java - 如何在具有动态下拉列表的Android中制作表单

Question

我是 android 的新手，我正在 android 中制作一个表单。我希望此表单有 2 个下拉列表。在第一个下拉列表中，用户必须选择州，第二个下拉列表应仅显示该州的城市，用户可以从中选择任何城市/地区。

Answer 1

首先，您需要创建 2 个不同的模型，如下所示:

像下面这样创建城市和州数据模型:

public class State{
    private int id;
    private String name;

    public State(int id, String name){
       this.id=id;
       this.name=name;
    }

    public int getId(){
       return id;
    }

    public void setId(int id){
       this.id= id;
    }
    public String getName(){
       return name;
    }

    public void setName(String name){
       this.name=name;
    }

}


public class City{
    private int id;
    private String name;
    private int stateId;

    public State(int id, String name, int stateId){
       this.id=id;
       this.name=name;
       this.stateId=stateId;
    }

    public int getId(){
       return id;
    }

    public void setId(int id){
       this.id= id;
    }
    public String getName(){
       return name;
    }

    public void setName(String name){
       this.name=name;
    }

    public int getStateId(){
       return stateId;
    }

    public void setStateId(int id){
       this.stateId= id;
    }

}

现在您需要为 State 创建 Custom Spinner 适配器:

public class StateSpinnerAdapter extends ArrayAdapter<State> {

    public StateSpinnerAdapter (Context context, ArrayList<State> dataList) {
        super(context, 0, dataList);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return initView(position, convertView, parent);
    }

    @Override
    public View getDropDownView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return initView(position, convertView, parent);
    }

    private View initView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(
                    R.layout.spinner_row, parent, false
            );
        }
        TextView textViewName = convertView.findViewById(R.id.tv_name);
        District currentItem = getItem(position);
        if (currentItem != null) {
            textViewName.setText(currentItem.getName());
        }
        return convertView;
    }
}

现在您需要制作如下所示的 CitySpinnerAdapter:

public class CitySpinnerAdapter extends ArrayAdapter<City> {

    public CitySpinnerAdapter (Context context, ArrayList<City> dataList) {
        super(context, 0, dataList);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return initView(position, convertView, parent);
    }

    @Override
    public View getDropDownView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return initView(position, convertView, parent);
    }

    private View initView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(
                    R.layout.spinner_row, parent, false
            );
        }
        TextView textViewName = convertView.findViewById(R.id.tv_name);
        Upazila currentItem = getItem(position);
        if (currentItem != null) {
            textViewName.setText(currentItem.getName());
        }
        return convertView;
    }
}

现在 MainActivity 应该是这样的:

public class MainActivity extends AppCompatActivity{

    private Context mContext;
    private Activity mActivity;
    private ArrayList<State> states;
    private ArrayList<City> cities;

    private StateSpinnerAdapter stateAdapter;
    private CitySpinnerAdapter cityAdapter;

   private Spinner spState, spCity;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initVariable();
        initView();
        initListener();
    }

    private void initVariable() {
        mContext = getApplicationContext();
        mActivity = MainActivity.this;


        states = new ArrayList<>();
        cities = new ArrayList<>();
    }
    private void initView() {
        setContentView(R.layout.activity_main);
        spState = findViewById(R.id.spState);
        spCity = findViewById(R.id.cityState);

        stateAdapter = new StateSpinnerAdapter(mContext,states);
        spState.setAdapter(stateAdapter);

        cityAdapter = new CitySpinnerAdapter(mContext,cities);
        spCity.setAdapter(cityAdapter);

        loadStateData();

    }

    private void initListener(){
        spState.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                loadCityData(states.get(i).getId());
            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {

            }
        });


    }

    private void loadStateData(){
       states.add(new State(1,"state 1"));
       states.add(new State(2,"state 1"));
       states.add(new State(3,"state 1"));
       states.add(new State(4,"state 1"));
       stateAdapter.notifyDataSetChanged();

    }

    private loadCityData(int stateId){
       ArrayList<City> cityList= new ArrayList<>();
       cityList.add(new City(1,"City 1", 1));
       cityList.add(new City(2,"City 2", 1));
       cityList.add(new City(3,"City 3", 2));
       cityList.add(new City(4,"City 4", 2));
       cityList.add(new City(5,"City 5", 3));
       cityList.add(new City(6,"City 6", 3));
       cityList.add(new City(7,"City 7", 4));
       cityList.add(new City(8,"City 8", 4));

       cities.addAll(cityList.stream().filter(city -> city.getStateId == stateId).collect(Collectors.toList()));
       cityAdapter.notifyDataSetChanged();

    }

}