Add option to activate an overlay underneath all other overlays with the same UIWindowLevel.

PiperOrigin-RevId: 723263384

Author: Nobody

components/OverlayWindow/src/MDCOverlayWindow.h

@@ -34,6 +34,18 @@
  */
 - (void)activateOverlay:(UIView *)overlay withLevel:(UIWindowLevel)level;
 
+/**
+ Notifies the window that the given overlay view should be shown at the bottom of the given level.
+ This overlay will get added underneath all other overlays with the given UIWindowLevel.
+
+ Overlay owners must call this method to ensure that the overlay is actually displayed over the
+ window's primary content.
+
+ @param overlay The overlay being displayed.
+ @param level The UIWindowLevel to display the overlay on.
+ */
+- (void)activateOverlay:(UIView *)overlay atBottomOfLevel:(UIWindowLevel)level;
+
 /**
  Notifies the window that the given overlay is no longer active.
 

components/OverlayWindow/src/MDCOverlayWindow.m

@@ -148,7 +148,17 @@ - (void)noteOverlayRemoved:(UIView *)overlay {
   [self updateOverlayHiddenState];
 }
 
+- (void)activateOverlay:(UIView *)overlay atBottomOfLevel:(UIWindowLevel)level {
+  [self activateOverlay:overlay withLevel:level bottomOfLevel:YES];
+}
+
 - (void)activateOverlay:(UIView *)overlay withLevel:(UIWindowLevel)level {
+  [self activateOverlay:overlay withLevel:level bottomOfLevel:NO];
+}
+
+- (void)activateOverlay:(UIView *)overlay
+              withLevel:(UIWindowLevel)level
+          bottomOfLevel:(BOOL)bottomOfLevel {
   if (!overlay) {
     return;
   }
@@ -163,10 +173,10 @@ - (void)activateOverlay:(UIView *)overlay withLevel:(UIWindowLevel)level {
   __block NSUInteger insertionIndex = self.overlays.count;
 
   // Because @c self.overlays is already sorted by level, we can pick the first index which has a
-  // level larger than @c level.
+  // level larger than / equal to @c level.
   [self.overlays enumerateObjectsUsingBlock:^(UIView *existing, NSUInteger idx, BOOL *stop) {
     UIWindowLevel existingLevel = [self windowLevelForOverlay:existing];
-    if (level < existingLevel) {
+    if ((bottomOfLevel && level == existingLevel) || (level < existingLevel)) {
       insertionIndex = idx;
       *stop = YES;
     }