Layout API Sizing
The easiest way to understand the compound dimension types in the Layout API is to see all the units in relation to one another.
ASDimension is essentially a normal CGFloat with support for representing either a point value, a relative percentage value, or an auto value.
This unit allows the same API to take in both fixed values, as well as relative ones.
// dimension returned is relative (%) ASDimensionMake(@"50%"); ASDimensionMakeWithFraction(0.5); // dimension returned in points ASDimensionMake(@"70pt"); ASDimensionMake(70); ASDimensionMakeWithPoints(70);
ASDimension is used to set the
flexBasis property on a child of an
flexBasis property specifies an object’s initial size in the stack dimension, where the stack dimension is whether it is a horizontal or vertical stack.
In the following view, we want the left stack to occupy
40% of the horizontal width and the right stack to occupy
60% of the width.
We do this by setting the
.flexBasis property on the two childen of the horizontal stack:
self.leftStack.style.flexBasis = ASDimensionMake(@"40%"); self.rightStack.style.flexBasis = ASDimensionMake(@"60%"); [horizontalStack setChildren:@[self.leftStack, self.rightStack]];
ASLayoutSize is similar to a
CGSize, but its width and height values may represent either a point or percent value. The type of the width and height are independent; either one may be a point or percent value.
ASLayoutSize is used for setting a layout element’s
.maxLayoutSize properties. It allows the same API to take in both fixed sizes, as well as relative ones.
// Dimension type "Auto" indicates that the layout element may // be resolved in whatever way makes most sense given the circumstances ASDimension width = ASDimensionMake(ASDimensionUnitAuto, 0); ASDimension height = ASDimensionMake(@"50%"); layoutElement.style.preferredLayoutSize = ASLayoutSizeMake(width, height);
If you do not need relative values, you can set the layout element’s
.maxSize properties. The properties take regular
Most of the time, you won’t want to constrain both width and height. In these cases, you can individually set a layout element’s size properties using
layoutElement.style.width = ASDimensionMake(@"50%"); layoutElement.style.minWidth = ASDimensionMake(@"50%"); layoutElement.style.maxWidth = ASDimensionMake(@"50%"); layoutElement.style.height = ASDimensionMake(@"50%"); layoutElement.style.minHeight = ASDimensionMake(@"50%"); layoutElement.style.maxHeight = ASDimensionMake(@"50%");
Size Range (
UIKit doesn’t provide a structure to bundle a minimum and maximum
ASSizeRange was created to support a minimum and maximum CGSize pair.
ASSizeRange is used mostly in the internals of the layout API. However, the
constrainedSize value passed as an input to
layoutSpecThatFits: is an
constrainedSize passed to an
layoutSpecThatFits: method is the minimum and maximum sizes that the node should fit in. The minimum and maximum
CGSizes contained in
constrainedSize can be used to size the node’s layout elements.