Question

我有一个ListView控件，其中也包含GridView控件。数据来自不同的表与数据库数据库方案：

图书（BookID，BookName，ISBN，CopyLeft）;
借款人（BorrowerID，BorrowerName，BorrowerLevel）;
交易（TransactionID，BorrowerID，BookID，BorrowDate，ReturnDate，IsReturned）;

相应的班级分别为Book，Borrower和Transaction。 GridView抓取使用数据绑定从这些表中TransactionID，BorrowerID，BorrowerName，BookName，BorrowDate和ReturnDate。 XAML代码：

 <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Transaction或Book或Borrower的对象吗？我的目标是选择一行并标识Transactions，Books表的相应条目，并增加CopyLeft并将“是”分配到IsReturned属性中。那我怎么能这样做呢？

另外：我试着像这样编码：

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”。然后我试图找到借来的BookList的类型：

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

显示匿名类型。

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();

选择列表视图项作为对象

1 个答案: