Fix Share Screen Crash on iPad (#48220)

Fixes flutter/flutter#138550

![Simulator Screenshot - iPad Air (5th generation) - 2023-11-21 at 03 33 37](https://github.com/flutter/engine/assets/36148254/15e10e43-816b-43b1-a5ab-75c8add90899)

Author: LouiseHsu

shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.mm

@@ -10,6 +10,8 @@
 #import <UIKit/UIKit.h>
 
 #include "flutter/fml/logging.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/UIViewController+FlutterScreenAndSceneIfLoaded.h"
 
@@ -154,10 +156,38 @@ - (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
 
 - (void)showShareViewController:(NSString*)content {
   UIViewController* engineViewController = [_engine.get() viewController];
+
   NSArray* itemsToShare = @[ content ?: [NSNull null] ];
   UIActivityViewController* activityViewController =
       [[[UIActivityViewController alloc] initWithActivityItems:itemsToShare
                                          applicationActivities:nil] autorelease];
+
+  if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
+    // On iPad, the share screen is presented in a popover view, and requires a
+    // sourceView and sourceRect
+    FlutterTextInputPlugin* _textInputPlugin = [_engine.get() textInputPlugin];
+    UITextRange* range = _textInputPlugin.textInputView.selectedTextRange;
+
+    // firstRectForRange cannot be used here as it's current implementation does
+    // not always return the full rect of the range.
+    CGRect firstRect = [(FlutterTextInputView*)_textInputPlugin.textInputView
+        caretRectForPosition:(FlutterTextPosition*)range.start];
+    CGRect transformedFirstRect = [(FlutterTextInputView*)_textInputPlugin.textInputView
+        localRectFromFrameworkTransform:firstRect];
+    CGRect lastRect = [(FlutterTextInputView*)_textInputPlugin.textInputView
+        caretRectForPosition:(FlutterTextPosition*)range.end];
+    CGRect transformedLastRect = [(FlutterTextInputView*)_textInputPlugin.textInputView
+        localRectFromFrameworkTransform:lastRect];
+
+    activityViewController.popoverPresentationController.sourceView = engineViewController.view;
+    // In case of RTL Language, get the minimum x coordinate
+    activityViewController.popoverPresentationController.sourceRect =
+        CGRectMake(fmin(transformedFirstRect.origin.x, transformedLastRect.origin.x),
+                   transformedFirstRect.origin.y,
+                   abs(transformedLastRect.origin.x - transformedFirstRect.origin.x),
+                   transformedFirstRect.size.height);
+  }
+
   [engineViewController presentViewController:activityViewController animated:YES completion:nil];
 }
 

shell/platform/darwin/ios/framework/Source/FlutterPlatformPluginTest.mm

@@ -166,6 +166,44 @@ - (void)testShareScreenInvoked {
   [self waitForExpectationsWithTimeout:1 handler:nil];
 }
 
+- (void)testShareScreenInvokedOnIPad {
+  FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"test" project:nil];
+  [engine runWithEntrypoint:nil];
+  std::unique_ptr<fml::WeakNSObjectFactory<FlutterEngine>> _weakFactory =
+      std::make_unique<fml::WeakNSObjectFactory<FlutterEngine>>(engine);
+
+  XCTestExpectation* presentExpectation =
+      [self expectationWithDescription:@"Share view controller presented on iPad"];
+
+  FlutterViewController* engineViewController = [[FlutterViewController alloc] initWithEngine:engine
+                                                                                      nibName:nil
+                                                                                       bundle:nil];
+  FlutterViewController* mockEngineViewController = OCMPartialMock(engineViewController);
+  OCMStub([mockEngineViewController
+      presentViewController:[OCMArg isKindOfClass:[UIActivityViewController class]]
+                   animated:YES
+                 completion:nil]);
+
+  id mockTraitCollection = OCMClassMock([UITraitCollection class]);
+  OCMStub([mockTraitCollection userInterfaceIdiom]).andReturn(UIUserInterfaceIdiomPad);
+
+  FlutterPlatformPlugin* plugin =
+      [[FlutterPlatformPlugin alloc] initWithEngine:_weakFactory->GetWeakNSObject()];
+  FlutterPlatformPlugin* mockPlugin = OCMPartialMock(plugin);
+
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"Share.invoke"
+                                                                    arguments:@"Test"];
+  FlutterResult result = ^(id result) {
+    OCMVerify([mockEngineViewController
+        presentViewController:[OCMArg isKindOfClass:[UIActivityViewController class]]
+                     animated:YES
+                   completion:nil]);
+    [presentExpectation fulfill];
+  };
+  [mockPlugin handleMethodCall:methodCall result:result];
+  [self waitForExpectationsWithTimeout:1 handler:nil];
+}
+
 - (void)testClipboardHasCorrectStrings {
   [UIPasteboard generalPasteboard].string = nil;
   FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"test" project:nil];

shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h

@@ -163,6 +163,10 @@ FLUTTER_DARWIN_EXPORT
 - (instancetype)initWithFrame:(CGRect)frame NS_UNAVAILABLE;
 - (instancetype)initWithOwner:(FlutterTextInputPlugin*)textInputPlugin NS_DESIGNATED_INITIALIZER;
 
+// TODO(louisehsu): These are being exposed to support Share in FlutterPlatformPlugin
+// Consider moving that feature into FlutterTextInputPlugin to avoid exposing extra methods
+- (CGRect)localRectFromFrameworkTransform:(CGRect)incomingRect;
+- (CGRect)caretRectForPosition:(UITextPosition*)position;
 @end
 
 @interface UIView (FindFirstResponder)