当我尝试删除保存文件时，我收到同样的错误。问题是，我已经成功创建了保存文件，但是当我尝试删除它们时，错误表明根本没有任何保存文件。但是，它们会跟踪我保存的保存文件数量。如果可能，有人可以免费查看我的代码吗？我愿意发送我的应用程序。
这里抛出了空引用异常：
LoadFile.cs
private void button2_Click(object sender, RoutedEventArgs e)
{
ViewDiskModel model = this.LayoutRoot.DataContext as ViewDiskModel;
int m_iSelectedLoad = lstBox1.SelectedIndex;
if (m_iSelectedLoad >= 0)
{
model.DeleteSelectedFiles.Execute(null);
}
MessageBox.Show("Files Successfully Deleted");
}
以下是负责上述代码的代码。
AddFileModel.cs
namespace WindowsPhoneApplication1.Model
{
public class AddFileModel : ModelBase
{
private string _filename;
public string FileName
{
get
{
return this._filename;
}
set
{
this._filename = value;
this.OnPropertyChanged("FileName");
}
}
private string _filetext10;
public string FileText10
{
get
{
return this._filetext10;
}
set
{
this._filetext10 = value;
this.OnPropertyChanged("FileText10");
}
}
private ICommand _saveFile;
public ICommand SaveFile
{
get
{
this._saveFile = this._saveFile ?? new DelegateCommand(this.OnSaveFile);
return this._saveFile;
}
}
private ICommand _readSelectedFiles;
public ICommand ReadSelectedFiles
{
get
{
this._readSelectedFiles = this._readSelectedFiles ?? new DelegateCommand(this.OnReadSelected);
return this._readSelectedFiles;
}
}
private void OnSaveFile()
{
if (!string.IsNullOrEmpty(this.FileName))
{
using (var store = IsolatedStorageFile.GetUserStoreForApplication())
{
if (store.FileExists(FileName))
store.DeleteFile(FileName);
using(StreamWriter writer = new StreamWriter(new IsolatedStorageFileStream(FileName, FileMode.OpenOrCreate, store)))
{
writer.WriteLine(this.FileText1 + this.FileText2 + this.FileText3 + this.FileText4 + this.FileText5 + this.FileText6 + this.FileText7 + this.FileText8 + this.FileText9 + this.FileText10);
writer.Close();
}
}
}
}
private void OnReadSelected()
{
using (var store = IsolatedStorageFile.GetUserStoreForApplication())
{
if (store.FileExists(FileName))
{
using (StreamReader reader = new StreamReader(new IsolatedStorageFileStream(FileName, FileMode.OpenOrCreate, store)))
{
string textData = this.FileText1 + this.FileText2 + this.FileText3 + this.FileText4 + this.FileText5 + this.FileText6 + this.FileText7 + this.FileText8 + this.FileText9 + this.FileText10;
textData = reader.ReadLine();
}
}
else
{
MessageBox.Show("File not found!");
}
}
}
}
}
ViewDiskModel.cs
namespace WindowsPhoneApplication1.Model
{
public class FileItem : ModelBase
{
public bool isChecked;
public bool IsChecked
{
get { return this.isChecked; }
set
{
this.isChecked = value;
this.OnPropertyChanged("IsChecked");
}
}
public string FileName { get; set; }
public string FileText { get; set; }
}
public class ViewDiskModel : ModelBase
{
private IsolatedStorageFile currentStore;
public IsolatedStorageFile Store
{
get
{
this.currentStore = this.currentStore ?? IsolatedStorageFile.GetUserStoreForApplication();
return this.currentStore;
}
}
private ObservableCollection<FileItem> _files;
public ObservableCollection<FileItem> Files
{
get
{
this._files = this._files ?? this.LoadFiles();
return this._files;
}
}
private ObservableCollection<FileItem> LoadFiles()
{
ObservableCollection<FileItem> files = new ObservableCollection<FileItem>();
foreach (string filePath in this.Store.GetFileNames())
files.Add(new FileItem { FileName = filePath });
return files;
}
private ICommand _deleteSelectedFiles;
public ICommand DeleteSelectedFiles
{
get
{
this._deleteSelectedFiles = this._deleteSelectedFiles ?? new DelegateCommand(this.OnDeleteSelected);
return this._deleteSelectedFiles;
}
}
private ICommand _readSelectedFiles;
public ICommand ReadSelectedFiles
{
get
{
this._readSelectedFiles = this._readSelectedFiles ?? new DelegateCommand(this.OnReadSelected);
return this._readSelectedFiles;
}
}
private void OnDeleteSelected()
{
IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication();
List<FileItem> removedItems = new List<FileItem>();
foreach (var item in this.Files)
{
if (item.IsChecked)
if (storage.FileExists(item.FileName))
{
storage.DeleteFile(item.FileName);
removedItems.Add(item);
}
}
foreach (var item in removedItems)
this.Files.Remove(item);
}
}
}
ModelBase.cs
namespace WindowsPhoneApplication1.Model
{
public class ModelBase : INotifyPropertyChanged
{
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventArgs eargs = new PropertyChangedEventArgs(propertyName);
if (this.PropertyChanged != null)
this.PropertyChanged(this, eargs);
}
#endregion
}
}
DelegateCommand.cs
namespace WindowsPhoneApplication1.Model
{
public class DelegateCommand : ICommand
{
private Action command;
public Action Command
{
get { return this.command; }
}
private Func<bool> canExecuteCommand;
public DelegateCommand(Action cmd, Func<bool> canexecute)
{
this.canExecuteCommand = canexecute;
this.command = cmd;
}
public DelegateCommand(Action cmd)
{
this.command = cmd;
}
#region ICommand Members
public bool CanExecute(object parameter)
{
if (this.canExecuteCommand != null)
return this.canExecuteCommand();
return true;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
if (this.command != null)
this.command();
}
#endregion
}
}
编辑:(这是我在加载页面的XAML中添加的内容）
ListBox ItemsSource =“{Binding Files}”Margin =“0,42,0,115”SelectionChanged =“ListBox_SelectionChanged”Name =“lstBox1”DataContext =“{StaticResource vmDiskModel}”＆gt; ListBox.ItemTemplate＆GT; DataTemplate＆gt; CheckBox IsChecked =“{Binding IsChecked}”Content =“{Binding FileName}”/＆gt; / DataTemplate中＆GT; /ListBox.ItemTemplate> /列表框＆GT;
答案 0 :(得分：0)
在不了解您的应用程序或阅读您发布的所有代码段的情况下，我非常确定您希望在button2_Click方法中添加空值检查：
ViewDiskModel model = this.LayoutRoot.DataContext as ViewDiskModel;
如果ViewDiskModel的类型为model，那么基本上就是将this.LayoutRoot.DataContext分配给ViewDiskModel。如果它是任何其他类型，它将null分配给`model。
尝试检查该行后是否model == null。