为了避免出现InvalidOperationException最佳实践:集合已修改? [英] Best practice to avoid InvalidOperationException: Collection was modified?
问题描述
很多时候我需要这样的事情:
的foreach(以线线线)
{
如果(line.FullfilsCertainConditions())
{
lines.Remove(线)
}
}
这是不行的,因为我总是一 InvalidOperationException异常
因为枚举器循环过程中发生了变化。
于是我改变了这样的我所有环路为以下内容:
名单,其中,线>删除=新的名单,其中,线>();
的foreach(以线线线)
{
如果(line.FullfilsCertainConditions())
{
remove.Add(线)
}
}
的foreach(线路输入删除线){
{
lines.Remove(线);
}
我不知道这是否真的是最好的方式,因为在最坏的情况下,我有超过原始列表迭代2倍,所以它需要n个时间2N,而不是。
有没有更好的方式来做到这一点?
编辑:
我是能够做到这一点使用马克的回答!但如果我的收藏不器具removeall过()?
例如一个
System.Windows.Controls.UIElementCollection
编辑2:
再次与马克的帮助,我现在可以进行以下调用来删除所有ScatterViewItems:
CollectionUtils.RemoveAll(manager.getWindow()IconDisplay.Items,ELEM => elem.GetType()== typeof运算(ScatterViewItem));
这是直接烤成名单,其中,T>
:
lines.RemoveAll(行=> line.FullfilsCertainConditions());
或C#2.0:
lines.RemoveAll(委托(行线){
返回line.FullfilsCertainConditions();
});
在非 - 名单,其中,T>
情况下(你编辑的问题),你可以换这个类似下面(未经测试):
静态类CollectionUtils
{
公共静态无效removeall过< T>(IList的< T>清单,predicate< T> predicate)
{
诠释计数= list.Count;
而(count--大于0)
{
如果(predicate(名单[计数]))list.RemoveAt(计数);
}
}
公共静态无效removeall过(IList的列表,predicate<对象> predicate)
{
诠释计数= list.Count;
而(count--大于0)
{
如果(predicate(名单[计数]))list.RemoveAt(计数);
}
}
}
由于 UIElementCollection
实现(非通用)的IList
这应该工作。而且比较方便,用C#3.0,你可以添加一个这
在的IList
/ 的IList< T&GT ;
,并把它作为一个扩展的方法。唯一需要说明的是,该参数的匿名法将对象
,所以你需要转换它扔掉。
Very often I need something like that:
foreach (Line line in lines)
{
if (line.FullfilsCertainConditions())
{
lines.Remove(line)
}
}
This does not work, because I always get a InvalidOperationException
because the Enumerator was changed during the loop.
So I changed all my loops of this kind to the following:
List<Line> remove = new List<Line>();
foreach (Line line in lines)
{
if (line.FullfilsCertainConditions())
{
remove.Add(line)
}
}
foreach (Line line in remove) {
{
lines.Remove(line);
}
I'm not sure if this is really the best way since in the worst case I have to iterate 2 times over the original list and so it needs time 2n instead of n.
Is there a better way to do this?
EDIT:
I was able to do that using Mark's answer!But what if my collection doesn't implements RemoveAll()?
For example a
System.Windows.Controls.UIElementCollection
EDIT 2:
Again with the help of Mark I'm now able to make the following call to remove all ScatterViewItems:
CollectionUtils.RemoveAll(manager.getWindow().IconDisplay.Items, elem => elem.GetType() == typeof(ScatterViewItem));
This is baked directly into List<T>
:
lines.RemoveAll(line => line.FullfilsCertainConditions());
or in C# 2.0:
lines.RemoveAll(delegate(Line line) {
return line.FullfilsCertainConditions();
});
In the non-List<T>
case (your edit to the question), you could wrap this something like below (untested):
static class CollectionUtils
{
public static void RemoveAll<T>(IList<T> list, Predicate<T> predicate)
{
int count = list.Count;
while (count-- > 0)
{
if (predicate(list[count])) list.RemoveAt(count);
}
}
public static void RemoveAll(IList list, Predicate<object> predicate)
{
int count = list.Count;
while (count-- > 0)
{
if (predicate(list[count])) list.RemoveAt(count);
}
}
}
Since UIElementCollection
implements the (non-generic) IList
this should work. And quite conveniently, with C# 3.0 you can add a this
before IList
/ IList<T>
and have it as an extension method. The only subtlety is that the parameter to the anon-method will be object
, so you'll need to cast it away.
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