无法将'string'类型转换为'int？'通过引用转换，装箱转换，拆箱转换，换行转换或空类型转换

C# accepts the following:

C#接受以下内容:

object o = "hello";
int? i = o as int?;

if (i == null) {
    // o was not a boxed int
}
else {
    // Can use i.Value to recover the original boxed value
}
object