删除数据

Question

此代码用于删除和显示数据，我尝试删除并在删除数据后我希望listview刷新。我有这个代码List.java：

package id.co.pips.databasecrud;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.database.SQLException;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

import id.co.pips.databasecrud.PDM.Mahasiswa;

import static id.co.pips.databasecrud.DbHelper.FIELD_MAHASISWA_NIM;
import static id.co.pips.databasecrud.R.id.nimItem;
import static id.co.pips.databasecrud.R.id.view;

public class ListNimNama extends AppCompatActivity {
    ListView lv;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_nim_nama);
        lv = (ListView) findViewById(R.id.listView);
        DbHelper db = new DbHelper(this);

        Cursor cursor = db.getAllNamaNimMahasiswa();

        String[] fromColumns = {DbHelper.FIELD_MAHASISWA_NIM, DbHelper.FIELD_MAHASISWA_NAMA};

        int[] toViews = {R.id.nimItem, R.id.namaItem};
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.activity_list_nim_nama, cursor, fromColumns, toViews, 0);

        lv.setAdapter(adapter);
        adapter.notifyDataSetChanged();

        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapter, View view, int position, long arg) {
                TextView nim = (TextView) view.findViewById(R.id.nimItem);
                TextView nama = (TextView) view.findViewById(R.id.namaItem);
                String vnim = nim.getText().toString();
                String vnama = nama.getText().toString();
                System.out.println("Nama = : " + vnama);
                System.out.println("NIM = : " + vnim);

                Intent app = new Intent(ListNimNama.this, editActivity.class);
                app.putExtra("nim", vnim);
                app.putExtra("nama", vnama);
                startActivity(app);
            }
        });

        lv.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> av, View v, int pos, long id) {
                // TODO: Get the position of the item clicked.
                //       Delete it from your collection eg.ArrayList.
                //       Call notifydatasetChanged so that it will refresh
                //       the views displaying updated list.

                AlertDialog.Builder alert = new AlertDialog.Builder(ListNimNama.this);
                alert.setTitle("Alert!!");
                alert.setMessage("Are you sure to delete this item ?");
                alert.setPositiveButton("YES", new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        //do your work here
                        delete();
                        dialog.dismiss();

                    }
                });
                alert.setNegativeButton("NO", new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                });

                alert.show();

                return true;

            }
        });

    }

    public void delete()
    {
        DbHelper dbAdmin;
        try
        {
            TextView nim = (TextView)findViewById(R.id.nimItem);
            String vnim = nim.getText().toString();
            dbAdmin = new DbHelper(this);
            dbAdmin.deleteMahasiswa(vnim);

            Toast.makeText(this, "Berhasil Delete Data " , Toast.LENGTH_LONG).show();

        }catch (SQLException e)
        {
            Toast.makeText(this, "Gagal Delete Data " , Toast.LENGTH_LONG).show();
        }
    }

}

已经放

adapter.notifyDataSetChanged();

List.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_list_nim_nama"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="id.co.pips.databasecrud.ListNimNama">

   <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/listView"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="0dp" />


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/nimItem"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="19dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/namaItem"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true" />

</RelativeLayout>

但删除数据后没有任何变化。或者我错了代码？

Answer 1

您应该在更新数据结构后调用adapter.notifyDataSetChanged();。

试试这个：

public void delete()
{
    DbHelper dbAdmin;
    try
    {
        TextView nim = (TextView)findViewById(R.id.nimItem);
        String vnim = nim.getText().toString();
        dbAdmin = new DbHelper(this);
        dbAdmin.deleteMahasiswa(vnim);

        Toast.makeText(this, "Berhasil Delete Data " , Toast.LENGTH_LONG).show();

    }catch (SQLException e)
    {
        Toast.makeText(this, "Gagal Delete Data " , Toast.LENGTH_LONG).show();
    }
    adapter.notifyDataSetChanged();  // <= Add this
}