Room : LiveData from Dao will trigger Observer.onChanged on every Update, even if the LiveData value has no change

Question

I found that the LiveData returned by Dao will call its observer whenever the row is updated in DB, even if the LiveData value is obviously not changed.

Consider a s

Answer 1

This situation is known as false positive notification of observer. Please check point number 7 mentioned in the link to avoid such issue.

Below example is written in kotlin but you can use its java version to get it work.

fun  LiveData.getDistinct(): LiveData {
    val distinctLiveData = MediatorLiveData()
    distinctLiveData.addSource(this, object : Observer {
        private var initialized = false
        private var lastObj: T? = null
        override fun onChanged(obj: T?) {
            if (!initialized) {
                initialized = true
                lastObj = obj
                distinctLiveData.postValue(lastObj)
            } else if ((obj == null && lastObj != null) 
                       || obj != lastObj) {
                lastObj = obj
                distinctLiveData.postValue(lastObj)
            }
        }
    })
    return distinctLiveData
}