在Maui中使用Sqlite

在maui项目中使用sqlite数据库，先在Nuget中搜索sqlite-net-pcl安装 ，再在搜索中输入sqlite空格green，搜索安装sqlitepclraw.bundle_green，如果不安装后者，将会报错。

在maui中体验一下sqlite，设计一个简单的笔记本simpleNotes，先建模型，在文件夹models中创建Note.cs。

using SQLite;

namespace SimpleNotes.Models
{
    public class Note
    {
        [PrimaryKey,AutoIncrement]
        public int NoteId { get; set; }

        public string Title { get; set; }
        public string Content { get; set; }

        public DateTime CreationTime { get; set; }

        public DateTime LastModifiedTime { get; set; }
    }
}

在models文件夹中再建一个常量类，方便使用，文件名constants.cs。

namespace SimpleNotes.Models
{
    public class Constants
    {
        private const string DBName = "notes.db3";
        public const SQLite.SQLiteOpenFlags Flags = SQLite.SQLiteOpenFlags.Create |
            SQLite.SQLiteOpenFlags.ReadWrite | SQLite.SQLiteOpenFlags.SharedCache;

        public static string DatabasePath => Path.Combine(FileSystem.AppDataDirectory, DBName);
    }
}

再在services文件夹建一个DatabaseService.cs，使用sqlite数据库的类。

using SimpleNotes.Models;
using SQLite;

namespace SimpleNotes.Services
{
    public class DatabaseService
    {
        SQLiteAsyncConnection conn;

        async Task Init()
        {
            if (conn is null)
            {
                conn = new SQLiteAsyncConnection(Constants.DatabasePath, Models.Constants.Flags);
                await conn.CreateTableAsync();
            }
        }

        public async Task> GetAll()
        {
            await Init();
            return await conn.Table().ToListAsync();
        }

        public async Task GetNote(Note note)
        {
            await Init();
            var local = note;
            if (local is not null)
            {
                return await conn.Table().Where(n => n.NoteId == local.NoteId).FirstOrDefaultAsync();
            }

            return null;
        }

        public async Task AddNoteAsync(Note note)
        {
            await Init();
            var local = note;
            if (local is not null)
            {
                if (local.NoteId == 0)
                {
                    local.CreationTime = DateTime.Now;
                    local.LastModifiedTime = DateTime.Now;
                    return await conn.InsertAsync(local);
                }
                else
                {
                    local.LastModifiedTime = DateTime.Now;
                    return await conn.UpdateAsync(local);
                }
            }
            return -1;
        }

        public async Task DeleteNoteAsync(Note note)
        {
            await Init();
            var local = note;
            if(local is not null)
            {
                var matchedNote = conn.Table().Where(n => n.NoteId == local.NoteId).FirstOrDefaultAsync();
                if(matchedNote is not null)
                {
                    return await conn.DeleteAsync(local);
                }
            }
            return 0;
        }        
    }
}

使用maui，不安装社区工具是不行的，真的是太方便了，提高效率，用nuget搜索安装communitytoolkit.maui和communitytoolkit.mvvm。

在viewmodels文件夹中创建AboutPageViewModel.cs。

namespace SimpleNotes.ViewModels
{
    public class AboutPageViewModel
    {
        public static string AppName => $"程序名称：{AppInfo.Name}";
        public static string Vertion => $"版本：{AppInfo.VersionString}";

        public static string MoreMessage => $"使用MAUI架构，C#语言，xaml设计界面，使用IOC容器技术。";
    }
}

在viewmodels文件夹中创建NotePageViewModel.cs。

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using SimpleNotes.Models;
using SimpleNotes.Services;

namespace SimpleNotes.ViewModels
{
    public class NotePageViewModel : ObservableObject, IQueryAttributable
    {
        DatabaseService db;
        Note _note = new Note();
        public NotePageViewModel(DatabaseService databaseService) 
        {  
            db = databaseService;
            AddNoteCommand = new AsyncRelayCommand(AddNote);
            DeleteNoteCommand = new AsyncRelayCommand(DeleteNote);
        }       

        public void ApplyQueryAttributes(IDictionary query)
        {
            if (query.ContainsKey("load"))
            {
                Note local = query["load"] as Note;
                _note = local;
                OnRefresh();
            }
            else if (query.ContainsKey("name"))
            {
                var name = query["name"] as string;
                if (name == "new")
                {
                    _note = new Note();
                    OnRefresh();
                }
            }
        }

        private void OnRefresh()
        {
            OnPropertyChanged(nameof(Title));
            OnPropertyChanged(nameof(Content));
            OnPropertyChanged(nameof(CreationTime));
            OnPropertyChanged(nameof(LastModifiedTime));
        }

        public string Title
        {
            get => _note.Title;
            set => SetProperty(_note.Title, value, _note, (n, v) => n.Title = v);
        }

        public string Content
        {
            get => _note.Content;
            set => SetProperty(_note.Content, value, _note, (n, v) => n.Content = v);
        }

        public DateTime CreationTime
        {
            get => _note.CreationTime;
            set => SetProperty(_note.CreationTime, value, _note, (n, v) => n.CreationTime = v);
        }

        public DateTime LastModifiedTime
        {
            get => _note.LastModifiedTime;
            set => SetProperty(_note.LastModifiedTime, value, _note, (n, v) => n.LastModifiedTime = v);
        }

        async Task AddNote()
        {
            await db.AddNoteAsync(_note);         
            await Shell.Current.GoToAsync("..");
        }

        public IAsyncRelayCommand AddNoteCommand { get; private set; }

        async Task DeleteNote()
        {
           await db.DeleteNoteAsync(_note);
            await Shell.Current.GoToAsync("..");
        }

        public IAsyncRelayCommand DeleteNoteCommand { get; private set; }
    }
}

再在viewmodels文件夹下创建主页面MainPageViewModels.cs。

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using SimpleNotes.Models;
using SimpleNotes.Services;
using SimpleNotes.Views;
using System.Collections.ObjectModel;

namespace SimpleNotes.ViewModels
{
    public class MainPageViewModel : ObservableObject
    {
        ObservableCollection notes;
        DatabaseService db;
        public ObservableCollection Notes
        {
            get => notes ??= new ObservableCollection();
            set => SetProperty(ref notes, value);
        }

        public MainPageViewModel(DatabaseService databaseService)
        {
            db = databaseService;
            InitializeCollectionCommand = new AsyncRelayCommand(InitializeCollection);
            SelectedNoteCommand = new AsyncRelayCommand(SelectedNote);
            NewNoteCommand = new AsyncRelayCommand(NewNote);
        }

        async Task InitializeCollection()
        {
            Notes.Clear();
            foreach (Note note in await db.GetAll())
            {
                Notes.Add(note);
            }
        }

        public IAsyncRelayCommand InitializeCollectionCommand { get; private set; }

        async Task SelectedNote(Note note)
        {
            if (note is not null)
            {
                var parameter = new Dictionary()
                {
                    {"load",note }
                };
                await Shell.Current.GoToAsync($"{nameof(NotePage)}", parameter);
            }

        }

        public IAsyncRelayCommand SelectedNoteCommand { get; private set; }

        async Task NewNote()
        {
            string name = "new";
            await Shell.Current.GoToAsync($"{nameof(NotePage)}?name={name}");
        }  

        public IAsyncRelayCommand NewNoteCommand { get; private set; }
    }
}

再在views文件夹下创建AboutPage.xaml界面文件。

在views文件夹下创建NotePage.xaml界面文件。

在views文件夹下创建MainPage.xaml界面文件。

修改AppShell.xaml文件。

再修改mauiProgram.cs文件，由于maui自带容器，我们可以用用，最好用的是它的扩展builder.Services.AddSingleton()，大家看看，把view和viewmodel一起注册，是不是非常非常方便？还有以下扩展builder.Services.AddSingletonWithShellRoute($"{nameof(NotePage)}")，不仅注册了view和viewmodel，还顺带把shell的路由也注册了，真是方便，完整内容。

using CommunityToolkit.Maui;
using Microsoft.Extensions.Logging;
using SimpleNotes.Services;
using SimpleNotes.ViewModels;
using SimpleNotes.Views;

namespace SimpleNotes;

public static class MauiProgram
{
	public static MauiApp CreateMauiApp()
	{
		var builder = MauiApp.CreateBuilder();
		builder
			.UseMauiApp()
			.UseMauiCommunityToolkit()
			.ConfigureFonts(fonts =>
			{
				fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
				fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
			});

		//注册service,viewmodels views;
		builder.Services.AddSingleton();
		builder.Services.AddSingleton();
		builder.Services.AddSingletonWithShellRoute($"{nameof(NotePage)}");

#if DEBUG
		builder.Logging.AddDebug();
#endif

		return builder.Build();
	}
}

修改NotePage.xaml.cs文件，由于我们在容器中注册了，所以可以在构造函数中直接引用注册的类型。

using SimpleNotes.ViewModels;
namespace SimpleNotes.Views;

public partial class NotePage : ContentPage
{
	public NotePage(NotePageViewModel viewmodel)
	{
		InitializeComponent();
		BindingContext = viewmodel;
	}
}

再修改MainPage.xaml.cs文件。

using SimpleNotes.ViewModels;

namespace SimpleNotes.Views;

public partial class MainPage : ContentPage
{
	public MainPage(MainPageViewModel viewmodel)
	{
		InitializeComponent();
		BindingContext = viewmodel;
	}

    private void MainPage_Appearing(object sender, EventArgs e)
    {
		((MainPageViewModel)BindingContext).InitializeCollectionCommand.Execute(null);
    }

    private void MainPage_NavigatedTo(object sender, NavigatedToEventArgs e)
    {
        notesCollection.SelectedItem = null;
    }
}

在maui页面间传递自定义的值是这样写，使用shell.current.GogoAsync的第二个签名。

​
 var parameter = new Dictionary()
  {
    {"load",note }
  };
 await Shell.Current.GoToAsync($"{nameof(NotePage)}", parameter);

​

第一个签名是这样写，自定义的只能用第二个。

string name = "new";
await Shell.Current.GoToAsync($"{nameof(NotePage)}?name={name}");

看看运行效果，达到预期。