Fixed notification issue and app crash

android/app/build.gradle

@@ -51,23 +51,36 @@ android {
         versionName flutterVersionName
     }
 
-    // added
-    signingConfigs {
-        release {
-            keyAlias keystoreProperties['keyAlias']
-            keyPassword keystoreProperties['keyPassword']
-            storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
-            storePassword keystoreProperties['storePassword']
-        }
-    }
-    // added
+     // added
+     signingConfigs {
+         release {
+             keyAlias keystoreProperties['keyAlias']
+             keyPassword keystoreProperties['keyPassword']
+             storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
+             storePassword keystoreProperties['storePassword']
+         }
+     }
+     // added
 
     buildTypes {
         release {
             // TODO: Add your own signing config for the release build.
             // Signing with the debug keys for now, so `flutter run --release` works.
             // signingConfig signingConfigs.debug
             signingConfig signingConfigs.release
+
+            minifyEnabled true
+
+            // Enables resource shrinking, which is performed by the
+            // Android Gradle plugin.
+            shrinkResources true
+
+            // Includes the default ProGuard rules files that are packaged with
+            // the Android Gradle plugin. To learn more, go to the section about
+            // R8 configuration files.
+            proguardFiles getDefaultProguardFile(
+                    'proguard-android-optimize.txt'),
+                    'proguard-rules.pro'
         }
     }
 }

android/app/proguard-rules.pro

@@ -0,0 +1,35 @@
+## Flutter wrapper
+-keep class io.flutter.app.** { *; }
+-keep class io.flutter.plugin.**  { *; }
+-keep class io.flutter.util.**  { *; }
+-keep class io.flutter.view.**  { *; }
+-keep class io.flutter.**  { *; }
+-keep class io.flutter.plugins.**  { *; }
+-dontwarn io.flutter.embedding.**
+
+## Gson rules
+# Gson uses generic type information stored in a class file when working with fields. Proguard
+# removes such information by default, so configure it to keep all of it.
+-keepattributes Signature
+
+# For using GSON @Expose annotation
+-keepattributes *Annotation*
+
+# Gson specific classes
+-dontwarn sun.misc.**
+#-keep class com.google.gson.stream.** { *; }
+
+# Prevent proguard from stripping interface information from TypeAdapter, TypeAdapterFactory,
+# JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
+-keep class * implements com.google.gson.TypeAdapter
+-keep class * implements com.google.gson.TypeAdapterFactory
+-keep class * implements com.google.gson.JsonSerializer
+-keep class * implements com.google.gson.JsonDeserializer
+
+# Prevent R8 from leaving Data object members always null
+-keepclassmembers,allowobfuscation class * {
+  @com.google.gson.annotations.SerializedName <fields>;
+}
+
+## flutter_local_notification plugin rules
+-keep class com.dexterous.** { *; }

android/app/src/main/res/raw/keep.xml

@@ -0,0 +1,3 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources xmlns:tools="http://schemas.android.com/tools"
+    tools:keep="@drawable/*,@raw/notification_sound" />