尝试更新视图的筛选器时，ICollectionView.Source返回null. [英] ICollectionView.Source returns null when trying to update the View's Filter.

问题描述

我创建了一个ICollectionView:

Hi,

I have created an ICollectionView:

private ObervableCollection<Apples> MyCollection = new ObervableCollection<Apples>();
public ICollectionView View {get; private set; }

private void Init()
{
 CollectionViewSource Cvs = new CollectionViewSource();
 Cvs.Source = ObervableCollection;
 View.Source =  Cvs.View; 
}

private void UpdateFilter(string Color)
{
 using (View.DeferRefresh) // Not required
    {
      View.Filter = (o) = > {return ((Apple)(o)).Color = Color;}
    }
}

代码编译错误可能在这里，我在另一台PC上..

问题是，当我从UI单击复选框以基于字符串重新应用过滤器时，当代码到达"View.Filter = ....."时，它将引发空引用异常(如果没有更多信息，则为您观察到，您可以看到View"SourceCollection"的属性为NULL).

正在执行的线程是MAIN线程. 我也尝试过使用Dispatcher中的Invoke或BeginInvoke，但是没有运气.
更多信息:
选中\取消选中UI中的复选框会更新绑定的后备属性ShowHide(Bool).
ShowHide调用UpdateFilter(string X)，然后出现问题..

在此先感谢

Code compile errors might exist here, I''m on another PC..

The problem is that when i click a checkbox from the UI to reapply the filter based on a string, when the code reaches the "View.Filter = ....." it throws a null reference exception(with no more Info BUT if you observe you can see that the property of the View "SourceCollection" is NULL).

The Thread Executing is the MAIN thread..
I also tried using Invoke or BeginInvoke from the Dispatcher but with no luck..

More info:
Checking\Unchecking the checkbox from the Ui updates the binded backing property ShowHide(Bool).
The ShowHide Calls the UpdateFilter(string X) and then the problem occurs..

Thanks in advance

推荐答案

 public class ViewModel
    {
        ObservableCollection<customer> CustomerList = new ObservableCollection<customer>();
        public ICollectionView BlueCustomersView { get; private set; }
        public ICollectionView BlackCustomersView { get; private set; }

        public ICollectionView RedCustomersView { get; private set; } //UnBound
        public ICollectionView CyanCustomersView { get; private set; } //UnBound
        public ICollectionView PinkCustomersView { get; private set; } //UnBound
        public ICollectionView OrangeCustomersView { get; private set; } //UnBound



        public ViewModel()
        {
            for (int i = 0; i < 10000; i++)
            {
                Customer Cust = new Customer();
                Cust.Name = i;
                Cust.Color = (i % 2 == 0) ? Brushes.AliceBlue : Brushes.Black;
                CustomerList.Add(Cust);
            }

            /****************************************************************************
             * Move this Outside of the function to make things work
             * *************************************************************************/
            CollectionViewSource CvBlue = new CollectionViewSource();
            CollectionViewSource CvBlack = new CollectionViewSource();

            CollectionViewSource CvRed = new CollectionViewSource(); //UnBound
            CollectionViewSource CvCyan = new CollectionViewSource(); //UnBound
            CollectionViewSource CvPink = new CollectionViewSource(); //UnBound
            CollectionViewSource CvOrange = new CollectionViewSource(); //UnBound
            /***************************************************************************/

            /************ Bound **************/
            CvBlue.Source = CustomerList;
            BlueCustomersView = CvBlue.View;

            CvBlack.Source = CustomerList;
            BlackCustomersView = CvBlack.View;
            /************ **************/


            /************ Un-Bound **************/
            CvRed.Source = CustomerList;
            RedCustomersView = CvRed.View;

            CvCyan.Source = CustomerList;
            CyanCustomersView = CvCyan.View;

            CvPink.Source = CustomerList;
            PinkCustomersView = CvPink.View;

            CvOrange.Source = CustomerList;
            OrangeCustomersView = CvOrange.View;
            /************ **************/
        }



        public void ApplyFiltering()
        {
            //Bound CollectionViews
            BlueCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.AliceBlue; };
            BlackCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Black; };

            // Unbound CollectionViews
            RedCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Red; };
            CyanCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Cyan; };
            PinkCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Pink; };
            OrangeCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Orange; };
        }
    }

</customer></customer>

为了防止Framework处置CollectionViewSource，应将其设置为全局类变量，而不是函数内部的变量.

如果将CollectionViewSource的Property View绑定到某个地方，或者简单地说它具有引用，那么即使它不是全局的，也可以正常工作.

但是，一旦丢失，该框架可能就是GCing并销毁它.
我怀疑CollectionView的Source属性是WeakReference
CollectionViewSource的View属性.


TestProject的链接: https://docs.google.com/open?id=0B4xi5POVxsrxNDJnWnMxZ3p5VzA [ ^ ]

In order to keep the Framework from disposing the CollectionViewSource you should make it a global class variable and not a variable inside a function.

If the Property View of the CollectionViewSource is binded somewhere or let''s simple say that it has a reference things will work fine even if it''s not global.

However once lost the Framework is probably GCing and dispocing it.
I suspect that either the Source Property of a CollectionView is a WeakReference
either the View Property of a CollectionViewSource.


Link of TestProject : https://docs.google.com/open?id=0B4xi5POVxsrxNDJnWnMxZ3p5VzA[^]

请参见此处:
http://marlongrech.wordpress.com/2008/11/22/icollectionview-explained/ [ ^ ]

我认为您的问题是如何填充ICollectionView，应该这样完成:

See here:
http://marlongrech.wordpress.com/2008/11/22/icollectionview-explained/[^]

I think your problem is how you populate you ICollectionView, it should be done like this:

ICollectionView view = CollectionViewSource.GetDefaultView(myData);

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