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using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace Xamarin.Forms
{
internal class NavigationProxy : INavigation
{
INavigation _inner;
Lazy<List<Page>> _modalStack = new Lazy<List<Page>>(() => new List<Page>());
Lazy<List<Page>> _pushStack = new Lazy<List<Page>>(() => new List<Page>());
public INavigation Inner
{
get { return _inner; }
set
{
if (_inner == value)
return;
_inner = value;
// reverse so that things go into the new stack in the same order
// null out to release memory that will likely never be needed again
if (ReferenceEquals(_inner, null))
{
_pushStack = new Lazy<List<Page>>(() => new List<Page>());
_modalStack = new Lazy<List<Page>>(() => new List<Page>());
}
else
{
if (_pushStack != null && _pushStack.IsValueCreated)
{
foreach (Page page in _pushStack.Value)
{
_inner.PushAsync(page);
}
}
if (_modalStack != null && _modalStack.IsValueCreated)
{
foreach (Page page in _modalStack.Value)
{
_inner.PushModalAsync(page);
}
}
_pushStack = null;
_modalStack = null;
}
}
}
public void InsertPageBefore(Page page, Page before)
{
OnInsertPageBefore(page, before);
}
public IReadOnlyList<Page> ModalStack
{
get { return GetModalStack(); }
}
public IReadOnlyList<Page> NavigationStack
{
get { return GetNavigationStack(); }
}
public Task<Page> PopAsync()
{
return OnPopAsync(true);
}
public Task<Page> PopAsync(bool animated)
{
return OnPopAsync(animated);
}
public Task<Page> PopModalAsync()
{
return OnPopModal(true);
}
public Task<Page> PopModalAsync(bool animated)
{
return OnPopModal(animated);
}
public Task PopToRootAsync()
{
return OnPopToRootAsync(true);
}
public Task PopToRootAsync(bool animated)
{
return OnPopToRootAsync(animated);
}
public Task PushAsync(Page root)
{
return PushAsync(root, true);
}
public Task PushAsync(Page root, bool animated)
{
if (root.RealParent != null)
throw new InvalidOperationException("Page must not already have a parent.");
return OnPushAsync(root, animated);
}
public Task PushModalAsync(Page modal)
{
return PushModalAsync(modal, true);
}
public Task PushModalAsync(Page modal, bool animated)
{
if (modal.RealParent != null)
throw new InvalidOperationException("Page must not already have a parent.");
return OnPushModal(modal, animated);
}
public void RemovePage(Page page)
{
OnRemovePage(page);
}
protected virtual IReadOnlyList<Page> GetModalStack()
{
INavigation currentInner = Inner;
return currentInner == null ? _modalStack.Value : currentInner.ModalStack;
}
protected virtual IReadOnlyList<Page> GetNavigationStack()
{
INavigation currentInner = Inner;
return currentInner == null ? _pushStack.Value : currentInner.NavigationStack;
}
protected virtual void OnInsertPageBefore(Page page, Page before)
{
INavigation currentInner = Inner;
if (currentInner == null)
{
int index = _pushStack.Value.IndexOf(before);
if (index == -1)
throw new ArgumentException("before must be in the pushed stack of the current context");
_pushStack.Value.Insert(index, page);
}
else
{
currentInner.InsertPageBefore(page, before);
}
}
protected virtual Task<Page> OnPopAsync(bool animated)
{
INavigation inner = Inner;
return inner == null ? Task.FromResult(Pop()) : inner.PopAsync(animated);
}
protected virtual Task<Page> OnPopModal(bool animated)
{
INavigation innerNav = Inner;
return innerNav == null ? Task.FromResult(PopModal()) : innerNav.PopModalAsync(animated);
}
protected virtual Task OnPopToRootAsync(bool animated)
{
INavigation currentInner = Inner;
if (currentInner == null)
{
Page root = _pushStack.Value.Last();
_pushStack.Value.Clear();
_pushStack.Value.Add(root);
return Task.FromResult(root);
}
return currentInner.PopToRootAsync(animated);
}
protected virtual Task OnPushAsync(Page page, bool animated)
{
INavigation currentInner = Inner;
if (currentInner == null)
{
_pushStack.Value.Add(page);
return Task.FromResult(page);
}
return currentInner.PushAsync(page, animated);
}
protected virtual Task OnPushModal(Page modal, bool animated)
{
INavigation currentInner = Inner;
if (currentInner == null)
{
_modalStack.Value.Add(modal);
return Task.FromResult<object>(null);
}
return currentInner.PushModalAsync(modal, animated);
}
protected virtual void OnRemovePage(Page page)
{
INavigation currentInner = Inner;
if (currentInner == null)
{
_pushStack.Value.Remove(page);
}
else
{
currentInner.RemovePage(page);
}
}
Page Pop()
{
List<Page> list = _pushStack.Value;
Page result = list[list.Count - 1];
list.RemoveAt(list.Count - 1);
return result;
}
Page PopModal()
{
List<Page> list = _modalStack.Value;
Page result = list[list.Count - 1];
list.RemoveAt(list.Count - 1);
return result;
}
}
}
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