MonoTouch.Dialog 崩溃

我有一个小型测试应用程序，它仅在 3 个页面之间循环。 这是应用程序委托：

    public override bool FinishedLaunching (UIApplication app, NSDictionary options)
    {
        _session = new Session();
        _session.NextScreen += (screenIndex) => 
        {
            window.RootViewController = _viewControllers[screenIndex];
        };

        _viewControllers.Add(new Screen0(_session));
        _viewControllers.Add(new Screen1(_session));
        _viewControllers.Add(new Screen2(_session));

        // create a new window instance based on the screen size
        window = new UIWindow (UIScreen.MainScreen.Bounds);

        // If you have defined a view, add it here:
        // window.AddSubview (navigationController.View);
        window.RootViewController = _viewControllers[0];

        // make the window visible
        window.MakeKeyAndVisible ();

        return true;

如果我在每个屏幕上放置一个按钮，我可以从一个页面导航到另一个页面，即

    public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();

        UIButton button = new UIButton(new RectangleF(30, 200, 80, 34));
        button.SetTitle("Go to 1", UIControlState.Normal);
        button.TouchUpInside += (sender, e) => 
        {
            _session.ExittingScreen = 0;
        };
        View.AddSubview(button);
    }

然而，当我使用 MonoTouch.Dialog 时，我会间歇性崩溃。这是我的代码：

    public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();

        var rootElement = new RootElement("Register")
        {
            new Section()
            {
                new EntryElement("First Name", "required", ""),
                new EntryElement("Last Name", "required", ""),
                new EntryElement("Email Address", "required", ""),
                new EntryElement("Password", "required", "")
            },
            new Section()
            {
                new StyledStringElement("Submit you information", () => { _session.ExittingScreen = 1; })
            }
        };
        var dialogViewController = new DialogViewController(rootElement);
        var navigationController = new UINavigationController(dialogViewController);

        View.Add (navigationController.View);

和转储：

at (包装器托管到本机) MonoTouch.UIKit.UIApplication.UIApplicationMain (int,string[],intptr,intptr) 在 MonoTouch.UIKit.UIApplication.Main (字符串[],字符串,字符串) 在 MTD.Application.Main (字符串[]) 在（包装器运行时调用）.runtime_invoke_void_object（对象，intptr，intptr，intptr）

本机堆栈跟踪：

0   MTD                                 0x00090b7c mono_handle_native_sigsegv + 284
1   MTD                                 0x00005f28 mono_sigsegv_signal_handler + 248
2   libsystem_c.dylib                   0x97da559b _sigtramp + 43
3   ???                                 0xffffffff 0x0 + 4294967295
4   UIKit                               0x02220952 -[UITableView _userSelectRowAtPendingSelectionIndexPath:] + 201
5   Foundation                          0x0173786d __NSFireDelayedPerform + 389
6   CoreFoundation                      0x01195966 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 22
7   CoreFoundation                      0x01195407 __CFRunLoopDoTimer + 551
8   CoreFoundation                      0x010f87c0 __CFRunLoopRun + 1888
9   CoreFoundation                      0x010f7db4 CFRunLoopRunSpecific + 212
10  CoreFoundation                      0x010f7ccb CFRunLoopRunInMode + 123
11  GraphicsServices                    0x04789879 GSEventRunModal + 207
12  GraphicsServices                    0x0478993e GSEventRun + 114
13  UIKit                               0x02190a9b UIApplicationMain + 1175
14  ???                                 0x09ff6774 0x0 + 167733108
15  ???                                 0x09ff5958 0x0 + 167729496
16  ???                                 0x09ff57f0 0x0 + 167729136
17  ???                                 0x09ff587f 0x0 + 167729279
18  MTD                                 0x0000a292 mono_jit_runtime_invoke + 722
19  MTD                                 0x0016a17e mono_runtime_invoke + 126
20  MTD                                 0x0016e264 mono_runtime_exec_main + 420
21  MTD                                 0x00173685 mono_runtime_run_main + 725
22  MTD                                 0x00067495 mono_jit_exec + 149
23  MTD                                 0x002116c9 main + 2825
24  MTD                                 0x000032e5 start + 53

25 ??? 0x00000005 0x0 + 5

我做错了什么，还是这是一个错误？谢谢。

避免以下模式：

var navigationController = new UINavigationController(dialogViewController);
View.Add (navigationController.View);

because navigationController不会被引用（在managed侧）一旦View.Add调用完成，垃圾收集器可以处置它（只要需要）。然而从native预计它会存在。返回的呼叫（来自native to managed）到已处置的实例将使您的应用程序崩溃。

正确的模式是声明navigationController作为您类型的字段（而不是局部变量）并在方法中创建/分配它。这将保留对navigationController只要父实例存在就处于活动状态（并确保任何回调都不会到达已处置的对象）。

E.g.

private UINavigationController navigationController;
...
public override void ViewDidLoad ()
{
    ...
    var dialogViewController = new DialogViewController(rootElement);
    navigationController = new UINavigationController(dialogViewController);

    View.Add (navigationController.View);
    ...
}