Fixed bug 4747 - [Patch] SDL_ShowMessageBox ignores BUTTON_RETURNKEY_DEFAULT flag

Caleb Cornett

SDL_ShowMessageBox on UIKit doesn't do anything special with buttons that are marked with the flag SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT. According to Apple's documentation on UIAlertController, a button can respond to a return key if it's marked as the preferredAction of the controller. SDL doesn't set a preferredAction currently, so I've attached a patch to fix that.
diff --git a/src/video/uikit/SDL_uikitmessagebox.m b/src/video/uikit/SDL_uikitmessagebox.m
index 7480f64..defb4d6 100644
--- a/src/video/uikit/SDL_uikitmessagebox.m
+++ b/src/video/uikit/SDL_uikitmessagebox.m
@@ -91,6 +91,10 @@
 				                            clickedindex = (int)(sdlButton - messageboxdata->buttons);
                                         }];
         [alert addAction:action];
+
+        if (sdlButton->flags & SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT) {
+            alert.preferredAction = action;
+        }
     }
 
     if (messageboxdata->window) {