LiveData remove Observer after first callback

by

There is a more convenient solution for Kotlin with extensions:

fun <T> LiveData<T>.observeOnce(lifecycleOwner: LifecycleOwner, observer: Observer<T>) {
    observe(lifecycleOwner, object : Observer<T> {
        override fun onChanged(t: T?) {
            observer.onChanged(t)
            removeObserver(this)
        }
    })
}

This extension permit us to do that:

liveData.observeOnce(this, Observer<Password> {
    if (it != null) {
        // do something
    }
})

So to answer your original question, we can do that:

val livedata = model.getDownloadByContentId(contentId)
livedata.observeOnce((AppCompatActivity) context, Observer<T> {
    if (it != null) {
        DownloadManager.this.downloadManagerListener.onDownloadManagerFailed(null, "this item already exists");
    }
    startDownload();
})

The original source is here: https://code.luasoftware.com/tutorials/android/android-livedata-observe-once-only-kotlin/

Update: @Hakem-Zaied is right, we need to use observe instead of observeForever.

More Related Contents:

  1. Room – LiveData observer does not trigger when database is updated
  2. Room : LiveData from Dao will trigger Observer.onChanged on every Update, even if the LiveData value has no change
  3. How to combine two live data one after the other?
  4. Android Room – simple select query – Cannot access database on the main thread
  5. Android Persistence room: “Cannot figure out how to read this field from a cursor”
  6. LiveData update on object field change
  7. Android Room: Insert relation entities using Room
  8. Notify Observer when item is added to List of LiveData
  9. LiveData prevent receive the last value when start observing
  10. Room Persistence: Error:Entities and Pojos must have a usable public constructor
  11. How to use Room Persistence Library with pre-populated database?
  12. Android Room – Get the id of new inserted row with auto-generate
  13. Android room persistent library – TypeConverter error of error: Cannot figure out how to save field to database”
  14. Difference of setValue() & postValue() in MutableLiveData
  15. How to dynamically query the room database at runtime?
  16. Why there’s a separate MutableLiveData subclass of LiveData?
  17. Android room persistent library – how to insert class that has a List object field
  18. Android Room – Select query with LIKE
  19. How can I represent a “many to many” relation with Android Room when column names are same?
  20. How to populate Android Room database table on first run?
  21. Room cannot verify the data integrity
  22. Return type for Android Room joins
  23. How to get rid of Incremental annotation processing requested warning?
  24. How to save enum field in the database room?
  25. How insert image in room persistence library?
  26. How to make primary key as autoincrement for Room Persistence lib
  27. Why LiveData observer is being triggered twice for a newly attached observer
  28. Observe LiveData from foreground service
  29. Backup Room database
  30. LinearLayout height in onCreate is 0

Leave a Comment