【Android】12.6 利用Intent实现记事本功能（NotePad）

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

xml version="1.0" encoding="utf-8"?>
<view xmlns:android="http://schemas.android.com/apk/res/android"
    class="MyDemos.SrcDemos.ch1205LinedEditText"
    android:id="@+id/note"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="5dip"
    android:scrollbars="vertical"
    android:fadingEdge="vertical"
    android:gravity="top"
    android:textSize="22sp"
    android:capitalize="sentences" />

（4）添加ch1205_Main.axml文件

xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:background="#ffffff"
    android:padding="10px">
  <ImageView
      android:id="@+id/icon"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:src="@drawable/ch12_app_notes" />
  <LinearLayout
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"
      android:paddingTop="6px">
    <TextView
        android:id="@+id/body"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/modified"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
  LinearLayout>
LinearLayout>

（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();
        }
    }
}

OK，这一章就讲到这了。