fix(ios): avoid reallocating views on RCTDevLoadingView showMessage calls

packages/react-native/React/CoreModules/RCTDevLoadingView.mm

@@ -116,19 +116,17 @@ - (void)showMessage:(NSString *)message
 
     self->_showDate = [NSDate date];
 
-    UIWindow *mainWindow = RCTKeyWindow();
-    self->_window = [[UIWindow alloc] initWithWindowScene:mainWindow.windowScene];
-    self->_window.windowLevel = UIWindowLevelStatusBar + 1;
-    self->_window.rootViewController = [UIViewController new];
-
-    self->_container = [[UIView alloc] init];
-    self->_container.backgroundColor = backgroundColor;
-    self->_container.translatesAutoresizingMaskIntoConstraints = NO;
-    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hide)];
-    [self->_container addGestureRecognizer:tapGesture];
-    self->_container.userInteractionEnabled = YES;
-
-    if (dismissButton) {
+    if (!self->_label) {
+      self->_label = [[UILabel alloc] init];
+      self->_label.translatesAutoresizingMaskIntoConstraints = NO;
+      self->_label.font = [UIFont monospacedDigitSystemFontOfSize:12.0 weight:UIFontWeightRegular];
+      self->_label.textAlignment = NSTextAlignmentCenter;
+      self->_label.numberOfLines = 0;
+    }
+    self->_label.textColor = color;
+    self->_label.text = message;
+
+    if (!self->_dismissButton) {
       CGFloat hue = 0.0;
       CGFloat saturation = 0.0;
       CGFloat brightness = 0.0;
@@ -154,52 +152,61 @@ - (void)showMessage:(NSString *)message
       self->_dismissButton = [UIButton buttonWithConfiguration:buttonConfig primaryAction:dismissAction];
       self->_dismissButton.translatesAutoresizingMaskIntoConstraints = NO;
     }
-
-    self->_label = [[UILabel alloc] init];
-    self->_label.translatesAutoresizingMaskIntoConstraints = NO;
-    self->_label.font = [UIFont monospacedDigitSystemFontOfSize:12.0 weight:UIFontWeightRegular];
-    self->_label.textAlignment = NSTextAlignmentCenter;
-    self->_label.textColor = color;
-    self->_label.text = message;
-    self->_label.numberOfLines = 0;
-
-    [self->_window.rootViewController.view addSubview:self->_container];
-    if (dismissButton) {
+    self->_dismissButton.hidden = !dismissButton;
+
+    if (!self->_container) {
+      self->_container = [[UIView alloc] init];
+      self->_container.translatesAutoresizingMaskIntoConstraints = NO;
+      UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hide)];
+      [self->_container addGestureRecognizer:tapGesture];
+      self->_container.userInteractionEnabled = YES;
+      [self->_container addSubview:self->_label];
       [self->_container addSubview:self->_dismissButton];
     }
-    [self->_container addSubview:self->_label];
+    self->_container.backgroundColor = backgroundColor;
 
+    UIWindow *mainWindow = RCTKeyWindow();
+    if (!self->_window) {
+      self->_window = [[UIWindow alloc] initWithWindowScene:mainWindow.windowScene];
+      self->_window.windowLevel = UIWindowLevelStatusBar + 1;
+      self->_window.rootViewController = [UIViewController new];
+      [self->_window.rootViewController.view addSubview:self->_container];
+    }
     CGFloat topSafeAreaHeight = mainWindow.safeAreaInsets.top;
-    self->_window.hidden = NO;
-
-    [self->_window layoutIfNeeded];
-
-    NSMutableArray *constraints = [NSMutableArray arrayWithArray:@[
-      // Container constraints
-      [self->_container.topAnchor constraintEqualToAnchor:self->_window.rootViewController.view.topAnchor],
-      [self->_container.leadingAnchor constraintEqualToAnchor:self->_window.rootViewController.view.leadingAnchor],
-      [self->_container.trailingAnchor constraintEqualToAnchor:self->_window.rootViewController.view.trailingAnchor],
-
+
+    // These constraints may update on each call, while the rest are constant
+    // (so only need to be activated once).
+    NSMutableArray *constraints = [NSMutableArray arrayWithArray: @[
+      // Dismiss button constraints
+      [self->_label.trailingAnchor constraintEqualToAnchor:dismissButton ? self->_dismissButton.leadingAnchor : self->_container.trailingAnchor
+                                                  constant:-10],
+
       // Label constraints
       [self->_label.topAnchor constraintEqualToAnchor:self->_container.topAnchor constant:topSafeAreaHeight + 8],
-      [self->_label.leadingAnchor constraintEqualToAnchor:self->_container.leadingAnchor constant:10],
-      [self->_label.bottomAnchor constraintEqualToAnchor:self->_container.bottomAnchor constant:-8],
     ]];
-
-    // Add button-specific constraints if button exists
-    if (dismissButton) {
+
+    if (!self->_constraintsActivated) {
       [constraints addObjectsFromArray:@[
+        // Dismiss button constraints
         [self->_dismissButton.trailingAnchor constraintEqualToAnchor:self->_container.trailingAnchor constant:-10],
         [self->_dismissButton.centerYAnchor constraintEqualToAnchor:self->_label.centerYAnchor],
         [self->_dismissButton.heightAnchor constraintEqualToConstant:22],
-        [self->_label.trailingAnchor constraintEqualToAnchor:self->_dismissButton.leadingAnchor constant:-10],
+
+        // Container constraints
+        [self->_container.topAnchor constraintEqualToAnchor:self->_window.rootViewController.view.topAnchor],
+        [self->_container.leadingAnchor constraintEqualToAnchor:self->_window.rootViewController.view.leadingAnchor],
+        [self->_container.trailingAnchor constraintEqualToAnchor:self->_window.rootViewController.view.trailingAnchor],
+
+        // Label constraints
+        [self->_label.leadingAnchor constraintEqualToAnchor:self->_container.leadingAnchor constant:10],
+        [self->_label.bottomAnchor constraintEqualToAnchor:self->_container.bottomAnchor constant:-8],
       ]];
-    } else {
-      [constraints addObject:[self->_label.trailingAnchor constraintEqualToAnchor:self->_container.trailingAnchor
-                                                                         constant:-10]];
     }
-
     [NSLayoutConstraint activateConstraints:constraints];
+    self->_constraintsActivated = YES;
+
+    self->_window.hidden = NO;
+    [self->_window layoutIfNeeded];
   });
 }