绑定的DataGrid ItemSource获取空或空白对象

Question

我的DataGrid的ItemSource返回空对象或null。 会是什么情况？ 所有属性均已绑定。 在添加数据时，它在Grid上显示正确，但是在获取数据时为null。

XML

  <DataGrid AutoGenerateColumns="False" Grid.Row="2" Height="208" HorizontalAlignment="Left" Margin="20,71,0,0" Name="dgvWell" VerticalAlignment="Top" Width="528" HorizontalScrollBarVisibility="Visible"
VerticalScrollBarVisibility="Visible" BorderBrush="#FFB7B39D" Background="LightYellow" RowBackground="LightGray" AlternatingRowBackground="#FFFFFFF5" BorderThickness="10" CanUserReorderColumns="False" CanUserSortColumns="False" FontSize="13" CanUserAddRows="False">
      <DataGrid.Columns>
          <DataGridTextColumn Header="Layer Name" Width="80" Binding="{Binding LayerName}"/>
          <DataGridTextColumn Width="100" Binding="{Binding Porosity}">
          <DataGridTextColumn.Header>
              <Grid Width="100">
                  <Grid.RowDefinitions>
                      <RowDefinition />
                      <RowDefinition/>
                  </Grid.RowDefinitions>
                  <TextBlock Text="Porosity" Grid.Row="0"/>
                  <ComboBox Grid.Row="1" Width="70" HorizontalAlignment="Center" Name="cboPorosity">
                      <ComboBoxItem Content="pascal" IsSelected="True" />
                      <ComboBoxItem Content="psi"/>
                      <ComboBoxItem Content="bar"/>
                      <ComboBoxItem Content="barye"/>
                  </ComboBox>
              </Grid>
          </DataGridTextColumn.Header>
          </DataGridTextColumn>   


          <DataGridTextColumn Header="Permeability" Binding="{Binding Permeability}"/>
          <DataGridTextColumn Width="120" Binding="{Binding Path= PerforationStartDepth,Mode=TwoWay}" ClipboardContentBinding="{Binding PerforationStartDepth}">
              <DataGridTextColumn.Header>

                  <Grid>
                      <Grid.RowDefinitions>
                          <RowDefinition Height="25"/>
                          <RowDefinition/>
                      </Grid.RowDefinitions>
                      <TextBlock Text="Perforation Start" Grid.Row="0"/>
                      <ComboBox Grid.Row="1" Width="60" Name="cboPerfStart">
                          <ComboBoxItem Content="ft" IsSelected="True" />
                          <ComboBoxItem Content="M"/>
                          <ComboBoxItem Content="cm"/>
                      </ComboBox>
                  </Grid>

              </DataGridTextColumn.Header>
          </DataGridTextColumn>
          <DataGridTextColumn Width="145"  Binding="{Binding PerforationEndDepth}">
              <DataGridTextColumn.Header>

                  <Grid>
                      <Grid.RowDefinitions>
                          <RowDefinition Height="25"/>
                          <RowDefinition/>
                      </Grid.RowDefinitions>
                      <TextBlock Text="Perforation End" Grid.Row="0"/>
                      <ComboBox Grid.Row="1" Width="60" Name="cboPerfEnd">
                          <ComboBoxItem Content="ft" IsSelected="True"/>
                          <ComboBoxItem Content="M"/>
                          <ComboBoxItem Content="cm"/>
                      </ComboBox>
                  </Grid>

              </DataGridTextColumn.Header>
          </DataGridTextColumn>

          <DataGridTextColumn Width="140"  Binding="{Binding ReservoirPressure,Mode=TwoWay}">
              <DataGridTextColumn.Header>                                    
                  <Grid>
                      <Grid.RowDefinitions>
                          <RowDefinition Height="25"/>
                          <RowDefinition/>
                      </Grid.RowDefinitions>
                      <TextBlock Text="Reservoir Pressure" Grid.Row="0"/>
                      <ComboBox Grid.Row="1" Width="60" Name="cboResPress">
                          <ComboBoxItem Content="pascal" IsSelected="True" />
                          <ComboBoxItem Content="psi"/>
                          <ComboBoxItem Content="bar"/>
                          <ComboBoxItem Content="barye"/>
                      </ComboBox>
                  </Grid>
              </DataGridTextColumn.Header>                               
          </DataGridTextColumn>
          <DataGridTextColumn Width="145" Header="Water Cut" Binding="{Binding WaterCut}"></DataGridTextColumn>
      </DataGrid.Columns>
</DataGrid>

后端对象：

public struct Step2Data
{
    public string LayerName { get; set; }
    public int Porosity { get; set; }
    public int Permeability { get; set; }
    public int PerforationStartDepth { get; set; }
    public int PerforationEndDepth { get; set; }
    public int ReservoirPressure { get; set; }
    public int WaterCut { get; set; }
}

 List<Step2Data> step2datas = dgvWell.ItemsSource as List<Step2Data>;

上面的检索返回null。

您能帮我知道吗，为什么这个网格没有返回正确的ItemSource。

编辑

根据您的实例，这极大地帮助了我，我实现了代码。 在我看来，我有一个组合框，可让用户选择一个数字。 基于该数字，将有许多行添加到网格中。 我尝试进行处理，但未显示任何行：

在我的模型课中：

public ObservableCollection<Step2Model> Step2ModelList 
{
    get {
        if (step2ModelList == null)
            step2ModelList = new ObservableCollection<Step2Model>();

        return step2ModelList;
    }
    set
    {
        step2ModelList = value;
        Changed("Step2ModelList");
    }
}

public void AddStep2ModelToList(Step2Model step2Model)
{
    Step2ModelList.Add(step2Model);
}

public void addRowsToList(int count)
{
    for (int i = 0; i < count; i++)
    {
        Step2ModelList.Add(new Step2Model());  // UPDATED
        /*
        AddItemCommand = new ActionCommand
        {
            ExecuteDelegate = o => Step2ModelList.Add(new Step2Model())
        };
        */
    }
}

DataGrid绑定到Step2ModelList

ItemsSource="{Binding Step2ModelList, Mode=TwoWay}">

在组合框选择上，

private void cboNumZones_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    int num = (int)cboNumZones.SelectedItem;
    Console.WriteLine("Numer of Zones SElected = " + num);
    if (num > 0)
    {
        Step2InfoData st = this.DataContext as Step2InfoData;
        st.addRowsToList(count);
    }
}

此后，网格将不会反映Step2ModelList中添加的2行。

Answer 1

我认为，您不了解DataGrid.ItemSource的概念。 阅读http://msdn.microsoft.com/zh-cn/library/system.windows.controls.datagrid.itemssource(v=vs.95).aspx

DataGrid.ItemSource用于填充DataGrid，而不是其他方式。

如果要访问DataGrid项，请使用：

dgvWell.Items;

更新，ObservableCollection示例：

视图模型：

public class DataGridSampleViewModel
{
    public ObservableCollection<Step2Data> Data { get; set; }
    public ICommand AddItemCommand { get; set; }

    public DataGridSampleViewModel()
    {
        Data = new ObservableCollection<Step2Data>();

        AddItemCommand = new ActionCommand
        {
            ExecuteDelegate = o => Data.Add(new Step2Data { LayerName = DateTime.Now.Ticks.ToString() })
        };
    }
}

查看后面的代码：

public partial class DataGridSampleView : Window
{
    public DataGridSampleView()
    {
        InitializeComponent();
        this.DataContext = new DataGridSampleViewModel();
    }
}

视图：

<Window x:Class="SimpleMVVMApp.DataGridSampleView"
        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:simpleMvvmApp="clr-namespace:SimpleMVVMApp"
        mc:Ignorable="d"
        Title="DataGridSampleView" Height="300" Width="300" 
        d:DataContext="{d:DesignInstance simpleMvvmApp:DataGridSampleViewModel}">
    <StackPanel>
        <Button Content="Add new item" Command="{Binding AddItemCommand}" />
        <ListBox ItemsSource="{Binding Data}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding LayerName}" />
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </StackPanel>
</Window>

完整的源代码可以在https://github.com/mswietlicki/SimpleMVVMApp中找到