WPF数据网格不与来自视图模型信息填充（数据绑定不工作）

Question

我有一个名为TagGridViewUserControl，并有相应TagGridViewModel其保持ObservableCollection<TagViewModel>在DataGrid使用数据绑定被显示。 TagViewModel公开了一些属性，我试图在DataGrid中显示。

我创建了一个按钮，添加一个项目到ObservableCollection<TagViewModel>并显示与收集的项目数和数据网格的项目计数一个消息。该集合正在获取所有项目，但DataGrid一致表示其计数为0。

这里是XAML代码与所述数据绑定：

<UserControl x:Class="Company.TagVisualizer.Views.TagGridView" 
      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" 
      mc:Ignorable="d" Width="Auto" Height="Auto" Name="TagGrid" DataContext="{Binding Source=TagGridContext}"> 
    <Grid> 
     <Grid.RowDefinitions> 
      <RowDefinition/> 
      <RowDefinition/> 
     </Grid.RowDefinitions> 
     <DataGrid Name="DataGridTag" Grid.Column="0" Grid.Row="0" ItemsSource="{Binding Path=TagsCollection}" Margin="0" CanUserReorderColumns="False" CanUserResizeColumns="True" CanUserAddRows="True" CanUserDeleteRows="True"> 
      <DataGrid.Columns> 
       <DataGridCheckBoxColumn Width="*" Header="Selected" /> 
       <DataGridTextColumn Width="3*" Binding="{Binding Path=TagName}" Header="Tag Name"/> 
       <DataGridTextColumn Width="3*" Binding="{Binding Detections.Count}" Header="Detections"/> 
       <DataGridTextColumn Width="3*" Binding="{Binding EarliestDetection}" Header="Earliest Detection"/> 
       <DataGridTextColumn Width="3*" Binding="{Binding LatestDetection}" Header="Latest Detection"/> 
      </DataGrid.Columns> 
     </DataGrid> 
     <Button Grid.Column="0" Grid.Row="1" Content="Add" Click="Add_OnClick"/> 
    </Grid> 

</UserControl> 

下面是TagGridView代码隐藏文件：

public partial class TagGridView : UserControl 
    { 
     private TagGridViewModel _tagGridViewModel = new TagGridViewModel(); 

     public TagGridView() 
     { 
      InitializeComponent(); 

     } 

     public TagGridViewModel TagGridContext { get { return _tagGridViewModel; } set { _tagGridViewModel = value; } } 

     private void Add_OnClick(object sender, RoutedEventArgs e) 
     { 
      TagGridContext.TagsCollection.Add(new TagViewModel("Boogie", 134.5, 145.8)); 

      MessageBox.Show(string.Format("Items in collection: {0}\nItems in Grid: {1}", TagGridContext.TagsCollection.Count, DataGridTag.Items.Count)); 
     } 
    } 

这里是TagGridViewModel类：

public class TagGridViewModel 
    { 
     private ObservableCollection<TagViewModel> _tagsCollection = new ObservableCollection<TagViewModel>(); 

     public ObservableCollection<TagViewModel> TagsCollection 
     { 
      get { return _tagsCollection; } 
      set 
      { 
       _tagsCollection = value; 
      } 
     } 
    } 

我不确定发生了什么事。我曾尝试在UserControl标记和DataGrid标记中设置DataContext。无论我做什么，DataGrid都不会向其自身添加任何项目。

Answer 1

这是用户控件的DataContext问题。请参考下面的代码进行数据绑定。

<UserControl x:Class="Tags_Learning.TagGridView" 
     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" 
     mc:Ignorable="d" 
     d:DesignHeight="300" d:DesignWidth="300" **DataContext="{Binding Path=TagGridContext, RelativeSource={RelativeSource Self}}"**> 
<Grid> 
    <Grid.RowDefinitions> 
     <RowDefinition/> 
     <RowDefinition/> 
    </Grid.RowDefinitions> 
    <DataGrid Name="DataGridTag" Grid.Column="0" Grid.Row="0" ItemsSource="{Binding Path=TagsCollection}" Margin="0" 
       CanUserReorderColumns="False" CanUserResizeColumns="True" CanUserAddRows="True" CanUserDeleteRows="True"> 
     <DataGrid.Columns> 
      <DataGridCheckBoxColumn Width="*" Header="Selected" /> 
      <DataGridTextColumn Width="3*" Binding="{Binding Path=TagName}" Header="Tag Name"/>     
      <DataGridTextColumn Width="3*" Binding="{Binding EarliestDetection}" Header="Earliest Detection"/> 
      <DataGridTextColumn Width="3*" Binding="{Binding LatestDetection}" Header="Latest Detection"/> 
     </DataGrid.Columns> 
    </DataGrid> 
    <Button Grid.Column="0" Grid.Row="1" Content="Add" Click="Add_OnClick"/> 
</Grid>