NullReferenceException未处理

Question

我只是抓住了Lightswitch，但是当我试图找出数据网格中的所选项目是否包含字母时，我一直收到空引用异常错误＆＃ 34; CMP＆＃34 ;.我到处都看，但我觉得我做错了什么。这是我的参考代码：

if(string.IsNullOrWhiteSpace(this.location.SelectedItem.locationID))
        {
            this.ShowMessageBox("test"); //not sure what to put there so I just made something up
        }
        else if (this.location.SelectedItem.locationID.Contains("CMP"))
        {
            this.FindControl("datePurchased").IsVisible = true;
            this.FindControl("age").IsVisible = true;
            this.FindControl("userList").IsVisible = true;
        }
        else
        {
                this.FindControl("datePurchased").IsVisible = false;
                this.FindControl("age").IsVisible = false;
                this.FindControl("userList").IsVisible = false;
        }

我也试过

if(this.location.selecteditem.locationID != null)

if(string.IsNullOrEmpty)

但它总是抛出同样的错误。任何帮助将非常感激！

Answer 1

我guss this.location或this.location.selecteditem可能为null，所以你得到了那个错误。 因此，请尝试使用此if条件，而不是if条件

if(this.location != null && this.location.selecteditem !=null && this.location.selecteditem.locationID != null)
{
       //Write your code here 
}

所以你的最终代码看起来像

        if(this.location == null && this.location.selecteditem ==null && this.location.selecteditem.locationID == null)
        {
          this.ShowMessageBox("test"); //not sure what to put there so I just made something up
        }    

        else if (this.location.SelectedItem.locationID.Contains("CMP"))
        {
            this.FindControl("datePurchased").IsVisible = true;
            this.FindControl("age").IsVisible = true;
            this.FindControl("userList").IsVisible = true;
        }
        else
        {
                this.FindControl("datePurchased").IsVisible = false;
                this.FindControl("age").IsVisible = false;
                this.FindControl("userList").IsVisible = false;
        }