如何迭代TDictionary和删除项目？ [英] How to iterate a TDictionary and delete item?

问题描述

我有一个TDictionary，并向其中添加了一些项目：

I have a TDictionary and add some items to it:

for index := 0 to 10 do
   dict.Add(IntToStr(index), index);

现在，我需要迭代容器并删除想要的物品：

Now, I need to iterate the container and remove items I wanted:

pairEnum := dict.GetEnumerator;
while pairEnum.MoveNext do
begin
  if pairEnum.Current.Value mod 2 = 0 then
     dict.Remove(pairEunm.Current.Key);
end;

我希望我现在在字典中只有奇数。但是我实际得到的是：

I expect I now only have odd number in the dictionary. But what I actually got are:

key=1 value=1
key=3 value=3
key=5 value=5
key=7 value=7
key=9 value=9
key=8 value=8 <-

为什么未从字典中删除 8？

Why the "8" wasn't removed from dictionary?

如果我添加更多项目。例如，

If I add more items. e.g.

for index := 0 to 12 do
   dict.Add(IntToStr(index), index);

然后，结果是正确的。这是为什么？如何正确迭代TDictionary并删除项目？谢谢。

Then, the result is correct. Why is that? How can I correctly iterate a TDictionary and remove items? Thanks.

推荐答案

在迭代可枚举的同时删除项是不安全的。您应该保留要删除的键的另一个列表，并在迭代完成后开始删除它们。

It is unsafe to remove items while iterating an enumerable. You should keep another list of the keys that you want to remove and start removing them once your iteration is completed.

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