绑定数据网格后，项目集合必须为空

Question

我从SQLite数据库填充datagrid

var mA = new System.Data.SQLite.SQLiteDataAdapter("SELECT * FROM users ORDER BY Name", DataHolder.SQLiteConnection);
var mT = new System.Data.DataTable();
if (dataGrid.Columns.Count > 0)
{
  return;
}
mA.Fill(mT);
if (mT.Rows.Count == 0)
{
  mT.Rows.Add(new object[mT.Columns.Count]);
}
dataGrid.ItemsSource = mT.DefaultView;

但是在我绑定DataGrid以更改单元格背景后，如果该代码的值等于0

<DataGrid x:Name="dataGrid" Margin="0,10,0,0" Loaded="dataGrid_Loaded" FontSize="14">
   <DataGridTextColumn Binding="{Binding Active}">
      <DataGridTextColumn.ElementStyle>
         <Style TargetType="{x:Type TextBlock}">
            <Setter Property="Background" Value="{Binding Active, Converter={StaticResource All}}"/>
         </Style>
      </DataGridTextColumn.ElementStyle>
   </DataGridTextColumn>
</DataGrid>

IValueConverter

public class All : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        string input = value as string;    

        if (System.Convert.ToByte(input) == 0)
        {
            return Brushes.Red;
        }
        else if (System.Convert.ToByte(input) > 0 && System.Convert.ToByte(input) < 5)
        {
            return Brushes.OrangeRed;
        }
        else
        {
            return DependencyProperty.UnsetValue;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }

}

我在运行时收到DataGrid错误消息

PresentationFramework.dll中发生类型为'System.InvalidOperationException'的异常，但未在用户代码中处理

附加信息：在使用ItemsSource之前，Items集合必须为空。

在dataGrid.ItemsSource = mT.DefaultView;

Answer 1

您忘记在XAML中添加DataGrid.Columns标记。 否则， DataGridTextColumn将被视为一项，并且由于您设置了ItemsSource ，因此会出现错误，您尝试从两个来源填充项

<DataGrid ...>
    <DataGrid.Columns> 
        <DataGridTextColumn>