绑定到 ComboBox 显示模型名称而不是属性内容

Question

我在 ViewModel 中使用属性为组合框设置了绑定。但是当我在设备上调试应用程序时，组合框的内容只是每个索引的型号名称，如 LC_Points.Model.Grade.

为了调试这个问题，我进行了以下检查：

检查属性是 public
检查清单不为空
检查 VM 中的正确绑定名称

有谁知道如何解决这个绑定问题？

包含列表的 ViewModel 是这样设置的：

namespace LC_Points.ViewModel
{

    public class MainViewModel : ViewModelBase
    {

        /// <summary>
        /// Initializes a new instance of the MainViewModel class.
        /// </summary>
        public MainViewModel()
        {
            //call methods to initilise list data
            GetGradeTypes();
            GetSubjectTypes();

        }


        public List<Grade> grades { get; set; }
        public List<Grade> subjects { get; set; }

        public void GetGradeTypes()
        {
            List<Grade> gradeList = new List<Grade>();

            // Adding Grades to List
            gradeList.Add(new Grade { grade = "A1" });
            gradeList.Add(new Grade { grade = "A2" });
            gradeList.Add(new Grade { grade = "B1" });
            gradeList.Add(new Grade { grade = "B2" });
            gradeList.Add(new Grade { grade = "B3" });
            gradeList.Add(new Grade { grade = "C1" });
            gradeList.Add(new Grade { grade = "C2" });
            gradeList.Add(new Grade { grade = "C3" });
            gradeList.Add(new Grade { grade = "D1" });
            gradeList.Add(new Grade { grade = "D2" });
            gradeList.Add(new Grade { grade = "D3" });
            gradeList.Add(new Grade { grade = "E,F,NG" });
            gradeList.Add(new Grade { grade = "Pass" });
            gradeList.Add(new Grade { grade = "Merit" });
            gradeList.Add(new Grade { grade = "Distinction" });


            grades = gradeList;

        }


        public void GetSubjectTypes()
        {
            List<Grade> subjectList = new List<Grade>();

            // Adding Subjects to List
            subjectList.Add(new Grade { subject = "Accounting" });
            subjectList.Add(new Grade { subject = "Agricultural Economics" });
            subjectList.Add(new Grade { subject = "Agricultural Science" });
            subjectList.Add(new Grade { subject = "Ancient Greek" });
            subjectList.Add(new Grade { subject = "Applied Math" });
            subjectList.Add(new Grade { subject = "Arabic" });
            subjectList.Add(new Grade { subject = "Art" });
            subjectList.Add(new Grade { subject = "Artistic & Creative Group" });
            subjectList.Add(new Grade { subject = "Biology" });
            subjectList.Add(new Grade { subject = "Business" });
            subjectList.Add(new Grade { subject = "Business Group" });
            subjectList.Add(new Grade { subject = "Chemistry" });
            subjectList.Add(new Grade { subject = "Classical Studies" });
            subjectList.Add(new Grade { subject = "Construction Studies" });
            subjectList.Add(new Grade { subject = "Design & Comm Graphics" });
            subjectList.Add(new Grade { subject = "Economics" });
            subjectList.Add(new Grade { subject = "Engineering" });
            subjectList.Add(new Grade { subject = "English" });
            subjectList.Add(new Grade { subject = "French" });
            subjectList.Add(new Grade { subject = "Geography" });
            subjectList.Add(new Grade { subject = "German" });
            subjectList.Add(new Grade { subject = "Hebrew Studies" });
            subjectList.Add(new Grade { subject = "History" });
            subjectList.Add(new Grade { subject = "Home Economics" });
            subjectList.Add(new Grade { subject = "Irish" });
            subjectList.Add(new Grade { subject = "Italian" });
            subjectList.Add(new Grade { subject = "Japanese" });
            subjectList.Add(new Grade { subject = "Languages & Humanities" });
            subjectList.Add(new Grade { subject = "Latin" });
            subjectList.Add(new Grade { subject = "Link Modules" });
            subjectList.Add(new Grade { subject = "Mathematics" });
            subjectList.Add(new Grade { subject = "Music" });
            subjectList.Add(new Grade { subject = "Other Language" });
            subjectList.Add(new Grade { subject = "Physics" });
            subjectList.Add(new Grade { subject = "Physics & Chemistry" });
            subjectList.Add(new Grade { subject = "Practical Group" });
            subjectList.Add(new Grade { subject = "Religious Education" });
            subjectList.Add(new Grade { subject = "Russian" });
            subjectList.Add(new Grade { subject = "Science Group" });
            subjectList.Add(new Grade { subject = "Social Group" });
            subjectList.Add(new Grade { subject = "Spanish" });
            subjectList.Add(new Grade { subject = "Technology" });

            subjects = subjectList;

        }

    }
}

而且我在 MainPage 视图中设置了这样的绑定：

<Page x:Class="LC_Points.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:local="using:LC_Points"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
      DataContext="{Binding Source={StaticResource Locator}}"
      mc:Ignorable="d">



    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="40*" />
            <RowDefinition Height="20*" />
            <RowDefinition Height="30*" />
            <RowDefinition Height="30*" />
            <RowDefinition Height="20*" />
            <RowDefinition Height="20*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="4.5*" />
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>


        <ComboBox x:Name="subjectCmbBx"
                  Grid.Row="1"
                  Grid.ColumnSpan="2"
                  Width="174"
                  HorizontalAlignment="Left"
                  VerticalAlignment="Top"
                  ItemsSource="{Binding subjects}" />
        <ComboBox x:Name="gradeCmbBx"
                  Grid.Row="1"
                  Grid.Column="0"
                  Grid.ColumnSpan="2"
                  Width="70"
                  HorizontalAlignment="Right"
                  ItemsSource="{Binding grades}" />
    </Grid>

</Page>

调试期间的输出如下所示：

Answer 1

除非您提供 DisplayMemberPath (https://msdn.microsoft.com/en-us/library/system.windows.controls.itemscontrol.displaymemberpath%28v=vs.110%29.aspx)，这是我推荐的做法，否则它将使用提供的 Grade::ToString() 实现。因此，您也可以覆盖它。

Answer 2

您需要告诉 ComboBox 如何显示其项目。否则它只会在绑定的项目上调用 ToString() 并显示一些奇怪的东西。

合理输出的三种方式：

在您的 DataObject 上定义合理的 ToString()。这是一个好主意，即使您执行其他操作之一也是如此，因为如果您不设置辅助功能信息，“讲述人”将会阅读此内容。
定义ComboBox上的DisplayMemberPath指向你要显示的属性。

<ComboBox x:Name="subjectCmbBx"
          Grid.Row="1"
          Grid.ColumnSpan="2"
          Width="174"
          HorizontalAlignment="Left"
          VerticalAlignment="Top"
          DisplayMemberPath="Name"
          ItemsSource="{Binding subjects}" />

为 ComboBox 定义一个 ItemTemplate 以完全控制每个项目的显示方式。这将允许显示绑定对象的多个属性、格式以及比纯文本更好的 UI。您可以通过右键单击设计器中的 ComboBox 并选择编辑其他 Templates.Edit 生成的项目 (ItemTemplate)... 生成一个空模板，然后根据需要填写它：

<ComboBox x:Name="subjectCmbBx"
          Grid.Row="1"
          Grid.ColumnSpan="2"
          Width="174"
          HorizontalAlignment="Left"
          VerticalAlignment="Top"
          ItemsSource="{Binding subjects}" >
    <ComboBox.Resources>
        <DataTemplate x:Key="DataTemplate1">
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto" />
                    <ColumnDefinition Width="*" />
                </Grid.ColumnDefinitions>
                <Image Source="{Binding Picture}" Grid.Column="0" />
                <TextBlock Text="{Binding Name}" Grid.Column="1" />
            </Grid>
        </DataTemplate>
    </ComboBox.Resources>
    <ComboBox.ItemTemplate>
        <StaticResource ResourceKey="DataTemplate1"/>
    </ComboBox.ItemTemplate>
</ComboBox>

对于大多数情况，我建议#1（作为可访问性的最低要求）和#3。

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