« Create your own LiveData implementation

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1package com.anish.createlivedatafromscratch
2
3import androidx.lifecycle.Lifecycle
4import androidx.lifecycle.LifecycleObserver
5import androidx.lifecycle.LifecycleOwner
6import androidx.lifecycle.OnLifecycleEvent
7
8class MyOwnLiveData<T> {
9
10    private var dataHolder: T? = null
11    private val hashMapOfObservers: HashMap<(T?) -> Unit, LifeCycleObserverWrapper> = HashMap()
12
13    fun postValue(value: T) {
14        dataHolder = value
15        hashMapOfObservers.values.forEach {
16            if (it.lifecycleOwner.lifecycle.currentState.isAtLeast(Lifecycle.State.STARTED)) {
17                it.observer.invoke(dataHolder)
18            }
19        }
20    }
21
22    fun getValue() = dataHolder
23
24    fun addObserver(lifecycleOwner: LifecycleOwner, observer: (T?) -> Unit) {
25        LifeCycleObserverWrapper(lifecycleOwner, observer).apply {
26            this.lifecycleOwner.lifecycle.addObserver(this)
27            hashMapOfObservers[observer] = this
28        }
29
30    }
31
32    fun removeObserver(observer: (T?) -> Unit) {
33        hashMapOfObservers[observer]?.run {
34            this.lifecycleOwner.lifecycle.removeObserver(this)
35        }
36    }
37
38    fun updateValue(observer: (T?) -> Unit) {
39        observer.invoke(dataHolder)
40    }
41
42    private inner class LifeCycleObserverWrapper(
43        val lifecycleOwner: LifecycleOwner, val observer: (T?) -> Unit
44    ) : LifecycleObserver {
45
46        @OnLifecycleEvent(Lifecycle.Event.ON_START)
47        fun doOnStart() {
48            updateValue(observer)
49        }
50
51        @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
52        fun doOnResume() {
53            updateValue(observer)
54        }
55
56        @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
57        fun doOnDestroy() {
58            removeObserver(observer)
59        }
60    }
61}

For full code please refer:

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1https://github.com/anishakd4/CreateLiveDataFromScratch