WPF入門教程系列二十八 ——DataGrid使用示例MVVM模式(6)

WPF入門教程系列目錄

WPF入門教程系列二——Application介紹

WPF入門教程系列三——Application介紹(續)

WPF入門教程系列四——Dispatcher介紹

WPF入門教程系列五——Window 介紹

WPF入門教程系列十一——依賴屬性（一）

WPF入門教程系列十五——WPF中的數據綁定(一)

 

 

 

八、在Command中傳遞參數

7.上面Buttom的Command類就是純命令，什麼參數都不接收，這次的ProvinceChangedCommand類在執行命令的時候，能夠傳參數！採用泛型的形式，給Action添加泛型參數。

8. 在Visual Studio 2022的解決方案資源管理器中，使用鼠標右鍵單擊“Command”文件夾，在彈出菜單中選擇“添加--> 類”，在彈出的“添加新項”對話框中，選擇添加 “ProvinceChangedCommand”類，這是一個我們要實現的保存操作指令，然後選擇“添加”。ProvinceChangedCommand的具體代碼如下：

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

using System.Threading.Tasks;
using System.Windows.Input;
 
namespace WpfGridDemo.NET7.Command
{
    public class ProvinceChangedCommand<T> : ICommand
    {
        /// <summary>
        /// 命令能否執行
        /// </summary>
        readonly Func<bool> _canExecute;
        /// <summary>
        /// 命令執行的方法
        /// </summary>
        readonly Action<T> _execute;
 
        /// <summary>
        /// 命令的構造函數
        /// </summary>
        /// <param name="action">命令需執行的方法</param>
        /// <param name="canExecute">命令是否可以執行的方法</param>
        public ProvinceChangedCommand(Action<T> action, Func<bool> canExecute)
        {
            _execute = action;
            _canExecute = canExecute;
        }
 
        /// <summary>
        /// 判斷命令是否可以執行
        /// </summary>
        /// <param name="parameter"></param>
        /// <returns></returns>
        public bool CanExecute(Object parameter)
        {
            if (_canExecute == null)
                return true;
            return _canExecute();
        }
 
        /// <summary>
        /// 執行命令
        /// </summary>
        /// <param name="parameter"></param>
        public void Execute(Object parameter)
        {
            _execute((T)parameter);
        }
 
        /// <summary>
        /// 事件追加、移除
        /// </summary>
        public event EventHandler CanExecuteChanged
        {
            add
            {
                if (_canExecute != null)
                    CommandManager.RequerySuggested += value;
            }
            remove
            {
                if (_canExecute != null)
                    CommandManager.RequerySuggested -= value;
            }
        }
 
    }
}
void ProviceSelectionChangedExecute(object sender)
        {
            try
            {
                if (sender is ComboBox)
                {
                    ComboBox drp=sender as ComboBox;
                    ProvinceCode=drp.SelectedValue.ToString();
                    GridDbContext db = new GridDbContext();
                    var list = db.City.AsTracking().ToList();
                    List<City> citys = list.Where(x => x.ProvinceCode == ProvinceCode).ToList();
                    cityList = new ObservableCollection<City>();
                    if (citys != null)
                    {
                        citys.ForEach((t) =>
 
                        { cityList.Add(t); }
                        );
                    }
 
                    var cityCodes = from city in citys
                                    select city.Code;
                    List<Area> areas = db.Area.AsTracking().ToList().Where(
x => cityCodes.Contains(x.CityCode)).ToList();

                    areaList = new ObservableCollection<Area>();
                    if (areas!=null)
                    {
                        areas.ForEach((t) =>

                        { areaList.Add(t); }
                        );
                    }
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

結果如圖：我們看到了省份下拉框中已經了省份信息。

 

9.通過綁定依賴屬性，實現自動刷新需要實現以下三步：

1.Model繼承並實現 INotifyPropertyChanged 接口；

2.數據集合使用ObservableCollection<T>集合；

3.View使用Binding數據對象屬性;

如果不行再看看集合在賦值前需要實例化，不然就出不來(必須要同一個源纔行)

10. 在Visual Studio 2022中打開MainWindows.xmal文件，並將文件中的代碼修改成如下：

<Window x:Class="WpfGridDemo.NET7.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
          xmlns:be="http://schemas.microsoft.com/xaml/behaviors"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfGridDemo.NET7"
        mc:Ignorable="d"
        Title="MainWindow" Height="600" Width="960" Loaded="Window_Loaded" >
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="100"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="25"></RowDefinition>
        </Grid.RowDefinitions>
        <WrapPanel Grid.Row="0" HorizontalAlignment="Left">
            <ComboBox x:Name="cboProvince" DisplayMemberPath="Name" SelectedValuePath="Code" >
 
                <be:Interaction.Triggers>

                    <be:EventTrigger EventName="SelectionChanged">
                        <be:InvokeCommandAction Command="{Binding ProviceChangedAction}" 
CommandParameter="{Binding  ElementName=cboProvince}"/>
                    </be:EventTrigger>
                </be:Interaction.Triggers>
 
            </ComboBox>
        </WrapPanel>

        <DataGrid x:Name="gridArea" Grid.Row="1" ItemsSource="{Binding GridAreaList}" 
AutoGenerateColumns="False" HorizontalAlignment="Left" VerticalAlignment="Top" 
SelectedItem="{Binding Path=AreaVM,
                                        Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}">

            <DataGrid.Columns>

                <DataGridComboBoxColumn Header="城市" Width="120" 
ItemsSource="{Binding Path=DataContext.GridCityList, 
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"  
x:Name="cboCity" ClipboardContentBinding="{x:Null}"
 SelectedValuePath="Code" SelectedValueBinding="{Binding Path=CityCode,
UpdateSourceTrigger=PropertyChanged}"  
DisplayMemberPath="Name" SelectedItemBinding="{x:Null}" />
                <DataGridTextColumn Header="縣區鎮" Width="*" Binding="{Binding Name}" 
ClipboardContentBinding="{x:Null}"/>
                <DataGridTextColumn Header="郵編" Width="100"  Binding="{Binding Code}" 
ClipboardContentBinding="{x:Null}"/>
                <DataGridTextColumn Header="創建時間" Width="160" Binding="{Binding Created}" 
ClipboardContentBinding="{x:Null}"/>
                <DataGridTextColumn Header="更新時間" Width="160" Binding="{Binding Updated}" 
ClipboardContentBinding="{x:Null}"/>
            </DataGrid.Columns>
        </DataGrid>
      

        <WrapPanel Grid.Row="2">
        <Button  x:Name="btnRefresh"  Height="22" Width="120" Click="btnRefresh_Click">刷新</Button>
<Button  x:Name="btnSave" Height="22" Width="120" Command="{Binding ClickSaveAction}" >保存</Button>
        </WrapPanel>
    </Grid>
</Window>

 

11. 在Visual Studio 2022中打開MainWindowsVM.cs文件，實現下拉框的選擇事件的Command命令綁定，將通過Command參數傳遞過來的省份信息，用於數據查詢，同時通知UI界面進行數據刷新。具體如下代碼：

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.DirectoryServices.ActiveDirectory;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Controls;
using System.Windows.Input;
using WpfGridDemo.NET7.Entitys;
 
namespace WpfGridDemo.NET7.ViewModel
{
    public class MainWindowVM: ViewModelBase
    {
        public MainWindowVM() {
            cityList = new ObservableCollection<City>();
            areaList = new ObservableCollection<Area>();
        }
        private Area m_Area;
        /// <summary>
        /// 縣鎮區數據
        /// </summary>
        public Area AreaVM
        {
            get { return m_Area; }
            set { m_Area = value; }
        }
        private string m_Province_Code;
        /// <summary>
        /// 省--代碼
        /// </summary>
        public string ProvinceCode { get => m_Province_Code; set => m_Province_Code = value; }
        private ObservableCollection<Area> areaList;
 
         public ObservableCollection<Area> GridAreaList
         {
             get { return areaList; }
             set
             {
                areaList = value;
                 RaisePropertyChanged("GridAreaList");
             }
        }
        private ObservableCollection<City> cityList;
 
        public ObservableCollection<City> GridCityList
        {
            get { return cityList; }
            set
            {
                cityList = value;
                RaisePropertyChanged("GridCityList");
            }
        }
    
        /// <summary>
        /// 命令要執行的方法
        /// </summary>
        void SaveExecute()
        {
            try
 
            {
                GridDbContext db = new GridDbContext();
                var list=db.Area.AsTracking().ToList();
                Area modifyArea = list.Where(x=>x.Id==AreaVM.Id).FirstOrDefault();
                if (modifyArea != null)
                {
                    modifyArea.Name = AreaVM.Name;
                    modifyArea.Updated = DateTime.Now;
                    db.SaveChanges();
                }
 
            }
            catch (Exception ex)
            {
 
                throw ex;
            }
        }
 
        /// <summary>
        /// 命令是否可以執行
        /// </summary>
        /// <returns></returns>
        bool CanSaveExecute()
        {
            return false;
        }
 
        /// <summary>
        /// 創建新命令
        /// </summary>
        public ICommand ClickSaveAction
        {
            get
            {
                return new Command.SaveCommand(SaveExecute, CanSaveExecute);
            }
        }
        //combobox
        /// <summary>
        /// 命令要執行的方法
        /// </summary>
        void ProviceSelectionChangedExecute(object sender)
        {
            try
 
            {
                if (sender is ComboBox)
                {
                    ComboBox drp=sender as ComboBox;
                    ProvinceCode=drp.SelectedValue.ToString();
                    GridDbContext db = new GridDbContext();
                    var list = db.City.AsTracking().ToList();

                    List<City> citys = list.Where(x => x.ProvinceCode == ProvinceCode).ToList();
                    var cityCodes = from city in citys
                                    select city.Code;
                    List<Area> areas = db.Area.AsTracking().ToList().Where(
x => cityCodes.Contains(x.CityCode)).ToList();
                    areaList.Clear();
                    if (areas!=null)
                    {
                        areas.ForEach((t) =>
 
                        { areaList.Add(t); }
                        );
                    }
 
                    cityList.Clear();
                    if (citys != null)
                    {
                        citys.ForEach((t) =>
 
                        { cityList.Add(t); }
                        );
                    }
                }
            }
            catch (Exception ex)
            {
 
                throw ex;
            }
        }
 
        /// <summary>
        /// 命令是否可以執行
        /// </summary>
        /// <returns></returns>
        bool CanSelectionChangedExecute()
        {
            return true;
        }

        /// <summary>
        /// 創建新命令
        /// </summary>
        public ICommand ProviceChangedAction
        {

            get
            {

                return new Command.ProvinceChangedCommand<object>(ProviceSelectionChangedExecute, 
CanSelectionChangedExecute);
            }
        }
    }

12.在Visual Studio 2022中按F5鍵，啓動WPF應用程序。然後使用鼠標點擊省份下拉框，能夠看到，界面中DataGrid中的數據，隨着下拉框的變化而隨之變化。如下圖。