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接上文WPF入门教程系列二十八 ——DataGrid使用示例MVVM模式(6)
13.通过Command指令，传递了下拉框所选择的省份，datagrid自动显示相应省份的城市信息，但是以上示例中有一个Bug，就是下拉框中绑定的数据无法显示。
这是由于DataGridComboBoxColumn若要填充下拉列表，请先使用以下选项之一设置 ItemsSource 属性 ComboBox ：
1）静态资源。 使用StaticResource 标记扩展。
2）x：Static 代码实体。 使用x:Static 标记扩展。
3）类型的内联集合 ComboBoxItem 。
14.比较适合的绑定方式是 2）x：Static 代码实体。 使用x:Static 标记扩展需要添加相应的命名空间。在Visual Studio 2022中打开MainWindows.xmal文件，并在文件的开头添加如下命名空间。
xmlns:v="clr-namespace:WpfGridDemo.NET7.ViewModel"
15. 在Visual Studio 2022中打开MainWindows.xmal文件。对DataGridComboBoxColumn的ItemsSource进行了数据绑定。具体代码如下：
<DataGridComboBoxColumn Header="城市" Width="120" x:Name="cboCity"
ItemsSource="{x:Static v:MainWindowVM.GridCityList}" ClipboardContentBinding="{x:Null}" SelectedValuePath="Code"
SelectedValueBinding="{Binding Path=CityCode,UpdateSourceTrigger=PropertyChanged}"
DisplayMemberPath="Name" SelectedItemBinding="{x:Null}" />
16.在Visual Studio 2022的解决方案资源管理器中，找到MainWindowVM.cs文件，将GridCityList属性改为静态属性，用于绑定DataGridComboBoxColumn的ItemsSource。具体如下代码：
private static ObservableCollection<City> cityList; public static ObservableCollection<City> GridCityList { get { return cityList; } set { cityList = value; new ViewModelBase().RaisePropertyChanged("GridCityList"); } }
17.在Visual Studio 2022中按F5键，启动WPF应用程序。然后使用鼠标点击省份下拉框，能够看到，界面中DataGrid中的数据，随着下拉框的变化而随之变化，但是城市下拉框中却没有任何数据。看来绑定失效了。如下图。
18. 使用静态代码实体的方式，实现省市县联动失败了。又不想使用其他两种方式。在一阵猛于虎的搜索之后，发现一种实现方式。在Visual Studio 2022中打开MainWindows.xmal文件。对DataGridComboBoxColumn进行了数据绑定。具体代码如下：
<DataGridComboBoxColumn Header="城市(Style)" SelectedValuePath="Code"
SelectedValueBinding="{Binding Path=CityCode,UpdateSourceTrigger=PropertyChanged}"
DisplayMemberPath="Name" SelectedItemBinding="{x:Null}" Width="1*"> <DataGridComboBoxColumn.EditingElementStyle> <Style TargetType="ComboBox"> <Setter Property="ItemsSource"
Value="{Binding Path=DataContext.GridCity,ElementName=gridArea}" /> </Style> </DataGridComboBoxColumn.EditingElementStyle> <DataGridComboBoxColumn.ElementStyle> <Style TargetType="ComboBox"> <Setter Property="ItemsSource"
Value="{Binding Path=DataContext.GridCity,ElementName=gridArea}" /> </Style> </DataGridComboBoxColumn.ElementStyle> </DataGridComboBoxColumn>
19.在Visual Studio 2022的解决方案资源管理器中，找到MainWindowVM.cs文件，添加一个GridCity属性，用于绑定DataGridComboBoxColumn的ItemsSource。以下是属性代码，更完整的代码，请参见下面类的完整代码。
private ObservableCollection<City> listCity; public ObservableCollection<City> GridCity { get { return listCity; } set { listCity = value; RaisePropertyChanged("GridCity"); } }
20.MainWindow.xmal的全部代码如下：
<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" xmlns:v="clr-namespace:WpfGridDemo.NET7.ViewModel" 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" x:Name="cboCity"
ItemsSource="{x:Static v:MainWindowVM.GridCityList}" ClipboardContentBinding="{x:Null}" SelectedValuePath="Code"
SelectedValueBinding="{Binding Path=CityCode,UpdateSourceTrigger=PropertyChanged}"
DisplayMemberPath="Name" SelectedItemBinding="{x:Null}" /> <DataGridComboBoxColumn Header="城市(Style)" SelectedValuePath="Code"
SelectedValueBinding="{Binding Path=CityCode,UpdateSourceTrigger=PropertyChanged}"
DisplayMemberPath="Name" SelectedItemBinding="{x:Null}" Width="1*"> <DataGridComboBoxColumn.EditingElementStyle> <Style TargetType="ComboBox"> <Setter Property="ItemsSource"
Value="{Binding Path=DataContext.GridCity,ElementName=gridArea}" /> </Style> </DataGridComboBoxColumn.EditingElementStyle> <DataGridComboBoxColumn.ElementStyle> <Style TargetType="ComboBox"> <Setter Property="ItemsSource"
Value="{Binding Path=DataContext.GridCity,ElementName=gridArea}" /> </Style> </DataGridComboBoxColumn.ElementStyle> </DataGridComboBoxColumn> <DataGridTextColumn Header="县区镇" Width="*"
Binding="{Binding Name}" ClipboardContentBinding="{x:Null}"/> <DataGridTextColumn Header="邮编" Width="100"
Binding="{Binding Code}" ClipboardContentBinding="{x:Null}"/> <DataGridTextColumn Header="创建时间" Width="160"
Binding="{Binding Created}" ClipboardContentBinding="{x:Null}"/> <DataGridTextColumn Header="更新时间" 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>
21. MainWindowsVM类的完整代码，如下：
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>(); listCity = new ObservableCollection<City>(); } private Area m_Area; /// <summary> /// 县镇区数据 /// </summary> public Area AreaVM { get { return m_Area; } set { m_Area = value; } } private string m_Province_Code; /// <summary> /// 省--代码 /// </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 static ObservableCollection<City> cityList; public static ObservableCollection<City> GridCityList { get { return cityList; } set { cityList = value; new ViewModelBase().RaisePropertyChanged("GridCityList"); } } private ObservableCollection<City> listCity; public ObservableCollection<City> GridCity { get { return listCity; } set { listCity = value; RaisePropertyChanged("GridCity"); } } /// <summary> /// 命令要执行的方法 /// </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> /// 命令是否可以执行 /// </summary> /// <returns></returns> bool CanSaveExecute() { return false; } /// <summary> /// 创建新命令 /// </summary> public ICommand ClickSaveAction { get { return new Command.SaveCommand(SaveExecute, CanSaveExecute); } } //combobox /// <summary> /// 命令要执行的方法 /// </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); } ); } listCity.Clear(); if (citys != null) { citys.ForEach((t) => { listCity.Add(t); } ); } } } catch (Exception ex) { throw ex; } } /// <summary> /// 命令是否可以执行 /// </summary> /// <returns></returns> bool CanSelectionChangedExecute() { return true; } /// <summary> /// 创建新命令 /// </summary> public ICommand ProviceChangedAction { get { return new Command.ProvinceChangedCommand<object>(ProviceSelectionChangedExecute
, CanSelectionChangedExecute); } } } }
22.在Visual Studio 2022中按F5键，启动WPF应用程序。然后使用鼠标点击省份下拉框，能够看到，界面中DataGrid中的数据，随着下拉框的变化而随之变化，其中使用静态实体代码绑定的城市下拉框中却没有任何数据。使用使用非静态资源，在<DataGridComboBoxColumn.EditingElementStyle>与 <DataGridComboBoxColumn.ElementStyle>两个样式中绑定combobox的itemSource属性方式，效果有效。如下图。
