Question

我们有一个传统的ListView与RecyclerView Adapter和Model类接口。当我们登录Firebase时，我们导航到ListView，ListView中没有加载任何内容。然后我们返回登录活动并重复该过程然后，所有数据都从一个非常简单的DB子节点表列表中加载我们厌倦了Firebase RecyclerAdapter没有运气我们可能有错误的UI或版本。我们的问题是为什么我们需要两次前往列表视图来加载数据？我们将发布ListView代码没有生成错误我们尝试将代码放在OnStart方法中没有运气

        db = FirebaseDatabase.getInstance().getReference();
    dbRef = db.child("Table List");

    dbRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            for (DataSnapshot child : dataSnapshot.getChildren())
                listArrayList.add(child.getValue(String.class));
            sz = listArrayList.size();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

    sz = listArrayList.size();

    if(sz == 0){
        tvNoData.setVisibility(View.VISIBLE);
        tvNoData.setText("No Quiz's Found\n\nClick On Make New Quiz");

        mRecyclerView = findViewById(R.id.recycleview);
        mRecyclerView.setHasFixedSize(true);

        mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        mAdapter = new TableTrackerAdapter(this,listArrayList);
        mRecyclerView.setAdapter(mAdapter);
    }

    if(sz > 0){
        tvNoData.setVisibility(View.INVISIBLE);

        mRecyclerView = findViewById(R.id.recycleview);
        mRecyclerView.setHasFixedSize(true);

        mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        mAdapter = new TableTrackerAdapter(this,listArrayList);
        mRecyclerView.setAdapter(mAdapter);

    }

Answer 1

之所以这样，是因为Firebase数据库是异步的，换句话说，在firebase完成加载数据之前，recyclelerview会填充一个空的arraylist，我之前遇到过类似的问题。

只需将依赖于你的arraylist的所有内容移动到firebase datachange中，问题就会像这样修复。

public void setupRecyclerView(){

    if(sz == 0){
        tvNoData.setVisibility(View.VISIBLE);
        tvNoData.setText("No Quiz's Found\n\nClick On Make New Quiz");

        mRecyclerView = findViewById(R.id.recycleview);
        mRecyclerView.setHasFixedSize(true);

        mLayoutManager = new LinearLayoutManager(MainActivity.this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        mAdapter = new TableTrackerAdapter(MainActivity.this,listArrayList);
        mRecyclerView.setAdapter(mAdapter);
    }

    if(sz > 0){
        tvNoData.setVisibility(View.INVISIBLE);

        mRecyclerView = findViewById(R.id.recycleview);
        mRecyclerView.setHasFixedSize(true);

        mLayoutManager = new LinearLayoutManager(MainActivity.this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        mAdapter = new TableTrackerAdapter(MainActivity.this,listArrayList);
        mRecyclerView.setAdapter(mAdapter);

    }
}

db = FirebaseDatabase.getInstance().getReference();
dbRef = db.child("Table List");
dbRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if(dataSnapshot != null){
            for (DataSnapshot child : dataSnapshot.getChildren()){
                listArrayList.add(child.getValue(String.class));
            }
        sz = listArrayList.size();
        setupRecyclerView();
        }

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

Firebase Recycler View适配器

1 个答案: