Android Aktualisierung der letzten ListView nach Fragmentwechsel

Question

Ich habe 2 verschiedene Fragmente und in ersten Fragment, ich füge einen neuen Studenteneintrag zu meiner benutzerdefinierten Student ArrayList. Ich habe auch eine ListView, um meine Schülerliste in meinem zweiten Fragment anzuzeigen. Wenn ich jedoch zu meinem zweiten Fragment gehe, wird das neueste ListView nicht aktualisiert. Meine Frage ist also, wie kann ich meine ListView aktualisieren, nachdem ich meine Fragment-Registerkarte geändert habe?

registerBtn fügt meiner studentsArrayList einfach einen neuen Eintrag hinzu.

Zuerst habe ich versucht, "Get" -Button zu verwenden, um meine ListView zu aktualisieren, aber es hat nicht funktioniert. Was ich tun möchte, ist, dass ich meine ListView immer dann aktualisiere, wenn ich an mein StudentsFragment übergebe.

RegisterFragment.java:

package com.rawsly.android.schoolprogram; 

import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.Fragment; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.widget.Toast; 

import java.util.ArrayList; 
import java.util.Random; 

public class RegisterFragment extends Fragment { 
    private static final String TAG = "RegisterFragment"; 
    public ArrayList<Students> studentsArrayList = new ArrayList<>(); 
    private ArrayList<Long> idList = new ArrayList<>(); 
    private TextView studentID; 
    private Button registerBtn, clearBtn, exitBtn; 
    private EditText editName, editLastName, editGender, editFaculty, editDepartment, editAdvisor; 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     View view = inflater.inflate(R.layout.register_fragment, container, false); 

     studentID = (TextView) view.findViewById(R.id.studentID); 
     studentID.setText(String.valueOf(generateID())); 
     editName = (EditText) view.findViewById(R.id.editName); 
     editLastName = (EditText) view.findViewById(R.id.editLastName); 
     editGender = (EditText) view.findViewById(R.id.editGender); 
     editFaculty = (EditText) view.findViewById(R.id.editFaculty); 
     editDepartment = (EditText) view.findViewById(R.id.editDepartment); 
     editAdvisor = (EditText) view.findViewById(R.id.editAdvisor); 

     registerBtn = (Button) view.findViewById(R.id.registerBtn); 
     registerBtn.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       String id = studentID.getText().toString(); 
       String name = editName.getText().toString(); 
       String lastName = editLastName.getText().toString(); 
       String gender = editGender.getText().toString(); 
       String faculty = editFaculty.getText().toString(); 
       String department = editDepartment.getText().toString(); 
       String advisor = editAdvisor.getText().toString(); 

       studentsArrayList.add(new Students(id, name, lastName, gender, faculty, department, advisor)); 
       Toast.makeText(getContext(), "New entry added.", Toast.LENGTH_SHORT).show(); 
      } 
     }); 

     clearBtn = (Button) view.findViewById(R.id.clearBtn); 
     clearBtn.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       editName.setText(null); 
       editLastName.setText(null); 
       editGender.setText(null); 
       editFaculty.setText(null); 
       editDepartment.setText(null); 
       editAdvisor.setText(null); 
       studentID.setText(String.valueOf(generateID())); 
      } 
     }); 

     exitBtn = (Button) view.findViewById(R.id.exitBtn); 
     exitBtn.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       System.exit(1); 
      } 
     }); 

     return view; 
    } 

    // Generates a random ID. 
    public long generateID() { 
     Random rnd = new Random(); 
     char [] digits = new char[11]; 
     digits[0] = (char) (rnd.nextInt(9) + '1'); 
     for(int i=1; i<digits.length; i++) { 
      digits[i] = (char) (rnd.nextInt(10) + '0'); 
     } 
     long result = Long.parseLong(new String(digits)); 
     if(idList.contains(result)) { 
      return generateID(); 
     } else { 
      return result; 
     } 
    } 
} 

StudentsFragment.java:

package com.rawsly.android.schoolprogram; 

import android.app.Dialog; 
import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.Fragment; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.ListView; 
import android.widget.TextView; 
import android.widget.Toast; 

import java.util.ArrayList; 

public class StudentsFragment extends Fragment { 
    private static final String TAG = "StudentsFragment"; 
    private EditText txtSearch; 
    private ListView studentsListView; 
    private Button getStudents, updateStudent, deleteStudent, exitBtn; 
    public StudentsAdapter adapter; 
    public ArrayList<Students> studentsArrayList = new ArrayList<>();; 
    public int selectedItem = -1; // to update or delete the data 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     View view = inflater.inflate(R.layout.students_fragment, container, false); 


     // Dummy Data 
     studentsArrayList.add(new Students("1122334455", "Ahmet", "Özdemir", "Male", "Mühendislik ve Doğa Bilimleri", "Bilgisayar Mühendisliği", "Tuğba Yıldız")); 
     studentsArrayList.add(new Students("1234567890", "Ezgi", "İmamoğlu", "Female", "Mühendislik ve Doğa Bilimleri", "Bilgisayar Mühendisliği", "Tuğba Yıldız")); 
     studentsArrayList.add(new Students("", "Enise", "Usta", "Female", "Sosyal ve Beşeri Bilimler Fakültesi", "Uluslararası İlişkiler", "Murat Orhun")); 
     studentsArrayList.add(new Students("1122445588", "Sinem", "Ünver", "Female", "Mühendislik ve Doğa Bilimleri", "Endüstri Mühendisliği", "Zehra Yılmaz")); 
     studentsArrayList.add(new Students("2546882547", "Zehra", "Gürçay", "Female", "Mühendislik ve Doğa Bilimleri", "Endüstri Mühendisliği", "Şule Gündüz")); 


     adapter = new StudentsAdapter(getContext(), studentsArrayList); 

     studentsListView = (ListView) view.findViewById(R.id.studentsListView); 
     studentsListView.setAdapter(adapter); 

     studentsListView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) { 
       selectedItem = position; 
       Toast.makeText(getContext(), "Selected entry: " + (selectedItem+1), Toast.LENGTH_LONG).show(); 
      } 
     }); 

     // Opens a dialog window 
     getStudents = (Button) view.findViewById(R.id.getStudents); 
     getStudents.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       adapter.notifyDataSetChanged(); 
       studentsListView.invalidate(); 
      } 
     }); // end of the add action 

     // To delete the selected School object 
     deleteStudent = (Button) view.findViewById(R.id.deleteStudent); 
     deleteStudent.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       if(selectedItem == -1) { 
        Toast.makeText(getContext(), "Please, select an entry first.", Toast.LENGTH_SHORT).show(); 
       } else { 
        studentsArrayList.remove(selectedItem); 
        selectedItem = -1; 
        adapter.notifyDataSetChanged(); 
        Toast.makeText(getContext(), "Selected entry is deleted.", Toast.LENGTH_SHORT).show(); 
       } 
      } 
     }); // end of the delete action 

     // To exit the program 
     exitBtn = (Button) view.findViewById(R.id.exitBtn); 
     exitBtn.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       System.exit(1); 
      } 
     }); // end of the exit action 

     // To update the selected School object 
     updateStudent = (Button) view.findViewById(R.id.updateStudent); 
     updateStudent.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       if(selectedItem == -1) { 
        Toast.makeText(getContext(), "Please, select an entry first.", Toast.LENGTH_SHORT).show(); 
       } else { 
        final Dialog dialog = new Dialog(getContext()); 
        dialog.setContentView(R.layout.update_student); 
        dialog.setTitle("Update An Entry"); 
        // Dialog components - EditText, Button 
        String id = studentsArrayList.get(selectedItem).id; 
        String name = studentsArrayList.get(selectedItem).name; 
        String lastName = studentsArrayList.get(selectedItem).lastName; 
        String gender = studentsArrayList.get(selectedItem).gender; 
        String faculty = studentsArrayList.get(selectedItem).faculty; 
        String department = studentsArrayList.get(selectedItem).department; 
        String advisor = studentsArrayList.get(selectedItem).advisor; 

        final TextView studentID = (TextView) dialog.findViewById(R.id.studentID); 
        final EditText editName = (EditText) dialog.findViewById(R.id.editName); 
        final EditText editLastName = (EditText) dialog.findViewById(R.id.editLastName); 
        final EditText editGender = (EditText) dialog.findViewById(R.id.editGender); 
        final EditText editFaculty = (EditText) dialog.findViewById(R.id.editFaculty); 
        final EditText editDepartment = (EditText) dialog.findViewById(R.id.editDepartment); 
        final EditText editAdvisor = (EditText) dialog.findViewById(R.id.editAdvisor); 

        studentID.setText(id); 
        editName.setText(name); 
        editLastName.setText(lastName); 
        editGender.setText(gender); 
        editFaculty.setText(faculty); 
        editDepartment.setText(department); 
        editAdvisor.setText(advisor); 

        Button updateStudent = (Button) dialog.findViewById(R.id.updateStudent); 
        Button clearStudent = (Button) dialog.findViewById(R.id.clearStudent); 
        Button cancelStudent = (Button) dialog.findViewById(R.id.cancelStudent); 

        // Updates the selected School object 
        updateStudent.setOnClickListener(new View.OnClickListener() { 
         @Override 
         public void onClick(View view) { 
          String id = studentID.getText().toString(); 
          String name = editName.getText().toString(); 
          String lastName = editLastName.getText().toString(); 
          String gender = editGender.getText().toString(); 
          String faculty = editFaculty.getText().toString(); 
          String department = editDepartment.getText().toString(); 
          String advisor = editAdvisor.getText().toString(); 
          studentsArrayList.get(selectedItem).setId(id); 
          studentsArrayList.get(selectedItem).setName(name); 
          studentsArrayList.get(selectedItem).setLastName(lastName); 
          studentsArrayList.get(selectedItem).setGender(gender); 
          studentsArrayList.get(selectedItem).setFaculty(faculty); 
          studentsArrayList.get(selectedItem).setDepartment(department); 
          studentsArrayList.get(selectedItem).setAdvisor(advisor); 

          adapter.notifyDataSetChanged(); 
          Toast.makeText(getContext(), "An entry is updated.", Toast.LENGTH_SHORT).show(); 
          dialog.dismiss(); 
         } 
        }); 

        // Clears all fields 
        clearStudent.setOnClickListener(new View.OnClickListener() { 
         @Override 
         public void onClick(View view) { 
          editName.setText(null); 
          editLastName.setText(null); 
          editGender.setText(null); 
          editFaculty.setText(null); 
          editDepartment.setText(null); 
          editAdvisor.setText(null); 
         } 
        }); 

        // Dismisses the dialog 
        cancelStudent.setOnClickListener(new View.OnClickListener() { 
         @Override 
         public void onClick(View view) { 
          dialog.dismiss(); 
         } 
        }); 

        dialog.show(); 
        adapter.notifyDataSetChanged(); // notifying adapter about changes 
       } 
      } 
     }); // end of the update action 

     return view; 
    } 
} 

Answer 1

„Fehlerbehebung

Wenn Aufruf notifyDataSetChanged(), um die Layout-Methoden nicht alle gewonnen funktioniert Ich glaube auch, dass die ListView korrekt aktualisiert wurde. Wenn Sie t Der Unterschied ist, dass Sie überprüfen müssen, woher die Daten in Ihrem Adapter stammen.

Wenn dies nur eine Sammlung ist, die Sie im Speicher behalten, überprüfen Sie, ob Sie das Element vor dem Aufruf von notifyDataSetChanged() tatsächlich aus der Sammlung gelöscht oder hinzugefügt haben.

Wenn Sie mit einem Datenbank- oder Service-Backend arbeiten, müssen Sie die Methode aufrufen, um die Informationen vor dem Aufruf von notifyDataSetChanged() erneut abzurufen (oder die Daten im Speicher zu bearbeiten).

Die Sache ist diese notifyDataSetChanged funktioniert nur, wenn das Dataset geändert hat. Das ist also der richtige Ort, wenn Sie keine Veränderungen feststellen können. Debuggen, wenn nötig „

Duplikat. How to refresh Android listview?