when building highly secured apps, it can be essential to stop the user from taking screenshots, while this is quite straightforward on Android, it gets a little bit tricky on the iOS part. I remember facing this challenge some months ago and I scanned through a couple of StackOverflow answers for hours, I was at the point of getting frustrated when I stumbled on one that was the solution for the iOS part:

For Android:

inside your mainActivity.(java/tk), import the following:

import io.flutter.embedding.android.FlutterFragmentActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugins.GeneratedPluginRegistrant
import android.view.WindowManager.LayoutParams

and you replace the content with:

class MainActivity: FlutterFragmentActivity() {
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        window.addFlags(LayoutParams.FLAG_SECURE)
        GeneratedPluginRegistrant.registerWith(flutterEngine)
    }
}

this does it for Android.

For iOS:

in your AppDelegate.swift you should create a window extension just like below:

  extension UIWindow {
  func makeSecure() {
      let field = UITextField()
        let view = UIView(frame: CGRect(x: 0, y: 0, width: field.frame.self.width, height: field.frame.self.height))
        field.isSecureTextEntry = true
        self.addSubview(field)
        self.layer.superlayer?.addSublayer(field.layer)
        field.layer.sublayers?.last!.addSublayer(self.layer)
        field.leftView = view
        field.leftViewMode = .always
    }
  }

then call the new window extension in your application function:

self.window.makeSecure()

your AppDelegate.swift should look like this:

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    self.window.makeSecure()
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

  extension UIWindow {
  func makeSecure() {
      let field = UITextField()
      field.isSecureTextEntry = true
      self.addSubview(field)
      field.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
      field.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
      self.layer.superlayer?.addSublayer(field.layer)
      field.layer.sublayers?.first?.addSublayer(self.layer)
    }
  }

Source: stackoverflow answer

thank you for reading, I hope this was helpful.

How to block Screenshots in your flutter app