java - 无法从 Firebase 检索信息到自定义 ListView Android

Question

我是 Android Studio 新手。我正在尝试开发库存管理应用程序，但无法在来自 Firebase 数据库的自定义 ListView 中显示信息。我在这里找到了类似的问题和解决方案，但对我不起作用。下面是 AccountHome(MainActivity) 的代码。当我多次关闭并重新启动应用程序时，此代码有时会起作用。希望得到一些可行的解决方案。谢谢Screenshot of Firebase Database

public class AccountHom extends AppCompatActivity {

    ListView listview;
    FirebaseDatabase database;
    DatabaseReference myRef;
    ArrayList<String> dept ;
    ArrayList<Long> total;
    AccountSetBudgetHelper accountSetBudgetHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.account_home_activity);

        accountSetBudgetHelper = new AccountSetBudgetHelper();
        listview = findViewById(R.id.set_budget_listview);
        database = FirebaseDatabase.getInstance();
        myRef = database.getReference("budget");
        dept = new ArrayList<>();
        total = new ArrayList<Long>();

        AccountSetBudgetAdaptr accountSetBudgetAdapter = new AccountSetBudgetAdaptr(AccountHom.this ,dept,total);

        myRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    accountSetBudgetHelper = ds.getValue(AccountSetBudgetHelper.class);
                    dept.add(accountSetBudgetHelper.getName());
                    total.add(accountSetBudgetHelper.getTotal());
                } }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });
        listview.setAdapter(accountSetBudgetAdapter);
    }
}
class AccountSetBudgetAdaptr extends ArrayAdapter {
    private final Activity context;
    private final ArrayList<String> dept;
    private final ArrayList<Long> total;

    AccountSetBudgetAdaptr(Activity context, ArrayList<String> dept, ArrayList<Long> total) {
        super(context, R.layout.single_row_listview_budget,dept);
        this.context = context;
        this.dept = dept;
        this.total = total;
    }
    @NonNull
    @Override
    public View getView(int position, View view, @NonNull ViewGroup parent) {

        Toast.makeText(getContext(), "this is a boy", Toast.LENGTH_SHORT).show();
        View rowView = view;
        if(rowView==null){
            LayoutInflater inflater = context.getLayoutInflater();
            rowView = inflater.inflate(R.layout.single_row_listview_budget, parent, false);
        }
        TextView mdept = rowView.findViewById(R.id.textView_setbudget_dept);
        TextView mtotal = rowView.findViewById(R.id.textView_setbudget_total);
        mdept.setText(dept.get(position));
        mtotal.setText(String.valueOf(total.get(position)));
        return rowView;
    }
}
class AccountSetBudgetHelpr {
    private String name;
    private Long total;
    public AccountSetBudgetHelpr() {
    }
    public AccountSetBudgetHelpr(String name, Long total) {
        this.name = name;
        this.total = total;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Long getTotal() {
        return total;
    }
    public void setTotal(Long total) {
        this.total = total;
    }
}[enter image description here][1]

Answer 1

您正在向两个列表添加数据，dept 和 total 但您没有将新数据通知适配器。因此，要解决此问题，请在 for 循环结束后立即添加以下代码行:

myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot ds : dataSnapshot.getChildren()) {
            accountSetBudgetHelper = ds.getValue(AccountSetBudgetHelper.class);
            dept.add(accountSetBudgetHelper.getName());
            total.add(accountSetBudgetHelper.getTotal());
        }
        accountSetBudgetAdapter.notifyDataSetChanged(); //Notify the adapter
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {}
});