Handling multiple buttons in UIToolbar

Question

I have a problem using multiple UIBarButtonItems within a UIToolbar on one side of a UINavigationController. I‘ve used one of the many examples on how to put multiple buttons in the navigation bar (using a toolbar), and while I got it displaying correctly now, I always get an unkown Objective-C exception thrown when a button is pressed.

This is the full test UIViewController I use for adding multiple buttons:

using System;
using System.Drawing;
using MonoTouch.UIKit;

namespace TestProject
{
    public class Test : UIViewController
    {
        public override void ViewDidLoad ()
        {
            base.ViewDidLoad();

            UIBarButtonItem btn1 = new UIBarButtonItem( "foo", UIBarButtonItemStyle.Bordered, delegate(object sender, EventArgs e) {
                Console.WriteLine( "asdf" );
            } );

            UIBarButtonItem btn2 = new UIBarButtonItem();
            btn2.Style = UIBarButtonItemStyle.Bordered;
            btn2.Title = "bar";
            btn2.Clicked += delegate(object sender, EventArgs e) {
                Console.WriteLine( "fdsa" );
            };

            UIToolbar tb = new UIToolbar( new RectangleF( 0, 0, 150, 44.0f ) );
            tb.SetItems( new UIBarButtonItem[] { btn1, btn2 }, false );
            NavigationItem.RightBarButtonItem = new UIBarButtonItem( tb );
        }
    }
}

I put that controller within a UINavigationController and display its view as the only window content. Everything works fine, until I click one of the buttons:

Error connecting stdout and stderr (127.0.0.1:10001)
Stacktrace:

  at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication.UIApplicationMain (int,string[],intptr,intptr) <IL 0x0009f, 0xffffffff>
  at MonoTouch.UIKit.UIApplication.Main (string[],string,string) [0x00038] in /Developer/MonoTouch/Source/monotouch/monotouch/UIKit/UIApplication.cs:26
  at TestProject.Application.Main (string[]) [0x00000] in /Users/Apple/Projects/TestProject/TestProject/Main.cs:16
  at (wrapper runtime-invoke) <Module>.runtime_invoke_void_object (object,intptr,intptr,intptr) <IL 0x00050, 0xffffffff>

Native stacktrace:

    0   TestProject                         0x000d0de8 mono_handle_native_sigsegv + 343
    1   TestProject                         0x0000f74c mono_sigsegv_signal_handler + 322
    2   libSystem.B.dylib                   0x906fc45b _sigtramp + 43
    3   ???                                 0xffffffff 0x0 + 4294967295
    4   UIKit                               0x01ee6cc3 -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 156
    5   UIKit                               0x01cd44fd -[UIApplication sendAction:to:from:forEvent:] + 119
    6   UIKit                               0x01d64799 -[UIControl sendAction:to:forEvent:] + 67
    7   UIKit                               0x01d66c2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
    8   UIKit                               0x01d657d8 -[UIControl touchesEnded:withEvent:] + 458
    9   UIKit                               0x01cf8ded -[UIWindow _sendTouchesForEvent:] + 567
    10  UIKit                               0x01cd9c37 -[UIApplication sendEvent:] + 447
    11  UIKit                               0x01cdef2e _UIApplicationHandleEvent + 7576
    12  GraphicsServices                    0x0404f992 PurpleEventCallback + 1550
    13  CoreFoundation                      0x00ea2944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    14  CoreFoundation                      0x00e02cf7 __CFRunLoopDoSource1 + 215
    15  CoreFoundation                      0x00dfff83 __CFRunLoopRun + 979
    16  CoreFoundation                      0x00dff840 CFRunLoopRunSpecific + 208
    17  CoreFoundation                      0x00dff761 CFRunLoopRunInMode + 97
    18  GraphicsServices                    0x0404e1c4 GSEventRunModal + 217
    19  GraphicsServices                    0x0404e289 GSEventRun + 115
    20  UIKit                               0x01ce2c93 UIApplicationMain + 1160
    21  ???                                 0x077efe64 0x0 + 125763172
    22  ???                                 0x077ef1e2 0x0 + 125759970
    23  ???                                 0x077ef0be 0x0 + 125759678
    24  ???                                 0x077ef145 0x0 + 125759813
    25  TestProject                         0x0000f507 mono_jit_runtime_invoke + 1332
    26  TestProject                         0x001ed259 mono_runtime_invoke + 137
    27  TestProject                         0x001ef940 mono_runtime_exec_main + 669
    28  TestProject                         0x001eed2a mono_runtime_run_main + 843
    29  TestProject                         0x000a3093 mono_jit_exec + 200
    30  TestProject                         0x002a163d main + 4060
    31  TestProject                         0x00002819 _start + 208
    32  TestProject                         0x00002748 start + 40

Debug info from gdb:

dyld: could not load inserted library: /Users/Apple/Library/Application Support/iPhone Simulator/4.3/Applications/86C48AC1-821F-49DD-B344-58471F02D31B/TestProject.app/monotouch-fixes.dylib


=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.
=================================================================

Does anyone know what‘s causing this, and more importantly how to avoid it? When setting just a single button as the RightBarButtonItem it works without any problems.

edit

Above error seems to randomly cycle with this one:

Error connecting stdout and stderr (127.0.0.1:10001)
2011-08-25 13:30:05.409 TestProject[1235:a0b] -[__NSCFSet InvokeAction:]: unrecognized selector sent to instance 0x7168980

Unhandled Exception: MonoTouch.Foundation.MonoTouchException: Objective-C exception thrown.  Name: NSInvalidArgumentException Reason: -[__NSCFSet InvokeAction:]: unrecognized selector sent to instance 0x7168980
  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) [0x00038] in /Developer/MonoTouch/Source/monotouch/monotouch/UIKit/UIApplication.cs:26 
  at TestProject.Application.Main (System.String[] args) [0x00000] in /Users/Apple/Projects/TestProject/TestProject/Main.cs:16 
[ERROR] FATAL UNHANDLED EXCEPTION: MonoTouch.Foundation.MonoTouchException: Objective-C exception thrown.  Name: NSInvalidArgumentException Reason: -[__NSCFSet InvokeAction:]: unrecognized selector sent to instance 0x7168980
  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) [0x00038] in /Developer/MonoTouch/Source/monotouch/monotouch/UIKit/UIApplication.cs:26 
  at TestProject.Application.Main (System.String[] args) [0x00000] in /Users/Apple/Projects/TestProject/TestProject/Main.cs:16 

Answer 1

Declare the buttons as class variables. The GC collects them so your event handlers are causing memory leaks.