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我在迭代Collection时尝试删除对象.但我得到例外.我怎样才能做到这一点？这是我的代码:

foreach (var gem in gems)
{
    gem.Value.Update(gameTime);

    if (gem.Value.BoundingCircle.Intersects(Player.BoundingRectangle))
    {
       gems.Remove(gem.Key); // I can't do this here, then How can I do?
       OnGemCollected(gem.Value, Player);
    }
}