实现GridLayout的ScrollTo

DemoTest/Pages/DefaultTestPage.xaml.cs

@@ -74,7 +74,7 @@ public DefaultTestPage()
  var headerButton = new Button() { Text = "Header GoTo End", VerticalOptions = LayoutOptions.Center, HorizontalOptions = LayoutOptions.Center };
  headerButton.Clicked += (s, e) =>
  {
- tableView.ScrollToItem(NSIndexPath.FromRowSection(10, ViewModel.Instance.models.Count - 1), ScrollPosition.Top, true);
+ tableView.ScrollToItem(NSIndexPath.FromRowSection(ViewModel.Instance.models[ViewModel.Instance.models.Count - 1].Count - 10, ViewModel.Instance.models.Count - 1), ScrollPosition.Top, false);
  Debug.WriteLine("Clicked Header");
  };
  var headerView = new MAUICollectionViewViewHolder(headerButton, "Header");
@@ -85,7 +85,7 @@ public DefaultTestPage()
  var footerButton = new Button() { Text = "Footer GoTo Start", VerticalOptions = LayoutOptions.Center, HorizontalOptions = LayoutOptions.Center };
  footerButton.Clicked += (s, e) =>
  {
- tableView.ScrollToItem(NSIndexPath.FromRowSection(10, 0), ScrollPosition.Top, true);
+ tableView.ScrollToItem(NSIndexPath.FromRowSection(10, 0), ScrollPosition.Top, false);
  Debug.WriteLine("Clicked Footer");
  };
  var footActivityIndicator = new ActivityIndicator() { Color = Colors.Red, IsVisible = false, IsRunning = false, VerticalOptions = LayoutOptions.Center, HorizontalOptions = LayoutOptions.Center };
@@ -152,10 +152,10 @@ public DefaultTestPage()
 
  ChangeLayout.Clicked += (sender, e) =>
  {
- if (tableView.ItemsLayout is CollectionViewFlatListLayout)
- tableView.ItemsLayout = new CollectionViewGridLayout(tableView);
- else
+ if (tableView.ItemsLayout is CollectionViewGridLayout)
  tableView.ItemsLayout = new CollectionViewFlatListLayout(tableView);
+ else
+ tableView.ItemsLayout = new CollectionViewGridLayout(tableView);
  tableView.ReMeasure();
  };
 

MauiUICollectionView/Layouts/CollectionViewFlatListLayout.cs

@@ -6,10 +6,26 @@ public CollectionViewFlatListLayout(MAUICollectionView collectionView) : base(co
  {
  }
 
+ #region Property or Field
+
+ /// <summary>
+ /// When jump to specify position, we use this tag tell <see cref="MeasureItems"/> if remeasure all item.
+ /// </summary>
+ protected bool isScrollingTo = false;
+
+ /// <summary>
+ /// store bounds of items at start in list.
+ /// </summary>
+ protected List<Rect> StartBoundsCache = new List<Rect> { };
+
+ #endregion
+
+ #region Method
+
  protected override double MeasureItems(double top, Rect inRect, Rect visibleRect, Dictionary<NSIndexPath, MAUICollectionViewViewHolder> availablePreparedItems)
  {
  if (CollectionView.IsScrolling &&
- isScrollToDirectly == false &&
+ isScrollingTo == false &&
  !HasOperation)
  {
  //MeasureItemsWhenScroll(inRect, availablePreparedItems);
@@ -18,8 +34,8 @@ protected override double MeasureItems(double top, Rect inRect, Rect visibleRect
  else
  {
  MeasureItems(top, inRect, availablePreparedItems);
- if (isScrollToDirectly)
- isScrollToDirectly = false;
+ if (isScrollingTo)
+ isScrollingTo = false;
  if (BaseLineItemUsually != null)
  BaseLineItemUsually = null;
  }
@@ -114,7 +130,7 @@ protected virtual void MeasureItems(double top, Rect inRect, Dictionary<NSIndexP
  {
  OnLayoutChildren(inRect, new LayoutInfor()
  {
- StartItem = EstimateItem(CollectionView.ScrollY),
+ StartItem = EstimateItem(0, CollectionView.ScrollY),
  StartBounds = new Rect(0, CollectionView.ScrollY, 0, 0),
  }, availablePreparedItems, isRemeasureAll);
  }
@@ -142,9 +158,9 @@ protected virtual double EstimateAverageHeight()
  /// <summary>
  /// Estimate the item displayed when scrolling to a certain position.
  /// </summary>
- /// <param name="scrollY"></param>
+ /// <param name="y"></param>
  /// <returns></returns>
- protected virtual NSIndexPath EstimateItem(double scrollY)
+ protected virtual NSIndexPath EstimateItem(double x, double y)
  {
  var firstItemBounds = StartBoundsCache.First();
  double averageHeight = EstimateAverageHeight();
@@ -154,9 +170,9 @@ protected virtual NSIndexPath EstimateItem(double scrollY)
  for (var section = 0; section < numberOfSections; section++)
  {
  var rowsInSection = CollectionView.NumberOfItemsInSection(section);
- if (scrollY - firstItemBounds.Top < allHeight + rowsInSection * averageHeight)
+ if (y - firstItemBounds.Top < allHeight + rowsInSection * averageHeight)
  {
- return NSIndexPath.FromRowSection((int)((scrollY - firstItemBounds.Top - allHeight) / averageHeight), section);
+ return NSIndexPath.FromRowSection((int)((y - firstItemBounds.Top - allHeight) / averageHeight), section);
  }
  else
  {
@@ -360,17 +376,12 @@ void LayoutFromBottomToTop(LayoutInfor bottomBaselineInfor)
  }
  }
 
- /// <summary>
- /// When jump to specify position, we need this avoid use <see cref="ScrollByOffset"/>.
- /// </summary>
- bool isScrollToDirectly = false;
-
  /// <summary>
  /// Jump to specify item immediately, no animation.
  /// </summary>
  /// <param name="targetIndexPath"></param>
  /// <param name="animated"></param>
- void ScrollToItem(NSIndexPath targetIndexPath)
+ protected virtual void ScrollToItem(NSIndexPath targetIndexPath)
  {
  /*
  * Estimate position of item, and set ScrollY
@@ -384,7 +395,7 @@ void ScrollToItem(NSIndexPath targetIndexPath)
  itemsOffset += CollectionView.ItemCountInRange(lastPreparedItem.Key, targetIndexPath) * lastPreparedItem.Value.ItemBounds.Height;
  BaseLineItemUsually = new LayoutInfor()
  {
- EndBounds = new Rect(0, 0, 0, CollectionView.ScrollY + itemsOffset + CollectionView.Bounds.Height),
+ EndBounds = new Rect(0, 0, 0, CollectionView.ScrollY + itemsOffset + CollectionView.Bounds.Height), //set this item at bottom of visible area.
  EndItem = targetIndexPath
  };
  CollectionView.ScrollToAsync(0, CollectionView.ScrollY + itemsOffset, false);
@@ -402,14 +413,8 @@ void ScrollToItem(NSIndexPath targetIndexPath)
  };
  CollectionView.ScrollToAsync(0, CollectionView.ScrollY - distanceFromTargetToFirstPrepared, false);
  }
- isScrollToDirectly = true;
  }
 
- /// <summary>
- /// store bounds of items at start in list.
- /// </summary>
- protected List<Rect> StartBoundsCache = new List<Rect> { };
-
  /// <summary>
  /// this layout support go to, so item's position is not accurate sometimes, we need adjust position to fit header's position.
  /// </summary>
@@ -476,7 +481,7 @@ void FitBoundsWhenCloseHeader(LayoutInfor visibleItems)
  StartBounds = new Rect(0, targetBounds.Top, 0, 0),
  StartItem = visibleFirst
  };
- isScrollToDirectly = true;
+ isScrollingTo = true;
  CollectionView.ScrollToAsync(0, targetBounds.Top, false);
  }
  }
@@ -489,7 +494,7 @@ void FitBoundsWhenCloseHeader(LayoutInfor visibleItems)
  StartBounds = new Rect(0, targetTop, 0, 0),
  StartItem = visibleFirst
  };
- isScrollToDirectly = true;
+ isScrollingTo = true;
  CollectionView.ScrollToAsync(0, targetTop, false);
  }
  }
@@ -508,7 +513,7 @@ void FitBoundsWhenCloseHeader(LayoutInfor visibleItems)
  StartBounds = new Rect(0, StartBoundsCache[0].Top, 0, 0),
  StartItem = firstItem
  };
- isScrollToDirectly = true;
+ isScrollingTo = true;
  CollectionView.ScrollToAsync(0, StartBoundsCache[0].Top, false);
  }
  }
@@ -534,15 +539,18 @@ public override void ScrollTo(NSIndexPath indexPath, ScrollPosition scrollPositi
 
  }
  ScrollToItem(target);
+ isScrollingTo = true;
  }, 0, end);
  anim.Commit(CollectionView, "ScrollTo", 16, 250, null, (v, b) =>
  {
  ScrollToItem(indexPath);
+ isScrollingTo = true;
  });
  }
  else
  {
  ScrollToItem(indexPath);
+ isScrollingTo = true;
  }
  }
 
@@ -565,7 +573,7 @@ public override Rect RectForItem(NSIndexPath indexPath)
  var itemViewHolder = item.Value;
  if (indexPath < itemIndexPath)
  {
- var count = CollectionView.ItemCountInRange(indexPath, itemIndexPath) + 1;
+ var count = CollectionView.ItemCountInRange(indexPath, itemIndexPath) + 1;//we need get top, so total height include height of target item, so +1.
  double averageHeight = EstimateAverageHeight();
  var allItemHeight = count * averageHeight;
  return new Rect(0, itemViewHolder.ItemBounds.Top - allItemHeight, itemViewHolder.ItemBounds.Width, averageHeight);
@@ -585,5 +593,7 @@ public override Rect RectForItem(NSIndexPath indexPath)
  }
  return rect;
  }
+
+ #endregion
  }
 }