlin Property Delegates and solve behavior of Fragment’s ViewLifecycleOwner.
• Simple one-liner ViewBinding in Fragments and Activities with Kotlin.
• Lightweight and simple library.

Medium article

Read ViewBinding Delegate — one line to get details about implementation.

Getting Started

1. Add the JitPack repository to your build file

Add it in your root build.gradle at the end of repositories:

• Kotlin

allprojects {
  repositories {
    ...
    maven(url = "https://jitpack.io")
  }
}

• Groovy

allprojects {
  repositories {
    ...
    maven { url 'https://jitpack.io' }
  }
}

2. Add the dependency

dependencies {
  implementation("com.github.hoc081098:ViewBindingDelegate:1.3.1")
}

3. Enable ViewBinding

https://developer.android.com/topic/libraries/view-binding#setup

Usage

import com.hoc081098.viewbindingdelegate.*

1. Activity (with reflection). See example

Click to expand

class MainActivity : AppCompatActivity(R.layout.activity_main) {
  private val viewBinding by viewBinding<ActivityMainBinding>()
  
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    
    viewBinding.button.setOnClickListener {
      startActivity(Intent(this@MainActivity, SecondActivity::class.java))
    }
  }
}

2. Activity (without reflection): Pass ::bind method reference. See example

Click to expand

class SecondActivity : AppCompatActivity(R.layout.activity_second) {
  private val binding by viewBinding(ActivitySecondBinding::bind)

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding.root
  }
}

3. Fragment (with reflection). See example

Click to expand

class FirstFragment : Fragment(R.layout.fragment_first) {
  private val binding by viewBinding<FragmentFirstBinding> {
    button.setOnClickListener(null)
  }
  
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    binding.button.setOnClickListener {
      findNavController().navigate(R.id.actionFirstFragmentToSecondFragment)
    }
  }
}

4. Fragment (without reflection): Pass ::bind method reference. See example

Click to expand

class SecondFragment : Fragment(R.layout.fragment_second) {
  private val binding by viewBinding(FragmentSecondBinding::bind)

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

5. Includes <merge/> tag layout: Create 2 ViewBinding property. See example

Click to expand

class ThirdFragment : Fragment(R.layout.fragment_third) {
  private val includeBinding by viewBinding<FragmentThirdIncludeBinding>()
  private val binding by viewBinding<FragmentThirdBinding> { buttonThird.setOnClickListener(null) }

  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    includeBinding.textViewThirdInclude.text = "Working..."
    binding.buttonThird.setOnClickListener {
      Toast.makeText(requireContext(), "Clicked", Toast.LENGTH_SHORT).show()
    }
  }
}

6. The Dialog of DialogFragmentSee example

Extends DefaultViewBindingDialogFragment or implements ViewBindingDialogFragment.

Click to expand

class DemoDialogFragment : DefaultViewBindingDialogFragment() {
  private val viewBinding by dialogFragmentViewBinding(R.id.root, DialogFragmentDemoBinding::bind)
  private val viewBinding2 by dialogFragmentViewBinding<DialogFragmentDemoBinding>(R.id.root)

  override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    return AlertDialog.Builder(requireContext())
      .setTitle("Demo dialog")
      .setNegativeButton("Cancel") { _, _ -> }
      .setPositiveButton("OK") { _, _ -> }
      .setView(R.layout.dialog_fragment_demo)
      .create()
  }

  override fun onResume() {
    super.onResume()

    viewBinding.textInputLayout
    viewBinding2.textInputLayout
  }
}

7. inflateViewBinding extension methods on ViewGroup/LayoutInflater/Context. See example

Can be used in RecyclerView.Adapter # onCreateViewHolder to easily create a RecyclerView.ViewHolder with a ViewBinding.

Click to expand

import com.hoc081098.viewbindingdelegate.inflateViewBinding

class DemoAdapter : ListAdapter<String, DemoAdapter.VH>(...) {
  override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = VH(parent inflateViewBinding false)

  override fun onBindViewHolder(holder: VH, position: Int) = holder.bind(getItem(position))

  class VH(private val binding: ItemRecyclerBinding) : RecyclerView.ViewHolder(binding.root) {
    fun bind(item: String) { ... }
  }
}

Note

1. Activity

Must setContentView before access ViewBinding property. This can be done easily with constructor:

public AppCompatActivity(@LayoutRes int contentLayoutId) { ... }

class MainActivity : AppCompatActivity(R.layout.activity_main) { ... }

2. Fragment

Fragment's View must be not null before access ViewBinding property. This can be done easily with constructor:

public Fragment(@LayoutRes int contentLayoutId) { ... }

class FirstFragment : Fragment(R.layout.fragment_first) { ... }

3. Proguard

If there is any problem with Proguard, add below to your app/proguard-rules.pro:

# ViewBindingDelegate uses Reflection.
-keepclassmembers class ** implements androidx.viewbinding.ViewBinding {
    public static ** bind(android.view.View);

    public static ** inflate(android.view.LayoutInflater, android.view.ViewGroup, boolean);

    public static ** inflate(android.view.LayoutInflater, android.view.ViewGroup);
}

4. Throws IllegalStateException: "Attempt to get view binding when fragment view is destroyed" when accessing delegate property in onDestroyView

Since version 1.0.0-alpha03 - Feb 16, 2021, we cannot access ViewBinding delegate property in onDestroyView (this causes many problems). Recommended way is passing a lambda to onDestroyView: (T.() -> Unit)? = null parameter of extension functions, eg.

- private val binding by viewBinding<FragmentFirstBinding>()

+ private val binding by viewBinding<FragmentFirstBinding> { /*this: FragmentFirstBinding*/
+   button.setOnClickListener(null)
+   recyclerView.adapter = null
+ }
 
  override fun onDestroyView() {
    super.onDestroyView()
-   binding.button.setOnClickListener(null)
-   binding.recyclerView.adapter = null
  }

5. Min SDK version

Since version 1.2.0, minSdkVersion has been changed to 14.

License

MIT License

Copyright (c) 2020-2021 Petrus Nguyễn Thái Học