LifecycleOwner implemented RecyclerView ViewHolder & Adapter (concept design)

HowToUseActivity.kt

import android.os.Bundle
import android.util.Log
import android.view.ViewGroup
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleObserver
import androidx.lifecycle.OnLifecycleEvent
import app.keima.android.recyclerviewsandbox.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main)

        binding.recyclerView.apply {
            adapter = MyAdapter(
                arrayOf(
                    "A", "B", "C", "D",
                    "A", "B", "C", "D",
                    "A", "B", "C", "D",
                    "A", "B", "C", "D"
                )
            )
        }
    }
}

class MyAdapter(private val dataset: Array<String>) :
    LifecycleRecyclerAdapter<MyAdapter.MyViewHolder>() {

    class MyViewHolder(private val textView: TextView) : LifecycleViewHolder(textView) {
        private val observer = MyObserver()

        init {
            lifecycle.addObserver(observer)
        }

        fun bindData(data: String) {
            textView.text = data
            observer.data = data
        }
    }

    class MyObserver() : LifecycleObserver {
        var data: String = "?"

        @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
        fun onCreate() {
            Log.d("MyObserver", "appear: $data")
        }

        @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
        fun onDestroy() {
            Log.d("MyObserver", "disappear: $data")
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        return MyViewHolder(TextView(parent.context).apply {
            setPadding(8, 40, 8, 40)
        })
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        holder.bindData("${dataset[position]} $position")
    }

    override fun getItemCount() = dataset.size

}

Licenses.md

This gist snippet is Public Domain.

LifecycleRecyclerAdapter.kt

import androidx.recyclerview.widget.RecyclerView

abstract class LifecycleRecyclerAdapter<T : LifecycleViewHolder> : RecyclerView.Adapter<T>() {

  override fun onViewAttachedToWindow(holder: T) {
    super.onViewAttachedToWindow(holder)
    holder.onAppear()
  }

  override fun onViewDetachedFromWindow(holder: T) {
    super.onViewDetachedFromWindow(holder)
    holder.onDisappear()
  }

}

LifecycleViewHolder.kt

import android.view.View
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LifecycleRegistry
import androidx.recyclerview.widget.RecyclerView

abstract class LifecycleViewHolder(itemView: View) :
    RecyclerView.ViewHolder(itemView), LifecycleOwner {

    private val lifecycleRegistry = LifecycleRegistry(this)

    init {
        lifecycleRegistry.currentState = Lifecycle.State.INITIALIZED
    }

    fun onAppear() {
        lifecycleRegistry.currentState = Lifecycle.State.CREATED
    }

    fun onDisappear() {
        lifecycleRegistry.currentState = Lifecycle.State.DESTROYED
    }

    override fun getLifecycle(): Lifecycle {
        return lifecycleRegistry
    }

}

I'm implementing something very close to this but I'm having a nasty bug. Sometimes my row gets attached to the new data before detaching from the old one, causing wrong data to display or bad data to flicker before settling. Have you experienced this?

onAppear should also call
lifecycleRegistry.markState(Lifecycle.State.STARTED)

also markState is deprecated now, and currentState should be used :)

thanks for sharing though

onAppear should also call
lifecycleRegistry.markState(Lifecycle.State.STARTED)

also markState is deprecated now, and currentState should be used :)

thanks for sharing though

yes, markState is deprecated. write onAppear() and onDisappear() as

fun onAppear() {
    lifecycleRegistry.currentState = Lifecycle.State.CREATED
  }

  fun onDisappear() {
    lifecycleRegistry.currentState = Lifecycle.State.DESTROYED
  }

i've added it to my recyclerview adapter library: https://github.com/kibotu/RecyclerViewPresenter/blob/master/lib/src/main/java/net/kibotu/android/recyclerviewpresenter/LifecycleViewHolder.kt#L13-L34

2019/10/24 Updated.

• Migrate AndroidX

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.core:core-ktx:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'androidx.recyclerview:recyclerview:1.0.0'

    def lifecycle_version = "2.1.0"
    implementation "androidx.lifecycle:lifecycle-runtime:$lifecycle_version"
    kapt "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"

Hi I try this。 But if you destroyed the lifecycleRegister , the reuse viewholder's lifcyclRegistery will never send event to liveData anymore. It will lose some status. What can i do fix it? Help thanks

Hi I try this。 But if you destroyed the lifecycleRegister , the reuse viewholder's lifcyclRegistery will never send event to liveData anymore. It will lose some status. What can i do fix it? Help thanks

init {
lifecycleRegistry.currentState = Lifecycle.State.INITIALIZED
lifecycleRegistry.currentState = Lifecycle.State.CREATED
}

fun onAppear() {
    lifecycleRegistry.currentState = Lifecycle.State.STARTED
    lifecycleRegistry.currentState = Lifecycle.State.RESUMED
}

fun onDisappear() {
    lifecycleRegistry.currentState = Lifecycle.State.STARTED
    lifecycleRegistry.currentState = Lifecycle.State.CREATED
}

fun Destroy()
{
lifecycleRegistry.currentState = Lifecycle.State. DESTROYED
}

ans call this destroy method when you are going out of screen means this method should be observed from parent lifecycle(recyclerview lifecycle), so when you are changing the screen or exiting from app.

Hi I try this。 But if you destroyed the lifecycleRegister , the reuse viewholder's lifcyclRegistery will never send event to liveData anymore. It will lose some status. What can i do fix it? Help thanks

init {
lifecycleRegistry.currentState = Lifecycle.State.INITIALIZED
lifecycleRegistry.currentState = Lifecycle.State.CREATED
}

fun onAppear() {
    lifecycleRegistry.currentState = Lifecycle.State.STARTED
    lifecycleRegistry.currentState = Lifecycle.State.RESUMED
}

fun onDisappear() {
    lifecycleRegistry.currentState = Lifecycle.State.STARTED
    lifecycleRegistry.currentState = Lifecycle.State.CREATED
}

fun Destroy()
{
lifecycleRegistry.currentState = Lifecycle.State. DESTROYED
}

ans call this destroy method when you are going out of screen means this method should be observed from parent lifecycle(recyclerview lifecycle), so when you are changing the screen or exiting from app.

Hi @abhinavjiit, I am trying to implement this. Would you mind giving us a light about how to properly call that destroy() method? I am out of ideas on how to do it...

Also asked on SO: https://stackoverflow.com/questions/68829954/how-to-implement-lifecycleowner-on-a-recycleradapter-viewholder

@jonathansds, this is my repo you can see there https://github.com/abhinavjiit/baseRecyclerview/blob/master/app/src/main/java/com/example/pristencare/adapter/RecyclerViewImageAdapter.kt

Also asked on SO: https://stackoverflow.com/questions/68829954/how-to-implement-lifecycleowner-on-a-recycleradapter-viewholder

i have replied you in stack overflow as well

@jonathands, this is my repo you can see there https://github.com/abhinavjiit/baseRecyclerview/blob/master/app/src/main/java/com/example/pristencare/adapter/RecyclerViewImageAdapter.kt

Amazing! I will have a look at it now, try to implement and run Leakcanary! Thanks a lot!!

@jonathansds, this is my repo you can see there https://github.com/abhinavjiit/baseRecyclerview/blob/master/app/src/main/java/com/example/pristencare/adapter/RecyclerViewImageAdapter.kt

Amazing! I will have a look at it now, try to implement and run Leakcanary! Thanks a lot!!

if you got something wrong or any memory leak, plz let me know as well

@jonathands, this is my repo you can see there https://github.com/abhinavjiit/baseRecyclerview/blob/master/app/src/main/java/com/example/pristencare/adapter/RecyclerViewImageAdapter.kt

Amazing! I will have a look at it now, try to implement and run Leakcanary! Thanks a lot!!

if you got something wrong or any memory leak, plz let me know as well

Sure! I am implementing it now. Might take a lil bit because I want to fully understand the logic behind it but I should be able to fully test it today :)

@jonathands, this is my repo you can see there https://github.com/abhinavjiit/baseRecyclerview/blob/master/app/src/main/java/com/example/pristencare/adapter/RecyclerViewImageAdapter.kt

could you fix your mention so I don't get the notifications?

@abhinavjiit It's working like a charm! No memory leaks, no excess of objects allocated... It's just perfectly working! Well done!

@abhinavjiit It's working like a charm! No memory leaks, no excess of objects allocated... It's just perfectly working! Well done!

@jonathansds Cool bro.

@abhinavjiit
Hi! - I think there is possibly something wrong: RecyclerView.getChildCount and RecyclerView.getChildAt only return visible items.

My implementation

class SimpleLifeCycleOwnerImpl : SimpleLifeCycleOwner {
    private var lifecycleRegistry: LifecycleRegistry? = null

    override fun getLifecycle() =
        lifecycleRegistry ?: run {
            initialize()
            lifecycleRegistry!!
        }

    override fun initialize() {
        // The object can be revived, create a new lifecycle
        lifecycleRegistry?.run {
            if (currentState != Lifecycle.State.DESTROYED)
                throw IllegalStateException("can be revived only after destroyed, get $currentState")
        }
        lifecycleRegistry = LifecycleRegistry(this)
    }

    override fun handleLifecycleEvent(event: Lifecycle.Event) {
        lifecycleRegistry!!.handleLifecycleEvent(event)
    }
}

// kotlin cannot inherit from type parameter like C++, we must use this class as base
// otherwise we need to copy the code for each adapter
abstract class LifecycleAdapter<VH : RecyclerView.ViewHolder>(lifecycleOwner: LifecycleOwner) :
    RecyclerView.Adapter<VH>() {
    private var recyclerView: RecyclerView? = null

    init {
        val observer = object : LifecycleEventObserver {
            private fun visibleChildApply(block: SimpleLifeCycleOwner.() -> Unit) =
                recyclerView?.run {
                    for (i in 0 until childCount)
                        getChildAt(i)?.let {
                            (getChildViewHolder(it) as? SimpleLifeCycleOwner)?.block()
                        }
                } ?: Unit

            private fun allChildApply(block: SimpleLifeCycleOwner.() -> Unit) =
                recyclerView?.run {
                    for (i in 0 until itemCount)
                        (findViewHolderForAdapterPosition(i) as? SimpleLifeCycleOwner)?.block()
                } ?: Unit

            override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) =
                when (event) {
                    Lifecycle.Event.ON_DESTROY -> allChildApply { handleLifecycleEvent(event) }
                    else -> visibleChildApply { handleLifecycleEvent(event) }
                }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
    }

    override fun onAttachedToRecyclerView(recyclerView: RecyclerView) {
        if (this.recyclerView != null)
            throw IllegalStateException("can be attached to only one RecyclerView")
        this.recyclerView = recyclerView
    }

    override fun onDetachedFromRecyclerView(recyclerView: RecyclerView) {
        throw IllegalStateException("must not be detached")
    }

    override fun onViewAttachedToWindow(holder: VH) =
        (holder as? SimpleLifeCycleOwner)?.run {
            handleLifecycleEvent(Lifecycle.Event.ON_START)
            handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
        } ?: Unit

    override fun onViewDetachedFromWindow(holder: VH) =
        (holder as? SimpleLifeCycleOwner)?.run {
            handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
            handleLifecycleEvent(Lifecycle.Event.ON_STOP)
        } ?: Unit

    override fun onBindViewHolder(holder: VH, position: Int) =
        (holder as? SimpleLifeCycleOwner)?.run {
            initialize()
            handleLifecycleEvent(Lifecycle.Event.ON_CREATE)
            // logical views are created here
        } :? Unit

    override fun onViewRecycled(holder: VH) =
        (holder as? SimpleLifeCycleOwner)?.run {
            handleLifecycleEvent(Lifecycle.Event.ON_DESTROY)
        } ?: Unit
}

It will cause memory leak, when RecyclerView detach from window, the onViewDetachedFromWindow callback will not invoked.