android - 无法在 Spinner Android 上选择 mysql 数据

Question

我已经使用了 Spinner 并在 mysql 中有数据库，现在我想从 Android 中的 Spinner 上的数据库检索数据或名字，我可以在 Spinner 上显示数据，但是当我选择其中一个时，Spinner 变为空白(数据未选择)

但是当我添加时

 ar.add("");

所选项目可以显示在微调器中。

任何人都可以帮助修复我的代码。

非常感谢 --- terima kasih :)

这是我的代码:

package com.app.example.mysqltest;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.method.ScrollingMovementMethod;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class MainActivity extends AppCompatActivity {

    TextView result;
    RequestQueue requestQueue;

    String showUrl   = "http://10.10.10.1/trial/mysql/showStudent.php";
    ArrayList<String> ar = new ArrayList<String>();



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

        result    = (TextView) findViewById(R.id.result);

        requestQueue = Volley.newRequestQueue(getApplicationContext());

        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, showUrl, new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {

                try {
                        JSONArray students = response.getJSONArray("students");

                        for (int i = 0; i < students.length(); i++ ){
                            JSONObject student = students.getJSONObject(i);

                            String firstname = student.getString("firstname");
                            ar.add(firstname);

                        }     

                ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_spinner_item, ar);
                adapter.notifyDataSetChanged();

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

            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                System.out.println(error.getMessage());
            }
        });
        requestQueue.add(jsonObjectRequest);




        **//ar.add("");**


        Spinner dropdown = (Spinner)findViewById(R.id.planets_spinner);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_dropdown_item, ar);
        dropdown.setAdapter(adapter);



    }

}

Answer 1

这是一个非常著名的问题，您尝试异步获取数据，但在收到数据后，您没有通过 notifyDataSetChanged 更新到适配器。在 for 循环后尝试:adapter.notifyDataSetChanged()像这样:

Spinner dropdown = (Spinner)findViewById(R.id.planets_spinner);
final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_dropdown_item, ar);
dropdown.setAdapter(adapter);
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, showUrl, new Response.Listener<JSONObject>() {
    @Override
    public void onResponse(JSONObject response) {
        try {
                JSONArray students = response.getJSONArray("students");

                for (int i = 0; i < students.length(); i++ ){
                    JSONObject student = students.getJSONObject(i);

                    String firstname = student.getString("firstname");
                    ar.add(firstname);
                }
               // Just 1 LOC
               adapter.notifyDataSetChanged();

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

    }
    }, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        System.out.println(error.getMessage());
    }
});
requestQueue.add(jsonObjectRequest);