c# - 如何在后面的代码上将View的自定义属性绑定(bind)到ViewModel？

我做了Page MainPage和UserControl Pager。两者都有其ViewModel。在Pager中，存在三个依赖项属性Rows，Columns和Source。我想将这些属性从Pager的View传递给Pager的ViewModel。我在View的代码后面进行了尝试。但这是行不通的...永远不会在调试时调用set中的PagerViewModel属性。请帮我...

这是详细机制:
MainPageViewModel
↓通过绑定(bind)传递值
MainPage
↓使用MainPagerViewModel中的值设置属性
Pager(后面的代码)

↓将属性绑定(bind)到PagerViewModel PagerViewModel
↓通过绑定(bind)传递值
Pager(XAML)

这是来源

[MainPageViewModel.cs]

using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
using Client.Model;

namespace Client.ViewModel
{
    public class MainPageViewModel : ViewModelBase
    {
        ...
        public ObservableCollection<IPagableEntry> PagerTableCategoriesItems { get { return TableCategoryRepository.Instance.TableCategories; } }

        public int PagerTableCategoriesRows { get { return 1; } }

        public int PagerTableCategoriesColumns { get { return 3; } }
        ...
    }
}

[MainPage.xaml]

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:view="clr-namespace:Client.View"
      xmlns:viewModel="clr-namespace:Client.ViewModel"
      xmlns:resStr="clr-namespace:Client.CommonResources.String"
      x:Class="Client.View.MainPage"
      Style="{StaticResource common}">
    <Page.DataContext>
        <viewModel:MainPageViewModel />
    </Page.DataContext>
    ...

    <view:Pager x:Name="pagerTableCategories"
                Source="{Binding Path=PagerTableCategoriesItems}"
                Rows="{Binding Path=PagerTableCategoriesRows}"
                Columns="{Binding Path=PagerTableCategoriesColumns}">
    </view:Pager>
    ...
</Page>

[Pager.xaml.cs]

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Input;
using Client.Model;
using Client.ViewModel;

namespace Client.View
{
    public partial class Pager
    {

        public static readonly DependencyProperty SourceProperty = DependencyProperty.Register("Source", typeof(ObservableCollection<IPagableEntry>), typeof(Pager), new PropertyMetadata(null, OnSourceChanged));
        public static readonly DependencyProperty RowsProperty = DependencyProperty.Register("Rows", typeof(int), typeof(Pager), new PropertyMetadata(1, OnRowsChanged));
        public static readonly DependencyProperty ColumnsProperty = DependencyProperty.Register("Columns", typeof(int), typeof(Pager), new PropertyMetadata(1, OnColumnsChanged));
        public static readonly DependencyProperty SelectedEntryProperty = DependencyProperty.Register("SelectedEntry", typeof(object), typeof(Pager), new PropertyMetadata(null, OnSelectedEntryChanged));

        public int Rows
        {
            get { return (int)GetValue(RowsProperty); }
            set { SetValue(RowsProperty, value); }
        }

        public int Columns
        {
            get { return (int)GetValue(ColumnsProperty); }
            set { SetValue(ColumnsProperty, value); }
        }

        public object SelectedEntry
        {
            get { return GetValue(SelectedEntryProperty); }
            set { SetValue(SelectedEntryProperty, value); }

        }

        public ObservableCollection<IPagableEntry> Source
        {
            get { return (ObservableCollection<IPagableEntry>)GetValue(SourceProperty); }
            set { SetValue(SourceProperty, value); }
        }

        public Pager()
        {
            InitializeComponent();

            // I want to bind the three custom properties(Rows, Columns, Source) to PagerViewModel's Rows, Columns, Collection
            Binding bindingRows = new Binding("Rows");
            bindingRows.Mode = BindingMode.TwoWay;
            bindingRows.Source = gridPager.DataContext;
            gridPager.SetBinding(RowsProperty, bindingRows);

            Binding bindingColumns = new Binding("Columns");
            bindingColumns.Mode = BindingMode.TwoWay;
            bindingColumns.Source = gridPager.DataContext;
            gridPager.SetBinding(ColumnsProperty, bindingColumns);

            Binding bindingSource = new Binding("Collection");
            bindingSource.Mode = BindingMode.TwoWay;
            bindingSource.Source = gridPager.DataContext;
            gridPager.SetBinding(SourceProperty, bindingSource);
        }

        private void ListBoxEntriesOnSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            SelectedEntry = (sender as ListBox).SelectedItem;
        }

        private static void OnSelectedEntryChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
        {
            (pager as Pager).SelectedEntry = e.NewValue;
        }

        private static void OnSourceChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
        {
            (pager as Pager).Source = (ObservableCollection<IPagableEntry>)e.NewValue;
        }

        private static void OnRowsChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
        {
            (pager as Pager).Rows = (int)e.NewValue;
        }

        private static void OnColumnsChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
        {
            (pager as Pager).Columns = (int)e.NewValue;
        }

    }
}

[Pager.xaml]

<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:view="clr-namespace:Client.View"
             xmlns:viewModel="clr-namespace:Client.ViewModel"
             xmlns:resStr="clr-namespace:Client.CommonResources.String"
             x:Class="Client.View.Pager">
    <Grid x:Name="gridPager">
        <Grid.DataContext>
            <viewModel:PagerViewModel />
        </Grid.DataContext>

        ...

        <ListBox x:Name="listBoxEntries"
                 ItemsSource="{Binding Path=Collection}"
                 BorderThickness="0"
                 Margin="0"
                 Style="{StaticResource common}"
                 HorizontalContentAlignment="Stretch"
                 VerticalContentAlignment="Stretch"
                 ItemTemplate="{StaticResource templateTableCategory}"
                 SelectedItem="{Binding Path=SelectedEntry, Mode=TwoWay}"
                 SelectionChanged="ListBoxEntriesOnSelectionChanged">
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <UniformGrid Rows="{Binding Path=Rows}"
                                 Columns="{Binding Path=Columns}"
                                 IsItemsHost="True"/>
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
        </ListBox>

        ...

    </Grid>
</UserControl>

[PagerViewModel.cs]

using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Windows.Data;
using System.Windows.Media;
using Client.Model;

namespace Client.ViewModel
{
    public class PagerViewModel : ViewModelBase
    {

        ...

        ListCollectionView _listCollectionView;
        ObservableCollection<IPagableEntry> _collection;
        int _rows;
        int _columns;

        public int Rows
        {
            get { return _rows; }
            set
            {
                _rows = value;
                OnPropertyChanged();
            }
        }

        public int Columns
        {
            get { return _columns; }
            set
            {
                _columns = value;
                OnPropertyChanged();
            }
        }

        public ListCollectionView ListCollectionView
        {
            get { return _listCollectionView; }
            set
            {
                _listCollectionView = value;
                OnPropertyChanged();
            }
        }

        public ObservableCollection<IPagableEntry> Collection
        {
            get
            {
                return _collection;
            }

            set
            {
                _collection = value;
                OnPropertyChanged();
            }
        }

        ...

    }
}

最佳答案

您发布的代码有两个明显的问题:

您的OnXXXChanged()处理程序不执行任何操作。他们正在响应依次更改的属性设置。 IE。他们只是重申要通知他们的属性设置，而不是在其他对象中设置属性值。

您正在尝试对不存在的属性设置绑定(bind)。 IE。 SetBinding()调用背后的代码的目标是gridPager对象，它只是一个Grid。它没有要设置的Rows，Columns或Source属性。

假设一会儿我们将使用绑定(bind)来完成此操作，那么您将遇到第三个问题:

您将尝试将两个不同的源属性绑定(bind)到同一目标属性。例如。 Pager.Rows已经是在 MainPage.xaml 中建立的绑定(bind)的目标，而PagerTableCategoriesRows作为源。它也不能成为与任何其他对象的绑定(bind)的目标(最重要的是，不是来自其自身的循环绑定(bind)，这是如果使用Pager.RowsProperty依赖项属性(如代码所尝试的那样)才有意义的唯一来源)。

我尚不清楚这样做的智慧。看来Pager元素可以直接直接绑定(bind)到Pager属性本身，从而从原始 View 模型继承值，而不是维护第二个完全独立但打算相同的 View 模型。

但是假设有一个我完全不理解的很好的理由，您打算在这里使用两个不同的 View 模型并希望使其保持同步，在我看来，您应该能够通过更改您的 View 来使其工作OnXXXChanged()处理程序，以便它们直接设置 View 模型值。例如。:

public partial class Pager
{

    public static readonly DependencyProperty SourceProperty = DependencyProperty.Register("Source", typeof(ObservableCollection<IPagableEntry>), typeof(Pager), new PropertyMetadata(null, OnSourceChanged));
    public static readonly DependencyProperty RowsProperty = DependencyProperty.Register("Rows", typeof(int), typeof(Pager), new PropertyMetadata(1, OnRowsChanged));
    public static readonly DependencyProperty ColumnsProperty = DependencyProperty.Register("Columns", typeof(int), typeof(Pager), new PropertyMetadata(1, OnColumnsChanged));
    public static readonly DependencyProperty SelectedEntryProperty = DependencyProperty.Register("SelectedEntry", typeof(object), typeof(Pager));

    public int Rows
    {
        get { return (int)GetValue(RowsProperty); }
        set { SetValue(RowsProperty, value); }
    }

    public int Columns
    {
        get { return (int)GetValue(ColumnsProperty); }
        set { SetValue(ColumnsProperty, value); }
    }

    public object SelectedEntry
    {
        get { return GetValue(SelectedEntryProperty); }
        set { SetValue(SelectedEntryProperty, value); }

    }

    public ObservableCollection<IPagableEntry> Source
    {
        get { return (ObservableCollection<IPagableEntry>)GetValue(SourceProperty); }
        set { SetValue(SourceProperty, value); }
    }

    public Pager()
    {
        InitializeComponent();
    }

    private void ListBoxEntriesOnSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        SelectedEntry = (sender as ListBox).SelectedItem;
    }

    private static void OnSourceChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
    {
        ((PagerViewModel)(pager as Pager).gridPager.DataContext).Collection =
            (ObservableCollection<IPagableEntry>)e.NewValue;
    }

    private static void OnRowsChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
    {
        ((PagerViewModel)(pager as Pager).gridPager.DataContext).Rows =
            (int)e.NewValue;
    }

    private static void OnColumnsChanged(DependencyObject pager, DependencyPropertyChangedEventArgs e)
    {
        ((PagerViewModel)(pager as Pager).gridPager.DataContext).Columns =
            (int)e.NewValue;
    }
}

顺便说一句:我不建议您在上面使用as。主要原因是，如果由于某种原因强制转换失败，那么第一个可见的症状就是不是很有帮助的NullReferenceException，而不是InvalidCastException。

我建议仅在预计某些时候转换会失败的情况下才使用as。当然，在这种情况下，您也将始终检查null结果并进行适当处理。

如果您打算强制转换将始终成功，请使用强制转换运算符。

关于c# - 如何在后面的代码上将View的自定义属性绑定(bind)到ViewModel？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/33198852/