Cupertino TextField Cursor Fix (#27697)

* Fix for #26261. Changes CupertinoTextField's cursorColor to read from CupertinoTheme instead of prior default of activeBlue. CursorColor will still default to activeBlue for light theme and activeOrange for dark theme if a primary color has not been specified for the CupertinoTheme.

* Reverted unnecessary changes in XCode file.

* Updated text_field.dart per suggestions from @gspencergoog

* Updated comments for cursorColor to reflect appropriate hyperlinks per @Hixie

* Simplified cursorColor assignment per @xster

* Added test in cupertino/text_field_test.dart to check for correct cursorColor based on CupertinoTheme per @Hixie & @xster.

packages/flutter/lib/src/cupertino/text_field.dart

@@ -172,7 +172,7 @@ class CupertinoTextField extends StatefulWidget {
     this.enabled,
     this.cursorWidth = 2.0,
     this.cursorRadius = const Radius.circular(2.0),
-    this.cursorColor = CupertinoColors.activeBlue,
+    this.cursorColor,
     this.keyboardAppearance,
     this.scrollPadding = const EdgeInsets.all(20.0),
   }) : assert(textAlign != null),
@@ -365,7 +365,9 @@ class CupertinoTextField extends StatefulWidget {
 
   /// The color to use when painting the cursor.
   ///
-  /// Defaults to the standard iOS blue color. Cannot be null.
+  /// Defaults to the [CupertinoThemeData.primaryColor] of the ambient theme,
+  /// which itself defaults to [CupertinoColors.activeBlue] in the light theme
+  /// and [CupertinoColors.activeOrange] in the dark theme.
   final Color cursorColor;
 
   /// The appearance of the keyboard.
@@ -401,6 +403,7 @@ class CupertinoTextField extends StatefulWidget {
     properties.add(IntProperty('maxLines', maxLines, defaultValue: 1));
     properties.add(IntProperty('maxLength', maxLength, defaultValue: null));
     properties.add(FlagProperty('maxLengthEnforced', value: maxLengthEnforced, ifTrue: 'max length enforced'));
+    properties.add(DiagnosticsProperty<Color>('cursorColor', cursorColor, defaultValue: null));
   }
 }
 
@@ -644,7 +647,7 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with AutomaticK
           rendererIgnoresPointer: true,
           cursorWidth: widget.cursorWidth,
           cursorRadius: widget.cursorRadius,
-          cursorColor: widget.cursorColor,
+          cursorColor: themeData.primaryColor,
           cursorOpacityAnimates: true,
           cursorOffset: cursorOffset,
           paintCursorAboveText: true,

packages/flutter/test/cupertino/text_field_test.dart

@@ -1345,4 +1345,46 @@ void main() {
     expect(setClient.method, 'TextInput.setClient');
     expect(setClient.arguments.last['keyboardAppearance'], 'Brightness.light');
   });
+
+  testWidgets('cursorColor respects theme', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CupertinoTextField(),
+      ),
+    );
+
+    final Finder textFinder = find.byType(CupertinoTextField);
+    await tester.tap(textFinder);
+    await tester.pump();
+
+    final EditableTextState editableTextState =
+    tester.firstState(find.byType(EditableText));
+    final RenderEditable renderEditable = editableTextState.renderEditable;
+
+    expect(renderEditable.cursorColor, CupertinoColors.activeBlue);
+
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CupertinoTextField(),
+        theme: CupertinoThemeData(
+          brightness: Brightness.dark,
+        ),
+      ),
+    );
+
+    await tester.pump();
+    expect(renderEditable.cursorColor, CupertinoColors.activeOrange);
+
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CupertinoTextField(),
+        theme: CupertinoThemeData(
+          primaryColor: Color(0xFFF44336),
+        ),
+      ),
+    );
+
+    await tester.pump();
+    expect(renderEditable.cursorColor, const Color(0xFFF44336));
+  });
 }