WPF异常在使用 ItemsSource 之前，项集合必须为空

Posted 2020-09-24 历史的尘埃

 1 <DataGrid x:Name="dataGrid" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="620" Height="269" AutoGenerateColumns="False" GridLinesVisibility="None" CanUserDeleteRows="False"
 2                     CanUserAddRows="False" ItemsSource="{Binding ListStudent}"> 
 3             <DataGridTextColumn Header="编号" Width="80" Binding="{Binding Student.studentid}"/>
 4             <DataGridTextColumn Header="姓名" Width="80" Binding="{Binding Student.name}"/>
 5             <DataGridTextColumn Header="年龄" Width="80" Binding="{Binding Student.age}"/>
 6             <DataGridTextColumn Header="性别" Width="80" Binding="{Binding Student.sex}"/>
 7             <DataGridTextColumn Header="特点" Width="120" Binding="{Binding Student.remark}"/>
 8             <DataGridTemplateColumn Header="选中" SortMemberPath="IsSelected" Width="120">
 9                 <DataGridTemplateColumn.CellTemplate>
10                     <DataTemplate>
11                         <CheckBox IsChecked="{Binding Path=IsSelected,UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Center" HorizontalAlignment="Center" Command="{Binding Path=DataContext.SelectStudentItemCommand,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type DataGrid}}}"
12                     />
13                     </DataTemplate>
14                 </DataGridTemplateColumn.CellTemplate>
15             </DataGridTemplateColumn> 
16         </DataGrid>

报错“在使用 ItemsSource 之前，项集合必须为空”

观察一下便可发现设计器里没有正确显示各列，是因为少了DataGrid.Columns节点

 1 <DataGrid x:Name="dataGrid" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="620" Height="269" AutoGenerateColumns="False" GridLinesVisibility="None" CanUserDeleteRows="False"
 2                     CanUserAddRows="False" ItemsSource="{Binding ListStudent}">
 3             <DataGrid.Columns>
 4             <DataGridTextColumn Header="编号" Width="80" Binding="{Binding Student.studentid}"/>
 5             <DataGridTextColumn Header="姓名" Width="80" Binding="{Binding Student.name}"/>
 6             <DataGridTextColumn Header="年龄" Width="80" Binding="{Binding Student.age}"/>
 7             <DataGridTextColumn Header="性别" Width="80" Binding="{Binding Student.sex}"/>
 8             <DataGridTextColumn Header="特点" Width="120" Binding="{Binding Student.remark}"/>
 9             <DataGridTemplateColumn Header="选中" SortMemberPath="IsSelected" Width="120">
10                 <DataGridTemplateColumn.CellTemplate>
11                     <DataTemplate>
12                         <CheckBox IsChecked="{Binding Path=IsSelected,UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Center" HorizontalAlignment="Center" Command="{Binding Path=DataContext.SelectStudentItemCommand,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type DataGrid}}}"
13                     />
14                     </DataTemplate>
15                 </DataGridTemplateColumn.CellTemplate>
16             </DataGridTemplateColumn>
17             </DataGrid.Columns>
18         </DataGrid>

改为以上即可