如何在XAML中转换以访问子类属性 [英] How to cast in XAML to access sub-class properties

问题描述

在我的项目中，我列出了一个用作DataGrid数据源的 Units 的列表。 单位类型有两种类型的子类， AUnits 和 BUnits 。列表中的每个单元是 AUnit 或 BUnit 。我的问题是当我尝试绑定到一个特定于一个子类单元类型的属性时，XAML看不到它，我只是回到0。通常情况下，如果这是在C＃中完成的，那么我只是将其转换并访问该属性，但是我不能在代码中这样做。绑定在C＃中创建，如下所示：

  dgtc.Header = Properties.Resources.MaxPressure; 
 dgtc.MinWidth = 25; 
 dgtc.Width = Properties.Settings.Default.MaxPressureColumnWidth; 
 dgtc.IsReadOnly = true; 
 dgtc.Binding = new Binding（Unit.MaxDepthRelativeToEntry）
 {
 Converter = new DistanceUnitsConverter（）
}; 
  

其中dgtc是DataGridTextColumn。 Unit.MaxDepthRelativeToEntry通过为0，因为它是 AUnit 的子类的属性，所以XAML认为我正在尝试访问不存在的属性。

我已阅读

如果我在代码隐藏中编写绑定而不是在XAML中，它也可以使用完全相同的方式：

  colB.Binding = new Binding（B）
  

In my project I have a list of Units which is being used as the source of data for a DataGrid. The Units type has two types of subclasses, AUnits and BUnits. Each Unit in the list is either an AUnit or aBUnit. My issue is when I try to bind to a property specific to one of the subclass unit types, XAML doesn't see it and I just get back 0's. Normally, if this was being done in C# I would just cast it and access the property, but I am not able to do that at this point in my code. The bindings are being created in C# like this:

 dgtc.Header = Properties.Resources.MaxPressure;
 dgtc.MinWidth = 25;
 dgtc.Width = Properties.Settings.Default.MaxPressureColumnWidth;
 dgtc.IsReadOnly = true;
 dgtc.Binding = new Binding("Unit.MaxDepthRelativeToEntry")
 {
     Converter = new DistanceUnitsConverter()
 };

Where dgtc is a DataGridTextColumn. Unit.MaxDepthRelativeToEntry comes through as 0 because it is a property on the subclass of an AUnit, so XAML thinks I am trying to access an non-existent property.

I have read this answer and so far I have tried some of the following syntaxes:

dgtc.Binding = new Binding("AUnit.MaxDepthRelativeToEntry")
dgtc.Binding = new Binding("Unit(MyNameSpace:AUnit).MaxDepthRelativeToEntry")
dgtc.Binding = new Binding("Unit(MyNameSpace:AUnit.MaxDepthRelativeToEntry)")

and was not able to get any of those to work. I have also tried doing this through a converter, but the issue is, I don't have the list of units available to me when I am constructing the DataGrid/ setting up the bindings/etc. so I am not able to grab the property out of the instance and return it. Does anyone know of any way that I can, preferably in XAML, get to the properties of a subclass type of the type I am binding to?

Edit:

My DataGrid has the following XAML:

<DataGrid x:Name="JobListView"
              AutoGenerateColumns="False"
              ItemsSource="{Binding UnitStatusCollection, Mode=TwoWay}"
              CanUserDeleteRows="False"
              Style="{StaticResource JobGridViewStyle}"
              SelectedItem="{Binding JobsListViewSelectedUnitInfo, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
              Utility:DataGridColumnsBehavior.BindableColumns="{Binding DataGridColumns}"
              ContextMenu="{StaticResource ListViewContextMenu}"
              Margin="10,5,10,2"
              Grid.Row="2"
              SelectionMode="Single"
              SelectionUnit="FullRow"
              HorizontalAlignment="Stretch"
              HorizontalContentAlignment="Stretch"
              RowStyle="{StaticResource DataGridRowStyle}"
              CellStyle="{StaticResource DataGridCellStyle}"
              AlternationCount="2"
              HorizontalScrollBarVisibility="Visible"
              VerticalScrollBarVisibility="Visible"
              CanUserResizeRows="False"
              HorizontalGridLinesBrush="#d6d6d6"
              VerticalGridLinesBrush="#d6d6d6"
              Background="#EAEAEA"
              >

The ItemsSource is set to the UnitStatusCollection which is an ObservableCollection of a class called UnitInfo which holds a Unit and a UnitStatus. I need to access the property MaxDepthRelativeToEntry in Unit of UnitInfo. But I need to be able to see Unit as AUnit

解决方案

If you are binding to a list of Unit objects, then the DataContext for your DataGridTextColumn should be the AUnit or BUnit object itself, so your binding path should just be new Binding("MaxDepthRelativeToEntry").

You might get some kind of runtime warning for properties that only exist on one SubClass but not others, but it shouldn't throw an exception.

Here's a quick code sample to give an example :

XAML :

<DataGrid x:Name="dgTest" AutoGenerateColumns="False" CanUserAddRows="False">
    <DataGrid.Columns>
        <DataGridTextColumn Header="A" Binding="{Binding A}" />
        <DataGridTextColumn Header="B" Binding="{Binding B}" />
        <DataGridTextColumn Header="C" Binding="{Binding C}" />
    </DataGrid.Columns>
</DataGrid>

Code-Behind :

var test = new List<ClassA>();
test.Add(new ClassB() { A = "A", B = "B" });
test.Add(new ClassC() { A = "A", C = "C" });
dgTest.ItemsSource = test;

where the classes are defined as

public class ClassA
{
    public string A { get; set; }
}

public class ClassB : ClassA
{
    public string B { get; set; }
}

public class ClassC : ClassA
{
    public string C { get; set; }
}

Output :

It also works the exact same way if I write the binding in code-behind instead of in XAML :

colB.Binding = new Binding("B")

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