showOnScreen method
- RenderObject? descendant,
- Rect? rect,
- Duration duration = Duration.zero,
- Curve curve = Curves.ease,
override
Attempt to make (a portion of) this or a descendant RenderObject visible on screen.
If descendant
is provided, that RenderObject is made visible. If
descendant
is omitted, this RenderObject is made visible.
The optional rect
parameter describes which area of that RenderObject
should be shown on screen. If rect
is null, the entire
RenderObject (as defined by its paintBounds) will be revealed. The
rect
parameter is interpreted relative to the coordinate system of
descendant
if that argument is provided and relative to this
RenderObject otherwise.
The duration
parameter can be set to a non-zero value to bring the
target object on screen in an animation defined by curve
.
See also:
- RenderViewportBase.showInViewport, which RenderViewportBase and SingleChildScrollView delegate this method to.
Implementation
@override
void showOnScreen({
RenderObject? descendant,
Rect? rect,
Duration duration = Duration.zero,
Curve curve = Curves.ease,
}) {
final PersistentHeaderShowOnScreenConfiguration? showOnScreen = showOnScreenConfiguration;
if (showOnScreen == null) {
return super.showOnScreen(descendant: descendant, rect: rect, duration: duration, curve: curve);
}
assert(child != null || descendant == null);
// We prefer the child's coordinate space (instead of the sliver's) because
// it's easier for us to convert the target rect into target extents: when
// the sliver is sitting above the leading edge (not possible with pinned
// headers), the leading edge of the sliver and the leading edge of the child
// will not be aligned. The only exception is when child is null (and thus
// descendant == null).
final Rect? childBounds = descendant != null
? MatrixUtils.transformRect(descendant.getTransformTo(child), rect ?? descendant.paintBounds)
: rect;
double targetExtent;
Rect? targetRect;
switch (applyGrowthDirectionToAxisDirection(constraints.axisDirection, constraints.growthDirection)) {
case AxisDirection.up:
targetExtent = childExtent - (childBounds?.top ?? 0);
targetRect = _trim(childBounds, bottom: childExtent);
case AxisDirection.right:
targetExtent = childBounds?.right ?? childExtent;
targetRect = _trim(childBounds, left: 0);
case AxisDirection.down:
targetExtent = childBounds?.bottom ?? childExtent;
targetRect = _trim(childBounds, top: 0);
case AxisDirection.left:
targetExtent = childExtent - (childBounds?.left ?? 0);
targetRect = _trim(childBounds, right: childExtent);
}
// A stretch header can have a bigger childExtent than maxExtent.
final double effectiveMaxExtent = math.max(childExtent, maxExtent);
targetExtent = clampDouble(
clampDouble(
targetExtent,
showOnScreen.minShowOnScreenExtent,
showOnScreen.maxShowOnScreenExtent,
),
// Clamp the value back to the valid range after applying additional
// constraints. Contracting is not allowed.
childExtent,
effectiveMaxExtent);
// Expands the header if needed, with animation.
if (targetExtent > childExtent && _controller?.status != AnimationStatus.forward) {
final double targetScrollOffset = maxExtent - targetExtent;
assert(
vsync != null,
'vsync must not be null if the floating header changes size animatedly.',
);
_updateAnimation(duration, targetScrollOffset, curve);
_controller?.forward(from: 0.0);
}
super.showOnScreen(
descendant: descendant == null ? this : child,
rect: targetRect,
duration: duration,
curve: curve,
);
}