Memory Considerations on Xamarin iOS

Question

Hello,

According to following video on Xamarin Developers chanel, you should always unsubsribe from events to prevent memory leaks.

https://www.youtube.com/watch?v=YebuM6_Gpcw

Moreover (or alternatively?) you could dispose your view, sth like myButton?.Dispose();

Have I got this right?

There is also a method named ReleaseDesignerOutlets on the partial class created along with every new ViewController which actually does this exact same thing for all the controls - buttons etc.

Is this method called somehow?

Thanks for any resposne.

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

If you want to prevent Xamarin iOS memory leaks for a view.

below extension methods to solve these memory leak issues. the DisposeEx method is like that laser and it disassociates all views and their connected objects and disposes them recursively and in a way that shouldn't crash your app.

Just call DisposeEx() on UIViewController's main view when you no longer need that view controller. If some nested UIView has special things to dispose, or you dont want it disposed, implement ISpecialDisposable.SpecialDispose which is called in place of IDisposable.Dispose.

   public static void DisposeEx(this UIView view) {  
   			const bool enableLogging = false;  
   			try {  
   				if (view.IsDisposedOrNull())  
   					return;  
     
   				var viewDescription = string.Empty;  
     
   				if (enableLogging) {  
   					viewDescription = view.Description;  
   					SystemLog.Debug("Destroying " + viewDescription);  
   				}  
     
   				var disposeView = true;  
   				var disconnectFromSuperView = true;  
   				var disposeSubviews = true;  
   				var removeGestureRecognizers = false; // WARNING: enable at your own risk, may causes crashes  
   				var removeConstraints = true;  
   				var removeLayerAnimations = true;  
   				var associatedViewsToDispose = new List<UIView>();  
   				var otherDisposables = new List<IDisposable>();  
     
   				if (view is UIActivityIndicatorView) {  
   					var aiv = (UIActivityIndicatorView)view;  
   					if (aiv.IsAnimating) {  
   						aiv.StopAnimating();  
   					}  
   				} else if (view is UITableView) {  
   					var tableView = (UITableView)view;  
     
   					if (tableView.DataSource != null) {  
   						otherDisposables.Add(tableView.DataSource);  
   					}  
   					if (tableView.BackgroundView != null) {  
   						associatedViewsToDispose.Add(tableView.BackgroundView);  
   					}  
     
   					tableView.Source = null;  
   					tableView.Delegate = null;  
   					tableView.DataSource = null;  
   					tableView.WeakDelegate = null;  
   					tableView.WeakDataSource = null;  
   					associatedViewsToDispose.AddRange(tableView.VisibleCells ?? new UITableViewCell[0]);  
   				} else if (view is UITableViewCell) {  
   					var tableViewCell = (UITableViewCell)view;  
   					disposeView = false;  
   					disconnectFromSuperView = false;  
   					if (tableViewCell.ImageView != null) {  
   						associatedViewsToDispose.Add(tableViewCell.ImageView);  
   					}  
   				} else if (view is UICollectionView) {  
   					var collectionView = (UICollectionView)view;  
   					disposeView = false;   
   					if (collectionView.DataSource != null) {  
   						otherDisposables.Add(collectionView.DataSource);  
   					}  
   					if (!collectionView.BackgroundView.IsDisposedOrNull()) {  
   						associatedViewsToDispose.Add(collectionView.BackgroundView);  
   					}  
   					//associatedViewsToDispose.AddRange(collectionView.VisibleCells ?? new UICollectionViewCell[0]);  
   					collectionView.Source = null;  
   					collectionView.Delegate = null;  
   					collectionView.DataSource = null;  
   					collectionView.WeakDelegate = null;  
   					collectionView.WeakDataSource = null;  
   				} else if (view is UICollectionViewCell) {  
   					var collectionViewCell = (UICollectionViewCell)view;  
   					disposeView = false;  
   					disconnectFromSuperView = false;  
   					if (collectionViewCell.BackgroundView != null) {  
   						associatedViewsToDispose.Add(collectionViewCell.BackgroundView);  
   					}  
   				} else if (view is UIWebView) {  
   					var webView = (UIWebView)view;  
   					if (webView.IsLoading)  
   						webView.StopLoading();  
   					webView.LoadHtmlString(string.Empty, null); // clear display  
   					webView.Delegate = null;  
   					webView.WeakDelegate = null;  
   				} else if (view is UIImageView) {  
   					var imageView = (UIImageView)view;  
   					if (imageView.Image != null) {  
   						otherDisposables.Add(imageView.Image);  
   						imageView.Image = null;  
   					}  
   				} else if (view is UIScrollView) {  
                       var scrollView = (UIScrollView)view;  
                       // Comment out extension method  
   					//scrollView.UnsetZoomableContentView();  
   				}  
     
   				var gestures = view.GestureRecognizers;  
   				if (removeGestureRecognizers && gestures != null) {  
   					foreach(var gr in gestures) {  
   						view.RemoveGestureRecognizer(gr);  
   						gr.Dispose();  
   					}  
   				}  
   					  
   				if (removeLayerAnimations && view.Layer != null) {  
   					view.Layer.RemoveAllAnimations();  
   				}  
     
   				if (disconnectFromSuperView && view.Superview != null) {  
   					view.RemoveFromSuperview();  
   				}  
     
   				var constraints = view.Constraints;  
   				if (constraints != null && constraints.Any() && constraints.All(c => c.Handle != IntPtr.Zero)) {  
   					view.RemoveConstraints(constraints);  
   					foreach(var constraint in constraints) {  
   						constraint.Dispose();  
   					}  
   				}  
     
   				foreach(var otherDisposable in otherDisposables) {  
   					otherDisposable.Dispose();  
   				}  
     
   				foreach(var otherView in associatedViewsToDispose) {  
   					otherView.DisposeEx();  
   				}  
     
   				var subViews = view.Subviews;  
   				if (disposeSubviews && subViews != null) {  
   					subViews.ForEach(DisposeEx);  
   				}					  
   			  
   				if (view is ISpecialDisposable) {  
   					((ISpecialDisposable)view).SpecialDispose();  
   				} else if (disposeView) {  
   					if (view.Handle != IntPtr.Zero)  
   						view.Dispose();  
   				}  
     
   				if (enableLogging) {  
   					SystemLog.Debug("Destroyed {0}", viewDescription);  
   				}  
     
   			} catch (Exception error) {  
   				SystemLog.Exception(error);  
   			}  
   		}  
     
   		public static void RemoveAndDisposeChildSubViews(this UIView view) {  
   			if (view == null)  
   				return;  
   			if (view.Handle == IntPtr.Zero)  
   				return;  
   			if (view.Subviews == null)  
   				return;  
   			view.Subviews.ForEach(RemoveFromSuperviewAndDispose);  
   		}  
     
   		public static void RemoveFromSuperviewAndDispose(this UIView view) {  
   			view.RemoveFromSuperview();  
   			view.DisposeEx();  
   		}  
     
   		public static bool IsDisposedOrNull(this UIView view) {  
   			if (view == null)  
   				return true;  
     
   			if (view.Handle == IntPtr.Zero)  
   				return true;;  
     
   			return false;  
   		}  
     
   		public interface ISpecialDisposable {  
   		    void SpecialDispose();  
   		}  

Here is a helpful thread, you can refer to it.

https://stackoverflow.com/questions/25532870/xamarin-ios-memory-leaks-everywhere

Best Regards,

Leon Lu

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