Intercept for SwiftUI

Intercept is a collection of extensions for SwiftUI that enable subtle yet important features.

It’s meant to be used in conjuction with Introspect for SwiftUI, hence the name.

Installation

.package(url: "https://github.com/freysie/intercept.git", branch: "main"),

.product(name: "Intercept", package: "intercept"),

Overview

List Clip Inset for macOS

The listClipInset() modifier insets the list view’s clip view by the specified insets.

objc_allocateClassPair() is used under the hood for this.

List(selection: $selection) {
  // …
  // …
  // …
}
.listClipInset(EdgeInsets(top: -5, leading: 0, bottom: 0, trailing: 0))

Due to an unfortunate side effect which makes the inset jump when the list first appears, it’s recommended you hide your list, or the window containing it, for a single run loop iteration.

Alternatives Considered

Why not use a negative padding? That could sort of work, but it messes up keyboard navigation.

List Double-Clicking for macOS

The modifier onListDoubleClick() intercepts the underlying tabel view’s doubleAction target-action invocation for a macOS List.

InterceptionProxy is used under the hood for this.

List(selection: $selection) {
  // …
  // …
  // …
}
.onListDoubleClick { sender in
  print(sender.selectedRow)
}

Note: This appears to have been introduced in macOS 13 with the contextAction() modifier.

Alternatives Considered

Why not use onTapGesture(count: 2)? It doesn’t reach all the way to the edge of the rows.

List Selection Emphasis for macOS

The listSelectionEmphasized() modifier sets NSTableRowView’s isEmphasized to true.

objc_allocateClassPair() is used under the hood for this.

List(selection: $selection) {
  // …
  // …
  // …
}
.listSelectionEmphasized()

Alternatives Considered

Why not simply draw an emphasized selection yourself? That doesn’t work 100% as there’s no isSelected environment value in SwiftUI, and the selection bindings in lists are not updated while the mouse is down.

Interception Proxy

InterceptionProxy is like a meddler-in-the-middle attack for Swift and Objective-C.

It’s an NSProxy subclass which allows you to override the behavior of existing methods.

Since NSInvocation and its related APIs are unavailable in Swift, the proxy is implemented in Objective-C.

- (void)forwardInvocation:(NSInvocation *)invocation {
  NSAssert(self.middleDelegate != self.originalDelegate, @"delegates should be unique");
  
  if ([self.middleDelegate respondsToSelector:invocation.selector]) {
    [invocation invokeWithTarget:self.middleDelegate];
  } else if ([self.originalDelegate respondsToSelector:invocation.selector]) {
    [invocation invokeWithTarget:self.originalDelegate];
  }
}

- (nullable NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
  id result = [self.middleDelegate methodSignatureForSelector:sel];

  if (!result) {
    result = [self.originalDelegate methodSignatureForSelector:sel];
  }

  return result;
}