Re-render shipping methods screen when shipping methods change

example/src/main/java/com/stripe/example/activity/PaymentSessionActivity.kt

@@ -246,16 +246,24 @@ class PaymentSessionActivity : AppCompatActivity() {
 
     private class ShippingInformationValidator : PaymentSessionConfig.ShippingInformationValidator {
         override fun isValid(shippingInformation: ShippingInformation): Boolean {
-            return shippingInformation.address?.country == Locale.US.country
+            return setOf(Locale.US.country, Locale.CANADA.country)
+                .contains(shippingInformation.address?.country.orEmpty())
         }
 
         override fun getErrorMessage(shippingInformation: ShippingInformation): String {
-            return "The country must be US."
+            return "The country must be US or Canada."
         }
     }
 
     private class ShippingMethodsFactory : PaymentSessionConfig.ShippingMethodsFactory {
-        override fun create(shippingInformation: ShippingInformation) = SHIPPING_METHODS
+        override fun create(
+            shippingInformation: ShippingInformation
+        ): List<ShippingMethod> {
+            return when (shippingInformation.address?.country) {
+                "CA" -> SHIPPING_METHODS_CA
+                else -> SHIPPING_METHODS_US
+            }
+        }
     }
 
     private fun hideProgressBar() {
@@ -327,7 +335,17 @@ class PaymentSessionActivity : AppCompatActivity() {
             "(555) 555-5555"
         )
 
-        private val SHIPPING_METHODS = listOf(
+        private val SHIPPING_METHODS_CA = listOf(
+            ShippingMethod(
+                "Canada Post",
+                "canada-post",
+                599,
+                "CAD",
+                "Arrives in 3-5 days"
+            )
+        )
+
+        private val SHIPPING_METHODS_US = listOf(
             ShippingMethod(
                 "UPS Ground",
                 "ups-ground",

stripe/src/main/java/com/stripe/android/view/PaymentFlowPagerAdapter.kt

@@ -11,6 +11,7 @@ import com.stripe.android.databinding.ShippingInfoPageBinding
 import com.stripe.android.databinding.ShippingMethodPageBinding
 import com.stripe.android.model.ShippingInformation
 import com.stripe.android.model.ShippingMethod
+import kotlin.properties.Delegates
 
 internal class PaymentFlowPagerAdapter(
     private val context: Context,
@@ -43,20 +44,23 @@ internal class PaymentFlowPagerAdapter(
             notifyDataSetChanged()
         }
 
-    internal var shippingMethods: List<ShippingMethod> = emptyList()
-        set(value) {
-            field = value
-            notifyDataSetChanged()
-        }
+    private var shouldRecreateShippingMethodsScreen = false
 
-    internal var selectedShippingMethod: ShippingMethod? = null
-        set(value) {
-            field = value
-            notifyDataSetChanged()
-        }
+    internal var shippingMethods: List<ShippingMethod> by Delegates.observable(
+        emptyList()
+    ) { _, oldValue, newValue ->
+        shouldRecreateShippingMethodsScreen = newValue != oldValue
+    }
+
+    internal var selectedShippingMethod: ShippingMethod? by Delegates.observable(
+        null
+    ) { _, oldValue, newValue ->
+        shouldRecreateShippingMethodsScreen = newValue != oldValue
+    }
 
     override fun instantiateItem(collection: ViewGroup, position: Int): Any {
-        val viewHolder = when (pages[position]) {
+        val page = pages[position]
+        val viewHolder = when (page) {
             PaymentFlowPage.ShippingInfo -> {
                 PaymentFlowViewHolder.ShippingInformationViewHolder(collection)
             }
@@ -81,6 +85,7 @@ internal class PaymentFlowPagerAdapter(
             }
         }
         collection.addView(viewHolder.itemView)
+        viewHolder.itemView.tag = page
         return viewHolder.itemView
     }
 
@@ -104,7 +109,22 @@ internal class PaymentFlowPagerAdapter(
         return context.getString(pages[position].titleResId)
     }
 
-    internal sealed class PaymentFlowViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
+    override fun getItemPosition(obj: Any): Int {
+        return if (obj is View && obj.tag == PaymentFlowPage.ShippingMethod &&
+            shouldRecreateShippingMethodsScreen
+        ) {
+            // if the shipping methods screen needs to be updated, return `POSITION_NONE` to
+            // indicate that the item is no longer valid and should be recreated
+            shouldRecreateShippingMethodsScreen = false
+            POSITION_NONE
+        } else {
+            super.getItemPosition(obj)
+        }
+    }
+
+    internal sealed class PaymentFlowViewHolder(
+        itemView: View
+    ) : RecyclerView.ViewHolder(itemView) {
         class ShippingInformationViewHolder(
             viewBinding: ShippingInfoPageBinding
         ) : PaymentFlowViewHolder(viewBinding.root) {

stripe/src/test/java/com/stripe/android/view/PaymentFlowPagerAdapterTest.kt

@@ -1,8 +1,6 @@
 package com.stripe.android.view
 
 import androidx.test.core.app.ApplicationProvider
-import com.nhaarman.mockitokotlin2.mock
-import com.stripe.android.CustomerSession
 import com.stripe.android.PaymentSessionFixtures
 import org.junit.runner.RunWith
 import org.robolectric.RobolectricTestRunner
@@ -12,14 +10,10 @@ import kotlin.test.assertEquals
 @RunWith(RobolectricTestRunner::class)
 class PaymentFlowPagerAdapterTest {
 
-    private val customerSession: CustomerSession = mock()
-
-    private val adapter: PaymentFlowPagerAdapter by lazy {
-        PaymentFlowPagerAdapter(
-            ApplicationProvider.getApplicationContext(),
-            PaymentSessionFixtures.CONFIG
-        )
-    }
+    private val adapter = PaymentFlowPagerAdapter(
+        ApplicationProvider.getApplicationContext(),
+        PaymentSessionFixtures.CONFIG
+    )
 
     @Test
     fun pageCount_updatesAfterSavingShippingInfo() {