在c#中是否有一些我没有遇到过的罕见的语言构造(比如我最近学过的一些,一些在Stack Overflow上)来获得表示foreach循环的当前迭代的值?
例如,我目前根据具体情况做这样的事情:
int i = 0;
foreach (Object o in collection)
{
// ...
i++;
}
在c#中是否有一些我没有遇到过的罕见的语言构造(比如我最近学过的一些,一些在Stack Overflow上)来获得表示foreach循环的当前迭代的值?
例如,我目前根据具体情况做这样的事情:
int i = 0;
foreach (Object o in collection)
{
// ...
i++;
}
当前回答
我只是遇到了这个问题,但在我的情况下思考这个问题给出了最好的解决方案,与预期的解决方案无关。
It could be quite a common case, basically, I'm reading from one source list and creating objects based on them in a destination list, however, I have to check whether the source items are valid first and want to return the row of any error. At first-glance, I want to get the index into the enumerator of the object at the Current property, however, as I am copying these elements, I implicitly know the current index anyway from the current destination. Obviously it depends on your destination object, but for me it was a List, and most likely it will implement ICollection.
i.e.
var destinationList = new List<someObject>();
foreach (var item in itemList)
{
var stringArray = item.Split(new char[] { ';', ',' }, StringSplitOptions.RemoveEmptyEntries);
if (stringArray.Length != 2)
{
//use the destinationList Count property to give us the index into the stringArray list
throw new Exception("Item at row " + (destinationList.Count + 1) + " has a problem.");
}
else
{
destinationList.Add(new someObject() { Prop1 = stringArray[0], Prop2 = stringArray[1]});
}
}
我认为,虽然不总是适用,但常常足以值得一提。
不管怎样,关键是有时在你的逻辑中已经有了一个不明显的解决方案……
其他回答
c# 7最终为我们提供了一种优雅的方式:
static class Extensions
{
public static IEnumerable<(int, T)> Enumerate<T>(
this IEnumerable<T> input,
int start = 0
)
{
int i = start;
foreach (var t in input)
{
yield return (i++, t);
}
}
}
class Program
{
static void Main(string[] args)
{
var s = new string[]
{
"Alpha",
"Bravo",
"Charlie",
"Delta"
};
foreach (var (i, t) in s.Enumerate())
{
Console.WriteLine($"{i}: {t}");
}
}
}
我只是遇到了这个问题,但在我的情况下思考这个问题给出了最好的解决方案,与预期的解决方案无关。
It could be quite a common case, basically, I'm reading from one source list and creating objects based on them in a destination list, however, I have to check whether the source items are valid first and want to return the row of any error. At first-glance, I want to get the index into the enumerator of the object at the Current property, however, as I am copying these elements, I implicitly know the current index anyway from the current destination. Obviously it depends on your destination object, but for me it was a List, and most likely it will implement ICollection.
i.e.
var destinationList = new List<someObject>();
foreach (var item in itemList)
{
var stringArray = item.Split(new char[] { ';', ',' }, StringSplitOptions.RemoveEmptyEntries);
if (stringArray.Length != 2)
{
//use the destinationList Count property to give us the index into the stringArray list
throw new Exception("Item at row " + (destinationList.Count + 1) + " has a problem.");
}
else
{
destinationList.Add(new someObject() { Prop1 = stringArray[0], Prop2 = stringArray[1]});
}
}
我认为,虽然不总是适用,但常常足以值得一提。
不管怎样,关键是有时在你的逻辑中已经有了一个不明显的解决方案……
像这样的怎么样?注意,如果myEnumerable为空,myDelimitedString可能为空。
IEnumerator enumerator = myEnumerable.GetEnumerator();
string myDelimitedString;
string current = null;
if( enumerator.MoveNext() )
current = (string)enumerator.Current;
while( null != current)
{
current = (string)enumerator.Current; }
myDelimitedString += current;
if( enumerator.MoveNext() )
myDelimitedString += DELIMITER;
else
break;
}
这样你就可以使用LINQ来使用索引和值:
ListValues.Select((x, i) => new { Value = x, Index = i }).ToList().ForEach(element =>
{
// element.Index
// element.Value
});
我不认为这应该很有效,但它确实有效:
@foreach (var banner in Model.MainBanners) {
@Model.MainBanners.IndexOf(banner)
}