无法转换类型WhereSelectListIterator 2 System.Collections.Generic.List的对象 [英] Unable to cast object of type WhereSelectListIterator 2 System.Collections.Generic.List

问题描述

我正在处理这些列表，以获取与组合框中的所选项目匹配的项目.

I am working on these lists to get an item that matches the selected item from the combobox.

private void InitializaMessageElement()
{
    if (_selectedTransactionWsName != null)
    {

1. 从此处的下拉列表中获取与所选项目匹配的交易Web服务名称，输出= TestWS是正确的

1. get a transaction webservice name matching the selected item from the drop down here the output=TestWS which is correct

var getTranTypeWsName = TransactionTypeVModel
     .GetAllTransactionTypes()
     .FirstOrDefault(transTypes => 
             transTypes.WsMethodName == _selectedTransactionWsName);

从treenode列表中圈出wsnames列表.在这里，它为我提供了所有正确的节点.

Loop the list of wsnames from the treenode list. Here it gives me all the node I have which is correct.

var wsNameList = MessageElementVModel
     .GetAllTreeNodes().Select(ame => 
             ame.Children).ToList();//. == getTranTypeWsName.WsMethodName);

在wsNameList中找到getTranTypeWsName.WsMethodName.这是我遇到的问题:

find the getTranTypeWsName.WsMethodName in the wsNameList. Here is where I have the problem:

      var msgElementList = wsNameList.Select(x => x.Where(ame => getTranTypeWsName != null && ame.Name == getTranTypeWsName.WsMethodName)).ToList();

我的MsgElement列表:

my MsgElement list:

    MsgElementObsList = new ObservableCollection<MessageElementViewModel>(msgElementList);
    this.messageElements = _msgElementList;
    NotifyPropertyChanged("MessageElements");
}

此处抛出了强制转换错误.为什么它不起作用?我是LINQ的新手.谢谢

Here it is throwing the cast error. why is it not working? I am new to LINQ. thanks

推荐答案

由于错误正告诉您，LINQ方法返回特殊的迭代器类型实现IEnumerable<T>;他们不返回List<T>.
这样可以推迟执行.

As the error is trying to tell you, LINQ methods return special iterator types the implement IEnumerable<T>; they do not return List<T>.
This enables deferred execution.

由于对象实际上不是List<T>，因此无法将其强制转换为不是的类型.

Since the object isn't actually a List<T>, you can't cast it to a type that it isn't.

如果需要List<T>，则可以调用ToList()，也可以完全跳过LINQ并使用List<T>.ConvertAll()，这与Select()类似，但是会返回List<T>.

If you need a List<T>, you can either call ToList(), or skip LINQ entirely and use List<T>.ConvertAll(), which is like Select(), but does return List<T>.

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