kevivforever

class DoubleLiveData<A, B>(a: LiveData<A>, b: LiveData<B>) : MediatorLiveData<Pair<A?, B?>>() {
    init {
        addSource(a) { value = it to b.value }
        addSource(b) { value = a.value to it }
    }
}

kevivforever

Creating observables

create() - Observable.create()
just() -  Observable.just("first", "second", "third", "fourth", "fifth", "sixth",
          "seventh", "eighth", "ninth", "tenth")
          .subscribeOn(Schedulers.io()) // What thread to do the work on
          .observeOn(AndroidSchedulers.mainThread())
range() - Observable.range(0,11)
repeat() - Observable.range(0,3)
        .repeat(2)

kevivforever

lambda expressions can’t have a return statement. The return type is either inferred from the variable which stores 
the lambda or from the last statement of the lambda body. Another missing thing is multiple return points you might 
often need. 

// 1
private fun isValidArtist(artist: String?): Boolean {
  // 2
  val artistValidator = fun(value: String?): Boolean {
  // 3
  if (value.isNullOrEmpty()) {

kevivforever

async function addInterestedCategories(uid, categories) {
    await User.findOneAndUpdate({ uid: uid },
        { $addToSet: { interested_categories: categories } }, { new: true}).exec()
}

exports.getPost = async (req, res, next) => {
    const postUpdate = await Post.findOneAndUpdate({ postID: req.params.postid
                                            , viewedBy: { $not: { $elemMatch: { uid: req.query.uid } } }
                                        },
                                            { $addToSet: { viewedBy: USER }, $inc: { totalViews: 1} }, { new: true })

kevivforever

private fun setTags(tagList: List<Tag>) {

       tagList.forEachIndexed { index, tag ->

           val chipView = getChipView().apply {
               configureChip(index, tag)
           }

           chipView.setOnCheckedChangeListener { chip, isChecked ->
               //resId is basically a index of a tag in passed tagList

kevivforever

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/user_Profile_appbarlayout"
        android:layout_width="match_parent"

kevivforever

class PagerAdapter(fragmentManager: FragmentManager) : FragmentStatePagerAdapter(fragmentManager) {

    // Returns total number of pages
    override fun getCount(): Int {
        return NUM_ITEMS
    }

    // Returns the fragment to display for that page
    override fun getItem(position: Int): Fragment? {
        when (position) {

kevivforever

public class Divider extends RecyclerView.ItemDecoration {

    private Drawable mDivider;
    private int mOrientation;

    public Divider(Context context, int orientation) {
        mDivider = ContextCompat.getDrawable(context, R.drawable.divider);
        if (orientation != LinearLayoutManager.VERTICAL) {
            throw new IllegalArgumentException("This Item Decoration can be used only with a RecyclerView that uses a LinearLayoutManager with vertical orientation");
        }

kevivforever

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">

    <solid
        android:color="@color/colorGreyIcon"/>

    <size
        android:width="60dp"

kevivforever

//Read data change on your ref
exports.functionname = functions.database.ref('/Items/{itemid}')
    .onWrite(event => {
        const item = event.data.val();
        // read data once from second node
        const locationRef = event.data.adminRef.root.child('location').child(event.params.itemid);
        locationRef.once('value').then(snapshot =>{
            const location = snapshot.val();
            const city = location.city;
            // data node where you want to write data