C# 如何测试空的 generic.dictionary 集合？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/2088937/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to test for an empty generic.dictionary collection?
提问by DEH
How do I test a generic dictionary object to see whether it is empty? I want to run some code as follows:
如何测试通用字典对象以查看它是否为空？我想按如下方式运行一些代码：
while (reportGraphs.MoveNext())
{
reportGraph = (ReportGraph)reportGraphs.Current.Value;
report.ContainsGraphs = true;
break;
}
The reportGraph object is of type System.Collections.Generic.Dictionary When running this code then the reportGraphs dictionary is empty and MoveNext() immediately throws a NullReferenceException. I don't want to put a try-catch around the block if there is a more performant way of handling the empty collection.
reportGraph 对象的类型为 System.Collections.Generic.Dictionary 运行此代码时，reportGraphs 字典为空，并且 MoveNext() 立即抛出 NullReferenceException。如果有更高效的处理空集合的方法，我不想在块周围放置 try-catch。
Thanks.
谢谢。
采纳答案by Reed Copsey
If it's a generic dictionary, you can just check Dictionary.Count. Count will be 0 if it's empty.
如果它是一个通用字典，你可以只检查Dictionary.Count。如果为空，计数将为 0。
However, in your case, reportGraphslooks like it's an IEnumerator<T>- is there a reason your enumerating your collection by hand?
但是，在您的情况下，reportGraphs看起来像是IEnumerator<T>- 您是否有理由手动枚举您的收藏？
回答by Darin Dimitrov
There's a difference between an emptydictionary and null. Calling MoveNexton an empty collection won't result in a NullReferenceException. I guess in your case you could test if reportGraphs != null.
这里有一个之间的差异empty词典null。调用MoveNext空集合不会导致NullReferenceException. 我想在您的情况下，您可以测试是否reportGraphs != null.
回答by Groo
As Darin said, reportGraphsis nullif it throws a NullReferenceException. The best way would be to ensure that it is never null (i.e. make sure that it is initialized in your class' constructor).
正如达林说，reportGraphs就是null如果它抛出一个NullReferenceException。最好的方法是确保它永远不会为空（即确保它在类的构造函数中初始化）。
Another way to do this (to avoid enumerating explicitly) would be to use a foreachstatement:
执行此操作的另一种方法（避免显式枚举）是使用foreach语句：
foreach (KeyValuePair<Key,Value> item in reportGraphs)
{
// do something
}
[Edit]Note that this example also presumes that reportGraphsis never null.
[编辑]请注意，此示例还假定reportGraphs永远不会null。
