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Improve support for variable-sized items.

pull/9677/head
Steven Kirk 4 years ago
parent
67d200c100
commit
14df77a897
1 changed files with 78 additions and 41 deletions
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  1. 119
      src/Avalonia.Controls/VirtualizingStackPanel.cs

119
src/Avalonia.Controls/VirtualizingStackPanel.cs
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@ -92,7 +92,7 @@ namespace Avalonia.Controls
// Recycle elements outside of the expected range.
_realizedElements.RecycleElementsBefore(viewport.firstIndex, _recycleElement);
_realizedElements.RecycleElementsAfter(viewport.estimatedLastIndex, _recycleElement);
_realizedElements.RecycleElementsAfter(viewport.lastIndex, _recycleElement);
// Do the measure, creating/recycling elements as necessary to fill the viewport. Don't
// write to _realizedElements yet, only _measureElements.
@ -307,8 +307,8 @@ namespace Avalonia.Controls
var viewportStart = Orientation == Orientation.Horizontal ? viewport.X : viewport.Y;
var viewportEnd = Orientation == Orientation.Horizontal ? viewport.Right : viewport.Bottom;
var (firstIndex, firstIndexU) = _realizedElements!.GetElementAt(viewportStart);
var (lastIndex, _) = _realizedElements.GetElementAt(viewportEnd);
var (firstIndex, firstIndexU) = _realizedElements.GetModelIndexAt(viewportStart);
var (lastIndex, _) = _realizedElements.GetModelIndexAt(viewportEnd);
var estimatedElementSize = -1.0;
var itemCount = items?.Count ?? 0;
@ -329,7 +329,7 @@ namespace Avalonia.Controls
return new MeasureViewport
{
firstIndex = MathUtilities.Clamp(firstIndex, 0, itemCount - 1),
estimatedLastIndex = MathUtilities.Clamp(lastIndex, 0, itemCount - 1),
lastIndex = MathUtilities.Clamp(lastIndex, 0, itemCount - 1),
viewportUStart = viewportStart,
viewportUEnd = viewportEnd,
startU = firstIndexU,
@ -353,23 +353,9 @@ namespace Avalonia.Controls
if (_realizedElements is null)
return _lastEstimatedElementSizeU;
var count = _realizedElements.Count;
var divisor = 0.0;
var total = 0.0;
for (var i = 0; i < count; ++i)
{
if (_realizedElements.Elements[i] is object)
{
total += _realizedElements.SizeU[i];
++divisor;
}
}
if (divisor == 0 || total == 0)
return _lastEstimatedElementSizeU;
_lastEstimatedElementSizeU = total / divisor;
var result = _realizedElements.EstimateElementSizeU();
if (result >= 0)
_lastEstimatedElementSizeU = result;
return _lastEstimatedElementSizeU;
}
@ -409,6 +395,10 @@ namespace Avalonia.Controls
var index = viewport.firstIndex;
var u = viewport.startU;
// The layout is likely invalid. Don't create any elements and instead rely on our previous
// element size estimates to calculate a new desired size and trigger a new layout pass.
if (index >= items.Count)
return;
do
{
var e = GetOrCreateElement(items, index);
@ -587,6 +577,7 @@ namespace Avalonia.Controls
private List<Control?>? _elements;
private List<double>? _sizes;
private double _startU;
private bool _startUUnstable;
/// <summary>
/// Gets the number of realized elements.
@ -671,6 +662,38 @@ namespace Avalonia.Controls
return null;
}
/// <summary>
/// Gets the model index and start U position of the element at the specified U position.
/// </summary>
/// <param name="u">The U position.</param>
/// <returns>
/// A tuple containing:
/// - The index of the item at the specified U position, or -1 if the item could not be
/// determined
/// - The U position of the start of the item, if determined
/// </returns>
public (int index, double position) GetModelIndexAt(double u)
{
if (_elements is null || _sizes is null || _startU > u || _startUUnstable)
return (-1, 0);
var index = 0;
var position = _startU;
while (index < _elements.Count)
{
var size = _sizes[index];
if (double.IsNaN(size))
break;
if (u >= position && u < position + size)
return (index + FirstModelIndex, position);
position += size;
++index;
}
return (-1, 0);
}
/// <summary>
/// Gets the element at the specified position on the primary axis, if realized.
/// </summary>
@ -700,33 +723,42 @@ namespace Avalonia.Controls
}
/// <summary>
/// Gets the position of an element on the primary axis, if realized.
/// Estimates the average U size of all elements in the source collection based on the
/// realized elements.
/// </summary>
/// <param name="modelIndex">The index in the source collection of the element.</param>
/// <param name="position">
/// When the method exits, contains the element's position on the primary axis, if
/// the element is realized.
/// </param>
/// <returns>
/// True if the requested element was found, otherwise false.
/// The estimated U size of an element, or -1 if not enough information is present to make
/// an estimate.
/// </returns>
public bool TryGetElementU(int modelIndex, out double position)
public double EstimateElementSizeU()
{
if (_sizes is null || modelIndex < FirstModelIndex || modelIndex > LastModelIndex)
var total = 0.0;
var divisor = 0.0;
// Start by averaging the size of the elements before the first realized element.
if (FirstModelIndex >= 0 && !_startUUnstable)
{
position = double.NaN;
return false;
total += _startU;
divisor += FirstModelIndex;
}
var index = modelIndex - FirstModelIndex;
position = StartU;
for (var i = 0; i < index; ++i)
// Average the size of the realized elements.
if (_sizes is not null)
{
position += _sizes[i];
foreach (var size in _sizes)
{
if (double.IsNaN(size))
continue;
total += size;
++divisor;
}
}
return true;
// We don't have any elements on which to base our estimate.
if (divisor == 0 || total == 0)
return -1;
return total / divisor;
}
/// <summary>
@ -781,7 +813,7 @@ namespace Avalonia.Controls
// The insertion point was within the realized elements, insert an empty space
// in _elements and _sizes.
_elements!.InsertMany(index, null, count);
_sizes!.InsertMany(index, 0.0, count);
_sizes!.InsertMany(index, double.NaN, count);
}
}
}
@ -840,9 +872,13 @@ namespace Avalonia.Controls
_sizes!.RemoveRange(start, end - start);
// If the remove started before and ended within our realized elements, then our new
// first index will be the index where the remove started.
// first index will be the index where the remove started. Mark StartU as unstable
// because we can't rely on it now to estimate element heights.
if (startIndex <= 0 && end < last)
{
_firstIndex = first = modelIndex;
_startUUnstable = true;
}
// Update the indexes of the elements after the removed range.
end = _elements.Count;
@ -942,6 +978,7 @@ namespace Avalonia.Controls
public void ResetForReuse()
{
_startU = _firstIndex = 0;
_startUUnstable = false;
_elements?.Clear();
_sizes?.Clear();
}
@ -950,7 +987,7 @@ namespace Avalonia.Controls
private struct MeasureViewport
{
public int firstIndex;
public int estimatedLastIndex;
public int lastIndex;
public double viewportUStart;
public double viewportUEnd;
public double measuredV;

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