How to add like counter Android Studio Firebase

Question

this is the database link 1can anybody help me to add a like counter to this.please please it should display the no:of likes and decease it when like is taken back my java code is below

 private void onLikeClicked(View v) {
    boolean isLiked = !btnLike.isSelected();
    final String currentUserKey = User.currentKey();

    DatabaseReference likes = FirebaseDatabase.getInstance().getReference().child(Const.kDataLikeKey);
    DatabaseReference curLike = likes.child(mPostRef.getKey()).child(currentUserKey).child("liked");

    // update Model
    curLike.setValue(isLiked);

    // update UI
    btnLike.setSelected(isLiked);
}

This increment like count but doesn't decrements it i want it to get decremented when clicked back

Answer 1

Your question is not entirely clear but if you are trying to make a functionality like social media post where users can like and unlike a post the this can help.

Data Structure

Post-> postId -> likes -> 1 
              ...

You can divide it in three parts:

1. To display number of likes for a post , postId & current user, userId1, has liked your post or not

   public void displayNumberOfLikes(String postId, String currentUserId){
       DatabaseReference likesRef = FirebaseDatabase.getInstance().getReference().child('Post').child(postId);
       likesRef.addValueEventListener(new ValueEventListener(){
           @Override
           public void onDataChange(DataSnapshot dataSnapshot) {
               if(dataSnapshot.exists()){
                   long numOfLikes = 0;
                   if(dataSnapshot.hasChild("likes")){
                       numOfLikes = dataSnapshot.child("likes").getValue(Long.class);
                   }
   
                   //Populate numOfLikes on post i.e. textView.setText(""+numOfLikes)
                   //This is to check if the user has liked the post or not
                   btnLike.setSelected(dataSnapshot.hasChild(userId));
               }
           }
   
           @Override
           public void onCancelled(DatabaseError databaseError) {
   
           }
       });
   }
   

2. On Like Clicked

   public void onLikeClicked(View v, String postId, String userId){
       DatabaseReference likesRef = FirebaseDatabase.getInstance().getReference().child('Post').child(postId).child("likes");
       likesRef.addListenerForSingleValueEvent(new ValueEventListener(){
           @Override
           public void onDataChange(DataSnapshot dataSnapshot) {
               long numLikes = 0;
               if(dataSnapshot.exists()){
                   numLikes = dataSnapshot.getValue(Long.class);
               }
               boolean isLiked = btnLike.isSelected();
               if(isLiked){
                  //If already liked then user wants to unlike the post
                  likesRef.set(numLikes-1);
               }else {
                  //If not liked already then user wants to like the post
                  likesRef.set(numLikes+1);
               }
           }
   
           @Override
           public void onCancelled(DatabaseError databaseError) {
   
           }
       });
   }
   

This way you can make your user like and unlike a post and display total number of likes. Hope it helps!