MvxCachingFragmentActivity.cs

// MvxCachingFragmentActivity.cs
// (c) Copyright Cirrious Ltd. http://www.cirrious.com
// MvvmCross is licensed using Microsoft Public License (Ms-PL)
// Contributions and inspirations noted in readme.md and license.txt
//
// Project Lead - Stuart Lodge, @slodge, me@slodge.com

using System;
using System.Collections.Generic;
using System.Linq;
using Android.OS;
using Android.Runtime;
using Android.Support.V4.App;
using MvvmCross.Binding.Droid.BindingContext;
using MvvmCross.Core.ViewModels;
using MvvmCross.Core.Views;
using MvvmCross.Droid.Platform;
using MvvmCross.Droid.Shared.Attributes;
using MvvmCross.Droid.Shared.Caching;
using MvvmCross.Droid.Shared.Fragments;
using MvvmCross.Droid.Shared.Presenter;
using MvvmCross.Droid.Views;
using MvvmCross.Platform;
using MvvmCross.Platform.Exceptions;
using MvvmCross.Platform.Platform;
using Fragment = Android.Support.V4.App.Fragment;

namespace MvvmCross.Droid.Support.V4
{
    public class MvxCachingFragmentActivity : MvxFragmentActivity, IFragmentCacheableActivity, IMvxFragmentHost
    {
		public const string ViewModelRequestBundleKey = "__mvxViewModelRequest";
		private const string SavedFragmentTypesKey = "__mvxSavedFragmentTypes";
		private IFragmentCacheConfiguration _fragmentCacheConfiguration;

		protected enum FragmentReplaceMode
		{
			NoReplace,
			ReplaceFragment,
			ReplaceFragmentAndViewModel
		}

		protected MvxCachingFragmentActivity()
		{
		}

		protected MvxCachingFragmentActivity(IntPtr javaReference, JniHandleOwnership transfer)
			: base(javaReference, transfer)
		{}

		protected override void OnPostCreate(Bundle savedInstanceState)
		{
			base.OnPostCreate(savedInstanceState);
			if (savedInstanceState == null) return;

			IMvxJsonConverter serializer;
			if (!Mvx.TryResolve(out serializer))
			{
				Mvx.Trace(
					"Could not resolve IMvxJsonConverter, it is going to be hard to create ViewModel cache");
				return;
			}

			FragmentCacheConfiguration.RestoreCacheConfiguration(savedInstanceState, serializer);
			// Gabriel has blown his trumpet. Ressurect Fragments from the dead.
			RestoreFragmentsCache();

			RestoreViewModelsFromBundle(serializer, savedInstanceState);
		}

		private static void RestoreViewModelsFromBundle(IMvxJsonConverter serializer, Bundle savedInstanceState)
		{
			IMvxSavedStateConverter savedStateConverter;
			IMvxMultipleViewModelCache viewModelCache;
			IMvxViewModelLoader viewModelLoader;

			if (!Mvx.TryResolve(out savedStateConverter))
			{
				Mvx.Trace("Could not resolve IMvxSavedStateConverter, won't be able to convert saved state");
				return;
			}

			if (!Mvx.TryResolve(out viewModelCache))
			{
				Mvx.Trace("Could not resolve IMvxMultipleViewModelCache, won't be able to convert saved state");
				return;
			}

			if (!Mvx.TryResolve(out viewModelLoader))
			{
				Mvx.Trace("Could not resolve IMvxViewModelLoader, won't be able to load ViewModel for caching");
				return;
			}

			// Harder ressurection, just in case we were killed to death.
			var json = savedInstanceState.GetString(SavedFragmentTypesKey);
			if (string.IsNullOrEmpty(json)) return;

			var savedState = serializer.DeserializeObject<Dictionary<string, Type>>(json);
			foreach (var item in savedState)
			{
				var bundle = savedInstanceState.GetBundle(item.Key);
				if (bundle.IsEmpty) continue;

				var mvxBundle = savedStateConverter.Read(bundle);
				var request = MvxViewModelRequest.GetDefaultRequest(item.Value);

				// repopulate the ViewModel with the SavedState and cache it.
				var vm = viewModelLoader.LoadViewModel(request, mvxBundle);
				viewModelCache.Cache(vm, item.Key);
			}
		}

		private void RestoreFragmentsCache()
		{
			// See if Fragments were just sleeping, and repopulate the _lookup (which is accesed in GetFragmentInfoByTag)
			// with references to them.

			// we do not want to restore fragments which aren't tracked by our cache
			foreach (var fragment in GetCurrentCacheableFragments())
			{
				// if used tag is proper tag such that:
				// it is unique and immutable
				// and fragment is properly registered
				// then there must be exactly one matching value in _lookup fragment cache container
				var fragmentTag = GetTagFromFragment(fragment);
				var fragmentInfo = GetFragmentInfoByTag(fragmentTag);

				fragmentInfo.CachedFragment = fragment as IMvxFragmentView;
			}
		}

		private Dictionary<string, Type> CreateFragmentTypesDictionary(Bundle outState)
		{
			IMvxSavedStateConverter savedStateConverter;
			if (!Mvx.TryResolve(out savedStateConverter))
			{
				return null;
			}

			var typesForKeys = new Dictionary<string, Type>();

			var currentFragsInfo = GetCurrentCacheableFragmentsInfo();
			foreach (var info in currentFragsInfo)
			{
				var fragment = info.CachedFragment as IMvxFragmentView;
				if (fragment == null)
					continue;

				var mvxBundle = fragment.CreateSaveStateBundle();
				var bundle = new Bundle();
				savedStateConverter.Write(bundle, mvxBundle);
				outState.PutBundle(info.Tag, bundle);

				if(!typesForKeys.ContainsKey(info.Tag))
					typesForKeys.Add(info.Tag, info.ViewModelType);
			}

			return typesForKeys;
		}

		protected virtual void ReplaceFragment(FragmentTransaction ft, IMvxCachedFragmentInfo fragInfo)
		{
			ft.Replace(fragInfo.ContentId, fragInfo.CachedFragment as Fragment, fragInfo.Tag);
		}

		protected override void OnSaveInstanceState(Bundle outState)
		{
			base.OnSaveInstanceState(outState);
			IMvxJsonConverter ser;
			if (FragmentCacheConfiguration.HasAnyFragmentsRegisteredToCache && Mvx.TryResolve(out ser))
			{
				FragmentCacheConfiguration.SaveFragmentCacheConfigurationState(outState, ser);

				var typesForKeys = CreateFragmentTypesDictionary(outState);
				if (typesForKeys == null)
					return;

				var json = ser.SerializeObject(typesForKeys);
				outState.PutString(SavedFragmentTypesKey, json);
			}
		}

		/// <summary>
		///     Show Fragment with a specific tag at a specific placeholder
		/// </summary>
		/// <param name="tag">The tag for the fragment to lookup</param>
		/// <param name="contentId">Where you want to show the Fragment</param>
		/// <param name="bundle">Bundle which usually contains a Serialized MvxViewModelRequest</param>
		/// <param name="forceAddToBackStack">If you want to force add the fragment to the backstack so on backbutton it will go back to it. Note: This will override IMvxCachedFragmentInfo.AddToBackStack configuration.</param>
		/// <param name="forceReplaceFragment">If you want the fragment to be re-created</param>
		protected virtual void ShowFragment(string tag, int contentId, Bundle bundle, bool forceAddToBackStack = false, bool forceReplaceFragment = false)
		{
			IMvxCachedFragmentInfo fragInfo;
			FragmentCacheConfiguration.TryGetValue(tag, out fragInfo);

			IMvxCachedFragmentInfo currentFragInfo = null;
			var currentFragment = SupportFragmentManager.FindFragmentById(contentId);

			if (currentFragment != null)
				FragmentCacheConfiguration.TryGetValue(currentFragment.Tag, out currentFragInfo);

			if (fragInfo == null)
				throw new MvxException("Could not find tag: {0} in cache, you need to register it first.", tag);

			// We shouldn't replace the current fragment unless we really need to.
			FragmentReplaceMode fragmentReplaceMode = FragmentReplaceMode.ReplaceFragmentAndViewModel;
			if (!forceReplaceFragment)
				fragmentReplaceMode = ShouldReplaceCurrentFragment(fragInfo, currentFragInfo, bundle);

			if (fragmentReplaceMode == FragmentReplaceMode.NoReplace)
				return;

			var ft = SupportFragmentManager.BeginTransaction();
			OnBeforeFragmentChanging(fragInfo, ft);

			fragInfo.ContentId = contentId;

			//If we already have a previously created fragment, we only need to send the new parameters
			if (fragInfo.CachedFragment != null && fragmentReplaceMode == FragmentReplaceMode.ReplaceFragment)
			{
				((Fragment)fragInfo.CachedFragment).Arguments.Clear();
				((Fragment)fragInfo.CachedFragment).Arguments.PutAll(bundle);
			}
			else
			{
				//Otherwise, create one and cache it
				fragInfo.CachedFragment = Fragment.Instantiate(this, FragmentJavaName(fragInfo.FragmentType),
					bundle) as IMvxFragmentView;
				OnFragmentCreated(fragInfo, ft);
			}

			ft.Replace(fragInfo.ContentId, fragInfo.CachedFragment as Fragment, fragInfo.Tag);

			//if replacing ViewModel then clear the cache after the fragment
			//has been added to the transaction so that the Tag property is not null
			//and the UniqueImmutableCacheTag property (if not overridden) has the correct value
			if (fragmentReplaceMode == FragmentReplaceMode.ReplaceFragmentAndViewModel)
			{
				var cache = Mvx.GetSingleton<IMvxMultipleViewModelCache>();
				cache.GetAndClear(fragInfo.ViewModelType, GetTagFromFragment(fragInfo.CachedFragment as Fragment));
			}

			if ((currentFragment != null && fragInfo.AddToBackStack) || forceAddToBackStack)
			{
				ft.AddToBackStack(fragInfo.Tag);
			}

			OnFragmentChanging(fragInfo, ft);
			ft.Commit();
			SupportFragmentManager.ExecutePendingTransactions();
			OnFragmentChanged(fragInfo);
		}

		protected virtual FragmentReplaceMode ShouldReplaceCurrentFragment(IMvxCachedFragmentInfo newFragment, IMvxCachedFragmentInfo currentFragment, Bundle replacementBundle)
		{
			var oldBundle = ((Fragment)newFragment.CachedFragment)?.Arguments;
			if (oldBundle == null) return FragmentReplaceMode.ReplaceFragment;

			var serializer = Mvx.Resolve<IMvxNavigationSerializer>();

			var json = oldBundle.GetString(MvxFragmentsPresenter.ViewModelRequestBundleKey);
			var oldRequest = serializer.Serializer.DeserializeObject<MvxViewModelRequest>(json);
			if (oldRequest == null) return FragmentReplaceMode.ReplaceFragment;

			json = replacementBundle.GetString(MvxFragmentsPresenter.ViewModelRequestBundleKey);
			var replacementRequest = serializer.Serializer.DeserializeObject<MvxViewModelRequest>(json);
			if (replacementRequest == null) return FragmentReplaceMode.ReplaceFragment;

			var areParametersEqual = ((oldRequest.ParameterValues == replacementRequest.ParameterValues) ||
				(oldRequest.ParameterValues.Count == replacementRequest.ParameterValues.Count &&
					!oldRequest.ParameterValues.Except(replacementRequest.ParameterValues).Any()));

			if (currentFragment?.Tag != newFragment.Tag)
			{
				return !areParametersEqual
					? FragmentReplaceMode.ReplaceFragmentAndViewModel
						: FragmentReplaceMode.ReplaceFragment;
			}
			else
				return !areParametersEqual
					? FragmentReplaceMode.ReplaceFragmentAndViewModel
						: FragmentReplaceMode.NoReplace;
		}

		public override void OnBackPressed()
		{
			if (SupportFragmentManager.BackStackEntryCount >= 1)
			{
				SupportFragmentManager.PopBackStackImmediate();

				if (FragmentCacheConfiguration.EnableOnFragmentPoppedCallback)
				{
					//NOTE(vvolkgang) this is returning ALL the frags. Should we return only the visible ones?
					var currentFragsInfo = GetCurrentCacheableFragmentsInfo();
					OnFragmentPopped(currentFragsInfo);
				}

				return;
			}

			base.OnBackPressed();
		}

		protected virtual List<IMvxCachedFragmentInfo> GetCurrentCacheableFragmentsInfo()
		{
			return GetCurrentCacheableFragments()
				.Select(frag => GetFragmentInfoByTag(GetTagFromFragment(frag)))
				.ToList();
		}

		protected virtual IEnumerable<Fragment> GetCurrentCacheableFragments()
		{
			var currentFragments = SupportFragmentManager.Fragments ?? Enumerable.Empty<Fragment>();

			return currentFragments
				.Where(fragment => fragment != null)
				// we are not interested in fragments which are not supposed to cache!
				.Where(fragment => fragment.GetType().IsFragmentCacheable(GetType()));
		}

		protected virtual IMvxCachedFragmentInfo GetLastFragmentInfo()
		{
			var currentCacheableFragments = GetCurrentCacheableFragments().ToList();
			if (!currentCacheableFragments.Any())
				throw new InvalidOperationException("Cannot retrieve last fragment as FragmentManager is empty.");

			var lastFragment = currentCacheableFragments.Last();
			var tagFragment = GetTagFromFragment(lastFragment);

			return GetFragmentInfoByTag(tagFragment);
		}

		protected virtual string GetTagFromFragment(Fragment fragment)
		{
			var mvxFragmentView = fragment as IMvxFragmentView;

			// ReSharper disable once PossibleNullReferenceException
			// Fragment can never be null because registered fragment has to inherit from IMvxFragmentView
			return mvxFragmentView.UniqueImmutableCacheTag;
		}

		protected override void OnCreate (Bundle bundle)
		{
			base.OnCreate (bundle);

			if (bundle == null) {
				var fragmentRequestText = Intent.Extras?.GetString (ViewModelRequestBundleKey);
				if (fragmentRequestText == null)
					return;

				var converter = Mvx.Resolve<IMvxNavigationSerializer> ();
				var fragmentRequest = converter.Serializer.DeserializeObject<MvxViewModelRequest> (fragmentRequestText);

				var mvxAndroidViewPresenter = Mvx.Resolve<IMvxAndroidViewPresenter> ();
				mvxAndroidViewPresenter.Show (fragmentRequest);
			}
		}

		/// <summary>
		/// Close Fragment with a specific tag at a specific placeholder
		/// </summary>
		/// <param name="tag">The tag for the fragment to lookup</param>
		/// <param name="contentId">Where you want to close the Fragment</param>
		protected virtual void CloseFragment(string tag, int contentId)
		{
			var frag = SupportFragmentManager.FindFragmentById(contentId);
			if (frag == null) return;

			SupportFragmentManager.PopBackStackImmediate(tag, 1);
		}

		protected virtual string FragmentJavaName(Type fragmentType)
		{
			var namespaceText = fragmentType.Namespace ?? "";
			if (namespaceText.Length > 0)
				namespaceText = namespaceText.ToLowerInvariant() + ".";
			return namespaceText + fragmentType.Name;
		}

		public virtual void OnBeforeFragmentChanging(IMvxCachedFragmentInfo fragmentInfo, FragmentTransaction transaction)
		{
		}

		// Called before the transaction is commited
		public virtual void OnFragmentChanging(IMvxCachedFragmentInfo fragmentInfo, FragmentTransaction transaction) { }

		public virtual void OnFragmentChanged(IMvxCachedFragmentInfo fragmentInfo)
		{
		}

		public virtual void OnFragmentPopped(IList<IMvxCachedFragmentInfo> currentFragmentsInfo)
		{
		}

		public virtual void OnFragmentCreated(IMvxCachedFragmentInfo fragmentInfo, FragmentTransaction transaction)
		{
		}

		protected IMvxCachedFragmentInfo GetFragmentInfoByTag(string tag)
		{
			IMvxCachedFragmentInfo fragInfo;
			FragmentCacheConfiguration.TryGetValue(tag, out fragInfo);

			if (fragInfo == null)
				throw new MvxException("Could not find tag: {0} in cache, you need to register it first.", tag);
			return fragInfo;
		}

		public IFragmentCacheConfiguration FragmentCacheConfiguration => _fragmentCacheConfiguration ?? (_fragmentCacheConfiguration = BuildFragmentCacheConfiguration());

		public virtual IFragmentCacheConfiguration BuildFragmentCacheConfiguration()
		{
			return new DefaultFragmentCacheConfiguration();
		}

		protected virtual string GetFragmentTag(MvxViewModelRequest request, Bundle bundle, Type fragmentType)
		{
			// THAT won't work properly if you have multiple instance of same fragment type in same FragmentHost.
			// Override that in such cases
			return request.ViewModelType.FullName;
		}

		public virtual bool Show(MvxViewModelRequest request, Bundle bundle, Type fragmentType, MvxFragmentAttribute fragmentAttribute)
		{
			var fragmentTag = GetFragmentTag(request, bundle, fragmentType);
			FragmentCacheConfiguration.RegisterFragmentToCache(fragmentTag, fragmentType, request.ViewModelType, fragmentAttribute.AddToBackStack);

			ShowFragment(fragmentTag, fragmentAttribute.FragmentContentId, bundle);
			return true;
		}

		public virtual bool Close(IMvxViewModel viewModel)
		{
			//Workaround for closing fragments. This will not work when showing multiple fragments of the same viewmodel type in one activity
			var frag = GetCurrentCacheableFragmentsInfo ().FirstOrDefault (x => x.ViewModelType == viewModel.GetType());
			if (frag == null)
			{
				return false;
			}
			// Close method can not be fully fixed at this moment. That requires some changes in main MvvmCross library
			CloseFragment(frag.Tag, frag.ContentId);
			return true;
		}
    }

    public abstract class MvxCachingFragmentActivity<TViewModel>
        : MvxCachingFragmentActivity
    , IMvxAndroidView<TViewModel> where TViewModel : class, IMvxViewModel
    {
        public new TViewModel ViewModel
        {
            get { return (TViewModel)base.ViewModel; }
            set { base.ViewModel = value; }
        }
    }
}