UWP開發之Mvvmlight實踐三：簡單MVVM實例開發(圖文詳解付代碼)，

UWP開發之Mvvmlight實踐三：簡單MVVM實例開發(圖文詳解付代碼)，

在做MVVM各種框架對比之前，我覺得有必要先自己做一個簡單的MVVM實現案例比較好，這樣就可以看到自己實現的時候有那些不方便的地方。而各種框架又是怎麼解決我們這些麻煩的。

1、創建UWP空項目

using System; using System.ComponentModel; using System.Runtime.CompilerServices; namespace MvvmDemo.Common { /// <summary> /// Viewmodel基類，屬性雙向綁定基礎 /// </summary> public class ViewModelBase : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; /// <summary> /// 屬性變更通知 /// </summary> /// <param name="propertyName">屬性名</param> public void NotifyPropertyChanged([CallerMemberName] String propertyName = "") { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } } }

4、創建Command基類

代碼如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace MvvmDemo.Common
{
    public class DelegateCommand<T>: ICommand
    {
        /// <summary>
        /// 命令
        /// </summary>
        private Action<T> _Command;
        /// <summary>
        /// 命令可否執行判斷
        /// </summary>
        private Func<T, bool> _CanExecute;
        /// <summary>
        /// 可執行判斷結束後通知命令執行
        /// </summary>
        public event EventHandler CanExecuteChanged;

        /// <summary>
        /// 構造函數
        /// </summary>
        /// <param name="command">命令</param>
        public DelegateCommand(Action<T> command):this(command,null)
        {
        }

        /// <summary>
        /// 構造函數
        /// </summary>
        /// <param name="command">命令</param>
        /// <param name="canexecute">命令可執行判斷</param>
        public DelegateCommand(Action<T> command,Func<T,bool> canexecute)
        {
            if(command==null)
            {
                throw new ArgumentException("command");
            }
            _Command = command;
            _CanExecute = canexecute;
        }

        /// <summary>
        /// 命令執行判斷
        /// </summary>
        /// <param name="parameter">判斷數據</param>
        /// <returns>判定結果（True：可執行，False：不可執行）</returns>
        public bool CanExecute(object parameter)
        {
            return _CanExecute == null ? true : _CanExecute((T)parameter);
        }

        /// <summary>
        /// 執行命令
        /// </summary>
        /// <param name="parameter">參數</param>
        public void Execute(object parameter)
        {
            _Command((T)parameter);
        }
    }
}

5、創建ViewModel

代碼如下：

using MvvmDemo.Common;
using MvvmDemo.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MvvmDemo.ViewModels
{
    public class MainViewModel : ViewModelBase
    {
        private string _userId;
        private string _userName;
        private DelegateCommand<string> _loginCommand;
        
        /// <summary>
        /// 用戶名
        /// </summary>
        public string UserId
        {
            get
            {
                return _userId;
            }

            set
            {
                _userId = value;
                NotifyPropertyChanged();
            }
        }
        /// <summary>
        /// 用戶名
        /// </summary>
        public string UserName
        {
            get
            {
                return _userName;
            }

            set
            {
                _userName = value;
                NotifyPropertyChanged();
            }
        }
        /// <summary>
        /// 登陸命令
        /// </summary>
        public DelegateCommand<string> LoginCommand
        {
            get
            {
                return _loginCommand
                    ??(_loginCommand=new DelegateCommand<string>(
                        s=>
                        {
                            UserName = new UserModel().GetUserName(s); 
                        },
                        s=>!string.IsNullOrEmpty(s)
                        ));
            }
        }
    }
}

6、創建View設置綁定

這裡直接就拿MainView做例子，更改下布局

<Page
    x:Class="MvvmDemo.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MvvmDemo"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" 
          VerticalAlignment="Center"
          HorizontalAlignment="Center">
        <Grid.RowDefinitions>
            <RowDefinition Height="50"/>
            <RowDefinition Height="50"/>
            <RowDefinition Height="50"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="Auto" />
        </Grid.ColumnDefinitions>

        <TextBlock Text="用戶ID：" Grid.Row="0" Grid.Column="0" Width="100" />
        <TextBlock Text="用戶名：" Grid.Row="1" Grid.Column="0" Width="100" />
        <TextBox x:Name="txtUserID" Grid.Row="0" Grid.Column="1" Width="150" Text="{x:Bind VM.UserId,Mode=OneWay}" />
        <TextBlock x:Name="txbUserName" Grid.Row="1" Grid.Column="1" Width="150" Text="{x:Bind VM.UserName,Mode=OneWay}"  />
        <Button x:Name="btnLogin" Content="Login" Grid.Row="2" Grid.ColumnSpan="2" Width="150" HorizontalAlignment="Center"
                Command="{x:Bind VM.LoginCommand,Mode=OneWay}"
                CommandParameter="{Binding Text,ElementName=txtUserID,Mode=OneWay}"/>
    </Grid>
</Page>

後台添加代碼

/// <summary>
    /// 可用於自身或導航至 Frame 內部的空白頁。
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public MainViewModel VM =>new MainViewModel();

        public MainPage()
        {
            this.InitializeComponent();
            this.DataContext = VM;    
        }
    }

7、創建Model

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MvvmDemo.Models
{
    public class UserModel
    {
        public string GetUserName(string userid)
        {
            return string.Format("取得成功:{0}",userid);
        }
    }
}

8、實行結果

輸入內容前按鈕自動不可用：

輸入內容後按鈕自動可用：

點擊Login按鈕：

9、總結

這種就是簡單的登陸實現，涉及到了MVVM的View，Viewmodel,Model。這裡按鈕是自動判斷是否可用，這個判斷實現就在我們的Viewmodel。例子中涉及到了Xbind，這個和Binding是有區別的，具體說明下節在續。可見自己實現Mvvm模式也不是很難的事情，不過隨著項目的復雜加深就會有很多問題，比如Viewmode之間通信等。