feat: add PaymentMethodMessaging widget (via PaymentMethodMessagingElement)

packages/stripe/lib/flutter_stripe.dart

@@ -8,4 +8,5 @@ export 'src/widgets/aubecs_debit_form.dart';
 export 'src/widgets/card_field.dart';
 export 'src/widgets/card_form_field.dart';
 // export 'src/widgets/google_pay_button.dart';
+export 'src/widgets/payment_method_messaging.dart';
 export 'src/widgets/platform_pay_button.dart';

packages/stripe/lib/src/widgets/payment_method_messaging.dart

@@ -0,0 +1,122 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+import 'package:stripe_platform_interface/stripe_platform_interface.dart';
+
+/// Renders Stripe's Klarna / Afterpay / Affirm promotional messaging element.
+///
+/// Backed by Stripe's `PaymentMethodMessagingElement` on both iOS (via
+/// `StripePaymentSheet`) and Android (via the `com.stripe:payment-method-messaging`
+/// artifact). The element is currently marked preview by Stripe (`@_spi` on
+/// iOS, `@OptIn(PaymentMethodMessagingElementPreview::class)` on Android), so
+/// its visual output may change in future SDK releases.
+///
+/// The widget auto-resizes: the native element reports its rendered height
+/// back to Dart, which drives the surrounding `SizedBox`. The optional
+/// [onHeightChange] callback receives the same value if callers want to react
+/// to height changes themselves.
+class PaymentMethodMessaging extends StatefulWidget {
+  const PaymentMethodMessaging({
+    required this.configuration,
+    this.onHeightChange,
+    super.key,
+  });
+
+  final PaymentMethodMessagingConfiguration configuration;
+  final ValueChanged<double>? onHeightChange;
+
+  @override
+  State<PaymentMethodMessaging> createState() =>
+      _PaymentMethodMessagingState();
+}
+
+class _PaymentMethodMessagingState extends State<PaymentMethodMessaging> {
+  static const _viewType = 'flutter.stripe/payment_method_messaging';
+
+  MethodChannel? _methodChannel;
+  double _height = 50;
+
+  void onPlatformViewCreated(int viewId) {
+    _methodChannel =
+        MethodChannel('flutter.stripe/payment_method_messaging/$viewId');
+    _methodChannel!.setMethodCallHandler((call) async {
+      if (call.method == 'onHeightChange') {
+        final args = Map<String, dynamic>.from(call.arguments);
+        final height = (args['height'] as num).toDouble();
+        if (mounted) {
+          setState(() {
+            _height = height;
+          });
+        }
+        widget.onHeightChange?.call(height);
+      }
+    });
+  }
+
+  @override
+  void didUpdateWidget(covariant PaymentMethodMessaging oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (widget.configuration != oldWidget.configuration) {
+      _methodChannel?.invokeMethod(
+        'updateConfiguration',
+        widget.configuration.toJson(),
+      );
+    }
+  }
+
+  @override
+  void dispose() {
+    _methodChannel?.setMethodCallHandler(null);
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final creationParams = widget.configuration.toJson();
+
+    Widget platform;
+    if (defaultTargetPlatform == TargetPlatform.iOS) {
+      platform = UiKitView(
+        viewType: _viewType,
+        creationParamsCodec: const StandardMessageCodec(),
+        creationParams: creationParams,
+        onPlatformViewCreated: onPlatformViewCreated,
+      );
+    } else if (defaultTargetPlatform == TargetPlatform.android) {
+      platform = PlatformViewLink(
+        viewType: _viewType,
+        surfaceFactory: (context, controller) {
+          return AndroidViewSurface(
+            controller: controller as AndroidViewController,
+            hitTestBehavior: PlatformViewHitTestBehavior.opaque,
+            gestureRecognizers:
+                const <Factory<OneSequenceGestureRecognizer>>{},
+          );
+        },
+        onCreatePlatformView: (params) {
+          onPlatformViewCreated(params.id);
+          return PlatformViewsService.initSurfaceAndroidView(
+              id: params.id,
+              viewType: _viewType,
+              layoutDirection: TextDirection.ltr,
+              creationParams: creationParams,
+              creationParamsCodec: const StandardMessageCodec(),
+            )
+            ..addOnPlatformViewCreatedListener(
+              params.onPlatformViewCreated,
+            )
+            ..create();
+        },
+      );
+    } else {
+      throw UnsupportedError('Unsupported platform view');
+    }
+
+    return SizedBox(
+      height: _height,
+      child: platform,
+    );
+  }
+}

packages/stripe_android/android/build.gradle

@@ -64,6 +64,13 @@ dependencies {
     implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.4.1"
     implementation "com.stripe:stripe-android:$stripe_version"
     implementation "com.stripe:financial-connections:$stripe_version"
+    implementation "com.stripe:payment-method-messaging:$stripe_version"
+    // Compose modules used by StripePaymentMethodMessagingPlatformView. The
+    // payment-method-messaging artifact declares these at runtime scope only,
+    // so consuming modules must add them to the compile classpath explicitly.
+    implementation "androidx.compose.ui:ui:1.10.4"
+    implementation "androidx.compose.foundation:foundation:1.10.4"
+    implementation "androidx.compose.runtime:runtime:1.10.4"
     implementation 'com.google.android.material:material:1.6.0'
     implementation 'androidx.appcompat:appcompat:1.4.1'
     implementation 'com.squareup.okhttp3:okhttp:5.3.2'

packages/stripe_android/android/src/main/kotlin/com/flutter/stripe/StripeAndroidPlugin.kt

@@ -77,6 +77,7 @@ class StripeAndroidPlugin : FlutterPlugin, MethodCallHandler, ActivityAware {
             .platformViewRegistry
             .registerViewFactory("flutter.stripe/add_to_wallet", StripeAddToWalletPlatformViewFactory(flutterPluginBinding, AddToWalletButtonManager()){stripeSdk})
         flutterPluginBinding.platformViewRegistry.registerViewFactory("flutter.stripe/address_sheet", StripeAddressSheetPlatformViewFactory(flutterPluginBinding, addressSheetFormViewManager ){stripeSdk})
+        flutterPluginBinding.platformViewRegistry.registerViewFactory("flutter.stripe/payment_method_messaging", StripePaymentMethodMessagingPlatformViewFactory(flutterPluginBinding))
     }
 
     override fun onMethodCall(call: MethodCall, result: Result) {

packages/stripe_android/android/src/main/kotlin/com/flutter/stripe/StripePaymentMethodMessagingPlatformView.kt

@@ -0,0 +1,157 @@
+package com.flutter.stripe
+
+import android.app.Activity
+import android.app.Application
+import android.content.Context
+import android.content.ContextWrapper
+import android.view.View
+import android.widget.FrameLayout
+import androidx.compose.foundation.layout.Box
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.layout.onSizeChanged
+import androidx.compose.ui.platform.ComposeView
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.platform.ViewCompositionStrategy
+import com.stripe.android.paymentmethodmessaging.element.PaymentMethodMessagingElement
+import com.stripe.android.paymentmethodmessaging.element.PaymentMethodMessagingElementPreview
+import com.stripe.android.model.PaymentMethod
+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+import io.flutter.plugin.platform.PlatformView
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.launch
+
+@OptIn(PaymentMethodMessagingElementPreview::class)
+class StripePaymentMethodMessagingPlatformView(
+    private val context: Context,
+    private val channel: MethodChannel,
+    creationParams: Map<String?, Any?>?,
+) : PlatformView {
+
+    private val container: FrameLayout = FrameLayout(context)
+    private val composeView: ComposeView = ComposeView(context).apply {
+        setViewCompositionStrategy(ViewCompositionStrategy.DisposeOnViewTreeLifecycleDestroyed)
+    }
+    private val scope: CoroutineScope = CoroutineScope(Dispatchers.Main + SupervisorJob())
+    private var configureJob: Job? = null
+    private var elementState: ((PaymentMethodMessagingElement?) -> Unit)? = null
+    private var lastReportedHeightPx: Int = -1
+
+    init {
+        container.addView(
+            composeView,
+            FrameLayout.LayoutParams(
+                FrameLayout.LayoutParams.MATCH_PARENT,
+                FrameLayout.LayoutParams.WRAP_CONTENT,
+            ),
+        )
+        composeView.setContent {
+            var element by remember { mutableStateOf<PaymentMethodMessagingElement?>(null) }
+            elementState = { element = it }
+            val density = LocalDensity.current
+            Box(
+                modifier = Modifier.onSizeChanged { size ->
+                    if (size.height != lastReportedHeightPx) {
+                        lastReportedHeightPx = size.height
+                        val heightDp = with(density) { size.height.toDp().value }
+                        channel.invokeMethod(
+                            "onHeightChange",
+                            mapOf("height" to heightDp.toDouble()),
+                        )
+                    }
+                },
+            ) {
+                element?.Content(PaymentMethodMessagingElement.Appearance())
+            }
+        }
+
+        channel.setMethodCallHandler { call, result -> handleMethodCall(call, result) }
+        applyConfiguration(creationParams)
+    }
+
+    private fun handleMethodCall(call: MethodCall, result: MethodChannel.Result) {
+        when (call.method) {
+            "updateConfiguration" -> {
+                @Suppress("UNCHECKED_CAST")
+                applyConfiguration(call.arguments as? Map<String?, Any?>)
+                result.success(null)
+            }
+            else -> result.notImplemented()
+        }
+    }
+
+    private fun applyConfiguration(params: Map<String?, Any?>?) {
+        configureJob?.cancel()
+        elementState?.invoke(null)
+        emitCollapsedHeight()
+
+        if (params == null) return
+
+        @Suppress("UNCHECKED_CAST")
+        val methodStrings = params["paymentMethods"] as? List<String> ?: return
+        val currency = params["currency"] as? String ?: return
+        val amount = (params["amount"] as? Number)?.toLong() ?: return
+        val countryCode = params["countryCode"] as? String
+        val locale = params["locale"] as? String
+
+        val types = methodStrings.mapNotNull { PaymentMethod.Type.fromCode(it) }
+        val application = context.findApplication() ?: return
+
+        val configuration = PaymentMethodMessagingElement.Configuration().apply {
+            amount(amount)
+            currency(currency)
+            locale?.let { locale(it) }
+            countryCode?.let { countryCode(it) }
+            if (types.isNotEmpty()) paymentMethodTypes(types)
+        }
+
+        configureJob = scope.launch {
+            val element = PaymentMethodMessagingElement.create(application)
+            val result = element.configure(configuration)
+            when (result) {
+                is PaymentMethodMessagingElement.ConfigureResult.Succeeded -> {
+                    elementState?.invoke(element)
+                }
+                is PaymentMethodMessagingElement.ConfigureResult.NoContent,
+                is PaymentMethodMessagingElement.ConfigureResult.Failed -> {
+                    elementState?.invoke(null)
+                    emitCollapsedHeight()
+                }
+            }
+        }
+    }
+
+    private fun emitCollapsedHeight() {
+        if (lastReportedHeightPx != 0) {
+            lastReportedHeightPx = 0
+            channel.invokeMethod("onHeightChange", mapOf("height" to 0.0))
+        }
+    }
+
+    override fun getView(): View = container
+
+    override fun dispose() {
+        configureJob?.cancel()
+        scope.cancel()
+        composeView.disposeComposition()
+        channel.setMethodCallHandler(null)
+    }
+}
+
+private fun Context.findApplication(): Application? {
+    var ctx: Context = this
+    while (ctx is ContextWrapper) {
+        if (ctx is Application) return ctx
+        if (ctx is Activity) return ctx.application
+        ctx = ctx.baseContext
+    }
+    return applicationContext as? Application
+}

packages/stripe_android/android/src/main/kotlin/com/flutter/stripe/StripePaymentMethodMessagingPlatformViewFactory.kt

@@ -0,0 +1,25 @@
+package com.flutter.stripe
+
+import android.content.Context
+import io.flutter.embedding.engine.plugins.FlutterPlugin
+import io.flutter.plugin.common.MethodChannel
+import io.flutter.plugin.common.StandardMessageCodec
+import io.flutter.plugin.platform.PlatformView
+import io.flutter.plugin.platform.PlatformViewFactory
+
+class StripePaymentMethodMessagingPlatformViewFactory(
+    private val flutterPluginBinding: FlutterPlugin.FlutterPluginBinding,
+) : PlatformViewFactory(StandardMessageCodec.INSTANCE) {
+    override fun create(context: Context?, viewId: Int, args: Any?): PlatformView {
+        if (context == null) {
+            throw AssertionError("Context is not allowed to be null when launching PaymentMethodMessaging view.")
+        }
+        val channel = MethodChannel(
+            flutterPluginBinding.binaryMessenger,
+            "flutter.stripe/payment_method_messaging/$viewId",
+        )
+        @Suppress("UNCHECKED_CAST")
+        val creationParams = args as? Map<String?, Any?>?
+        return StripePaymentMethodMessagingPlatformView(context, channel, creationParams)
+    }
+}