选择其他父微调器时微调器项目未设置为默认值

Question

我是 android 编程的新手。这可能是一个愚蠢的问题。 我制作了 2 个微调器项目。选择第一个微调器时，第二个微调器项目视图不会在第一次刷新。但是第二个微调器的内容显示正确！

public class SpinnerActivity extends AppCompatActivity {
    Spinner spinner,spinner1;
    TextView textView;
    String jsonString=null;
    JSONObject jsonObject;
    ArrayList<String> countries;
    ArrayList<String> cities;
    ArrayAdapter arrayAdapter;
    ArrayAdapter arrayAdapter1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_spinner);

        textView=findViewById(R.id.textView5);
        spinner=findViewById(R.id.spinner);
        spinner1=findViewById(R.id.spinner1);

        countries=new ArrayList<>();
        cities=new ArrayList<>();

        jsonString=getStringFromJsonFile();

        arrayAdapter=getCountryFromJson();
        spinner.setAdapter(arrayAdapter);
        spinner.setPrompt("Select Country");

        arrayAdapter1=getCityFromCountry("Afghanistan");
        spinner1.setAdapter(arrayAdapter1);
        spinner1.setPrompt("Select City");

        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                arrayAdapter1=getCityFromCountry(countries.get(position));
                textView.setText(cities.get(0));
                arrayAdapter.notifyDataSetChanged();
                arrayAdapter1.notifyDataSetChanged();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });

        spinner1.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                textView.setText(cities.get(position));
            }

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

            }
        });
    }

    public ArrayAdapter getCityFromCountry(String s) {

        try {
            cities.clear();
            JSONArray cityJR=jsonObject.getJSONArray(s);
            for(int i=0;i<cityJR.length();i++)
            {
                cities.add(cityJR.get(i).toString());
            }
            Collections.sort(cities);
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, cities);
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        overridePendingTransition(R.anim.slide_from_left,R.anim.slide_to_right);
    }

    public String getStringFromJsonFile(){

        try {
            InputStream jsonIpStream=getApplicationContext().getAssets().open("countries.txt");
            byte[] bytes = new byte[1000];
            StringBuilder x = new StringBuilder();
            int numRead = 0;
            while ((numRead = jsonIpStream.read(bytes)) >= 0) {
                x.append(new String(bytes, 0, numRead));
            }
            return x.toString();

        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    public ArrayAdapter getCountryFromJson(){

        try {
            countries.clear();
            jsonObject=new JSONObject(jsonString);
            JSONArray countryJR=jsonObject.names();
            for(int i = 0; i<countryJR.length(); i++)
            {
                countries.add(countryJR.get(i).toString());
            }
            Collections.sort(countries);
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, countries);
    }
}

Answer 1

在下面的代码中：

spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            arrayAdapter1=getCityFromCountry(countries.get(position));
            textView.setText(cities.get(0));
            arrayAdapter.notifyDataSetChanged();
            arrayAdapter1.notifyDataSetChanged();
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
});

替换这一行

arrayAdapter1.notifyDataSetChanged();

与

spinner1.setAdapter(arrayAdapter1);