我正在处理一个需求,需要为实体添加任意数量的动态属性。这些动态属性可以在数据表格列中显示,与实际对象属性并列。
为了尊重现有的架构,这些属性被存储在列表中:
public List<AdaErgaenzungsfeldEntity> Ergaenzungsfelder { get; set; }
为了将列表中的每个属性绑定起来,我已经将在网格中显示的值公开如下:
public Dictionary<Guid, object> ErgaenzungsfeldValues {
get { return m_ergaenzungsfeldValues; }
}
列表和字典在Ergaenzungsfelder列表发生变化时进行同步:
private void RefreshErgaenzungsfeldValues() {
if (m_ergaenzungsfeldValues == null) {
m_ergaenzungsfeldValues = new Dictionary<Guid, object>();
}
m_ergaenzungsfeldValues.Clear();
foreach (AdaErgaenzungsfeldEntity entity in Ergaenzungsfelder) {
m_ergaenzungsfeldValues.Add(entity.Ergaenzungsfeld.ID, entity.Value);
}
}
绑定到网格的最终操作如下所示:
List<ErgaenzungsfeldEntity> ergaenzungsfeldEntities = m_presenter.ErgaenzungsfeldService.GetAllErgaenzungsfeldEntities();
foreach (ErgaenzungsfeldEntity entity in ergaenzungsfeldEntities) {
m_lstAdas.Columns.Add(new Column {
Title = entity.Name,
FieldName = string.Format("ErgaenzungsfeldValues[{0}]", entity.ID)
});
}
这种实现方式的问题在于,字典并没有为所有实体的动态字段提供值,这显然会导致找不到键的异常:
System.Windows.Data Error: 16 : Cannot get 'Item[]' value (type 'Object') from 'ErgaenzungsfeldValues' (type 'Dictionary
2').
BindingExpression:Path=ErgaenzungsfeldValues[04d1be1c-2d83-48ba-b179-aaa9f0d0f7bc];
DataItem='AdaEntity' (HashCode=-800079524); target element is
'DataCell' (Name=''); target property is 'Content' (type 'Object')
TargetInvocationException:'System.Reflection.TargetInvocationException:
Exception has been thrown by the target of an invocation. --->
System.Collections.Generic.KeyNotFoundException: The given key was not
present in the dictionary. at
System.ThrowHelper.ThrowKeyNotFoundException() at
System.Collections.Generic.Dictionary
2.get_Item(TKey key) --- End
of inner exception stack trace --- at
System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[]
arguments, SignatureStruct& sig, MethodAttributes methodAttributes,
RuntimeTypeHandle typeOwner) at
System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[]
arguments, Signature sig, MethodAttributes methodAttributes,
RuntimeTypeHandle typeOwner) at
System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags
invokeAttr, Binder binder, Object[] parameters, CultureInfo culture,
Boolean skipVisibilityChecks) at
System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags
invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimePropertyInfo.GetValue(Object obj,
BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo
culture) at MS.Internal.Data.PropertyPathWorker.GetValue(Object
item, Int32 level) at
MS.Internal.Data.PropertyPathWorker.RawValue(Int32 k)实体并不知道所有可能的字段,因此不能为每个动态属性的每个实体添加默认值。
问题:如何正确地将这些动态值绑定到数据表格中,以避免上述异常?
我创建了一个小应用程序来说明这种行为。
MainWindow.xaml:
<Window x:Class="DynamicdataGridBindingTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
Title="MainWindow"
Height="350"
Width="525">
<Grid>
<xcdg:DataGridControl
Name="m_dataGridControl"
AutoCreateColumns="False"
AutoRemoveColumnsAndDetailConfigurations="False"
ReadOnly="True"
ItemsSource="{Binding TestEntities}">
<xcdg:DataGridControl.Columns>
<xcdg:Column Title="Property"
FieldName="DefinedProperty" />
</xcdg:DataGridControl.Columns>
</xcdg:DataGridControl>
</Grid>
</Window>
MainWindow.xaml.cs:
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using Xceed.Wpf.DataGrid;
namespace DynamicdataGridBindingTest {
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow {
private readonly Dictionary<Guid, string> m_dynamicColumnNames = new Dictionary<Guid, string> {
{Guid.NewGuid(),"DynText"},
{Guid.NewGuid(),"DynBool"},
{Guid.NewGuid(),"DynArray"}
};
public ObservableCollection<TestEntity> TestEntities { get; private set; }
public MainWindow() {
//Licenser.LicenseKey = "xxx";
TestEntities = new ObservableCollection<TestEntity>();
InitializeComponent();
InitializeEntities();
InitializedataGridColumns();
}
private void InitializeEntities() {
TestEntity testEntity1 = new TestEntity {
DefinedProperty = "Property Value 1",
};
testEntity1.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(0).Key, "My text");
testEntity1.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(1).Key, true);
testEntity1.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(2).Key, new[] { "val1.1", "val1.2", "val1.3" });
TestEntities.Add(testEntity1);
TestEntity testEntity2 = new TestEntity {
DefinedProperty = "Property Value 2"
};
testEntity2.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(0).Key, "My text 2");
TestEntities.Add(testEntity2);
}
private void InitializedataGridColumns() {
foreach (string columnName in m_dynamicColumnNames.Values) {
m_dataGridControl.Columns.Add(new Column {
Title = columnName,
FieldName = string.Format("DynamicProperties[{0}]", m_dynamicColumnNames.First(kv => kv.Value == columnName).Key)
});
}
}
}
}
TestEntity.cs:
namespace DynamicdataGridBindingTest {
public class TestEntity {
public string DefinedProperty { get; set; }
public Dictionary<Guid, object> DynamicProperties { get; private set; }
public TestEntity() {
DynamicProperties = new Dictionary<Guid, object>();
}
}
}
当运行时,它看起来是这样的: