Question

我正在使用Dictionary

private Dictionary<int, List<SpawnGroup>> spawnsByMapId 
             = new Dictionary<int, List<SpawnGroup>>();

但是在使用此代码时出现错误'KeyNotFoundException'：

List<SpawnGroup> a = spawnsByMapId[worldId];//KeyNotFoundException
if (a == null)
{
     // do something with a
}

我想要字典spawnsByMapId[worldId]添加到List<SpawnGroup>，但如果spawnsByMapId[worldId]的密钥不存在，则return null进入List<SpawnGroup>

那么我需要做什么？

Answer 1

使用ContainsKey和三元运算符：

List<SpawnGroup> a = spawnByMapId.ContainsKey(worldId) ? spawnsByMapId[worldId] : null;
if(a != null)
{
     // a is not null here.
}

或TryGetValue：

List<SpawnGroup> a = null;
if(spawnsByMapId.TryGetValue(worldId, out a))
{
    // a is not null here.
}

听起来（来自评论）就像您尝试这样做：

List<SpawnGroup> a = null;
if(!spawnsByMapId.TryGetValue(worldId, out a))
{
    // add new record to spawnsByMapId
    spawnsByMapId.Add(worldId, new List<SpawnGroup>());
}

Answer 2

我的标准模式如果您想使用嵌套字典，请执行以下操作：

Called from: SubClass1
other_arg1: -3, other_arg2: [-1;-2]

Called from: SubClass2
other_arg1: 3, other_arg2: [1;2]

使用Dictionary时获取KeyNotFoundException

2 个答案: