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Stick to visible content #37

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Stick to visible content #37

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25 changes: 21 additions & 4 deletions lib/sticky_headers/render.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -28,17 +28,20 @@ class RenderStickyHeader extends RenderBox
RenderStickyHeaderCallback _callback;
ScrollableState _scrollable;
bool _overlapHeaders;
bool _stickToVisibleContent;

RenderStickyHeader({
@required ScrollableState scrollable,
RenderStickyHeaderCallback callback,
bool overlapHeaders: false,
bool stickToVisibleContent: false,
RenderBox header,
RenderBox content,
}) : assert(scrollable != null),
_scrollable = scrollable,
_callback = callback,
_overlapHeaders = overlapHeaders {
_overlapHeaders = overlapHeaders,
_stickToVisibleContent = stickToVisibleContent {
if (content != null) add(content);
if (header != null) add(header);
}
Expand Down Expand Up @@ -73,6 +76,14 @@ class RenderStickyHeader extends RenderBox
markNeedsLayout();
}

set stickToVisibleContent(bool newValue) {
if (_stickToVisibleContent == newValue) {
return;
}
_stickToVisibleContent = newValue;
markNeedsLayout();
}

@override
void attach(PipelineOwner owner) {
super.attach(owner);
Expand Down Expand Up @@ -117,7 +128,7 @@ class RenderStickyHeader extends RenderBox
contentParentData.offset = new Offset(0.0, _overlapHeaders ? 0.0 : headerHeight);

// determine by how much the header should be stuck to the top
final double stuckOffset = determineStuckOffset();
final double stuckOffset = determineStuckOffset(height);

// place header over content relative to scroll offset
final double maxOffset = height - headerHeight;
Expand All @@ -131,11 +142,17 @@ class RenderStickyHeader extends RenderBox
}
}

double determineStuckOffset() {
double determineStuckOffset(double height) {
final scrollBox = _scrollable.context.findRenderObject();
if (scrollBox?.attached ?? false) {
try {
return localToGlobal(Offset.zero, ancestor: scrollBox).dy;
double scrollOffset = localToGlobal(Offset.zero, ancestor: scrollBox).dy;

if (_stickToVisibleContent && scrollBox is RenderRepaintBoundary) {
scrollOffset = max(scrollOffset, scrollBox.constraints.maxHeight - height);
}

return scrollOffset;
} catch (e) {
// ignore and fall-through and return 0.0
}
Expand Down
13 changes: 12 additions & 1 deletion lib/sticky_headers/widget.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@ class StickyHeader extends MultiChildRenderObjectWidget {
@required this.header,
@required this.content,
this.overlapHeaders: false,
this.stickToVisibleContent: false,
this.callback,
}) : super(
key: key,
Expand All @@ -50,6 +51,9 @@ class StickyHeader extends MultiChildRenderObjectWidget {
/// If true, the header will overlap the Content.
final bool overlapHeaders;

/// If true, the header starts scrolling once the bottom of the content is visible.
final bool stickToVisibleContent;

/// Optional callback with stickyness value. If you think you need this, then you might want to
/// consider using [StickyHeaderBuilder] instead.
final RenderStickyHeaderCallback callback;
Expand All @@ -62,6 +66,7 @@ class StickyHeader extends MultiChildRenderObjectWidget {
scrollable: scrollable,
callback: this.callback,
overlapHeaders: this.overlapHeaders,
stickToVisibleContent: this.stickToVisibleContent,
);
}

Expand All @@ -70,7 +75,8 @@ class StickyHeader extends MultiChildRenderObjectWidget {
renderObject
..scrollable = Scrollable.of(context)
..callback = this.callback
..overlapHeaders = this.overlapHeaders;
..overlapHeaders = this.overlapHeaders
..stickToVisibleContent = this.stickToVisibleContent;
}
}

Expand All @@ -88,6 +94,7 @@ class StickyHeaderBuilder extends StatefulWidget {
@required this.builder,
this.content,
this.overlapHeaders: false,
this.stickToVisibleContent: false,
}) : super(key: key);

/// Called when the sticky amount changes for the header.
Expand All @@ -100,6 +107,9 @@ class StickyHeaderBuilder extends StatefulWidget {
/// If true, the header will overlap the Content.
final bool overlapHeaders;

/// If true, the header starts scrolling once the bottom of the content is visible.
final bool stickToVisibleContent;

@override
_StickyHeaderBuilderState createState() => new _StickyHeaderBuilderState();
}
Expand All @@ -111,6 +121,7 @@ class _StickyHeaderBuilderState extends State<StickyHeaderBuilder> {
Widget build(BuildContext context) {
return new StickyHeader(
overlapHeaders: widget.overlapHeaders,
stickToVisibleContent: widget.stickToVisibleContent,
header: new LayoutBuilder(
builder: (context, _) => widget.builder(context, _stuckAmount ?? 0.0),
),
Expand Down