gistfile1.txt

using System;
using System.Drawing;
using MonoTouch.ObjCRuntime;
using MonoTouch.Foundation;
using MonoTouch.UIKit;

namespace NSPredicateProblem
{
	public partial class NSPredicateProblemViewController : UIViewController
	{
		static bool UserInterfaceIdiomIsPhone {
			get { return UIDevice.CurrentDevice.UserInterfaceIdiom == UIUserInterfaceIdiom.Phone; }
		}

		public NSPredicateProblemViewController ()
			: base (UserInterfaceIdiomIsPhone ? "NSPredicateProblemViewController_iPhone" : "NSPredicateProblemViewController_iPad", null)
		{
		}

		public override void DidReceiveMemoryWarning ()
		{
			// Releases the view if it doesn't have a superview.
			base.DidReceiveMemoryWarning ();
			
			// Release any cached data, images, etc that aren't in use.
		}

		UILabel counter;
		UILabel failedAttemptsLabel;
		
		public override void ViewDidLoad ()
		{
			base.ViewDidLoad ();

			View.AutosizesSubviews = true;
			// Perform any additional setup after loading the view, typically from a nib.

			counter = new UILabel(new RectangleF(0,20,320,50)) {
				Lines = 0
			};
			this.View.Add(counter);

			failedAttemptsLabel = new UILabel(new RectangleF(0,70,320,250)){
				Lines = 0,
			};
			this.View.Add(failedAttemptsLabel);

		}

		public override void ViewDidAppear (bool animated)
		{
			base.ViewDidAppear (animated);



			InvokeInBackground (() =>  {
				int failedAttemptsNonSingleton = 0;
				int failedAttemptsDirect = 0;
				int failedAttemptsMethod = 0;
				int failedAttemptsMethod2 = 0;
				int failedAttemptsNull = 0;

				for (long i = 0; i < long.MaxValue; i++) {

					System.GC.Collect();

					// monotouch is missing support for these two bindings
					// + (NSPredicate *)predicateWithFormat:(NSString *)format,, ...
					// + (NSPredicate *)predicateWithFormat:(NSString *)format arguments:(va_list)argList

					// Should be allowed to pass null to predicateWithFormat
					// https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSPredicate_Class/Reference/NSPredicate.html
					
					NSPredicate predicate = null;
					try {
						
						// fails always
						// this fails because binding for NSPredicate.FromFormat calls predicateWithFormat:argumentArray:
						//NSPredicate.FromFormat("TRUEPREDICATE",null);
						
						// passes always
						// IntPtr_IntPtr version of needed binding
						// NSPredicate predicate = NSPredicateExtensions.FromFormat("a == %@",new NSString("b"));
						predicate = NSPredicate.FromFormat("a == %@", (NSObject) null);
						
						// WORKS
						// IntPtr version of needed binding
						//NSPredicate predicate = NSPredicateExtensions.FromFormat("TRUEPREDICATE");
					}
					catch (Exception e) {
						
						failedAttemptsNull++;
					}
					
					// Passing Predicate Method - fails
					
					// passing empty NSObject[] array to NSPredicate.FromFormat fails when predicate is passed to 
					// NSCompoundPredicate. something is looks wrong with retain count


					try {
						predicate = NSPredicate.FromFormat ("TRUEPREDICATE");
						// note: predicate.retainCount is -1
						predicate = AppendDeletedPredicate (predicate);
					}
					catch (Exception e) {
						failedAttemptsMethod++;
					}


					// unrolled NSCompoundPredicate, same as above - doesn't fail

					try {
						NSPredicate[] predicates = new NSPredicate[]
						{
							NSPredicate.FromFormat ("FALSEPREDICATE"),
							NSPredicate.FromFormat("(markedDeleted == NO)")
						};
						predicate = new NSCompoundPredicate(NSCompoundPredicateType.And, predicates);

					}
					catch {
						failedAttemptsDirect++;
					}
					
					// Passing Predicate Method using correct binding - fails far less but still returns an eroor
					
					// passing empty NSObject[] array to NSPredicate.FromFormat fails when predicate is passed to 
					// NSCompoundPredicate. something is looks wrong with retain count

					try {
						
						predicate = NSPredicate.FromFormat("TRUEPREDICATE");
						predicate = AppendDeletedPredicate2 (predicate);
					}
					catch (Exception e) {
						failedAttemptsMethod2++;
					}

					

					BeginInvokeOnMainThread (() =>  {
						counter.Text = String.Format ("iteration i:{0}  NSPredicate.FromFormat", i);
						failedAttemptsLabel.Text = String.Format ("Passing Null to Predicate failed:{0}\rNSCompoundPredicate from method failed:{1}\rNSCompoundPredicate unrolled failed:{2} NSCompoundPredicate w/ correct binding from method failed:{3}", 
							failedAttemptsNull, failedAttemptsMethod, failedAttemptsDirect, failedAttemptsMethod2);
					});
				}

			});
		}

		public static NSPredicate AppendDeletedPredicate(NSPredicate predicate)
		{
			NSPredicate[] predicates = new NSPredicate[]
			{
				predicate,
				NSPredicate.FromFormat("(markedDeleted == NO)")
			};
			return new NSCompoundPredicate(NSCompoundPredicateType.And, predicates);
		}
		
		public static NSPredicate AppendDeletedPredicate2(NSPredicate predicate)
		{
			NSPredicate[] predicates = new NSPredicate[]
			{
				predicate,
				NSPredicate.FromFormat("(markedDeleted == %@)", NSNull.Null)
			};
			return new NSCompoundPredicate(NSCompoundPredicateType.And, predicates);
		}
	}
}