[英]System.InvalidCastException: Unable to cast object of type 'System.DBNull' to type 'System.String'
[英]unhandled exception of type 'System.InvalidCastException' occurred…Unable to cast object of type 'System.String' to type
有人可以帮我吗? 遵循我的代码和“ GelatoProject.exe中发生了'System.InvalidCastException类型的未处理的异常”
附加信息:无法将类型为“ System.String”的对象转换为类型为“ GelatoProject.RecipeVariables”的消息。”。
// ...
using (var db = new GelatoProjectDBEntities())
{
RecipeVariables selected =
(RecipeVariables)comboBoxRecipeDetail.SelectedItem;
var results = (from x in db.Recipe_Parameters
select new RecipeVariables
{
Id = x.Id,
RecipeDetail = x.recipeDetail,
Parameter = x.parameter,
RangeDetail = x.rangeDetail,
RangeValue = x.value.ToString()
}
)
.Where(x => x.RecipeDetail == selected.RecipeDetail && x.Parameter == "totalsolids" && x.RangeDetail == "Max")
.FirstOrDefault();
totsolidsRangeMax = decimal.Parse(results.RangeValue);
MessageBox.Show(totsolidsRangeMax.ToString());
}
// ...
class RecipeVariables
{
public int Id { get; set; }
public string NameIngredient { get; set; }
public string Brand { get; set; }
public string LBName { get { return NameIngredient + " - " + Brand;}}
public string RecipeDetail { get; set; }
public string Parameter { get; set; }
public string RangeDetail { get; set; }
public string RangeValue { get; set; }
}
RecipeVariables selected = (RecipeVariables)comboBoxRecipeDetail.SelectedItem;
comboBoxRecipeDetail.SelectedItem
是一个字符串-单击组合框时看到的文本。 不能RecipeVariables
为RecipeVariables
将您的代码更改为:
using (var db = new GelatoProjectDBEntities())
{
RecipeVariables selected = new RecipeVariables()
{
RecipeDetail = (string)comboBoxRecipeDetail.SelectedItem
};
// var results = ...
}
这将创建一个新的RecipeVariables对象,然后将其RecipeDetail属性设置为所选组合框项目的文本。
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