Introduction

Lima is a Swift package for simplifying development of UIKit-based iOS applications. The project's name comes from the nautical L or Lima flag, representing the first letter of the word "layout":

For example, the following code creates an instance of Lima's LMColumnView class containing an image view and a label:

let columnView = LMColumnView(
    UIImageView(image: UIImage(named: "world.png"), contentMode: .scaleAspectFit),
    UILabel(text: "Hello, World!", textAlignment: .center)
)

The result is shown below:

The complete source code for this example can be found here.

Lima requires iOS 16 or later.

Lima Classes

Auto layout in UIKit is implemented via layout constraints, which, while powerful, are not particularly convenient to work with. To simplify the process, Lima provides a set of view classes whose sole responsibility is managing the size and position of their respective subviews. These classes use layout constraints internally, allowing developers to easily take advantage of auto layout while eliminating the need to manage constraints directly:

• LMRowView - arranges subviews in a horizontal line, optionally aligning to baseline
• LMColumnView - arranges subviews in a vertical line, optionally aligning nested elements to a grid
• LMAnchorView - anchors subviews to one or more edges

Additionally, the LMSpacer class can be used to create fixed or flexible space between other views.

Lima adds the following properties to UIView to control how subviews are sized and positioned by a layout view:

• width - assigns a fixed width to a view
• height - assigns a fixed height to a view
• weight - when used with row and column views, determines how excess space is allocated within the parent
• anchor - when used with anchor views, determines the edges to which the view will be anchored within the parent

Lima also provides the following classes to simplify the use of some common UIKit types:

• LMScrollView - extends UIScrollView to automatically adapt to content size
• LMTableViewCell - extends UITableViewCell to automatically pin content to edges
• LMTableViewHeaderFooterView - extends UITableViewHeaderFooterView to automatically pin content to edges

Finally, Lima adds initializers to common UIKit views and controls to simplify their declaration in a view hieararchy. These initializers support callbacks that can be used to further customize the instantiated views and are discussed in more detail later.

LMRowView and LMColumnView

The LMRowView and LMColumnView classes arrange subviews in a horizontal or vertical line, respectively. Both classes extend the abstract LMBoxView class, which defines the following properties:

• horizontalAlignment
• verticalAlignment
• spacing

Horizontal alignment options include fill, leading, trailing, and center. Vertical alignment options include fill, top, bottom, and center. Both values are set to fill by default, which pins subviews along both axes. Other values pin subviews to a single edge or center them along a given axis:

The spacing property defines the amount of space reserved between subviews. For row views, this refers to the horizontal space between the subviews; for column views, it refers to the vertical space. If unspecified, a default (system-dependent) value is used.

Baseline Alignment

The isAlignToBaseline property enables baseline alignment in a row view. When this property is set to true, subviews are aligned to their respective baselines. For example:

Grid Alignment

The isAlignToGrid property enables grid alignment in a column view. When this property is set to true, the subviews of every LMRowView in the column are vertically aligned in a grid, as in a spreadsheet or HTML table. For example:

View Weights

Often, a row or column view will be given more space than it needs to accommodate the intrinsic sizes of its subviews. The weight property can be used to specify the amount of excess space that should be allocated to a subview, relative to other weighted subviews. For row views, weights apply to the excess horizontal space, and for column views to the excess vertical space.

Note that explicitly defined width and height values take priority over weights. If a view has both a weight and a fixed dimension, the weight value will be ignored.

LMAnchorView

The LMAnchorView class optionally anchors subviews to one or more of its own edges. Anchors are specified as an option set that defines the edges to which the view will be anchored within the parent. For example:

If no anchor is specified for a given dimension, the subview will be centered within the parent for that dimension.

LMSpacer

The LMSpacer class has a default weight of 1 and is typically used to create flexible space between other views. However, the width and height properties can be used to assign a fixed size to a spacer view. For example, this code creates a half-pixel wide spacer with a gray background:

LMSpacer(width: 0.5, backgroundColor: .gray)

LMScrollView

The LMScrollView class extends UIScrollView to simplify the declaration of scrollable content. The following properties determine how the content will be presented:

• isFitToWidth
• isFitToHeight

When both values are false (the default), the scroll view will automatically display scroll bars when needed, allowing the user to pan in both directions to see the content in its entirety.

When fitToWidth is true, the scroll view will ensure that the width of its content matches the width of its adjusted content area, causing the content to wrap and scroll in the vertical direction only. The vertical scroll bar will appear when necessary, and the horizontal scroll bar will never be shown.

When fitToHeight is true, the scroll view will ensure that the height of its content matches the height of its adjusted content area, causing the content to wrap and scroll in the horizontal direction only. The horizontal scroll bar will appear when necessary, and the vertical scroll bar will never be shown.

Setting both properties to true produces the same behavior as anchoring a subview to all sides of an LMAnchorView.

LMTableViewCell and LMTableViewHeaderFooterView

The LMTableViewCell and LMTableViewHeaderFooterView classes facilitate the declaration of custom table view content. For example:

They can also be used as the base class for custom cell and header/footer view classes. For example:

Initializer Callbacks

All Lima initializers provide a callback parameter that can be used to further customize the instantiated view. This callback is automatically invoked by the initializer before it returns.

A common use of initializer callbacks is to associate view instances with controller member variables, or "outlets". For example: