/// <summary>
/// Updates the foldings in this <see cref="FoldingManager"/> using the given new foldings.
/// This method will try to correlate new foldings with existing foldings and will attempt
/// to keep the state (<see cref="FoldingSection.IsFolded"/>) of existing foldings.
/// </summary>
/// <remarks>
/// Based on original code from: https://github.com/icsharpcode/AvalonEdit/blob/master/ICSharpCode.AvalonEdit/Folding/FoldingManager.cs
/// This custom version was created in order to fix an issue where only the first collapsed folding was preserved.
/// See: https://github.com/icsharpcode/AvalonEdit/issues/86
/// </remarks>
public static void UpdateFoldings(this FoldingManager manager, IEnumerable <NewFolding> newFoldings)
{
if (newFoldings == null)
{
throw new ArgumentNullException(nameof(newFoldings));
}
var oldFoldings = manager.AllFoldings.ToArray();
int oldFoldingIndex = 0;
int previousStartOffset = 0;
// Merge new foldings into old foldings so that sections keep being collapsed.
// Both oldFoldings and newFoldings are sorted by start offset.
foreach (var newFolding in newFoldings)
{
// ensure newFoldings are sorted correctly
if (newFolding.StartOffset < previousStartOffset)
{
throw new ArgumentException(nameof(newFoldings) + " must be sorted by start offset");
}
previousStartOffset = newFolding.StartOffset;
if (newFolding.StartOffset == newFolding.EndOffset)
{
continue; // ignore zero-length foldings
}
// Remove old foldings that were skipped.
while (oldFoldingIndex < oldFoldings.Length && newFolding.StartOffset > oldFoldings[oldFoldingIndex].StartOffset)
{
manager.RemoveFolding(oldFoldings[oldFoldingIndex++]);
}
// Reuse current folding if its matching.
FoldingSection section;
if (oldFoldingIndex < oldFoldings.Length && newFolding.StartOffset == oldFoldings[oldFoldingIndex].StartOffset)
{
section = oldFoldings[oldFoldingIndex++];
section.Length = newFolding.EndOffset - newFolding.StartOffset;
}
else
{
// No matching current folding; create a new one.
section = manager.CreateFolding(newFolding.StartOffset, newFolding.EndOffset);
section.IsFolded = newFolding.DefaultClosed;
section.Tag = newFolding;
}
section.Title = newFolding.Name;
}
// Remove all outstanding old foldings.
while (oldFoldingIndex < oldFoldings.Length)
{
var oldSection = oldFoldings[oldFoldingIndex++];
manager.RemoveFolding(oldSection);
}
}