无涯教程-Dart - Single函数

检查列表是否只有一个元素并返回它。

Single - 语法

List.single 

Single - 示例

void main() { 
   var lst=new List(); 
   lst.add(12);
   print("The list has only one element: ${lst.single}"); 
}  

它将产生以下输出-

The list values in reverse order: (13, 12) 

它将产生以下输出-

The list has only one element: 12 

如果列表中包含多个元素，则此属性将引发异常。以下示例说明了相同的内容-

void main() { 
   var lst=new List(); 
   lst.add(12); 
   lst.add(10); 
   print(lst.single); 
}

如果列表包含多个元素，则相同的代码将引发以下异常 -

Unhandled exception: 
Bad state: Too many elements 
#0 List.single (dart:core-patch/growable_array.dart:234) 
#1 main (file:///D:/Learnfk/Boolean.dart:6:13) 
#2 _startIsolate.<anonymous closure> (dart:isolatepatch/isolate_patch.dart:261) 
#3 _RawReceivePortImpl._handleMessage (dart:isolatepatch/isolate_patch.dart:148)

参考链接

https://www.learnfk.com/dart-programming/dart-programming-list-single-method.html