我正在使用Retrofit库开发一个动态的Android应用程序。该应用程序将请求发送到服务器端php文件，并从他们那里收到json响应。我正在关注登录注册系统的this教程。从mysql数据库检索的值首先存储在SharedPreferences中，然后设置为相应的TextView。
一切正常。但是，当我更改数据库中的值时，用户需要注销并再次登录才能看到更新的值。我试过在我的ProfileFragment.java中创建一个函数
private void refreshProcess(String email1){
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(Constants.BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build();
RequestInterface requestInterface = retrofit.create(RequestInterface.class);
User user = new User();
user.setEmail(email1);
ServerRequest request = new ServerRequest();
request.setOperation(Constants.REFRESH_OPERATION);
request.setUser(user);
Call<ServerResponse> response = requestInterface.operation(request);
response.enqueue(new Callback<ServerResponse>() {
@Override
public void onResponse(Call<ServerResponse> call, retrofit2.Response<ServerResponse> response) {
ServerResponse resp = response.body();
Snackbar.make(getView(), resp.getMessage(), Snackbar.LENGTH_LONG).show();
if(resp.getResult().equals(Constants.SUCCESS)){
SharedPreferences.Editor editor = pref.edit();
editor.putBoolean(Constants.IS_LOGGED_IN,true);
editor.putString(Constants.EMAIL,resp.getUser().getEmail());
editor.putString(Constants.NAME,resp.getUser().getName());
editor.putString(Constants.ROLLNO,resp.getUser().getRollno());
editor.putString(Constants.TOTL_FEES,resp.getUser().getTotl_fees());
editor.putString(Constants.PAID_FEES,resp.getUser().getPaid_fees());
editor.putString(Constants.REM_FEES,resp.getUser().getRem_fees());
editor.putString(Constants.MON_ATT,resp.getUser().getMon_att());
editor.putString(Constants.TUE_ATT,resp.getUser().getTue_att());
editor.putString(Constants.WED_ATT,resp.getUser().getWed_att());
editor.putString(Constants.THRS_ATT,resp.getUser().getThrs_att());
editor.putString(Constants.FRI_ATT,resp.getUser().getFri_att());
editor.putString(Constants.SAT_ATT,resp.getUser().getSat_att());
editor.putString(Constants.SUN_ATT,resp.getUser().getSun_att());
editor.putString(Constants.TST1_DATE,resp.getUser().getTst1_date());
editor.putString(Constants.TST1_DATE,resp.getUser().getTst1_date());
editor.putString(Constants.TST1_MARKS,resp.getUser().getTst1_marks());
editor.putString(Constants.TST1_RANK,resp.getUser().getTst1_rank());
editor.putString(Constants.TST2_DATE,resp.getUser().getTst2_date());
editor.putString(Constants.TST2_MARKS,resp.getUser().getTst2_marks());
editor.putString(Constants.TST2_RANK,resp.getUser().getTst2_rank());
editor.putString(Constants.TST3_DATE,resp.getUser().getTst3_date());
editor.putString(Constants.TST3_MARKS,resp.getUser().getTst3_marks());
editor.putString(Constants.TST3_RANK,resp.getUser().getTst3_rank());
editor.putString(Constants.TST4_DATE,resp.getUser().getTst4_date());
editor.putString(Constants.TST4_MARKS,resp.getUser().getTst4_marks());
editor.putString(Constants.TST4_RANK,resp.getUser().getTst4_rank());
editor.putString(Constants.TST5_DATE,resp.getUser().getTst5_date());
editor.putString(Constants.TST5_MARKS,resp.getUser().getTst5_marks());
editor.putString(Constants.TST5_RANK,resp.getUser().getTst5_rank());
editor.putString(Constants.UNIQUE_ID,resp.getUser().getUnique_id());
editor.putString(Constants.PERSONAL_MSG,resp.getUser().getPersonalMsg());
editor.putString(Constants.BROADCAST_MSG,resp.getUser().getBroadcast_msg());
editor.apply();
goToProfile();
}
progress.setVisibility(View.INVISIBLE);
}
private void goToProfile(){
Fragment profile = new ProfileFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.fragment_frame,profile);
ft.commit();
}
@Override
public void onFailure(Call<ServerResponse> call, Throwable t) {
progress.setVisibility(View.INVISIBLE);
Log.d(Constants.TAG,"failed");
Snackbar.make(getView(), t.getLocalizedMessage(), Snackbar.LENGTH_LONG).show();
}
});
}
该函数发送初始化为当前登录用户的电子邮件字符串。它作为字符串存储在Constants.java类中，该类具有设置值，该值在用户登录时存储在SharedPreferences中。
String email1=pref.getString(Constants.EMAIL,"");
refreshProcess(email1);
在服务器端，我有index.php文件检查操作刷新
if ($operation == 'refresh') {
$user = $data -> user;
$email = $user -> email;
echo $fun -> refreshUserData($email);
}
functions.php文件具有refreshUserData函数
public function refreshUserData($email){
$db = $this -> db;
$result = $db -> refreshData($email);
if(!$result) {
$response["result"] = "failure";
$response["message"] = "Failed to Refresh";
return json_encode($response);
} else {
$response["result"] = "success";
$response["message"] = "Refresh Complete";
$response["user"] = $result;
return json_encode($response);
}
}
以下是文件refreshData
DBOperations.php
public function refreshData($email){
$sql = 'SELECT * FROM users WHERE email = :email';
$query = $this -> conn -> prepare($sql);
$query -> execute(array(':email' => $email));
$data = $query -> fetchObject();
$user["name"] = $data -> name;
$user["attendance"] = $data -> attendance;
$user["email"] = $data -> email;
$user["unique_id"] = $data -> unique_id;
$user["rollno"] = $data -> rollno;
$user["totl_fees"] = $data -> totl_fees;
$user["paid_fees"] = $data -> paid_fees;
$user["rem_fees"] = $data -> rem_fees;
$user["mon_att"] = $data -> mon_att;
$user["tue_att"] = $data -> tue_att;
$user["wed_att"] = $data -> wed_att;
$user["thrs_att"] = $data -> thrs_att;
$user["fri_att"] = $data -> fri_att;
$user["sat_att"] = $data -> sat_att;
$user["sun_att"] = $data -> sun_att;
$user["tst1_date"] = $data -> tst1_date;
$user["tst1_marks"] = $data -> tst1_marks;
$user["tst1_rank"] = $data -> tst1_rank;
$user["tst2_date"] = $data -> tst2_date;
$user["tst2_marks"] = $data -> tst2_marks;
$user["tst2_rank"] = $data -> tst2_rank;
$user["tst3_date"] = $data -> tst3_date;
$user["tst3_marks"] = $data -> tst3_marks;
$user["tst3_rank"] = $data -> tst3_rank;
$user["tst4_date"] = $data -> tst4_date;
$user["tst4_marks"] = $data -> tst4_marks;
$user["tst4_rank"] = $data -> tst4_rank;
$user["tst5_date"] = $data -> tst5_date;
$user["tst5_marks"] = $data -> tst5_marks;
$user["tst5_rank"] = $data -> tst5_rank;
$user["personal_msg"] = $data -> personal_msg;
$user["broadcast_msg"] = $data -> broadcast_msg;
return $user;
}
完成所有这些传奇之后，当我点击调用功能refreshProcess()的按钮Refresh时，应用程序停止。这是logcat
06-08 18:09:50.101 2544-2544/net.softglobe.learn2crack E/AndroidRuntime: FATAL EXCEPTION: main
Process: net.softglobe.learn2crack, PID: 2544
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
at net.softglobe.learn2crack.ProfileFragment$5.onResponse(ProfileFragment.java:293)
at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
请提供令人满意的解决方案，帮助我解决这个问题，因为我花了很长时间来做这个并在各处搜索如何实现这一目标，但没有得到回应。