[Dialogs] Adding accessoryViewHorizontalInset API

The API allows setting horizontal insets for the accessory view that are different from the message. This is most often used for dialogs that have both a message and an accessory view, as demonstrated in the attached example.

Additionally, this example demonstrates how to add an horizontal hairline as shown on the material.io spec for Confirmation Dialogs.

Note:
This new API is needed because clients do not always have control over the view that is being used as an accessory view, or that the view is used in multiple areas in the app, and cannot be customized.
Additionally, there's no way currently to set 0 insets for the accessory view, while still keeping the 24 value insets for the message, which is a relatively common scenario.
PiperOrigin-RevId: 334142026

components/Dialogs/examples/DialogsAccessoryExampleViewController.swift

@@ -140,7 +140,7 @@ class DialogsAccessoryExampleViewController: MDCCollectionViewController {
     return alert
   }
 
-  // Demonstrate a confirmation dialog with a custom table view.d
+  // Demonstrate a confirmation dialog with a custom table view.
   func performConfirmationDialog() -> MDCAlertController {
     let alert = MDCAlertController(title: "Phone ringtone", message: "Please select a ringtone:")
     alert.addAction(MDCAlertAction(title: "OK", handler: handler))
@@ -153,6 +153,8 @@ class DialogsAccessoryExampleViewController: MDCCollectionViewController {
       alertView.contentInsets.bottom = 0
       // Decreasing vertical margin between the accessory view and the message
       alertView.accessoryViewVerticalInset = 8
+      // Aligning the accessory view with the dialog's edge by removing all horizontal insets.
+      alertView.accessoryViewHorizontalInset = -alertView.contentInsets.left
     }
 
     alert.mdc_adjustsFontForContentSizeCategory = true  // Enable dynamic type.
@@ -305,6 +307,7 @@ class ExampleTableSeparatorView: UIView, UITableViewDataSource {
 
   func setup() {
     tableView.dataSource = self
+    tableView.alwaysBounceVertical = false
     addSubview(tableView)
 
     let separator = UIView(frame: .zero)
@@ -315,7 +318,7 @@ class ExampleTableSeparatorView: UIView, UITableViewDataSource {
     separator.translatesAutoresizingMaskIntoConstraints = false
 
     NSLayoutConstraint.activate([
-      tableView.topAnchor.constraint(equalTo: self.topAnchor),
+      tableView.topAnchor.constraint(lessThanOrEqualTo: self.topAnchor),
       tableView.leadingAnchor.constraint(equalTo: self.leadingAnchor),
       tableView.trailingAnchor.constraint(equalTo: self.trailingAnchor),
       separator.topAnchor.constraint(equalTo: tableView.bottomAnchor),
@@ -341,7 +344,7 @@ class ExampleTableSeparatorView: UIView, UITableViewDataSource {
   func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
     let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
     cell.textLabel?.text = ringtones[indexPath.row]
-    cell.indentationWidth = 0
+    cell.indentationLevel = 1
     return cell
   }
 }

components/Dialogs/src/MDCAlertControllerView.h

@@ -59,8 +59,8 @@
 @property(nonatomic, assign) UIEdgeInsets titleInsets;
 
 /**
- The edge insets around the content view (which includes the message and/or the accessory view)
- against the dialog edges or its neighbor elements, the title and the actions.
+ The edge insets around the content view (which includes the message, and the accessory view if it
+ is set) against the dialog edges or its neighbor elements, the title and the actions.
 
  Default value is UIEdgeInsets(top: 24, leading: 24, bottom: 24, trailing: 24).
  */
@@ -105,6 +105,23 @@
  */
 @property(nonatomic, assign) CGFloat accessoryViewVerticalInset;
 
+/**
+The horizontal inset that sets the leading and trailing margins of the accessory view. The accessory
+insets are added to the contentInsets.leading and contentInsets.trailing values when calculating the
+leading and trailing margins of the accessory view.
+
+@note: Unlike the content's horizontal insets, the accessory insets use a single value for both
+       leading and trailing edge, while the final margins are calculated using both the content and
+       the accessory insets.
+
+@note: You may use a negative `accessoryViewHorizontalInset` value in order to to decreases the
+       leading and trailing margins of the accessory view.
+
+Default value is 0 (meaning, the accessory view's horizontal insets are determined soley by the
+                    horizontal contentInsets values).
+*/
+@property(nonatomic, assign) CGFloat accessoryViewHorizontalInset;
+
 @end
 
 @interface MDCAlertControllerView (ToBeDeprecated)

components/Dialogs/src/private/MDCAlertControllerView+Private.m

@@ -70,6 +70,7 @@ - (instancetype)initWithFrame:(CGRect)frame {
     self.actionsHorizontalMargin = 8.0f;
     self.actionsVerticalMargin = 12.0f;
     self.accessoryViewVerticalInset = 20.0f;
+    self.accessoryViewHorizontalInset = 0.0f;
 
     self.titleScrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
     [self addSubview:self.titleScrollView];
@@ -676,6 +677,9 @@ - (CGSize)calculatePreferredContentSizeForBounds:(CGSize)boundsSize {
 // @param boundingWidth should not include any internal margins or padding
 - (CGSize)calculateContentSizeThatFitsWidth:(CGFloat)boundingWidth {
   CGFloat contentInsets = self.contentInsets.left + self.contentInsets.right;
+  if (self.accessoryViewHorizontalInset > 0) {
+    contentInsets += self.accessoryViewHorizontalInset * 2.0;
+  }
   CGFloat titleInsets = self.titleInsets.left + self.titleInsets.right;
   CGSize boundsSize = CGRectInfinite.size;
 
@@ -829,8 +833,9 @@ - (void)layoutSubviews {
   CGRect titleFrame = [self titleFrameWithTitleSize:titleSize];
   CGRect messageFrame = [self messageFrameWithSize:messageSize];
   CGRect accessoryViewFrame = CGRectMake(
-      self.contentInsets.left, CGRectGetMaxY(messageFrame) + [self accessoryVerticalInset],
-      accessoryViewSize.width, accessoryViewSize.height);
+      self.contentInsets.left + self.accessoryViewHorizontalInset,
+      CGRectGetMaxY(messageFrame) + [self accessoryVerticalInset],
+      accessoryViewSize.width - self.accessoryViewHorizontalInset * 2.0, accessoryViewSize.height);
 
   self.titleLabel.frame = titleFrame;
   self.messageTextView.frame = messageFrame;

components/Dialogs/tests/snapshot/MDCAlertControllerInsetsTests.m

@@ -311,6 +311,7 @@ - (void)testAlertContentAccessoryHaveCustomInsets {
   // When
   self.alertView.contentInsets = UIEdgeInsetsMake(10.f, 10.f, 10.f, 10.f);
   self.alertView.accessoryViewVerticalInset = 0.f;
+  self.alertView.accessoryViewHorizontalInset = -5.0f;
 
   // Then
   [self generateSizedSnapshotAndVerifyForAlert:self.alertController];