Android access view binding val outside onCreate activity

user_14681023 0
Viewed 2302

I have an activity that has a button. On the button click I want to update text in text view. I want to use ViewBinding instead of the normal findViewById

This is how I created the val binding

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

    val binding = ActivityMainBinding.inflate(layoutInflater);
    setContentView(binding.root)

    binding.btnRoll.setOnClickListener {
        rollDice()
    }
}

Now in rollDice I want to update the text view but I'm not able to access binding which make sense because its scope is limited to onCreate() , so what is the best practice for this?

  private fun rollDice() {
       val random = Random().nextInt(6) + 1
       binding.txt_random.setText("random")
    }
android-viewbinding kotlin android
3 Answers

You have two options.

1. Store in a property

Since the inflated content of Activity is fully bound to it's lifecycle, it's safe to keep the reference as a property

class MainActivity : AppCompatActivity() {
  lateinit var binding: ActivityMainBinding

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    
    binding = ActivityMainBinding.inflate(layoutInflater);
    setContentView(binding.root)

    binding.btnRoll.setOnClickListener {
      rollDice()
    }
  }

  private fun rollDice() {
    val random = Random().nextInt(6) + 1
    binding.txt_random.setText("random")
  }
}

2. Pass the binding to the methods

That's what I usually do, it avoids creating a property where it's not really a necessity

class MainActivity : AppCompatActivity() {

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    
    val binding = ActivityMainBinding.inflate(layoutInflater);
    setContentView(binding.root)

    binding.btnRoll.setOnClickListener {
      rollDice(binding)
    }
  }

  private fun rollDice(binding: ActivityMainBinding) {
    val random = Random().nextInt(6) + 1
    binding.txt_random.setText("random")
  }
}

Both options are valid ways to make the binding visible to Activities methods.

user_42248110

Store the binding in an instance variable on the Activity. Then you have access to it from all the methods in the Activity.

user_21046650

As the question has accepted answer and it is already addressed but here is my approach to the viewBinding

    class MainActivity : AppCompatActivity() {
      private val binding by lazy{
         ActivityMainBinding.inflate(layoutInflater)
       }  
    
      override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(binding.root)
    
        binding.btnRoll.setOnClickListener {
          rollDice()
        }
      }
    
      private fun rollDice() {
        val random = Random().nextInt(6) + 1
        binding.txt_random.setText("random")
      }
    }

I go with lazy initialization of binding so that way it is only intitialized if it is required. More you can read about lazy initialization here https://www.baeldung.com/kotlin/lazy-initialization

user_97838470
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