java - 如何实时修改View-pager

Question

我是 Android 新手。我创建了一个 View 寻呼机，它从 firebase 获取图像。并且运行良好。但该 View 寻呼机有一些漏洞我未能解决。

1) 我的 View 寻呼机没有实时更新。意味着当我修改 firebase 中的图像时。它不会影响实时。我必须关闭我的应用程序，然后必须再次启动它才能看到这些更新。

2) 当我从 firebase 列表中删除项目时。我的应用程序崩溃了，在 Logcat 中抛出了这个异常。

java.lang.IndexOutOfBoundsException: Index: -1, Size: 5
    at java.util.ArrayList.add(ArrayList.java:483)
    at com.release.pack.lootbox.Fragments.HomeFragment$7.onEvent(HomeFragment.java:294)
    at com.release.pack.lootbox.Fragments.HomeFragment$7.onEvent(HomeFragment.java:281)

这是我的代码:

slider 图像适配器:

public class SliderImageAdapter extends SliderViewAdapter<SliderImageAdapter.SliderAdapterVH> {

    public List<Banner> bannerList;
    public Context context;

    public SliderImageAdapter(Context context, List<Banner> bannerList) {

        this.bannerList = bannerList;
        this.context = context;

    }

    @Override
    public SliderAdapterVH onCreateViewHolder(ViewGroup parent) {
        View inflate = LayoutInflater.from(parent.getContext()).inflate(R.layout.image_slider_myshop, parent, false);
        return new SliderAdapterVH(inflate);
    }

    @Override
    public void onBindViewHolder(final SliderAdapterVH viewHolder, final int position) {


        Glide.with(viewHolder.itemView)
                .load(bannerList.get(position).getmSliderImage())
                .fitCenter()
                .into(viewHolder.imageViewBackground);
    }

    @Override
    public int getCount() {
        return bannerList.size();
    }


    class SliderAdapterVH extends SliderViewAdapter.ViewHolder {

        View itemView;
        ImageView imageViewBackground;
        ImageView imageGifContainer;
        TextView textViewDescription;
        public ProgressBar progressBar;
        public ImageView imageViewFailed;

        public SliderAdapterVH(View itemView) {
            super(itemView);
            imageViewBackground = itemView.findViewById(R.id.iv_auto_image_slider);
            imageGifContainer = itemView.findViewById(R.id.iv_gif_container);
            textViewDescription = itemView.findViewById(R.id.tv_auto_image_slider);
            progressBar = itemView.findViewById(R.id.featured_deal_progress);
            imageViewFailed = itemView.findViewById(R.id.featured_deal_img_failed_to_load);

            this.itemView = itemView;
        }
    }
}

首页 fragment :

private SliderImageAdapter sliderImageAdapter;
    private List<Banner> bannerList;

bannerList = new ArrayList<>();
        sliderImageAdapter = new SliderImageAdapter(getActivity(),bannerList);

sliderMyshop = view.findViewById(R.id.imageSlider);
        sliderMyshop.setSliderAdapter(sliderImageAdapter);
        sliderMyshop.setIndicatorAnimation(IndicatorAnimations.WORM); //set indicator animation by using SliderLayout.IndicatorAnimations. :WORM or THIN_WORM or COLOR or DROP or FILL or NONE or SCALE or SCALE_DOWN or SLIDE and SWAP!!
        sliderMyshop.setSliderTransformAnimation(SliderAnimations.SIMPLETRANSFORMATION);
        sliderMyshop.setIndicatorSelectedColor(Color.WHITE);
        sliderMyshop.setIndicatorUnselectedColor(Color.GRAY);
        sliderMyshop.startAutoCycle();



    mFirestore.collection("Banner").orderBy("priority", Query.Direction.DESCENDING).addSnapshotListener(new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(@javax.annotation.Nullable QuerySnapshot documentSnapshots, @javax.annotation.Nullable FirebaseFirestoreException e) {
                if (e != null) {
                    Log.d(TAG, "Error : " + e.getMessage());
                }
                assert documentSnapshots != null;

                for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {

                    if (doc.getType() == DocumentChange.Type.ADDED) {
                        String doc_id = doc.getDocument().getId();
                        Banner banner = doc.getDocument().toObject(Banner.class).withDocId(doc_id);
                        bannerList.add(doc.getNewIndex(), banner);
                        sliderImageAdapter.notifyDataSetChanged();

                    } else if (doc.getType() == DocumentChange.Type.MODIFIED) {
                        String docID = doc.getDocument().getId();
                        Banner changedModel = doc.getDocument().toObject(Banner.class).withDocId(docID);
                        if (doc.getOldIndex() == doc.getNewIndex()) {
                            // Item changed but remained in same position
                            bannerList.set(doc.getOldIndex(), changedModel);
//                            sliderImageAdapter.notifyItemChanged(doc.getOldIndex());
                        } else {
                            // Item changed and changed position
                            bannerList.remove(doc.getOldIndex());
                            bannerList.add(doc.getNewIndex(), changedModel);
//                            sliderImageAdapter.notifyItemMoved(doc.getOldIndex(), doc.getNewIndex());
                        }
                    } else if (doc.getType() == DocumentChange.Type.REMOVED) {
                        // remove
                        bannerList.remove(doc.getOldIndex());
//                        sliderImageAdapter.notifyItemRemoved(doc.getOldIndex());
                    }
                }
            }
        });

当我在 firebase 中添加新图像时，它会实时更新。但当我修改图像时则不然。或从我的列表中删除该项目。

Answer 1

Getting crashed

bannerList.add(doc.getNewIndex(), banner);

这一行是IndexOutOfBoundsException的原因。

(java.lang.IndexOutOfBoundsException: Index: -1, Size: 5)

doc.getNewIndex() 返回-1。并且 list 不能接受 -1 作为索引。所以请检查您的 doc.getNewIndex()。

For realtime update

bannerList.clear();

在 for 循环之前添加此代码，否则将添加冗余数据，并且您无法更新新的更改。

参见this :每次查询结果发生更改(即添加、删除或修改文档时)，快照处理程序都会收到新的查询快照。

for every changes whole collection will be fetched