java - 改变图像颜色

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

Using context in a fragment (31 个回答)

已关闭 5 年前。

我目前正在尝试更改 ImageView 的颜色。我正在尝试从一个 fragment 中执行此操作，并且在我切换 Activity 之前它工作正常。当我返回到用于更改图像颜色的 fragment 时，出现此错误，

Attempt to invoke virtual method 'int android.content.Context.getColor(int)' on a null object reference

我使用以下代码来更改图像的颜色，

imgUpvote.setColorFilter(ContextCompat.getColor(getContext(), R.color.lGrey));

有人知道解决方法吗？仅当我切换 Activity 时才会出现此错误，感谢您的回答。

编辑:这里是代码所在的位置，

firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<postsGetInfo, postsGetInfoViewHolder>(postsGetInfo.class, R.layout.posts_layout,postsGetInfoViewHolder.class,postRef) {
                @Override
                protected void populateViewHolder(final postsGetInfoViewHolder viewHolder, postsGetInfo model, int position) {
                    final String postKey = getRef(position).getKey();
                    UpdateTheDisplayVotes(postKey); //Displays the votes at the start of creation
                    postRef.removeEventListener(VoteListener);

                    defaultVote = VotesRef.addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            if (!dataSnapshot.hasChild(postKey)) {
                                VotesRef.child(postKey).child(current_user_id).child("votes").setValue("none");
                            }
                            String voteStatus = dataSnapshot.child(postKey).child(current_user_id).child("votes").getValue().toString();
                           if (voteStatus.equals("upvoted")){
                                ImageView btnUpvote = viewHolder.myView.findViewById(R.id.imgUpvote);
                                ImageView btnDownvote = viewHolder.myView.findViewById(R.id.imgDownvote);
                               btnUpvote.setColorFilter(ContextCompat.getColor(getActivity(), R.color.lBlue));
                                btnDownvote.setColorFilter(ContextCompat.getColor(getActivity(), R.color.lGrey));
                            }if (voteStatus.equals("downvoted")){
                                ImageView btnUpvote = viewHolder.myView.findViewById(R.id.imgUpvote);
                                ImageView btnDownvote = viewHolder.myView.findViewById(R.id.imgDownvote);
                                btnUpvote.setColorFilter(ContextCompat.getColor(getActivity(), R.color.lGrey));
                                btnDownvote.setColorFilter(ContextCompat.getColor(getActivity(), R.color.Black));
                            }if (voteStatus.equals("none")){
                                ImageView btnUpvote = viewHolder.myView.findViewById(R.id.imgUpvote);
                                ImageView btnDownvote = viewHolder.myView.findViewById(R.id.imgDownvote);
                                btnUpvote.setColorFilter(ContextCompat.getColor(getActivity(), R.color.lGrey));
                                btnDownvote.setColorFilter(ContextCompat.getColor(getActivity(), R.color.lGrey));
                            }
                        }

Answer 1

尝试在您的 fragment 中获取Context，如下所示

public class BlankFragment extends Fragment {


    public BlankFragment() {

    }

    Context mContext;

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        mContext = context;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment


        return inflater.inflate(R.layout.fragment_blank, container, false);
    }

}

而不是像这样使用

kimgUpvote.setColorFilter(ContextCompat.getColor(mContext, R.color.lGrey));