使用自定义列表使用ItemSource之前，Items集合必须为空 [英] Items collection must be empty before using ItemSource using custom list

问题描述

在我的班级 ResultEntity 中，如果我这样做:

In my class ResultEntity if I do:

_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此错误消息，并且我已经阅读了帖子，但是我不明白为什么我看到此消息.如果我只是声明 _resultMulti 而不初始化新列表，则应用程序将加载.我不明白为什么呢?

I have seen lots of people also have had this error message and I've read the posts but I don't understand why I'm seeing this message. If I just declare _resultMulti without initialising a new list the application loads. I don't understand why though?

我有以下课程:

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; }         
    }

结果基金

    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>

推荐答案

您直接将 DataGridTextColumns 作为 DataGrid 的项添加，因此您同时设置了 Items 和 ItemsSource 属性，您只能同时使用一个.通过使用 Columns 附加属性来修复您的列配置:

You are adding your DataGridTextColumns directly as items of the DataGrid, thus you are setting both the Items and ItemsSource property and you can only use one at the same time. Fix your columns configuration by using the Columns attached property:

<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>

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