c# - 使用 WPF 和 MVVM 模式将值从子窗口传递到父窗口

Question

我有一个父窗口，其中包含名为“SchoolName”的文本框和一个名为“Lookup school Name”的按钮。

该按钮打开一个包含学校名称列表的子窗口。现在，当用户从子窗口中选择学校名称，并单击“使用所选学校”按钮时。我需要在父 View 的文本框中填充所选学校。

注意:我采纳了 Sam 和其他人的建议来使这段代码工作。我已经更新了我的代码，以便其他人可以简单地使用它。

SelectSchoolView.xaml(父窗口)

<Window x:Class="MyProject.UI.SelectSchoolView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Parent" Height="202" Width="547">
<Grid>
    <TextBox Height="23" Width="192" 
     Name="txtSchoolNames"  
     Text="{Binding Path=SchoolNames, UpdateSourceTrigger=PropertyChanged, 
     Mode=TwoWay}" 
     />

    <Label Content="School Codes" Height="28" HorizontalAlignment="Left" 
     Margin="30,38,0,0" Name="label1" VerticalAlignment="Top" />
    <Button Content="Lookup School Code" Height="30" HorizontalAlignment="Left" 
     Margin="321,36,0,0" Name="button1" VerticalAlignment="Top" Width="163" 
     Command="{Binding Path=DisplayLookupDialogCommand}"/>
</Grid>
</Window>

SchoolNameLookup.xaml(查找学校名称的子窗口)

<Window x:Class="MyProject.UI.SchoolNameLookup"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:toolkit="http://schemas.microsoft.com/wpf/2008/toolkit"
    Title="SchoolCodeLookup" Height="335" Width="426">

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="226*" />
        <RowDefinition Height="70*" />
    </Grid.RowDefinitions>

    <toolkit:DataGrid Grid.Row="0" Grid.Column="1"   x:Name="dgSchoolList" 
                          ItemsSource="{Binding Path=SchoolList}" 
                          SelectedItem="{Binding Path=SelectedSchoolItem, Mode=TwoWay}" 
                          Width="294"
                          AutoGenerateColumns="False"
                          CanUserAddRows="False" 
                          CanUserDeleteRows="False"
                          CanUserResizeRows="False" 
                          CanUserSortColumns="True" 
                          SelectionMode="Single">

        <Button Grid.Row="1" Grid.Column="1" Content="Use Selected School Name" 
         Height="23" Name="btnSelect" Width="131" Command="{Binding 
         Path=UseSelectedSchoolNameCommand}"  />
 </Grid>
</Window>

SchoolNameLookupViewModel

   private string _schoolNames;
   public string SchoolNames
   {
        get { return _schoolNames; }
        set
        {
            _schoolNames= value;
            OnPropertyChanged(SchoolNames);
        }
   }

   private ICommand _useSelectedSchoolNameCommand;
   public ICommand UseSelectedSchoolNameCommand{
   get
    {
    if (_useSelectedSchoolNameCommand== null)
        _useSelectedSchoolNameCommand= new RelayCommand(a => 
            DoUseSelectedSchollNameItem(), p => true);
            return _useSelectedSchoolNameCommand;
      }
    set
       {
         _useSelectedSchoolNameCommand= value;
       }

    }

    private void DoUseSelectedSchoolNameItem() {
        StringBuilder sfiString = new StringBuilder();
        ObservableCollection<SchoolModel> oCol = 
                new ObservableCollection<SchoolModel>();
        foreach (SchoolModel itm in SchollNameList)
        {
            if (itm.isSelected) {
                sfiString.Append(itm.SchoolName + "; ");
                _schoolNames = sfiString.ToString();
            }
        }
                OnPropertyChanged(SchoolNames);
    }

    private ICommand _displayLookupDialogCommand;
    public ICommand DisplayLookupDialogCommand
    {
        get
        {
            if (_displayLookupDialogCommand== null)
                _displayLookupDialogCommand= new
                    RelayCommand(a => DoDisplayLookupDialog(), p => true);
            return _displayLookupDialogCommand;
        }
        set
        {
            _displayLookupDialogCommand= value;
        }
    }

    private void DoDisplayLookupDialog()
    {
        SchoolNameLookup snl = new SchoolNameLookup();
        snl.DataContext = this; //==> This what I was missing. Now my code works as I was expecting
        snl.Show();
    }

Answer 1

我的解决方案是将两个窗口绑定(bind)到同一个 ViewModel，然后定义一个属性来保存代码的结果值，我们称之为 CurrentSchoolCodes，将标签绑定(bind)到该属性。确保 CurrentSchoolCodes 引发 INotifyPropertyChanged 事件。 然后在 DoUseSelectedSchoolNameItem 中设置 CurrentSchoolCodes 的值。

对于模型中的属性，我建议您在需要时加载它们(延迟加载模式)。我用这个方法检查你的属性的 get 访问器是否仍然为 null，加载并为其分配值。代码就像这个代码片段:

private ObservableCollection<SchoolModel> _schoolList;
public ObservableCollection<SchoolModel> SchoolList{
    get {
        if ( _schoolList == null )
            _schoolList = LoadSchoolList();
        return _schoolList;
    }
}

通过这种方式，绑定(bind)到此 SchoolList 属性的 WPF 控件第一次尝试获取此属性的值时，该值将被加载和缓存，然后返回。

注意:我不得不说这种属性应该谨慎使用，因为加载数据可能是一个耗时的过程。最好在后台线程中加载数据以保持 UI 响应。