dialog: display adaptive dialogs and action buttons based on the target platform

AlertDialog was changed to AlertDialog.adaptive to the effect described in #996.
_adaptiveAction was implemented to display a platform appropriate action for
AlertDialog.adaptive's actions param, as was also discussed in #996.
tests in dialog_test were updated to perform platform appropriate tests.

Author: u7088495

lib/widgets/dialog.dart

@@ -1,7 +1,9 @@
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
+import 'package:flutter/foundation.dart';
 
-Widget _dialogActionText(String text) {
+Widget _materialDialogActionText(String text) {
   return Text(
     text,
 
@@ -15,6 +17,20 @@ Widget _dialogActionText(String text) {
   );
 }
 
+/// A platform-appropriate action for [AlertDialog.adaptive]'s [actions] param.
+Widget _adaptiveAction({required VoidCallback onPressed, required String text}) {
+  switch (defaultTargetPlatform) {
+    case TargetPlatform.android:
+    case TargetPlatform.fuchsia:
+    case TargetPlatform.linux:
+    case TargetPlatform.windows:
+      return TextButton(onPressed: onPressed, child: _materialDialogActionText(text));
+    case TargetPlatform.iOS:
+    case TargetPlatform.macOS:
+      return CupertinoDialogAction(onPressed: onPressed, child: Text(text));
+  }
+}
+
 /// Tracks the status of a dialog, in being still open or already closed.
 ///
 /// See also:
@@ -42,13 +58,13 @@ DialogStatus showErrorDialog({
   final zulipLocalizations = ZulipLocalizations.of(context);
   final future = showDialog<void>(
     context: context,
-    builder: (BuildContext context) => AlertDialog(
+    builder: (BuildContext context) => AlertDialog.adaptive(
       title: Text(title),
       content: message != null ? SingleChildScrollView(child: Text(message)) : null,
       actions: [
-        TextButton(
+        _adaptiveAction(
           onPressed: () => Navigator.pop(context),
-          child: _dialogActionText(zulipLocalizations.errorDialogContinue)),
+          text: zulipLocalizations.errorDialogContinue),
       ]));
   return DialogStatus(future);
 }
@@ -63,15 +79,15 @@ void showSuggestedActionDialog({
   final zulipLocalizations = ZulipLocalizations.of(context);
   showDialog<void>(
     context: context,
-    builder: (BuildContext context) => AlertDialog(
+    builder: (BuildContext context) => AlertDialog.adaptive(
       title: Text(title),
       content: SingleChildScrollView(child: Text(message)),
       actions: [
-        TextButton(
+        _adaptiveAction(
           onPressed: () => Navigator.pop(context),
-          child: _dialogActionText(zulipLocalizations.dialogCancel)),
-        TextButton(
+          text: zulipLocalizations.dialogCancel),
+        _adaptiveAction(
           onPressed: onActionButtonPress,
-          child: _dialogActionText(actionButtonText ?? zulipLocalizations.dialogContinue)),
+          text: actionButtonText ?? zulipLocalizations.dialogContinue),
       ]));
 }

test/widgets/dialog_checks.dart

@@ -1,3 +1,5 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -6,21 +8,40 @@ import 'package:flutter_test/flutter_test.dart';
 /// Checks for an error dialog matching an expected title
 /// and, optionally, matching an expected message. Fails if none is found.
 ///
-/// On success, returns the widget's "OK" button.
+/// On success, returns the widget's "OK" button
+/// 
 /// Dismiss the dialog by calling `tester.tap(find.byWidget(okButton))`.
 Widget checkErrorDialog(WidgetTester tester, {
   required String expectedTitle,
   String? expectedMessage,
 }) {
-  final dialog = tester.widget<AlertDialog>(find.byType(AlertDialog));
-  tester.widget(find.descendant(matchRoot: true,
-    of: find.byWidget(dialog.title!), matching: find.text(expectedTitle)));
-  if (expectedMessage != null) {
-    tester.widget(find.descendant(matchRoot: true,
-      of: find.byWidget(dialog.content!), matching: find.text(expectedMessage)));
+  switch (defaultTargetPlatform) {
+    case TargetPlatform.android:
+    case TargetPlatform.fuchsia:
+    case TargetPlatform.linux:
+    case TargetPlatform.windows: {
+      final dialog = tester.widget<Dialog>(find.byType(Dialog));
+      tester.widget(find.widgetWithText(Dialog, expectedTitle));
+      if (expectedMessage != null) {
+        tester.widget(find.widgetWithText(Dialog, expectedMessage));
+      }
+      return tester.widget(
+        find.descendant(of: find.byWidget(dialog),
+          matching: find.widgetWithText(TextButton, 'OK')));
+    }
+    case TargetPlatform.iOS:
+    case TargetPlatform.macOS: {
+      final dialog = tester.widget<CupertinoAlertDialog>(
+        find.byType(CupertinoAlertDialog));
+      tester.widget(find.descendant(matchRoot: true,
+        of: find.byWidget(dialog.title!), matching: find.text(expectedTitle)));
+      if (expectedMessage != null) {
+        tester.widget(find.descendant(matchRoot: true,
+          of: find.byWidget(dialog.content!), matching: find.text(expectedMessage)));
+      }
+      return tester.widget(find.descendant(of: find.byWidget(dialog),
+        matching: find.widgetWithText(CupertinoDialogAction, 'OK')));
+    }
   }
-
-  return tester.widget(
-    find.descendant(of: find.byWidget(dialog),
-      matching: find.widgetWithText(TextButton, 'OK')));
+    
 }