如何在以前的用户输入仍然存在的情况下打开 activity Xamarin

Question

我正在制作一个提醒应用程序，我希望用户能够添加提醒，然后稍后再进行编辑。

目前当用户选择编辑提醒时，所有字段的开头都是空白的。像这样：

https://i.stack.imgur.com/WCwja.gif

不过我希望它是这样的：

这是我的部分代码：

namespace ReminderApp.Models
{
    public class Reminder
    {
        public int Id { get; set; }
        public string Date { get; set; }
        public string Time { get; set; }
        public string Note { get; set; }
        public Reminder()
        {
        }
    }
}

我的数据库：

using Android.Content;
using Android.Database.Sqlite;

namespace ReminderApp.HelperRepository
{
    public class DataStore : SQLiteOpenHelper
    {
        private static string _DatabaseName = "reminderDB.db";
        public DataStore(Context context) : base(context, _DatabaseName, null, 1)
        {

        }

        public override void OnCreate(SQLiteDatabase db)
        {
            db.ExecSQL(ReminderHelper.CreateQuery);
        }

        public override void OnUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
        {
            db.ExecSQL(ReminderHelper.DeleteQuery);
            OnCreate(db);
        }
    }
}

我的数据库助手删除、更新和添加提醒：

using System;
using System.Collections.Generic;
using Android.Content;
using Android.Database.Sqlite;
using ReminderApp.Models;
using Android.Database;
namespace ReminderApp.HelperRepository
{
    public class ReminderHelper
    {
        private const string TableName = "reminderTable";
        private const string ColumnID = "Id";
        private const string ColumnDate = "Date";
        private const string ColumnTime = "Time";
        private const string ColumnNote = "Note";
        public const string CreateQuery = "CREATE TABLE " + TableName + " ( "
            + ColumnID + " INTEGER PRIMARY KEY,"
               + ColumnDate + " TEXT,"
               + ColumnTime + " TEXT,"
               + ColumnNote + " TEXT)";


        public const string DeleteQuery = "DROP TABLE IF EXISTS " + TableName;

        public ReminderHelper()
        {
        }

        public static void InsertReminderData(Context context, Reminder reminder)
        {
            SQLiteDatabase db = new DataStore(context).WritableDatabase;
            ContentValues contentValues = new ContentValues();
            contentValues.Put(ColumnDate, reminder.Date);
            contentValues.Put(ColumnTime, reminder.Time);
            contentValues.Put(ColumnNote, reminder.Note);

            db.Insert(TableName, null, contentValues);
            db.Close();
        }

        public static void EditReminderData(Context context, Reminder reminder)
        {
            SQLiteDatabase db = new DataStore(context).WritableDatabase;
            ContentValues contentValues = new ContentValues();
            contentValues.Put(ColumnDate, reminder.Date);
            contentValues.Put(ColumnTime, reminder.Time);
            contentValues.Put(ColumnNote, reminder.Note);

            db.Update(TableName, contentValues, null, null);
            db.Close();
        }

        public static List<Reminder> GetReminderList(Context context)
        {
            List<Reminder> reminder = new List<Reminder>();
            SQLiteDatabase db = new DataStore(context).ReadableDatabase;
            string[] columns = new string[] { ColumnID, ColumnDate, ColumnTime, ColumnNote };

            using (ICursor cursor = db.Query(TableName, columns, null, null, null, null, null))
            {
                while (cursor.MoveToNext())
                {
                    reminder.Add(new Reminder
                    {
                        Id = cursor.GetInt(cursor.GetColumnIndexOrThrow(ColumnID)),
                        Date = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnDate)),
                        Time = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnTime)),
                        Note = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnNote))
                    });
                }
            }
            db.Close();
            return reminder;
        }

        public static void DeleteReminder(Context context, Reminder reminder)
        {
            SQLiteDatabase db = new DataStore(context).WritableDatabase;
            db.Delete(TableName, ColumnDate + "=? AND " + ColumnTime + "=? OR " + ColumnID + "=" + reminder.Id, new string[] { reminder.Date, reminder.Time });
            db.Close();
        }

        public static Reminder SelectReminder(Context context)
        {
            Reminder reminder;
            SQLiteDatabase db = new DataStore(context).WritableDatabase;
            string[] columns = new string[] { ColumnID, ColumnDate, ColumnTime, ColumnNote };
            string datetime = DateTime.Now.ToString();
            string[] dt = datetime.Split(' ');
            var date = dt[0];
            var tt = dt[1].Split(':');
            var time = tt[0] + ":" + tt[1] + " " + dt[2];


            using (ICursor cursor = db.Query(TableName, columns, ColumnDate + "=? AND " + ColumnTime + "=?", new string[] { date, time }, null, null, null))
            {
                if (cursor.MoveToNext())
                {
                    reminder = new Reminder
                    {
                        Id = cursor.GetInt(cursor.GetColumnIndexOrThrow(ColumnID)),
                        Date = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnDate)),
                        Time = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnTime)),
                        Note = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnNote))
                    };
                }
                else
                {
                    reminder = null;
                }
            }
            return reminder;
        }
    }
}

和 activity 编辑提醒：

using System;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Widget;
using Newtonsoft.Json;
using ReminderApp.Models;
using ReminderApp.HelperRepository;
using System.Threading;

namespace ReminderApp
{
    [Activity(Label = "EditActivity")]
    public class EditActivity : Activity
    {
        public Reminder reminder;
        EditText _dateDisplay;
        EditText _timeDisplay;
        EditText _txtNote;
        Button _saveButton;
        Button _btnList;

        #region DateOperation  
        [Obsolete]
        void DateSelect_OnClick(object sender, EventArgs eventArgs)
        {
            DatePickerFragment frag = DatePickerFragment.NewInstance(delegate (DateTime time)
            {
                _dateDisplay.Text = time.ToString().Split(' ')[0];
                reminder.Date = _dateDisplay.Text + " ";
            });
            frag.Show(FragmentManager, DatePickerFragment.TAG);
        }
        #endregion

        #region TimeOperation  
        [Obsolete]
        void TimeSelectOnClick(object sender, EventArgs eventArgs)
        {
            TimePickerFragment frag = TimePickerFragment.NewInstance(
                delegate (DateTime time)
                {
                    _timeDisplay.Text = time.ToShortTimeString();
                    reminder.Time = _timeDisplay.Text + " ";
                });

            frag.Show(FragmentManager, TimePickerFragment.TAG);
        }
        #endregion

        #region SaveDetails  
        void SaveRecords(object sender, EventArgs eventArgs)
        {
            reminder.Note = _txtNote.Text;
            if (Vaidate())
            {
                DateTime currentDT = DateTime.Now;
                DateTime selectedDT = Convert.ToDateTime(reminder.Date + " " + reminder.Time);

                if (selectedDT > currentDT)
                {
                    ReminderHelper.EditReminderData(this, reminder);

                    var reminderEdited = new Intent(this, typeof(ReminderEdited));
                    reminderEdited.PutExtra("reminder", JsonConvert.SerializeObject(reminder));
                    StartActivity(reminderEdited);
                }
                else
                {
                    Toast.MakeText(this, "This is invalid selelction of Date, Time!", ToastLength.Short).Show();
                }
            }

        }

        bool Vaidate()
        {
            if (reminder.Date == string.Empty || reminder.Time == string.Empty || reminder.Note == string.Empty)
            {
                Toast.MakeText(this, "Enter the details of all fields!", ToastLength.Short).Show();
                return false;
            }
            return true;
        }
        #endregion

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.activity_edit);
            reminder = new Reminder();
            var id = Intent.GetIntExtra("Id", 0);
            var note = Intent.GetStringExtra("Note");
            var time = Intent.GetStringExtra("Time");
            var date = Intent.GetStringExtra("Date");
            if (id != 0)
                reminder.Id = id;
            reminder.Note = note;
            reminder.Date = date;
            reminder.Time = time;


            _dateDisplay = FindViewById<EditText>(Resource.Id.date_display);
            _timeDisplay = FindViewById<EditText>(Resource.Id.time_display);
            _txtNote = FindViewById<EditText>(Resource.Id.txtNote);

            _saveButton = FindViewById<Button>(Resource.Id.save);
            _btnList = FindViewById<Button>(Resource.Id.btnList);

            _dateDisplay.Click += DateSelect_OnClick;
            _timeDisplay.Click += TimeSelectOnClick;
            _saveButton.Click += SaveRecords;
            _btnList.Click += (sender, e) => {
                StartActivity(new Intent(this, typeof(ListReminder)));
            };
        }
    }
}

当我尝试像这样放置 _dateDisplay = (EditText)reminder.Date 时：

我收到错误消息“对象引用未设置为对象的瞬间”

如何更改我的代码，以便当用户选择编辑提醒时，字段包含用户之前输入内容的详细信息。

如果您需要，这是我的完整申请：https://github.com/CrazyDanyal1414/ReminderApp

感谢任何帮助！

Answer 1

我在我这边测试了你的代码，问题是数据没有从存储中正确获取。您已将 Intent 的数据发送到 EditActivity class:

public class ListReminder : Activity
{
    ...
    private void List_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
    {
        ...
        alert.SetButton2("Edit", (c, ev) =>
        {
            var intent = new Intent(this, typeof(EditActivity));
            intent.PutExtra("Id", listitem[e.Position].Id);
            StartActivity(intent);
        });
    }
}

可以在EditActivity中获取idclass，然后尝试从Helper中获取对应的数据模型class.Check代码：

public class EditActivity : Activity
{
    ...
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.activity_edit);
        reminder = new Reminder();

        var id = Intent.GetIntExtra("Id", 0);
        var array = ReminderHelper.GetReminderList(this).ToArray();

        var data = array[id - 1] as Reminder;

        _dateDisplay = FindViewById<EditText>(Resource.Id.date_display);
        _timeDisplay = FindViewById<EditText>(Resource.Id.time_display);
        _txtNote = FindViewById<EditText>(Resource.Id.txtNote);

        _dateDisplay.Text = data.Note;
        _timeDisplay.Text = data.Time;
        _txtNote.Text = data.Date;
        _...
    }
}

Answer 2

在ReminderHelper中创建方法，通过Id获取提醒对象

ReminderHelper.cs

public static Reminder SelectReminder(Context context, int reminderId)
        {
            Reminder reminder;
            SQLiteDatabase db = new DataStore(context).ReadableDatabase;
            string[] columns = new string[] { ColumnID, ColumnDate, ColumnTime, ColumnNote };
            using (ICursor cursor = db.Query(TableName, columns, ColumnID + "=" + reminderId, null, null, null, null))
            {
                if (cursor.MoveToNext())
                {
                    reminder = new Reminder
                    {
                        Id = cursor.GetInt(cursor.GetColumnIndexOrThrow(ColumnID)),
                        Date = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnDate)),
                        Time = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnTime)),
                        Note = cursor.GetString(cursor.GetColumnIndexOrThrow(ColumnNote))
                    };
                }
                else
                {
                    reminder = null;
                }
            }
            return reminder;
        }

然后在EditRemider中使用上述方法获取提醒对象

EditReminder.cs

protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.activity_main);
            var id = Intent.GetIntExtra("Id", 0);
            if (id != 0)
            {
                reminder = ReminderHelper.SelectReminder(this, id);
            }
            if (reminder == null)
                reminder = new Reminder();

            _dateDisplay = FindViewById<EditText>(Resource.Id.date_display);
            _timeDisplay = FindViewById<EditText>(Resource.Id.time_display);
            _txtNote = FindViewById<EditText>(Resource.Id.txtNote);

            _dateDisplay.Text = reminder.Date;
            _timeDisplay.Text = reminder.Time;
            _txtNote.Text = reminder.Note;

            _saveButton = FindViewById<Button>(Resource.Id.save);
            _btnList = FindViewById<Button>(Resource.Id.btnList);

            _dateDisplay.Click += DateSelect_OnClick;
            _timeDisplay.Click += TimeSelectOnClick;
            _saveButton.Click += SaveRecords;
            _btnList.Click += (sender, e) => {
                StartActivity(new Intent(this, typeof(ListReminder)));
            };
        }

如何在以前的用户输入仍然存在的情况下打开 activity Xamarin

How to open an activity with previous user input still there Xamarin

c#

xamarin.android