public ScrollToCodeGallery(IItemsLayout itemsLayout, ScrollToMode mode = ScrollToMode.Position, Func <DataTemplate> dataTemplate = null, Func <CollectionView> createCollectionView = null)
{
createCollectionView = createCollectionView ?? (() => new CollectionView());
Title = $"ScrollTo (Code, {itemsLayout})";
var layout = new Grid
{
RowDefinitions = new RowDefinitionCollection
{
new RowDefinition {
Height = GridLength.Auto
},
new RowDefinition {
Height = GridLength.Auto
},
new RowDefinition {
Height = GridLength.Star
}
}
};
var itemTemplate = dataTemplate == null?ExampleTemplates.ScrollToIndexTemplate() : dataTemplate();
var collectionView = createCollectionView();
collectionView.ItemsLayout = itemsLayout;
collectionView.ItemTemplate = itemTemplate;
var generator = new ItemsSourceGenerator(collectionView, initialItems: 50);
layout.Children.Add(generator);
if (mode == ScrollToMode.Position)
{
var scrollToControl = new ScrollToIndexControl(collectionView);
layout.Children.Add(scrollToControl);
Grid.SetRow(scrollToControl, 1);
}
else
{
var scrollToControl = new ScrollToItemControl(collectionView);
layout.Children.Add(scrollToControl);
Grid.SetRow(scrollToControl, 1);
}
layout.Children.Add(collectionView);
Grid.SetRow(collectionView, 2);
Content = layout;
generator.GenerateItems();
}
async void OnScrollToRequested(object sender, ScrollToRequestedEventArgs e)
{
ClearRtlScrollCheck();
// Adding items into the view while scrolling to the end can cause it to fail, as
// the items have not actually been laid out and return incorrect scroll position
// values. The ScrollViewRenderer for Android does something similar by waiting up
// to 10ms for layout to occur.
int cycle = 0;
while (Element != null && !Element.IsInNativeLayout)
{
await Task.Delay(TimeSpan.FromMilliseconds(1));
cycle++;
if (cycle >= 10)
{
break;
}
}
if (Element == null)
{
return;
}
double x = e.ScrollX, y = e.ScrollY;
ScrollToMode mode = e.Mode;
if (mode == ScrollToMode.Element)
{
Point pos = Element.GetScrollPositionForElement((VisualElement)e.Element, e.Position);
x = pos.X;
y = pos.Y;
mode = ScrollToMode.Position;
}
if (mode == ScrollToMode.Position)
{
Control.ChangeView(x, y, null, !e.ShouldAnimate);
}
Element.SendScrollFinished();
}
void OnScrollToRequested(object sender, ScrollToRequestedEventArgs e)
{
double x = e.ScrollX, y = e.ScrollY;
ScrollToMode mode = e.Mode;
if (mode == ScrollToMode.Element)
{
Point pos = Controller.GetScrollPositionForElement((VisualElement)e.Element, e.Position);
x = pos.X;
y = pos.Y;
mode = ScrollToMode.Position;
}
if (mode == ScrollToMode.Position)
{
Control.ChangeView(x, y, null, !e.ShouldAnimate);
}
}
/// <summary>
/// Selects the specified row
/// </summary>
/// <param name="Index">row Index</param>
/// <param name="Animated">If set to <c>true</c> animated, default(true)</param>
/// <param name="Mode">Scroll Mode, default(None)</param>
/// <param name="AdditonalOffset">Additonal offset(default(0)</param>
public void SelectRow(int Index, bool Animated = true, ScrollToMode Mode = ScrollToMode.None, float AdditonalOffset = 0)
{
Processor.UpdateSelection(Index);
nfloat top = -1;
switch (Mode)
{
case ScrollToMode.None:
{
top = this.ContentOffset.Y;
}
break;
case ScrollToMode.Top:
{
top = Processor.TopYForRow(Index);
}
break;
case ScrollToMode.Middle:
{
top = Processor.TopYForRow(Index);
var bottomOffset = (this.Frame.Height - Processor.RowHeight) + this.Theme.HeaderHeight;
bottomOffset = (((bottomOffset - this.Frame.Top) - 20) - AdditonalOffset);
top -= ((bottomOffset / 2) - (Processor.RowHeight / 2));
}
break;
case ScrollToMode.Bottom:
{
top = Processor.TopYForRow(Index);
var bottomOffset = (this.Frame.Height - Processor.RowHeight) + this.Theme.HeaderHeight;
top -= (((bottomOffset - this.Frame.Top) - 20) - AdditonalOffset);
}
break;
}
this.ContentOffset = new CGPoint(0, top);
}
private void OnScrollToRequested(object sender, ScrollToRequestedEventArgs e)
{
double x = e.ScrollX, y = e.ScrollY;
ScrollToMode mode = e.Mode;
if (mode == ScrollToMode.Element)
{
Point pos = Controller.GetScrollPositionForElement((VisualElement)e.Element, e.Position);
x = pos.X;
y = pos.Y;
mode = ScrollToMode.Position;
}
if (mode == ScrollToMode.Position)
{
Control.Hadjustment.Value = x;
Control.Vadjustment.Value = y;
}
Controller.SendScrollFinished();
}
