If your problem is that the flutter build (APK, bundle) isn't making API calls in a real device, this is because you need to add the Internet permission to Android Manifest before creating the release/build.

By default, "internet use" will work fine on the emulator but not on a real device.

To fix this, simply:

Open the file "android/app/src/main/AndroidManifest.xml" and add the proper user-permission:

<manifest> 
...
 <uses-permission android:name="android.permission.INTERNET"/>
...
</manifest>

And then create your build again.

I had facing same problem "Application work properly in Debug mode but not in release mode". I don't know why... but finally, I have solved by adding these lines shrinkResources false minifyEnabled false in android/app/build.gradle file.

 buildTypes {
     release {
         signingConfig signingConfigs.config
         shrinkResources false
         minifyEnabled false
     }
 }

When you are creating new Flutter project (from Android Studio menu), in file:

/android/app/build.gradle

which is there:

you have:

buildTypes {
    release {
        signingConfig signingConfigs.debug    //   <--- HERE YOU ARE USING DEBUG KEY
    }
}

Which means that release build (e.g. triggered from menu Build -> Flutter -> Build APK) will use debug key for signing.

Full build.gradle file (created by Android Studio):

Solution

Change from:

signingConfig signingConfigs.debug

to:

signingConfig signingConfigs.release

so (in build.gradle) you should have:

buildTypes {
    release {
        signingConfig signingConfigs.release
    }
}

Error

When you have error Could not get unknown property 'release' for SigningConfig - just add section release in build.gradle, so:

1. Create new .jks file (via Generate Signed Bundle / APK...

2. Put credentials in build.gradle (:app):

   

1. you can change in local.properties android project

       sdk.dir=D:/SDK               //your android SDK location
       flutter.sdk=D:\\Flutter\\flutter  //your flutter SDK location
       flutter.versionName=1.0.0
       flutter.versionCode=2
       flutter.buildMode=release
   

2. changes in your android/app/build.gradle file

        buildTypes {
               release {
                   // if everything ok then not add 
                   //minifyEnabled true 
                   //another you can remove minifyEnabled true
                   proguardFiles getDefaultProguardFile('proguard- 
                    android.txt'), 'proguard-rules.pro'
                   signingConfig signingConfigs.release
               }
           }
   

3. you can also changes in android/app/build.gradle defaultConfig method body.

     multiDexEnabled true
   

4. if you want to migrate to androidx then do it setup.

   dependencies { testImplementation 'junit:junit:4.12' androidTestImplementation 'androidx.test:runner:1.1.1' androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1' implementation 'androidx.multidex:multidex:2.0.1'

   }

   5. and clean before create build folder by following this cmd.

       - flutter clean
      
       - flutter build apk --release
      
       - flutter install
      

6.Release Apk location.

        in `android studio termial` or inside `project-root` you can navigate to this.

        cd build\app\outputs\apk\release

If you're using an API Call#

Make sure you have the Internet Permission on you android Manifest

<manifest> 
...
 <uses-permission android:name="android.permission.INTERNET"/>
...
</manifest>

If you're using Shared Preferences plugin

In android\build.gradle set your dependencies to use the classpath 'com.android.tools.build:gradle:3.5.1'

NOT classpath 'com.android.tools.build:gradle:4.1.0

Like this:

dependencies {
        classpath 'com.android.tools.build:gradle:3.5.1'
        ...
    }

1).

add following lines in android\app\src\mainAndroid manifest

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

and then add these lines in android\app\build.gradle

   buildTypes {
   release {
        shrinkResources false
        minifyEnabled false
   }}

2).

Building apk using the below commands.

flutter build apk --no-shrink

or

flutter build apk --split-per-abi --no-shrink

Both Solutions worked for me but personally I recommend second one

I hope this can help someone. I ran into a problem that my release version does not works and there are no any error messages in logcat. The problem turned out to be that I had FutureBuilder in which i start Future<void>. By running flutter run it works properly (snapshot.hasData was true), but in release version it was always false. Of course, documentation of the FutureBuilder says that hasData should be false in this case. But in fact in debug mode it has different behaviour.

P.S. Another possible problems: Now my app still not working, but this time i saw on logcat next error:

Unhandled Exception: MissingPluginException(No implementation found for method getAll on channel plugins.flutter.io/shared_preferences)

Downgrading gradle plugin version from 7.* to 3.5.4 solves this issue.

classpath 'com.android.tools.build:gradle:3.5.4'

I decide to open the MyProject/android folder in android studio and build the apk from android studio. It finally worked properly.

flutter build apk // this generate apk 

flutter build appbundle // this generate aab

And remember that you need to execute flutter clean before execute flutter build apk

I simply deleted the build folder and that solved the problem.
However, to prevent it from happening again, you should change your folder structure — do not use spaces in the path. For example:

/irayshi/my code/project_1

should be changed to:

/irayshi/my_code/project_1

flutter clean
flutter pub get
flutter build apk --release