c# - 代码中的无效表达式项错误

Question

• 错误 1 ​​'int.TryParse(string, out int)' 的最佳重载方法匹配有一些无效参数

• 错误 2 参数 1:无法从“int”转换为“string”

  它在“int.TryParse(surveys.First(), out id);”中给我错误

     L
        var surveys = (from su in DbContext.Surveys
                                 where su.userName == su.userName 
                                 select su.ID);
  if(surveys.Count() > 0)
              {
               int id = 0;
               int.TryParse(surveys.First(), out id);
                 return id;
               }
               return 0;
  

Answer 1

从 TryParse() 中删除 int；

int.TryParse(surveys.First(), out int id);

应该是

int.TryParse(surveys.First(), out id);

改变:-

List<SurveyContext> surveys = (from su in DbContext.Surveys
                                          where su.userName == su.userName 
                                          select su.ID).ToList();

到

List<string> surveys = (from su in DbContext.Surveys
                                          where su.userName == su.userName 
                                          select su.ID);

您正在尝试选择 string输入 Linq 并将其放入 List<SomeType>应该是 List<int> .

  var surveys = (from su in DbContext.Surveys
                                              where su.userName == su.userName 
                                              select su.ID);

  //Code follows
  int.TryParse(surveys.First(), out id);