private void LayoutSectionHeader(Dictionary <string, LayoutInfo> layoutInfos, int section, ref CGRect frame)
{
if (ScrollDirection == ListViewBaseScrollDirection.Horizontal)
{
throw new NotImplementedException("The section header for a horizontal listview is not implemented.");
}
var createLayoutInfo = layoutInfos != null;
if (section > 0)
{
frame.Y += IntersectionSpacing;
}
var sectionHeaderSize = GetSectionHeaderSize();
frame.Height = sectionHeaderSize.Height;
if (createLayoutInfo)
{
var sectionHeaderLayoutInfo = layoutInfos.FindOrCreate(ListViewBase.ListViewSectionHeaderElementKind, () => new LayoutInfo());
//indexPath acts to uniquely identify this instance of ListViewSectionHeaderElementKind (one per section)
var indexPath = NSIndexPath.FromRowSection(0, section);
var layoutAttributes = UICollectionViewLayoutAttributes.
CreateForSupplementaryView <UICollectionViewLayoutAttributes>(ListViewBase.ListViewSectionHeaderElementKindNS, indexPath);
layoutAttributes.Frame = new CGRect(Margin.Left, frame.Y, frame.Width, sectionHeaderSize.Height);
sectionHeaderLayoutInfo[indexPath] = layoutAttributes;
}
frame.Y += frame.Height + LineSpacing;
}
public override UICollectionViewLayoutAttributes LayoutAttributesForSupplementaryView(NSString kind, NSIndexPath indexPath)
{
var attrs = UICollectionViewLayoutAttributes.CreateForSupplementaryView(kind, indexPath);
attrs.Frame = new CGRect(0, 0, CollectionView.Frame.Width, Header.HeightRequest);
return(attrs);
}
/// <summary>
/// Adjusts the size of the frame by calculating the required space of the footer.
/// </summary>
private void LayoutFooter(Dictionary <string, LayoutInfo> layoutInfos, ref CGRect frame)
{
if (ScrollDirection == ListViewBaseScrollDirection.Horizontal)
{
throw new NotImplementedException("The footer for an horizontal listview is not implemented.");
}
var createLayoutInfo = layoutInfos != null;
var footerSize = GetFooterSize();
frame.Height = footerSize.Height;
if (createLayoutInfo)
{
var footerLayoutInfo = new LayoutInfo();
var indexPath = NSIndexPath.FromRowSection(0, 0);
var layoutAttributes = UICollectionViewLayoutAttributes.CreateForSupplementaryView <UICollectionViewLayoutAttributes>(ListViewBase.ListViewFooterElementKindNS, indexPath);
layoutAttributes.Frame = new CGRect(Margin.Left, frame.Y, frame.Width, footerSize.Height);
footerLayoutInfo[indexPath] = layoutAttributes;
layoutInfos[ListViewBase.ListViewFooterElementKind] = footerLayoutInfo;
}
frame.Y += frame.Height + LineSpacing;
}
/// <summary>
/// Adjusts the size of the frame by calculating the required space of the header.
/// </summary>
private void LayoutHeader(Dictionary <string, LayoutInfo> layoutInfos, ref CGRect frame)
{
if (ScrollDirection == ListViewBaseScrollDirection.Horizontal)
{
throw new NotImplementedException("The header for an horizontal listview is not implemented.");
}
var createLayoutInfo = layoutInfos != null;
var headerSize = GetHeaderSize();
frame.Height = headerSize.Height;
if (createLayoutInfo)
{
var headerLayoutInfo = new LayoutInfo();
//"It is up to you to decide how to use the indexPath parameter to identify a given supplementary view. Typically, you use the elementKind parameter to identify the type
//of the supplementary view and the indexPath information to distinguish between different instances of that view."
//https://developer.apple.com/library/ios/documentation/UIKit/Reference/UICollectionViewLayoutAttributes_class/#//apple_ref/occ/clm/UICollectionViewLayoutAttributes/layoutAttributesForSupplementaryViewOfKind:withIndexPath:
var indexPath = NSIndexPath.FromRowSection(0, 0);
var layoutAttributes = UICollectionViewLayoutAttributes.CreateForSupplementaryView <UICollectionViewLayoutAttributes>(ListViewBase.ListViewHeaderElementKindNS, indexPath);
layoutAttributes.Frame = new CGRect(Margin.Left, frame.Y, frame.Width, headerSize.Height);
headerLayoutInfo[indexPath] = layoutAttributes;
layoutInfos[ListViewBase.ListViewHeaderElementKind] = headerLayoutInfo;
}
frame.Y += frame.Height + LineSpacing;
}
private void CreateSectionHeaderLayoutInfo(Dictionary <NSIndexPath, UICollectionViewLayoutAttributes> headerLayoutInfo, int section, CGRect sectionHeaderFrame)
{
var indexPath = GetNSIndexPathFromRowSection(0, section);
var layoutAttributes = UICollectionViewLayoutAttributes
.CreateForSupplementaryView <UICollectionViewLayoutAttributes>(ListViewBase.ListViewSectionHeaderElementKindNS, indexPath);
layoutAttributes.Frame = sectionHeaderFrame;
headerLayoutInfo[indexPath] = layoutAttributes;
_inlineHeaderFrames[section] = sectionHeaderFrame;
}
public override UICollectionViewLayoutAttributes LayoutAttributesForSupplementaryView(NSString kind, NSIndexPath indexPath)
{
if (Forms.IsiOS11OrNewer)
{
return(base.LayoutAttributesForSupplementaryView(kind, indexPath));
}
// iOS 10 and lower doesn't create these and will throw an exception in GetViewForSupplementaryElement
// without them, so we need to do it manually here
return(UICollectionViewLayoutAttributes.CreateForSupplementaryView(kind, indexPath));
}
public override void PrepareLayout()
{
if (_cache.Count > 0 || CollectionView == null)
{
return;
}
_contentHeight = 0;
var columnWidth = (float)CollectionView.Frame.Width / ColumnCount;
var xOffsets = new List <float>();
var yOffsets = new List <float>();
for (var i = 0; i < ColumnCount; i++)
{
xOffsets.Add(i * columnWidth);
yOffsets.Add(0);
}
if (Header != null)
{
var indexPath = NSIndexPath.FromRowSection(0, 0);
var frame = new CGRect(0, 0, CollectionView.Frame.Width, Header.HeightRequest);
var attrs = UICollectionViewLayoutAttributes.CreateForSupplementaryView(UICollectionElementKindSection.Header, indexPath);
attrs.Frame = frame;
_cache.Add(attrs);
for (var i = 0; i < ColumnCount; i++)
{
yOffsets[i] = (float)frame.Height;
}
}
var column = 0;
for (var r = 0; r < ItemsSource.Count; r++)
{
var isHeader = HeaderIndexes.Contains(r);
var width = columnWidth;
double cellHeight;
if (GetHeightForCellDelegate != null)
{
cellHeight = GetHeightForCellDelegate(ItemsSource[r]);
}
else
{
cellHeight = new Random().Next((int)MinCellHeight, (int)MaxCellHeight);
}
var y = yOffsets[column];
if (isHeader) // HEADER
{
width = (float)CollectionView.Frame.Width;
cellHeight = HeaderTemplateHeight;
y = (float)_contentHeight;
column = 0;
}
var indexPath = NSIndexPath.FromRowSection(r, 0);
var frame = new CGRect(xOffsets[column], y, width, cellHeight);
var attrs = UICollectionViewLayoutAttributes.CreateForCell(indexPath);
attrs.Frame = frame;
_contentHeight = Math.Max((float)_contentHeight, (float)frame.GetMaxY());
if (isHeader)
{
for (var i = 0; i < ColumnCount; i++)
{
yOffsets[i] = (float)_contentHeight;
}
column = 0;
}
else
{
yOffsets[column] = (float)(yOffsets[column] + cellHeight);
column = column == ColumnCount - 1 ? 0 : column + 1;
}
_cache.Add(attrs);
}
}
public override void PrepareLayout()
{
base.PrepareLayout();
// Get the number of sections
var numberofSections = CollectionView.NumberOfSections();
if (numberofSections == 0)
{
return;
}
// Reset collections
_headersAttributes.Clear();
_footersAttributes.Clear();
_unionRects.Clear();
_columnHeights.Clear();
_allItemAttributes.Clear();
_sectionItemAttributes.Clear();
// Initialize column heights
for (int n = 0; n < ColumnCount; n++)
{
_columnHeights.Add((nfloat)0);
}
// Process all sections
nfloat top = 0.0f;
var attributes = new UICollectionViewLayoutAttributes();
var columnIndex = 0;
for (nint section = 0; section < numberofSections; ++section)
{
// Calculate section specific metrics
var minimumInterItemSpacing = (MinimumInterItemSpacingForSection == null) ? MinimumColumnSpacing :
MinimumInterItemSpacingForSection(CollectionView, this, section);
// Calculate widths
var width = CollectionView.Bounds.Width - SectionInset.Left - SectionInset.Right;
var itemWidth = (nfloat)Math.Floor((width - ((ColumnCount - 1) * MinimumColumnSpacing)) / ColumnCount);
// Calculate section header
var heightHeader = (HeightForHeader == null) ? HeaderHeight :
HeightForHeader(CollectionView, this, section);
if (heightHeader > 0)
{
attributes = UICollectionViewLayoutAttributes.CreateForSupplementaryView(UICollectionElementKindSection.Header, NSIndexPath.FromRowSection(0, section));
attributes.Frame = new CGRect(0, top, CollectionView.Bounds.Width, heightHeader);
_headersAttributes.Add(section, attributes);
_allItemAttributes.Add(attributes);
top = attributes.Frame.GetMaxY();
}
top += SectionInset.Top;
for (int n = 0; n < ColumnCount; n++)
{
_columnHeights [n] = top;
}
// Calculate Section Items
var itemCount = CollectionView.NumberOfItemsInSection(section);
List <UICollectionViewLayoutAttributes> itemAttributes = new List <UICollectionViewLayoutAttributes> ();
for (nint n = 0; n < itemCount; n++)
{
var indexPath = NSIndexPath.FromRowSection(n, section);
columnIndex = NextColumnIndexForItem(n);
var xOffset = SectionInset.Left + (itemWidth + MinimumColumnSpacing) * (nfloat)columnIndex;
var yOffset = _columnHeights [columnIndex];
var itemSize = (SizeForItem == null) ? new CGSize(0, 0) : SizeForItem(CollectionView, this, indexPath);
nfloat itemHeight = 0.0f;
if (itemSize.Height > 0.0f && itemSize.Width > 0.0f)
{
itemHeight = (nfloat)Math.Floor(itemSize.Height * itemWidth / itemSize.Width);
}
attributes = UICollectionViewLayoutAttributes.CreateForCell(indexPath);
attributes.Frame = new CGRect(xOffset, yOffset, itemWidth, itemHeight);
itemAttributes.Add(attributes);
_allItemAttributes.Add(attributes);
_columnHeights [columnIndex] = attributes.Frame.GetMaxY() + MinimumInterItemSpacing;
}
_sectionItemAttributes.Add(itemAttributes);
// Calculate Section Footer
nfloat footerHeight = 0.0f;
columnIndex = LongestColumnIndex();
top = _columnHeights [columnIndex] - MinimumInterItemSpacing + SectionInset.Bottom;
footerHeight = (HeightForFooter == null) ? FooterHeight : HeightForFooter(CollectionView, this, section);
if (footerHeight > 0)
{
attributes = UICollectionViewLayoutAttributes.CreateForSupplementaryView(UICollectionElementKindSection.Footer, NSIndexPath.FromRowSection(0, section));
attributes.Frame = new CGRect(0, top, CollectionView.Bounds.Width, footerHeight);
_footersAttributes.Add(section, attributes);
_allItemAttributes.Add(attributes);
top = attributes.Frame.GetMaxY();
}
for (int n = 0; n < ColumnCount; n++)
{
_columnHeights [n] = top;
}
}
var i = 0;
var attrs = _allItemAttributes.Count;
while (i < attrs)
{
var rect1 = _allItemAttributes [i].Frame;
i = (int)Math.Min(i + _unionSize, attrs) - 1;
var rect2 = _allItemAttributes [i].Frame;
_unionRects.Add(CGRect.Union(rect1, rect2));
i++;
}
}
public override void PrepareLayout()
{
if (_cache.IsNullOrEmpty())
{
var cellSizes = new CGSize[CollectionView.NumberOfItemsInSection(0)];
for (int index = 0; index < cellSizes.Length; index++)
{
var indexPath = NSIndexPath.FromRowSection(index, 0);
var cellSize = Delegate?.SizeForCellAtIndexPath(CollectionView, indexPath) ?? CGSize.Empty;
cellSizes[index] = cellSize;
}
var column = 0;
var yOffset = new nfloat[NumberOfColumns];
var supplementaryAttr = UICollectionViewLayoutAttributes.CreateForSupplementaryView(UICollectionElementKindSection.Header, NSIndexPath.FromRowSection(0, 0));
supplementaryAttr.Frame = new CGRect(CGPoint.Empty, HeaderReferenceSize);
_cache.Add(supplementaryAttr);
//add begin Y offset to each column
for (int i = 0; i < NumberOfColumns; i++)
{
yOffset[i] = HeaderReferenceSize.Height == 0 ? 0 : HeaderReferenceSize.Height + MinimumLineSpacing / 2;
}
var previousCellPoint = CGPoint.Empty;
for (int index = 0; index < CollectionView.NumberOfItemsInSection(0); index++)
{
CGSize previousCellSize = index == 0 ? CGSize.Empty : cellSizes[index - 1];
CGSize currentCellSize = cellSizes[index];
var width = currentCellSize.Width + (MinimumInteritemSpacing * 2);
var height = currentCellSize.Height + MinimumLineSpacing;
//check that width of next cell in column [1; NumberOfColumns) does not go beyond the borders of content width
var previuosCellsWidth = previousCellPoint.X + previousCellSize.Width + MinimumInteritemSpacing;
if (column != 0 && previuosCellsWidth + width > ContentWidth)
{
//add Y offset to current column
yOffset[column] = yOffset[column] + height;
//switch column number to zero
column = 0;
previousCellPoint = CGPoint.Empty;
}
//get cell real frame
var frame = new CGRect(column == 0 ? 0 : previuosCellsWidth, yOffset[column], width, height + MinimumLineSpacing);
var insetFrame = frame.Inset(MinimumInteritemSpacing, MinimumLineSpacing);
//get cell atribute for frame
var indexPath = NSIndexPath.FromRowSection(index, 0);
var attributes = UICollectionViewLayoutAttributes.CreateForCell(indexPath);
attributes.Frame = insetFrame;
//add attribute to cache
_cache.Add(attributes);
//update content height
_contentHeight = (nfloat)Math.Max(_contentHeight, frame.Bottom);
//add Y offset to column
yOffset[column] = yOffset[column] + height;
//save previous cell point
previousCellPoint = column >= (NumberOfColumns - 1) ? CGPoint.Empty : new CGPoint(insetFrame.X, insetFrame.Y);
//increment column number
column = column >= (NumberOfColumns - 1) ? 0 : ++column;
}
}
}
