Question

当我在UITableView上按下一行时，我试图这样做，它会将一些数据发送到另一个UIViewController并制作一个seque。

然而，当测试它时，它给了我：

System.NullReferenceException已抛出对象引用未设置到对象的实例

错误似乎在这里显示：

viewController.NavigationController.PushViewController (detail, true);

这是我的“RowSelected”

public override void RowSelected (UITableView tableView, NSIndexPath indexPath)
{
    Console.WriteLine ("Row: " + tableItems [indexPath.Row].Heading);

    //new UIAlertView("Row Selected", tableItems[indexPath.Row].Heading, null, "OK", null).Show();
    tableView.DeselectRow (indexPath, true);

    // Specially for Storyboard !!
    var detail = viewController.Storyboard.InstantiateViewController("detail") as HolsteinItemViewController;
    detail.Title = tableItems[indexPath.Row].Heading;
    detail.LoadUrl (tableItems[indexPath.Row].SubHeading);
    viewController.NavigationController.PushViewController (detail, true);
}

发现异常：

System.NullReferenceException: Object reference not set to an instance of an object
  at Holstein.TableSource.RowSelected (MonoTouch.UIKit.UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath) [0x0008e] in /Users/Emil/Projects/Holstein/Holstein/Code/TableSource.cs:41
  at at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
  at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:38
  at Holstein.Application.Main (System.String[] args) [0x00008] in /Users/Emil/Projects/Holstein/Holstein/Main.cs:16

TableSource.cs第46行

viewController.NavigationController.PushViewController (detail, true);

Main.cs第16行

UIApplication.Main (args, null, "AppDelegate");

Answer 1

您的viewController.NavigationController属性为空。根据iOS UIViewController参考here

如果接收者或其祖先之一是导航的孩子 controller，此属性包含拥有的导航控制器。如果视图控制器未嵌入到a中，则此属性为nil 导航控制器。

显然，该视图控制器不是UINavigationController堆栈的一部分。

RowSelected - NullReferenceException

1 个答案: