我正在使用longlistselector，我想获取Hold事件中所选项目中的文字。不幸的是，Hold没有创建SelectedItem所以我必须做一个解决方法。我已经阅读了很多关于这个问题的内容，但无法获得完全可行的解决方案。这是我得到的错误：Unable to cast object of type PhoneApp2.Favs键入'System.String'。仅当我按住项目中文本旁边的空白区域时才会出现此错误。我该如何解决这个问题？
相关C＃：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Navigation;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;
using System.Windows.Media;
using System.Collections.ObjectModel;
using System.Xml;
using PhoneApp2.Resources;
using System.Xml.Linq;
using System.IO;
using System.IO.IsolatedStorage;
using System.Windows.Resources;
namespace PhoneApp2
{
public class Favs
{
private string drank;
public string Name
{
get { return drank; }
set { drank = value; }
}
public Favs(string addition)
{
this.Name = addition;
}
}
public partial class Favorites : PhoneApplicationPage
{
ObservableCollection<Favs> Favlist = new ObservableCollection<Favs>();
Array list;
Boolean alpha = false;
public Favorites()
{
InitializeComponent();
}
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
//Populate LLL listBar
listFavs.ItemsSource = Favlist;
try
{
// copy the xml file to isolated storage
using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
{
if (!file.FileExists("favorites.xml"))
{
StreamResourceInfo sr_en = Application.GetResourceStream(new Uri("Resources\\favorites.xml", UriKind.Relative));
using (BinaryReader br_en = new BinaryReader(sr_en.Stream))
{
byte[] data = br_en.ReadBytes((int)sr_en.Stream.Length);
//Write the file.
using (BinaryWriter bw = new BinaryWriter(file.CreateFile("favorites.xml")))
{
bw.Write(data);
bw.Close();
}
}
}
// work with file at isolatedstorage
using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("favorites.xml", FileMode.Open, file))
{
XDocument xDoc = XDocument.Load(stream, LoadOptions.None);
list = xDoc.Descendants("cocktail").Select(n => n.Value).ToArray();
Array.Sort(list);
alpha = true;
foreach (string name in list)
{
Favlist.Add(new Favs(name));
}
}
}
Dispatcher.BeginInvoke(() =>
{
pbLoading.IsIndeterminate = false;
pbLoading.Visibility = Visibility.Collapsed;
});
}
catch (IOException IOExc)
{
MessageBox.Show(IOExc.Message);
}
catch (XmlException XmlExc)
{
MessageBox.Show(XmlExc.Message);
}
catch (Exception myExc)
{
MessageBox.Show(myExc.Message);
}
}
private void listFavs_Hold(object sender, System.Windows.Input.GestureEventArgs e)
{
try
{
FrameworkElement element = (FrameworkElement)e.OriginalSource;
String item = (String)element.DataContext;
var booze = item.ToString();
Dispatcher.BeginInvoke(() =>
{
CustomMessageBox messageBox = new CustomMessageBox()
{
Caption = "Delete " + booze,
Message = "Are you sure you want to remove " + booze + " from your favorites? This cannot be made undone!",
LeftButtonContent = "Yes",
RightButtonContent = "No"
};
messageBox.Dismissed += (s1, e1) =>
{
switch (e1.Result)
{
case CustomMessageBoxResult.LeftButton:
using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
{
using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("favorites.xml", FileMode.Open, file))
{
XDocument xDoc = XDocument.Load(stream, LoadOptions.None);
// delete node
xDoc.Descendants("data").Elements("cocktail").Where(x => x.Value == booze).DescendantsAndSelf().Remove();
xDoc.Save(stream);
Favlist.Clear();
list = xDoc.Descendants("cocktail").Select(n => n.Value).ToArray();
Array.Sort(list);
alpha = true;
foreach (string name in list)
{
Favlist.Add(new Favs(name));
}
}
}
break;
case CustomMessageBoxResult.RightButton:
//do nothing
break;
case CustomMessageBoxResult.None:
//do nothing
break;
default:
break;
}
};
messageBox.Show();
});
}
catch (InvalidCastException ICExc)
{
MessageBox.Show(ICExc.Message);
}
catch (IOException IOExc)
{
MessageBox.Show(IOExc.Message);
}
catch (XmlException XmlExc)
{
MessageBox.Show(XmlExc.Message);
}
catch (NullReferenceException NRExc)
{
MessageBox.Show(NRExc.Message);
}
catch (Exception myExc)
{
MessageBox.Show(myExc.Message);
}
}
}
}
XAML：
<phone:PhoneApplicationPage
x:Class="PhoneApp2.Favorites"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
Foreground="{StaticResource PhoneForegroundBrush}"
SupportedOrientations="Portrait" Orientation="Portrait"
mc:Ignorable="d"
shell:SystemTray.IsVisible="True">
<!--LayoutRoot is the root grid where all page content is placed-->
<Grid x:Name="LayoutRoot">
<Grid.Background>
<ImageBrush Stretch="Fill" ImageSource="/Assets/AlignmentGrid.png"/>
</Grid.Background>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid x:Name="Header" Grid.Row="0" Margin="12,17,0,616" Grid.RowSpan="2">
<TextBlock Text="Cocktail" Style="{StaticResource PhoneTextNormalStyle}" Margin="12,0,242,46"/>
<TextBlock Text="Favorites" Style="{StaticResource PhoneTextTitle1Style}" Margin="10,50,101,0" FontWeight="Bold"/>
<Button x:Name="btnSettings" Content="" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="367,60,0,-50" Height="86" Width="91" Click="btnSettings_Click" BorderThickness="0">
<Button.Foreground>
<ImageBrush Stretch="Fill"/>
</Button.Foreground>
<!--<Button.Background>
<ImageBrush Stretch="Fill" ImageSource="feature.settings.png"/>
</Button.Background>-->
</Button>
</Grid>
<!--ContentPanel - place additional content here-->
<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,157,12,0">
<phone:LongListSelector x:Name="listFavs" HorizontalAlignment="Left" Height="601" VerticalAlignment="Top" Width="456" Tap="listFavs_Tap" Hold="listFavs_Hold">
<phone:LongListSelector.ItemTemplate>
<DataTemplate>
<Button Content="{Binding Name}" FontSize="36" HorizontalContentAlignment="left" HorizontalAlignment="Left" Height="82" Margin="0,-11,0,0" VerticalAlignment="Top" Width="456" Padding="0,0,0,0" BorderThickness="0">
</Button>
</DataTemplate>
</phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>
<ProgressBar x:Name="pbLoading" HorizontalAlignment="Left" Height="20" Margin="127,271,0,0" VerticalAlignment="Top" Width="200" IsIndeterminate="True"/>
</Grid>
</Grid>
</phone:PhoneApplicationPage>
答案 0 :(得分：3)
可能在您的情况下element.DataContext是您的自定义类Favs。
所以你应该进行以下投射：
private void listFavs_Hold(object sender, System.Windows.Input.GestureEventArgs e)
{
try
{
FrameworkElement element = (FrameworkElement)e.OriginalSource;
string item = null;
if(element.DataContext is Favs)
{
Favs itemTmp = (Favs)element.DataContext;
item = itemTmp.Name;
}
else
{
item = (string)element.DataContext;
}
....
答案 1 :(得分：0)
这是因为你捕获了许多不同的FrameworkElements（TextBlock，Border等），只有TextBlock可以投射到string：
private void listFavs_Hold(object sender, System.Windows.Input.GestureEventArgs e)
{
try
{
FrameworkElement element = (FrameworkElement)e.OriginalSource;
if (element is TextBlock)
{
String item = (String)element.DataContext;
var booze = item.ToString();
// rest of code
}
}
此代码仅在用户持有Text时才有效。如果用户在Text之后保留一个空格，那么它是Border DataContext为Favs - 你可以执行合适的演员并取出你的变量。