我正在尝试为 Windows Phone 8 创建一个数据库应用程序。当我尝试在数据库的一个表中添加一个新表条目时，我收到这样的错误。
{System.InvalidCastException: Could not convert from type 'System.Byte[]' to type 'System.String'.
at System.Data.Linq.DBConvert.ChangeType(Object value, Type type)
at System.Data.Linq.ChangeDirector.StandardChangeDirector.DoResultSetAutoSync(TrackedObject item)
at System.Data.Linq.ChangeDirector.StandardChangeDirector.DoResultSetInsert(TrackedObject item)
at System.Data.Linq.ChangeDirector.StandardChangeDirector.Insert(TrackedObject item)
at System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode failureMode)
at System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode)
at System.Data.Linq.DataContext.SubmitChanges()
at CygnusModel.ViewModel.CygnusViewModel.AddNewSem(CygSem NewCygSem)
at Cygnus.AddSemView.Save_sem(Object sender, EventArgs e)
at Microsoft.Phone.Shell.ApplicationBarItemContainer.FireEventHandler(EventHandler handler, Object sender, EventArgs args)
at Microsoft.Phone.Shell.ApplicationBarIconButtonContainer.ClickEvent()
at Microsoft.Phone.Shell.ApplicationBar.OnCommand(UInt32 idCommand, Boolean isButton)
at Microsoft.Phone.Shell.Interop.NativeCallbackInteropWrapper.OnCommand(UInt32 idCommand, Boolean isButton)}
这是我使用的代码
if (CygSemName.Text.Length > 0)
{
CygSem NewCygSem = new CygSem
{
SemName = (string)CygSemName.Text,
SemStart = (DateTime)CygSemStart.Value,
SemEnd = (DateTime)CygSemEnd.Value
};
App.ViewModel.AddNewSem(NewCygSem);
if (NavigationService.CanGoBack)
{
NavigationService.GoBack();
}
有人可以帮我解决这个问题吗？请记住，我是 c# 和 Windows Phone 开发的新手。
视图模型：
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
//Includes DataModel Classes
using CygnusModel.Model;
namespace CygnusModel.ViewModel
{
public class CygnusViewModel : INotifyPropertyChanged
{
private CygDataContext CygDb;
//Class Constructor Creating the connection between Model & View
public CygnusViewModel(string CygDataConnectionString)
{
CygDb = new CygDataContext(CygDataConnectionString);
}
//Save changing Method
private void CygSaveChanges()
{
CygDb.SubmitChanges();
}
//Contains Change tracking INotify Events
#region INotifies
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
//All The Semesters
private ObservableCollection<CygSem> _allSems;
public ObservableCollection<CygSem> AllSems
{
get
{
return _allSems;
}
set
{
_allSems = value;
NotifyPropertyChanged("AllSems");
}
}
//All The Subjects
private ObservableCollection<CygSubs> _allSubs;
public ObservableCollection<CygSubs> AllSubs
{
get
{
return _allSubs;
}
set
{
_allSubs = value;
NotifyPropertyChanged("AllSubs");
}
}
//All The Lectures
private ObservableCollection<CygLect> _allLects;
public ObservableCollection<CygLect> AllLects
{
get
{
return _allLects;
}
set
{
_allLects = value;
NotifyPropertyChanged("AllLects");
}
}
//All The Exams
private ObservableCollection<CygExam> _allExam;
public ObservableCollection<CygExam> AllExam
{
get
{
return _allExam;
}
set
{
_allExam = value;
NotifyPropertyChanged("AllExam");
}
}
//All The Instructors
private ObservableCollection<CygInst> _allInsts;
public ObservableCollection<CygInst> AllInsts
{
get
{
return _allInsts;
}
set
{
_allInsts = value;
NotifyPropertyChanged("AllInsts");
}
}
//All The Holidays
private ObservableCollection<CygHoli> _allHolis;
public ObservableCollection<CygHoli> AllHolis
{
get
{
return _allHolis;
}
set
{
_allHolis = value;
NotifyPropertyChanged("AllHolis");
}
}
//All the lectures of today
private ObservableCollection<CygLect> _todayLect;
public ObservableCollection<CygLect> TodayLect
{
get
{
return _todayLect;
}
set
{
_todayLect = value;
NotifyPropertyChanged("TodayLect");
}
}
//All the Exams of today
private ObservableCollection<CygExam> _todayExam;
public ObservableCollection<CygExam> TodayExam
{
get
{
return _todayExam;
}
set
{
_todayExam = value;
NotifyPropertyChanged("TodayExam");
}
}
// Query database and load the all the data
public void LoadAllAvailables()
{
}
//Query DB and load all the semester
public void LoadAllSems()
{
var Sems = from CygSem semes in CygDb.Semesters select semes;
AllSems = new ObservableCollection<CygSem>(Sems);
}
//Query DB and load all Holidays
public void LoadAllHolis()
{
var Holis = from CygHoli holid in CygDb.Holidays select holid;
AllHolis = new ObservableCollection<CygHoli>(Holis);
}
//Query DB and load Subjects based on Semester
public void LoadSemBasedSubs()
{
}
//Query DB and load all the Lectures and exams per day
public void LoadForTheDay()
{
}
//Query the DB and load Lectures and Exams per Subject
public void LoadForTheSub()
{
}
//Add New Sem
public void AddNewSem(CygSem NewCygSem)
{
CygDb.Semesters.InsertOnSubmit(NewCygSem);
CygDb.SubmitChanges();
AllSems.Add(NewCygSem);
}
//Add New Holiday
public void AddNewHoli(CygHoli NewCygHoli)
{
CygDb.Holidays.InsertOnSubmit(NewCygHoli);
CygDb.SubmitChanges();
}
}
}
模型：
//Semester Class
[Table]
public class CygSem : INotifyPropertyChanging, INotifyPropertyChanged
{
//_version variable. Binary Datatype
[Column(IsVersion = true)]
private string _version;
//Contains Change tracking INotify Events
#region INotifies
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string PropertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
}
}
public event PropertyChangingEventHandler PropertyChanging;
private void NotifyPropertyChanging(string PropertyName)
{
if (PropertyChanging != null)
{
PropertyChanging(this, new PropertyChangingEventArgs(PropertyName));
}
}
#endregion
//Semester ID Variable
private int _semID;
[Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "INT NOT NULL Identity",
CanBeNull = false, AutoSync = AutoSync.OnInsert)]
public int SemID
{
get
{
return _semID;
}
set
{
NotifyPropertyChanging("SemID");
_semID = value;
NotifyPropertyChanged("SemID");
}
}
////Semester Name
//private string _semName;
//[Column]
//public string SemName
//{
// get
// {
// return _semName.ToString();
// }
// set
// {
// NotifyPropertyChanging("SemName");
// _semName = value.ToString();
// NotifyPropertyChanged("SemName");
// }
//}
//Semester Start Date
private DateTime _semStart;
[Column]
public DateTime SemStart
{
get
{
return _semStart;
}
set
{
NotifyPropertyChanging("SemStart");
_semStart = value;
NotifyPropertyChanged("SemStart");
}
}
//Semester End Date
private DateTime _semEnd;
[Column]
public DateTime SemEnd
{
get
{
return _semEnd;
}
set
{
NotifyPropertyChanging("SemEnd");
_semEnd = value;
NotifyPropertyChanged("SemEnd");
}
}
#region Subject Set
// Define the entity set for the collection side of the relationship.
private EntitySet<CygSubs> _subs;
[Association(Storage = "_subs", OtherKey = "_cygSemID", ThisKey = "SemID")]
public EntitySet<CygSubs> Subs
{
get
{
return this._subs;
}
set
{
this._subs.Assign(value);
}
}
// Assign handlers for the add and remove operations, respectively.
public CygSem()
{
_subs = new EntitySet<CygSubs>(
new Action<CygSubs>(this.attach_sem),
new Action<CygSubs>(this.dettach_sem)
);
}
// Called during an add operation
private void attach_sem(CygSubs _subj)
{
NotifyPropertyChanging("CygSubs");
_subj.Semester = this;
}
// Called during a remove operation
private void dettach_sem(CygSubs _subj)
{
NotifyPropertyChanging("CygSubs");
_subj.Semester = null;
}
#endregion
}
数据上下文：
[Database]
public class CygDataContext : DataContext
{
//Pass The Connection String to the base class.
public CygDataContext(string ConnectionString)
: base(ConnectionString)
{ }
//Specify table Semesters
public Table<CygSem> Semesters;
//Specify table Subjects
public Table<CygSubs> Subjects;
//Specify table Lecture
public Table<CygLect> Lectures;
//Specify table Exams
public Table<CygExam> Exams;
//Specify table Instructors
public Table<CygInst> Insts;
//Specify table Holidays
public Table<CygHoli> Holidays;
}