Java ArrayList函数在Android中返回null

我试图从远程服务器返回值，将其添加到

ArrayList

中，并将其显示在Android studio中我的抽屉中，但我得到了

null

。volley中的名字和姓氏包含来自我的远程服务器的名字，但是名称

ArrayList

返回

null

GetName.java

  public List<String> getDriverName(Context contenxt){
    String COMPLETE_URL = TRANSACTION_DETAIL_URL +  Preferences.getDefaults("email", contenxt);
    Log.i("url", COMPLETE_URL);

    name = new ArrayList<String>();

    StringRequest stringRequest = new StringRequest(Request.Method.GET, COMPLETE_URL, new Response.Listener<String>() {


        @Override
        public void onResponse(String response) {
            Log.i("info", response.toString());

            JSONObject jsonObject = null;
            try {
                jsonObject = new JSONObject(response);
                JSONArray jsonArray = jsonObject.getJSONArray("success");
                if (jsonArray.length() > 0){
                    for (int i=0; i <= jsonArray.length()-1; i++){
                        JSONObject productJson = jsonArray.getJSONObject(i);
                        first_name =productJson.getString("firstName");
                        last_name = productJson.getString("lastName");
                        name.add(first_name);
                        name.add(last_name);
                        Log.d(null, "onResponse: " + last_name);

                    }

                }else{
                    first_name = "";
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            first_name = "";            }
    });
    int socketTimeout = 10000;
    RetryPolicy retryPolicy = new DefaultRetryPolicy(socketTimeout, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);
    RequestQueue requestQueue = Volley.newRequestQueue(contenxt);
    requestQueue.add(stringRequest);

    return name;
}

结果

D/: result: []

W/art: Before Android 4.1, method int     
android.support.v7.widget.DropDownListView.lookForSelectablePosition(int, 
boolean) would have incorrectly overridden the package-private method in 
android.widget.ListView
I/info: {"success":[{"firstName":"usfdh","lastName":"hseheh"}]}
D/: onResponse: hseheh

---

在数据尚未到达之前，您正在返回name变量

在数据到达并分配给变量后，您应该对name变量进行处理

您可以这样做：

NameAndEmail nameAndEmail = new NameAndEmail();

getDriverName(getApplicationContext()); // Remove return params from method.

您的getDriverName（）方法如下：

public void getDriverName(Context contenxt){
    String COMPLETE_URL = TRANSACTION_DETAIL_URL +  Preferences.getDefaults("email", contenxt);
    Log.i("url", COMPLETE_URL);

    name = new ArrayList<String>();

    StringRequest stringRequest = new StringRequest(Request.Method.GET, COMPLETE_URL, new Response.Listener<String>() {


        @Override
        public void onResponse(String response) {
            Log.i("info", response.toString());

            JSONObject jsonObject = null;
            try {
                jsonObject = new JSONObject(response);
                JSONArray jsonArray = jsonObject.getJSONArray("success");
                if (jsonArray.length() > 0){
                    for (int i=0; i <= jsonArray.length()-1; i++){
                        JSONObject productJson = jsonArray.getJSONObject(i);
                        first_name =productJson.getString("firstName");
                        last_name = productJson.getString("lastName");
                        name.add(first_name);
                        name.add(last_name);
                        Log.d(null, "onResponse: " + last_name);

                        /******************************
                        ****** DO PROCESS HERE ********
                        ******************************/

                    }

                }else{
                    first_name = "";
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            first_name = "";            }
    });
    int socketTimeout = 10000;
    RetryPolicy retryPolicy = new DefaultRetryPolicy(socketTimeout, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);
    RequestQueue requestQueue = Volley.newRequestQueue(contenxt);
    requestQueue.add(stringRequest);
}

public void getDriverName（上下文上下文）{
String COMPLETE\u URL=事务\u DETAIL\u URL+首选项.getDefaults（“email”，contenxt）；
Log.i（“url”，完整的url）；
name=新的ArrayList（）；
StringRequest StringRequest=新建StringRequest（Request.Method.GET，COMPLETE_URL，new Response.Listener（））{
@凌驾
公共void onResponse（字符串响应）{
Log.i（“info”，response.toString（））；
JSONObject JSONObject=null；
试一试{
jsonObject=新的jsonObject（响应）；
JSONArray JSONArray=jsonObject.getJSONArray（“成功”）；
if（jsonArray.length（）>0）{
for（int i=0；i Empty和null不是一回事。考虑到打印日志消息的顺序，您似乎存在异步问题，您的方法在数据到达之前返回
public void getDriverName(Context contenxt){
    String COMPLETE_URL = TRANSACTION_DETAIL_URL +  Preferences.getDefaults("email", contenxt);
    Log.i("url", COMPLETE_URL);

    name = new ArrayList<String>();

    StringRequest stringRequest = new StringRequest(Request.Method.GET, COMPLETE_URL, new Response.Listener<String>() {


        @Override
        public void onResponse(String response) {
            Log.i("info", response.toString());

            JSONObject jsonObject = null;
            try {
                jsonObject = new JSONObject(response);
                JSONArray jsonArray = jsonObject.getJSONArray("success");
                if (jsonArray.length() > 0){
                    for (int i=0; i <= jsonArray.length()-1; i++){
                        JSONObject productJson = jsonArray.getJSONObject(i);
                        first_name =productJson.getString("firstName");
                        last_name = productJson.getString("lastName");
                        name.add(first_name);
                        name.add(last_name);
                        Log.d(null, "onResponse: " + last_name);

                        /******************************
                        ****** DO PROCESS HERE ********
                        ******************************/

                    }

                }else{
                    first_name = "";
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            first_name = "";            }
    });
    int socketTimeout = 10000;
    RetryPolicy retryPolicy = new DefaultRetryPolicy(socketTimeout, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);
    RequestQueue requestQueue = Volley.newRequestQueue(contenxt);
    requestQueue.add(stringRequest);
}