c# - 在使用自定义列表使用 ItemSource 之前，项目集合必须为空

Question

在我的类(class) ResultEntity 中，如果我这样做:

_resultMulti = new List<ResultTaskFund>(); 

我看到以下错误消息:

"Exception: Items collection must be empty before using ItemSource."

我看到很多人也收到了这条错误消息，我已经阅读了这些帖子，但我不明白为什么会看到这条消息。如果我只是声明 _resultMulti 而没有初始化应用程序加载的新列表。我不明白为什么？

我有以下类(class):

结果摘要

 public class ResultEntity : INotifyPropertyChanged
    {

        public List<ResultTaskFund> ResultsMulti
        {
            get { return _resultsMulti; }
            set { _resultsMulti = value; OnPropertyChanged("ResultsMulti"); }
        }

        List<ResultTaskFund> _resultMulti;


        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

ResultTaskFund

 public class ResultTaskFund : INotifyPropertyChanged
    {            
        public string TaskName { get; set; }
        public ResultFund ABBC { get; set; }
        public ResultFund BBCA { get; set; }
        public ResultFund CCCA { get; set; }         
    }

成果基金

    public class ResultFund
    {
        public string FundCode { get; set; }
        public ErrorAndWarningCodes  ErrCode { get; set; }
        public bool FundRequried { get; set; }
        public bool CheckRequired { get; set; }
        public string DisplayString { get; set; }
    }

XAML

 <DataGrid Grid.Row="0"
                      DataContext="{Binding ResultSummary}"
                      x:Name="dataGridResultMulti"
                      ItemsSource="{Binding ResultsMulti, UpdateSourceTrigger=PropertyChanged}"
                      Style="{StaticResource DataGridTemplate}"
                      ColumnHeaderStyle="{StaticResource DG_ColumnHeader}"                                            
                      RowStyle="{StaticResource DG_Row}"
                      CellStyle="{StaticResource DG_Cell}"                                    
                      RowDetailsTemplate="{StaticResource DG_RowDetail}" 
                      RowHeaderStyle="{StaticResource DG_RowHeader}"
                      AutoGenerateColumns="False"
                      HorizontalAlignment="Stretch" 
                      VerticalAlignment="Stretch"
                      Background="Silver"
                      RowHeaderWidth="30"                      
                      Margin="25,5,20,15">
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Task" IsReadOnly="True" Binding="{Binding TaskName}"/>
                    <DataGridTextColumn Header="ABBC" IsReadOnly="True" Binding="{Binding ABBC.DisplayString}"/>
                    <DataGridTextColumn Header="BBCA" IsReadOnly="True" Binding="{Binding BBCA.DisplayString}"/>
                    <DataGridTextColumn Header="CCCA" IsReadOnly="True" Binding="{Binding CCCA.DisplayString}"/>
                    <DataGrid.Columns>
            </DataGrid>

Answer 1

您将 DataGridTextColumns 直接添加为 DataGrid 的项目，因此您同时设置了 Items 和 ItemsSource 属性，同时只能使用一个。使用 Columns 附加属性修复您的列配置:

<DataGrid.Columns>
    <DataGridTextColumn Header="Task" IsReadOnly="True" Binding="{Binding TaskName}"/>        
    <DataGridTextColumn Header="ABBC" IsReadOnly="True" Binding="{Binding ABBC.DisplayString}"/>
    <DataGridTextColumn Header="BBCA" IsReadOnly="True" Binding="{Binding BBCA.DisplayString}"/>
    <DataGridTextColumn Header="CCCA" IsReadOnly="True" Binding="{Binding CCCA.DisplayString}"/>
</DataGrid.Columns>