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[操作系统]13.4 使用SQLite.NET.Async


分类:C#、Android、VS2015;

创建日期:2016-02-27

一、简介

这一节演示如何利用以异步方式(async、await)访问SQLite数据库。

二、示例4运行截图

下面左图为初始页面,右图为单击【创建数据库】按钮后的结果。

image  image

 

下面左图为单击【添加单行】按钮的结果,右图为单击【添加多行】按钮的结果。

image  image

注意:不想再像上一节的例子那样逐个添加页面了,毕竟例子的目的仅仅是为了演示最基本的异步操作用法,代码太多容易冲淡要关注的内容,所以该例子并没有去解决重复添加相同学号的记录引起的冲突问题,只是简单地把捕获的异常直接显示出来了。但是,在实际项目中,你如果也像这个例子这样去简单处理,那你肯定会挨训,呵呵。

三、主要设计步骤

1、添加对SQLite.NET.Async-PCL程序包的引用

鼠标右击项目中的【引用】à【管理NuGet程序包】,数据源选择【NuGet official package source】,在搜索框中输入【sqlite】,找到【SQLite.NET.Async-PCL】,选择最新的版本(本示例使用的是3.1.1版),然后单击【安装】。

安装程序包以后,在【解决方案资源管理器】中,就可以看出它已经替你自动添加了对SQLite.Net.Async的引用。安装的程序包及其依赖项的名称和版本见本章开头(13.0节)列出的packages.config文件。

2、创建数据库和表

在SrcDemos文件夹下添加一个MyDb4Model文件夹,该文件夹用于保存与“MyDb4.db”数据库相关的.cs文件。

(1)添加Student.cs文件

using System;using SQLite.Net.Attributes;namespace MyDemos.SrcDemos.MyDb4Model{  [Table("Student")]  public class Student  {    //主键,自动增量    [PrimaryKey,AutoIncrement]    public int id { get; set; }    //学号    [Unique, NotNull]    public string XueHao { get; set; }    //姓名    [MaxLength(30), NotNull]    public string Name { get; set; }    //出生日期    public DateTime BirthDate { get; set; }    public override string ToString()    {      return string.Format(        "[学号={0}, 姓名={1}, 出生日期={2:yyyy-MM-dd}]\n",        XueHao, Name, BirthDate);    }  }}

(2)添加MyDb4.cs文件

using System;using System.IO;using SQLite.Net;using SQLite.Net.Async;using SQLite.Net.Platform.XamarinAndroid;namespace MyDemos.SrcDemos.MyDb4Model{  public static class MyDb4  {    private static readonly string dbPath = Path.Combine(      Environment.GetFolderPath(Environment.SpecialFolder.Personal),      "MyDb4.db");    public static SQLiteAsyncConnection GetAsyncConnection()    {      SQLitePlatformAndroid platform = new SQLitePlatformAndroid();      SQLiteConnectionString connStr = new SQLiteConnectionString(dbPath, false);      return new SQLiteAsyncConnection(()=> new SQLiteConnectionWithLock(platform, connStr));    }  }}

3、添加ch1304_Main.a<??><LinearLayout ="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:weightSum="1"> <LinearLayout android:orientation="horizontal" android:minWidth="25px" android:minHeight="25px" android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/linearLayout1" android:layout_weight=".2" android:gravity="center"> <Button android:text="创建数据库" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btnCreateDB" /> <Button android:text="添加单行" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btnCreateSingle" /> <Button android:text="添加多行" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btnCreateList" /> </LinearLayout> <LinearLayout android:orientation="vertical" android:minWidth="25px" android:minHeight="25px" android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/linearLayout2" android:layout_weight="0.6" android:layout_marginLeft="5dp" android:layout_marginRight="5dp"> <TextView android:text="结果" android:textAppearance="?android:attr/textAppearanceMedium" android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/textView1" android:textColor="#fff" /> <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/txtResults" android:layout_marginTop="5dp" /> </LinearLayout> <LinearLayout android:orientation="horizontal" android:minWidth="25px" android:minHeight="25px" android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/linearLayout3" android:layout_weight="0.2" /></LinearLayout>

4、添加ch1304MainActivity.cs文件

using System;using System.Collections.Generic;using Android.App;using Android.OS;using Android.Widget;using MyDemos.SrcDemos.MyDb4Model;using SQLite.Net;using System.Threading.Tasks;namespace MyDemos.SrcDemos{  [Activity(Label = "【例13-4】SQLite基本用法4")]  public class ch1304MainActivity : Activity  {    protected override void OnCreate(Bundle savedInstanceState)    {      base.OnCreate(savedInstanceState);      SetContentView(Resource.Layout.ch1304_Main);      var btnCreate = FindViewById<Button>(Resource.Id.btnCreateDB);      var btnSingle = FindViewById<Button>(Resource.Id.btnCreateSingle);      var btnList = FindViewById<Button>(Resource.Id.btnCreateList);      var txtResult = FindViewById<TextView>(Resource.Id.txtResults);      // 数据库创建之前禁用相关按钮      btnSingle.Enabled = btnList.Enabled = false;      btnCreate.Click += async delegate      {        try        {          var conn = MyDb4.GetAsyncConnection();          await conn.CreateTableAsync<Student>();          await conn.DeleteAllAsync<Student>();          txtResult.Text = "创建成功。";          btnList.Enabled = btnSingle.Enabled = true;        }        catch (SQLiteException ex)        {          txtResult.Text = "创建失败:" + ex.Message;        }      };      btnSingle.Click += async delegate      {        var student = new Student { XueHao = "01001", Name = "张三", BirthDate = new DateTime(1995, 4, 7) };        try        {          var conn = MyDb4.GetAsyncConnection();          int x = await conn.InsertAsync(student);          await conn.UpdateAsync(student);          txtResult.Text = $"添加了 {x} 条记录。\n";          txtResult.Text += await GetStudents();        }        catch (SQLiteException ex)        {          txtResult.Text = "Error:" + ex.Message;        }      };      btnList.Click += async delegate      {        var list = new List<Student>{          new Student { XueHao="01002", Name = "李四", BirthDate = new DateTime(1995,4,8) },          new Student { XueHao="01003", Name = "王五", BirthDate = new DateTime(1995,4,9) },          new Student { XueHao="01004", Name = "赵六", BirthDate = new DateTime(1995,4,10) }        };        try        {          var conn = MyDb4.GetAsyncConnection();          int x = await conn.InsertAllAsync(list);          await conn.UpdateAllAsync(list);          txtResult.Text = $"添加了 {x} 条记录。\n";          txtResult.Text += await GetStudents();        }        catch (SQLiteException ex)        {          txtResult.Text = "Error:" + ex.Message;        }      };    }    private static async Task<string> GetStudents()    {      var conn = MyDb4.GetAsyncConnection();      int count = await conn.Table<Student>().CountAsync();      string s = $"当前记录数:{count}\n";      var data = await conn.Table<Student>().ToListAsync();      foreach (var v in data)      {        s += v.ToString();      }      return s;    }  }}