Fix payment cancellation on back press during processing

paymentsheet-example/src/main/java/com/stripe/android/paymentsheet/example/playground/activity/PaymentSheetPlaygroundActivity.kt

@@ -557,6 +557,8 @@ class PaymentSheetPlaygroundActivity : AppCompatActivity() {
             disableViews()
         }
 
+        println("JAMES: ${paymentResult.toString()}")
+
         viewModel.status.value = paymentResult.toString()
     }
 

paymentsheet/src/main/java/com/stripe/android/paymentsheet/PaymentSheetActivity.kt

@@ -8,6 +8,7 @@ import android.view.ViewGroup
 import android.view.WindowManager
 import android.widget.ScrollView
 import android.widget.TextView
+import androidx.activity.addCallback
 import androidx.activity.viewModels
 import androidx.annotation.IdRes
 import androidx.annotation.VisibleForTesting

paymentsheet/src/main/java/com/stripe/android/paymentsheet/ui/BaseSheetActivity.kt

@@ -13,6 +13,7 @@ import android.view.WindowInsets
 import android.view.WindowMetrics
 import android.widget.ScrollView
 import android.widget.TextView
+import androidx.activity.addCallback
 import androidx.annotation.DrawableRes
 import androidx.annotation.StringRes
 import androidx.annotation.VisibleForTesting
@@ -186,12 +187,15 @@ internal abstract class BaseSheetActivity<ResultType> : AppCompatActivity() {
         overridePendingTransition(AnimationConstants.FADE_IN, AnimationConstants.FADE_OUT)
     }
 
+    @Deprecated("Deprecated in Java")
     override fun onBackPressed() {
-        if (supportFragmentManager.backStackEntryCount > 0) {
-            clearErrorMessages()
-            super.onBackPressed()
-        } else {
-            viewModel.onUserCancel()
+        if (viewModel.processing.value == false) {
+            if (supportFragmentManager.backStackEntryCount > 0) {
+                clearErrorMessages()
+                super.onBackPressed()
+            } else {
+                viewModel.onUserCancel()
+            }
         }
     }