分类：C#、Android、VS2015；
创建日期：2016-02-23
一、简介
这个例子演示如何实现一个简单的记事本功能。
该例子提前使用了后面章节将要介绍的SQLLite数据库。
二、示例—ch1205NotePadDemo
1、运行截图
单击右上角【…】会弹出【添加】菜单项，长按某条记录会弹出快捷菜单【删除】项。
2、主要设计步骤
（1）添加引用
鼠标右击【引用】à【添加引用】，在弹出的窗口中勾选“System.Data”和“System.Data.SQlite”，如下图所示：
注意：不需要通过NuGet添加SQLite程序包，只需要按这种方式添加即可。
（2）添加图片
到Android SDK API 23的Samples的NotePad例子下找到app_notes.png，将其添加到该项目中，并将其换名为ch12_app_notes.png。
（3）添加ch1205_NoteEditor.axml文件
（4）添加ch1205_Main.axml文件
（5）添加ch1205Note.cs文件
using System;namespace MyDemos.SrcDemos{ class ch1205Note : Java.Lang.Object { public long Id { get; set; } public string Body { get; set; } public DateTime ModifiedTime { get; set; } public ch1205Note() { Id = -1L; Body = string.Empty; } public ch1205Note(long id, string body, DateTime modified) { Id = id; Body = body; ModifiedTime = modified; } public override string ToString() { return ModifiedTime.ToString(); } }} （6）添加ch1205LinedEditText.cs文件
using Android.Content;using Android.Runtime;using Android.Widget;using Android.Graphics;using Android.Util;namespace MyDemos.SrcDemos{ [Register("MyDemos.SrcDemos.ch1205LinedEditText")] class ch1205LinedEditText : EditText { private Rect rect; private Paint paint; // 为了LayoutInflater需要提供此构造函数 public ch1205LinedEditText(Context context, IAttributeSet attrs) : base(context, attrs) { rect = new Rect(); paint = new Paint(); paint.SetStyle(Android.Graphics.Paint.Style.Stroke); paint.Color = Color.LightGray; } protected override void OnDraw(Canvas canvas) { int count = LineCount; for (int i = 0; i < count; i++) { int baseline = GetLineBounds(i, rect); canvas.DrawLine(rect.Left, baseline + 1, rect.Right, baseline + 1, paint); } base.OnDraw(canvas); } }} （7）添加ch1205NoteRepository.cs文件
using System;using System.Collections.Generic;using Mono.Data.Sqlite;namespace MyDemos.SrcDemos{ class ch1205NoteRepository { private static string db_file = "notes.db3"; private static SqliteConnection GetConnection() { var dbPath = System.IO.Path.Combine( System.Environment.GetFolderPath( System.Environment.SpecialFolder.Personal), db_file); bool exists = System.IO.File.Exists(dbPath); if (!exists) SqliteConnection.CreateFile(dbPath); var conn = new SqliteConnection("Data Source=" + dbPath); if (!exists) CreateDatabase(conn); return conn; } private static void CreateDatabase(SqliteConnection connection) { var sql = "CREATE TABLE ITEMS (Id INTEGER PRIMARY KEY AUTOINCREMENT, Body ntext, Modified datetime);"; connection.Open(); using (var cmd = connection.CreateCommand()) { cmd.CommandText = sql; cmd.ExecuteNonQuery(); } // Create a sample note to get the user started sql = "INSERT INTO ITEMS (Body, Modified) VALUES (@Body, @Modified);"; using (var cmd = connection.CreateCommand()) { cmd.CommandText = sql; cmd.Parameters.AddWithValue("@Body", "今天有个约会"); cmd.Parameters.AddWithValue("@Modified", DateTime.Now); cmd.ExecuteNonQuery(); } connection.Close(); } public static IEnumerable GetAllNotes() { var sql = "SELECT * FROM ITEMS;"; using (var conn = GetConnection()) { conn.Open(); using (var cmd = conn.CreateCommand()) { cmd.CommandText = sql; using (var reader = cmd.ExecuteReader()) { while (reader.Read()) { yield return new ch1205Note( reader.GetInt32(0), reader.GetString(1), reader.GetDateTime(2)); } } } } } public static ch1205Note GetNote(long id) { var sql = "SELECT * FROM ITEMS WHERE Id = id;"; using (var conn = GetConnection()) { conn.Open(); using (var cmd = conn.CreateCommand()) { cmd.CommandText = sql; using (var reader = cmd.ExecuteReader()) { if (reader.Read()) return new ch1205Note(reader.GetInt32(0), reader.GetString(1), reader.GetDateTime(2)); else return null; } } } } public static void DeleteNote(ch1205Note note) { var sql = string.Format("DELETE FROM ITEMS WHERE Id = {0};", note.Id); using (var conn = GetConnection()) { conn.Open(); using (var cmd = conn.CreateCommand()) { cmd.CommandText = sql; cmd.ExecuteNonQuery(); } } } public static void SaveNote(ch1205Note note) { using (var conn = GetConnection()) { conn.Open(); using (var cmd = conn.CreateCommand()) { if (note.Id < 0) { // Do an insert cmd.CommandText = "INSERT INTO ITEMS (Body, Modified) VALUES (@Body, @Modified); SELECT last_insert_rowid();"; cmd.Parameters.AddWithValue("@Body", note.Body); cmd.Parameters.AddWithValue("@Modified", DateTime.Now); note.Id = (long)cmd.ExecuteScalar(); } else { // Do an update cmd.CommandText = "UPDATE ITEMS SET Body = @Body, Modified = @Modified WHERE Id = @Id"; cmd.Parameters.AddWithValue("@Id", note.Id); cmd.Parameters.AddWithValue("@Body", note.Body); cmd.Parameters.AddWithValue("@Modified", DateTime.Now); cmd.ExecuteNonQuery(); } } } } }} （8）添加ch1205NoteAdapter.cs文件
using Android.App;using Android.Content;using Android.Widget;namespace MyDemos.SrcDemos{ class ch1205NoteAdapter : ArrayAdapter { private Activity activity; public ch1205NoteAdapter(Activity activity, Context context, int textViewResourceId, ch1205Note[] objects) : base(context, textViewResourceId, objects) { this.activity = activity; } public override Android.Views.View GetView(int position, Android.Views.View convertView, Android.Views.ViewGroup parent) { //Get our object for this position var item = (ch1205Note)GetItem(position); // 如果convertView不为null则重用它，否则从当前布局中填充（inflate）它。 // 由于这种方式不是每次都填充一个新的view，因此可提高性能。 var view = (convertView ?? activity.LayoutInflater.Inflate( Resource.Layout.ch1205_Main, parent, false)) as LinearLayout; view.FindViewById (Resource.Id.body).Text = Left(item.Body.Replace("\n", " "), 25); view.FindViewById (Resource.Id.modified).Text = item.ModifiedTime.ToString(); return view; } private string Left(string text, int length) { if (text.Length <= length) return text; return text.Substring(0, length); } }} （9）添加ch1205NoteEditorActivity.cs文件
using Android.App;using Android.Content;using Android.OS;using Android.Widget;using Android.Content.PM;namespace MyDemos.SrcDemos{ [Activity(Label = "ch1205NoteEditorActivity", ScreenOrientation = ScreenOrientation.Sensor, ConfigurationChanges = ConfigChanges.KeyboardHidden | ConfigChanges.Orientation)] public class ch1205NoteEditorActivity : Activity { private ch1205Note note; private EditText text_view; protected override void OnCreate(Bundle savedInstanceState) { base.OnCreate(savedInstanceState); SetContentView(Resource.Layout.ch1205_NoteEditor); text_view = FindViewById (Resource.Id.note); var note_id = Intent.GetLongExtra("note_id", -1L); if (note_id < 0) note = new ch1205Note(); else note = ch1205NoteRepository.GetNote(note_id); } protected override void OnResume() { base.OnResume(); text_view.SetTextKeepState(note.Body); } protected override void OnPause() { base.OnPause(); // 如果是新建的记事本且没有内容，不保存直接返回。 if (IsFinishing && note.Id == -1 && text_view.Text.Length == 0) return; // 保存记事本 note.Body = text_view.Text; ch1205NoteRepository.SaveNote(note); } }} （10）添加ch1205NotePadMain.cs文件
using System.Linq;using Android.App;using Android.Content;using Android.OS;using Android.Views;using Android.Widget;namespace MyDemos.SrcDemos{ [Activity(Label = "ch1205NotePadMain")] public class ch1205NotePadMain : ListActivity { // 菜单项 public const int MenuItemDelete = Menu.First; public const int MenuItemInsert = Menu.First + 1; protected override void OnCreate(Bundle savedInstanceState) { base.OnCreate(savedInstanceState); SetDefaultKeyMode(DefaultKey.Shortcut); ListView.SetOnCreateContextMenuListener(this); PopulateList(); } public void PopulateList() { // 获取存放到列表中的所有记事本项 var notes = ch1205NoteRepository.GetAllNotes(); var adapter = new ch1205NoteAdapter(this, this, Resource.Layout.ch1205_Main, notes.ToArray()); ListAdapter = adapter; } public override bool OnCreateOptionsMenu(IMenu menu) { base.OnCreateOptionsMenu(menu); menu.Add(0, MenuItemInsert, 0, "添加") .SetShortcut('3', 'a') .SetIcon(Android.Resource.Drawable.IcMenuAdd); return true; } public override bool OnOptionsItemSelected(IMenuItem item) { switch (item.ItemId) { case MenuItemInsert: // 通过intent添加新项 var intent = new Intent(this, typeof(ch1205NoteEditorActivity)); intent.PutExtra("note_id", -1L); StartActivityForResult(intent, 0); return true; } return base.OnOptionsItemSelected(item); } public override void OnCreateContextMenu(IContextMenu menu, View view, IContextMenuContextMenuInfo menuInfo) { var info = (AdapterView.AdapterContextMenuInfo)menuInfo; var note = (ch1205Note)ListAdapter.GetItem(info.Position); menu.Add(0, MenuItemDelete, 0, "删除"); } public override bool OnContextItemSelected(IMenuItem item) { var info = (AdapterView.AdapterContextMenuInfo)item.MenuInfo; var note = (ch1205Note)ListAdapter.GetItem(info.Position); switch (item.ItemId) { case MenuItemDelete: // 删除该记事本项 ch1205NoteRepository.DeleteNote(note); PopulateList(); return true; } return false; } protected override void OnListItemClick(ListView l, View v, int position, long id) { var selected = (ch1205Note)ListAdapter.GetItem(position); // 执行activity，查看/编辑当前选中的项 var intent = new Intent(this, typeof(ch1205NoteEditorActivity)); intent.PutExtra("note_id", selected.Id); StartActivityForResult(intent, 0); } protected override void OnActivityResult(int requestCode, Result resultCode, Intent data) { base.OnActivityResult(requestCode, resultCode, data); // 当列表项发生变化时，这里仅关心如何刷新它，并没有处理选定的项 PopulateList(); } }}