c# - 选择一个列表视图项目作为对象

Question

我也有一个ListView包含控件的GridView控件。数据来自数据库数据库方案的不同表：

1. 书籍（BookID、BookName、ISBN、CopyLeft）；
2. 借款人（BorrowerID、BorrowerName、BorrowerLevel）；
3. 交易（TransactionID、BorrowerID、BookID、BorrowDate、ReturnDate、IsReturned）；

对应的类分别Book是Borrower和Transaction。 使用数据绑定从这些表中获取GridView、 TransactionID、BorrowerID、BorrowerName和。XAML 代码：BookNameBorrowDateReturnDate

 <Grid>
    <ListView Margin="15,57,58,57" Name="borrowedBookList" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding }" KeyDown="borrowedBookList_KeyDown">
        <ListView.View>
            <GridView>
                <GridView.Columns>
                    <GridViewColumn  Width="80" Header="Borrower ID" DisplayMemberBinding="{Binding Path=BorrowerID}"/>
                    <GridViewColumn Width="220" Header="Borrower Name" DisplayMemberBinding="{Binding Path=BorrowerName}"/>
                    <GridViewColumn Width="220" Header="Book Name" DisplayMemberBinding="{Binding Path=BookName}"/>
                    <GridViewColumn Width="100" Header="Date" DisplayMemberBinding="{Binding Path=BorrowDate}"/>
                    <GridViewColumn Width="100" Header="Return Date" DisplayMemberBinding="{Binding Path=ReturnDate}"/>
                   </GridView.Columns>
            </GridView>
        </ListView.View>
    </ListView>
    <Label Content="Borrowed Book List" Height="34" HorizontalAlignment="Left" Margin="310,12,0,0" Name="label1" VerticalAlignment="Top" Width="151" />
    <Button Content="Close" Height="31" HorizontalAlignment="Left" Margin="636,535,0,0" Name="close" VerticalAlignment="Top" Width="106" Click="close_Click"/>
    <Button Content="Return This Book" Height="31" HorizontalAlignment="Left" Margin="454,535,0,0" Name="return" VerticalAlignment="Top" Width="115" Click="return_Click"/>
</Grid>

现在，我可以选择一行作为TransactionorBook或的对象Borrower吗？我的目标是选择一行并识别Transactions,Books表的相应条目并递增CopyLeft并将“YES”分配给IsReturned属性。那么我该怎么做呢？

另外：我尝试这样编写代码：

var selectedTran = this.borrowedBookList.selectedItem as Transaction;
var selectedBook=this.borrowedBookList.selectedItem as Book;
try
{
    selectedBook.CopyLeft++;
    selectedTran.isReturned="YES";
}
catch(Exception ex)
{
    MessageBox.Show(ex.message);
}

异常显示“对象引用未设置为对象的实例”。然后我试图像这样找到所借书列表的类型：

MessageBox.Show(borrowedBookList.SelectedItem.GetType().ToString());

它显示了一个匿名类型。

Answer 1

您的查询可能会导致匿名类型：

    var query = from b in ctx.books 
                ... 
                select new 
                { BorrowerID = b.ID, BorrowerName = b.Name , ... 
                }

您的网格的 selectedItem 属性包含此类型，而不是您的原始实体类。所以我会使用一个命名类，你应该在其中包含主键 ID，并使用所选项目中的主键更新相应的实体：

public class ForYourGrid
{
    public int BorrowerID { get; set; }
    public string BorrowerName { get; set; }
...
}

    var query2 = from b in ctx.books 
                ... 
                select new ForYourGrid 
                { BorrowerID = b.ID, BorrowerName = b.Name , ... 
                }


    var selected = this.borrowedBookList.selectedItem as ForYourGrid;

    var selectedTran = ctx.Transactions.SingleOrDefault(e => e.TransactionID == selected.TransactionID);
    selectedTran.isReturned = "YES";

    var selectedBook = ctx.Books.SingleOrDefault(e => e.BookID == selected.BookID);
    selectedBook.CopyLeft++;

    ctx.SaveChanges();