Java 空数组

Question

目前我正在尝试使用 Volley 库（使用 http 请求）从 mysql 数据库接收信息。但是当我想在我的 android 应用程序中显示信息时，我收到了很多错误。

10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: FATAL EXCEPTION: main 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: Process: com.example.jamie.fysio, PID: 11718 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: java.lang.NullPointerException: Attempt to read from null array 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.example.jamie.fysio.Home.showJSON(Home.java:79) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.example.jamie.fysio.Home.access[=13=]0(Home.java:28) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.example.jamie.fysio.Home.onResponse(Home.java:55) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.example.jamie.fysio.Home.onResponse(Home.java:52) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:60) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:30) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at android.os.Looper.loop(Looper.java:145) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:6872) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404) 10-07 20:51:27.205 11718-11718/com.example.jamie.fysio E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)

这是我解析 JSON:

的方法

public class parseJSON {
    public static String[] adres;

    public static final String JSON_ARRAY = "result";
    public static final String ADRES = "adres";

    private JSONArray users = null;

    private String json;


    public parseJSON(String json){
        this.json = json;
    }

    protected void parseJSONMeth(){
        JSONObject jsonObject=null;
        try {
            jsonObject = new JSONObject(json);
            users = jsonObject.getJSONArray(JSON_ARRAY);

            adres = new String[users.length()];

            for(int i=0;i<users.length();i++){
                JSONObject jo = users.getJSONObject(i);
                adres[i] = jo.getString(ADRES);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
}

这是我的发送请求：

private void sendRequest(){

    StringRequest stringRequest = new StringRequest(Request.Method.POST,JSON_URL,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    showJSON(response);
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(Home.this, error.getMessage(), Toast.LENGTH_LONG).show();
                }
            }) {
    @Override
    protected Map<String, String> getParams() throws AuthFailureError {
        Map<String, String> map = new HashMap<String, String>();
        map.put(KEY_USERNAME, gebruikersnaam);
        return map;
    }
};

    RequestQueue requestQueue = Volley.newRequestQueue(this);
    requestQueue.add(stringRequest);
}

private void showJSON(String json) {
    parseJSON pj = new parseJSON(json);
    pj.parseJSONMeth();
    adres.setText(parseJSON.adres[0]);
}

}

我对 volley 库不是很熟悉我做错了什么？

Answer 1

您从 onResponse(String response) 获得的 response 似乎没有通过有效的 JSONObject，这导致 JSONException 在 adres 之前被捕获已分配。

检查你的JSON_URL。

顺便说一句 adres 不应该是静态的，应该通过 pj.

访问

Java 空数组

Java empty array

java

android

android-volley