将UserControl的SelectedValue绑定到ViewModel

Question

在我的解决方案; 我有两个项目:一个是WPF UserControl库,另一个是WPF应用程序.

用户控件非常简单; 它是一个标签和一个组合框,将显示已安装的打印机.

在WPF应用程序中; 我想使用这个usercontrol.所选值将存储在用户设置中.

我遇到的问题是我似乎无法获得正确的绑定工作.我需要做的是能够在MainWindow加载时设置UserControl的SelectedValue; 以及当我去保存我的设置时访问UserControl的SelectedValue.

我的代码在下面,有人能指出我正确的方向吗？

PrintQueue用户控件:

<UserControl x:Class="WpfControls.PrintQueue"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:wpfControls="clr-namespace:WpfControls"
             mc:Ignorable="d">
    <UserControl.DataContext>
        <wpfControls:PrintQueueViewModel/>
    </UserControl.DataContext>
    <Grid>
        <StackPanel Orientation="Horizontal">
            <Label Content="Selected Printer:"></Label>
            <ComboBox ItemsSource="{Binding Path=PrintQueues, Mode=OneWay}" DisplayMemberPath="Name" SelectedValuePath="Name" Width="200" SelectedValue="{Binding Path=SelectedPrinterName, Mode=TwoWay}"></ComboBox>
        </StackPanel>
    </Grid>
</UserControl>

打印队列代码隐藏:

public partial class PrintQueue : UserControl
{
    public static readonly DependencyProperty CurrentPrinterNameProperty =
        DependencyProperty.Register("CurrentPrinterName", typeof (string), typeof (PrintQueue), new PropertyMetadata(default(string)));

    public string CurrentPrinterName
    {
        get { return (DataContext as PrintQueueViewModel).SelectedPrinterName; }
        set { (DataContext as PrintQueueViewModel).SelectedPrinterName = value; }
    }


    public PrintQueue()
    {
        InitializeComponent();
        DataContext = new PrintQueueViewModel();
    }
}

PrintQueue查看型号:

public class PrintQueueViewModel : ViewModelBase
{
    private ObservableCollection<System.Printing.PrintQueue> printQueues;
    public ObservableCollection<System.Printing.PrintQueue> PrintQueues
    {
        get { return printQueues; }
        set
        {
            printQueues = value;
            NotifyPropertyChanged(() => PrintQueues);
        }
    }


    private string selectedPrinterName;
    public string SelectedPrinterName
    {
        get { return selectedPrinterName; }
        set
        {
            selectedPrinterName = value;
            NotifyPropertyChanged(() => SelectedPrinterName);
        }
    }

    public PrintQueueViewModel()
    {
        PrintQueues = GetPrintQueues();
    }


    private static ObservableCollection<System.Printing.PrintQueue> GetPrintQueues()
    {
        var ps = new PrintServer();
        return new ObservableCollection<System.Printing.PrintQueue>(ps.GetPrintQueues(new[]
            {
                EnumeratedPrintQueueTypes.Local,
                EnumeratedPrintQueueTypes.Connections
            }));
    }
}

主窗口:

<Window x:Class="WPFApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfControls="clr-namespace:WpfControls;assembly=WpfControls" xmlns:wpfApp="clr-namespace:WPFApp"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <wpfApp:MainWindowViewModel/>
    </Window.DataContext>
    <Grid>
        <StackPanel>
            <wpfControls:PrintQueue CurrentPrinterName="{Binding RelativeSource={RelativeSource AncestorType=Window}, Path=DataContext.PrinterName, Mode=TwoWay}"></wpfControls:PrintQueue>
        </StackPanel>
    </Grid>
</Window>

主窗口视图模型:

public class MainWindowViewModel : ViewModelBase
{
    private string printerName;

    public string PrinterName
    {
        get { return printerName; }
        set
        {
            printerName = value;
            NotifyPropertyChanged(() => PrinterName);
        }
    }

    public MainWindowViewModel()
    {
        PrinterName = "Lexmark T656 PS3";
    }
}

Answer 1

库中的控件需要公开可以在视图中绑定的DependencyProperties.就像WPF TextBox公开Text财产一样.

您的PrintQueue控件不会公开任何内容,而是将其所有状态保存在一个外部无法访问的视图模型中.你MainWindowViewModel无法进入内部的东西PrintQueueViewModel.

您需要SelectedPrinterName在PrintQueue xaml后面的代码中公开DependencyProperty.然后在MainWindow.xaml中绑定它MainWindowViewModel.PrinterName.

如果您想要一直使用ViewModels,那么MainWindowViewModel应该创建PrintQueueViewModel自己以便它可以访问其中的属性.

根据您的更新/评论:

不幸的是,DependencyProperties不能那样工作.getter/setter甚至在大多数时候都没有使用,它们应该只更新属性本身.你现在处于两个世界之间.

如果我在你的位置,并假设您可以更改库,以便PrintQueue.xaml在视图中没有硬编码的VM实例,我将自己创建PrintQueueViewModel.这就是MVVM应该如何工作:

视图模型:

public class MainWindowViewModel : ViewModelBase
{
    public PrintQueueViewModel PrintQueue { get; private set; }

    public MainWindowViewModel()
    {
        PrintQueue = new PrintQueueViewModel();
        PrintQueue.SelectedPrinterName = "Lexmark T656 PS3";
    }
}

视图:

<Window x:Class="WPFApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfControls="clr-namespace:WpfControls;assembly=WpfControls" xmlns:wpfApp="clr-namespace:WPFApp"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <wpfApp:MainWindowViewModel/>
    </Window.DataContext>
    <Grid>
        <StackPanel>
            <wpfControls:PrintQueue DataContext="{Binding PrintQueue}"/>
        </StackPanel>
    </Grid>
</Window>

尽管如此,控制库通常没有视图模型,并且通过依赖属性公开它们的状态,因为它们被设计为在XAML中使用.

组件库可能会公开视图模型,但在这种情况下,它们不会在视图中对视图模型进行硬编码.

你写过这个图书馆吗？如果没有,作者是如何期望人们使用它的呢？