C# 选择listview项作为对象
我得到了一个C# 选择listview项作为对象,c#,.net,linq,xaml,dynamic-linq,C#,.net,Linq,Xaml,Dynamic Linq,我得到了一个ListView控件,它也包含一个GridView控件。数据来自数据库的不同表 数据库方案: 图书(BookID、BookName、ISBN、CopyLeft) 借款人(借款ID、借款名称、借款级别) 交易记录(TransactionID、借入ID、BookID、借入日期、归还日期、IsReturned) 相应的类别分别是图书、借款人和交易。 GridViewfetches 交易ID,借用ID,借用名称,书名,借用日期和返回日期使用数据绑定从这些表中删除。 XAML代码: <
ListView
控件,它也包含一个GridView
控件。数据来自数据库的不同表
数据库方案:
图书
、借款人
和交易
。
GridView
fetches
交易ID
,借用ID
,借用名称
,书名
,借用日期
和返回日期
使用数据绑定从这些表中删除。
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>
异常显示“对象引用未设置为对象的实例”。然后我尝试按如下方式查找借阅书目的类型:
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);
}
MessageBox.Show(borrowedBookList.SelectedItem.GetType().ToString());
显示匿名类型。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 , ...
}
网格的selectedItem属性包含此类型,而不是原始实体类。因此,我将使用一个命名类,其中应包含主键ID,并使用所选项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();
CopyLeft是Book类的整数类型变量。