在MVVM中加载LongListSelector
我第一次使用MVVM Light,所以请容忍我 我的主页上有一个LongListSelector,在加载页面时,我使用RelayCommand从SQLCE数据库中加载数据 在我的MainViewModel中,我有一个属性:在MVVM中加载LongListSelector,mvvm,mvvm-light,windows-phone-7,Mvvm,Mvvm Light,Windows Phone 7,我第一次使用MVVM Light,所以请容忍我 我的主页上有一个LongListSelector,在加载页面时,我使用RelayCommand从SQLCE数据库中加载数据 在我的MainViewModel中,我有一个属性: public const string WorkoutsPropertyName = "Workouts"; private PublicGrouping<DateTime, Workout> _workouts; public PublicGrouping,D
public const string WorkoutsPropertyName = "Workouts";
private PublicGrouping<DateTime, Workout> _workouts;
public PublicGrouping,DateDime, Workout> Workouts
{
get { return workouts; }
set
{
if (_workouts == value) { return; }
_workouts = value;
RaisePropertyChanged(WorkoutsPropertyName);
}
}
public const string Workouts属性name=“Workouts”;
私人健身活动;
公共分组、DateDime、训练>训练
{
获取{返回训练;}
设置
{
如果(_workouts==value){return;}
_训练=价值;
RaisePropertyChanged(作业属性名称);
}
}
然后,在构造函数中,我创建LoadedCommand:
public MainViewModel()
{
LoadedCommand = new RelayCommand(() =>
{
context = new XLogDataContext();
using (context)
{
if (context.Workouts.Count() > 0)
{
var workoutsByDate = from workout in context.Workouts
group workout by workout.WorkoutDate
into c
orderby c.Key
select c;
Workouts = workoutsByDate as PublicGrouping<DateTime, Workout>;
}
}
});
}
public主视图模型()
{
LoadedCommand=新的RelayCommand(()=>
{
context=new XLogDataContext();
使用(上下文)
{
如果(context.Workouts.Count()>0)
{
var workoutsByDate=来自上下文中的训练。训练
按训练分组训练。训练日期
变成c
orderby c.Key
选择c;
训练=作为公共分组的训练日期;
}
}
});
}
当RelayCommand运行时,训练始终返回null。我知道有数据返回,所以我认为问题在于将LINQ查询转换为PublicGrouping。我还尝试将属性创建为
ObservableCollection<PublicGrouping<DateTime, Workout>>
observedcollection
但这也不行
更新:
我更改了RelayCommand以使用此行:
Workouts = new PublicGrouping<DateTime, Workout>(workoutsByDate);
Workouts=新的公共分组(workoutsByDate);
并为PublicGrouping添加了此构造函数:
private readonly IGrouping<TKey, TElement> _internalGrouping;
public PublicGrouping(IOrderedQueryable<IGrouping<DateTime, Workout>> workoutsByDate)
{
_internalGrouping = (IGrouping<TKey, TElement>) workoutsByDate;
}
private readonly iGroup\u internalGrouping;
公共分组(IOrderedQueryable workoutsByDate)
{
_internalGrouping=(i分组)workoutsByDate;
}
我仍然在构造函数中的_internalgroupingassignment上获得InvalidCastException。实际上,您的强制转换将失败,并且在您的情况下,使用
as
操作符不会抛出InvalidCastException
,因此它被屏蔽
创建PublicGrouping
的构造函数,该构造函数接受worksByDate
包含的任何内容的IEnumerable
这种类型的转换(称为显式转换):
如果无法将o
的内部类型转换为字符串,则引发InvalidCastException
。as
运算符不会引发此异常,而是返回null。这应该可以:
public const string WorkoutsPropertyName = "Workouts";
private List<PublicGrouping<DateTime, Workout>> _workouts;
public List<PublicGrouping<DateTime, Workout>> Workouts
{
get { return _workouts; }
set
{
if (_workouts == value)
{
return;
}
_workouts = value;
RaisePropertyChanged(WorkoutsPropertyName);
}
}
public MainViewModel()
{
LoadedCommand = new RelayCommand(() =>
{
context = new XLogDataContext();
using (context)
{
if (context.Workouts.Count() > 0)
{
var workoutsByDate = from workout in context.Workouts
group workout by workout.WorkoutDate
into c
orderby c.Key
select new PublicGrouping<DateTime, Workout>(c);
Workouts = workoutsByDate.ToList();
}
}
});
}
public const string Workouts属性name=“Workouts”;
私人健身清单;
公开列表训练
{
获取{返回_训练;}
设置
{
如果(_训练==值)
{
返回;
}
_训练=价值;
RaisePropertyChanged(作业属性名称);
}
}
公共主视图模型()
{
LoadedCommand=新的RelayCommand(()=>
{
context=new XLogDataContext();
使用(上下文)
{
如果(context.Workouts.Count()>0)
{
var workoutsByDate=来自上下文中的训练。训练
按训练分组训练。训练日期
变成c
orderby c.Key
选择新分组(c);
Workouts=workoutsByDate.ToList();
}
}
});
}
public const string WorkoutsPropertyName = "Workouts";
private List<PublicGrouping<DateTime, Workout>> _workouts;
public List<PublicGrouping<DateTime, Workout>> Workouts
{
get { return _workouts; }
set
{
if (_workouts == value)
{
return;
}
_workouts = value;
RaisePropertyChanged(WorkoutsPropertyName);
}
}
public MainViewModel()
{
LoadedCommand = new RelayCommand(() =>
{
context = new XLogDataContext();
using (context)
{
if (context.Workouts.Count() > 0)
{
var workoutsByDate = from workout in context.Workouts
group workout by workout.WorkoutDate
into c
orderby c.Key
select new PublicGrouping<DateTime, Workout>(c);
Workouts = workoutsByDate.ToList();
}
}
});
}