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Build multiple apps with different assets but using the same code

I am currently changing my apps, made with Swift and Java, to Flutter, however, right now I have 5 Apps for android and iOS, all using the same code (5 in Swift, 5 in Java), and, for each one I have different assets, like images, strings, API url's etc. In case of an iOS app I was currently creating different Targets on XCode, with different user-defined variables that i use in the code, and then I chose which target I want to build and send to the corespondent iTunesConnect app. In android I do more or less the same, but using Android flavors.
My doubt is how can I do this in flutter without being forced to create a different Flutter project for each app I want to build.
Any ideas on what approach should I use?

I use a custom build script that creates a symlink depending on the flavor name
From my Grinder build script
Future<void> _setTenant(Tenant tenant) async {
const symlinkPath = 'assets/tenant';
final link = Link(symlinkPath);
if (link.existsSync() &&
link.targetSync() == '../assets/${tenant.identifier}') {
return;
}
if (link.existsSync()) {
link.updateSync('../assets/${tenant.identifier}');
} else {
Link(symlinkPath).createSync('../assets/${tenant.identifier}');
}
}
Tenant is a custom class and Tenant.identifier returns a string that is valid as directory/symlink name.
I created https://github.com/flutter/flutter/issues/21682 to get direct support for that in Flutter.

In React Native how do you bundle a text file and read it's value at runtime?

A few reasons why I might do this:
To create some webviews and inject javascript loaded from files
To separate large chunks of text into separate files rather than forcing them into views
To include raw data of an arbitrary format (eg, CSV) to be used in the app
In React Native you can use require to import an image file, but as far as I've seen, this only works for image files. And it (strangely) also works for JSON files (see Importing Text from local json file in React native). However, I haven't seen anywhere talking about importing plain old text files.

After looking and asking around, the best I can come up with is to use a
fork of the react-native-fs library to access android "assets". This fork is a pull request out and as soon as it gets merged you can use it.
Note that in android dev, "assets" specifically refer to accessing the raw contents of a file. In order to do this sort of thing on the react native side, you need to write a native module to interface with react, hence the library above. See here (and search for assets).
In your react native project, make a file called something like android/app/src/main/assets/text.txt. Using the version of react-native-fs mentioned above, you do:
RNFS.readFileAssets('test.txt').then((res) => {
console.log('read file res: ', res);
})
update: If you want the pull request that would enable this ability to go through, you should go let the author know you want it by giving it a thumbs up on github.

There is a library that solves this exact problem: React-Native-Local-Resource. The library allows you to asynchronously load any type of text file in Android and iOS at runtime.

Here is a simple react-native project example of implementing FS and read files for both IOS and Android .
https://github.com/baselka/kindleapp
(Implement a simple application to render 2 files (book file) in an android and iOS application on a tablet. The app must emulate the functionality where you are reading a book file in your app like in a kindle app)

Here's how I did it synchronously in Swift and JS for iOS/tvOS/macOS, based on the React Native docs: Exporting Constants.
Disadvantage: Note that the file will be loaded into memory once upon startup, and won't be dynamically re-loadable.
Advantage: It's synchronous, simple, and works at run-time whether in native or JS.
MyJSFile.js
import { NativeModules } from "react-native";
console.log(NativeModules.MyNativeModule.MyFileContents);
We import our native module and access the MyFileContents constant that we expose upon it. It works synchronously with no bridge-crossing (as far as I understand, it's injected into the React Native JSContext via JavaScriptCore).
In Build Phases, ensure that this file is added into Copy Bundle Resources. Otherwise your app will quickly crash upon trying to read it.
MyNativeModule.swift
import Foundation
#objc(MyNativeModule)
class MyNativeModule: RCTEventEmitter {
#objc override func constantsToExport() -> [AnyHashable : Any]! {
let contents: String = try! String(contentsOfFile: Bundle.main.path(forResource: "MyFile.min", ofType: "js")!)
return [
"MyFileContents": contents
]
}
#objc override func supportedEvents() -> [String]! {
return []
}
#objc override static func requiresMainQueueSetup() -> Bool {
return false
}
}
One can likely make a simpler/slimmer native module than this one (by subclassing something with less functionality than RCTEventEmitter), but this is the file I had lying around to work with, so here it is.
MyProject-Bridging-Header.h
#import <React/RCTBridge.h>
#import <React/RCTBridgeModule.h>
#import <React/RCTUIManager.h>
#import <React/RCTEventEmitter.h>
#import <React/RCTBundleURLProvider.h>
#import <React/RCTJavaScriptLoader.h>
#import <React/RCTLinkingManager.h>
#import <React/RCTRootView.h>
#import <React/RCTEventDispatcher.h>
Here's the bridging header I'm using. It exposes a lot more headers than are strictly necessary, but you may need them for other native modules later anyway.
As this approach uses Swift, make sure to enter your Build Settings and set Always Embed Swift Standard Libraries to Yes if you haven't already. And if this is the first time building your app with Swift embedded, you may want to clear DerivedData for luck before building.
... Or simply rewrite that same Swift code in Obj-C, as the documentation shows how.

Is it possible to pixelate an image in appcelerator Titanium?

I'm writing an Android and IOS app using Appcelerator Titanium, and I can't find a way to pixelate an image. The app that I'm writing, needs to do that: pixelate a given image with a parameter given by user, (the greater the number, the greater the pixels). I have found a way to do it with Xcode for IOS, and in Android SDK for Android, but if possible, I would like to do it in Titanium to avoid writing the whole app twice, one for Android and other for IOS.
Is there a way to do it?
Thank you.

If you have a native way in iOS and both Android you should wrap these as native modules and then include them in the project.
Follow this guide here on the Community wiki ->
https://wiki.appcelerator.org/display/guides2/Creating+a+New+Titanium+Module
Then you can write a function that wraps the modules and returned the processed object. eg.
var processImage = function() {
if (Titanium.Platform.name == 'android') {
// Android stuff
var imageProcess = require('ti.imageProcess');
return imageProcess.doImage('/voo/bar', /*more options */)
} else {
// etc
}
};
Instead of writing and maintaining two modules you could use a webView and use a JS library or the canvas object to pixelate the image.
A JS canvas solution to this can be found here:
https://stackoverflow.com/a/19129822/2132015

Do I need to do anything when I create my own internal packages for my Android code?

I am refactoring my code, and I am organizing my classes into packages. But I find that my program doesn't run when I create my own subpackages (Java, not android, packages). Is there anything special I need to do if I have several internal packages in my code?

The only Android-specific change you should have to make is updating your AndroidManifest to use the full class names (e.g. com.example.ClassName). Post your errors if this doesn't fit it.
(Of course, you will also need to change the imports just like in any other Java application.)

How do I add the javax.swing.* packages to my libs for my android project?

First of all I'd like to mention I am very new to Java programming. This Android project is my first experience with Java. So for one task I need to strip HTML tags from a string. I was thinking about using this answer Remove HTML tags from a String to do this task. In order to do this I need to be able to import javax.swing.text.html.* and javax.swing.text.html.parser.*.
I went to the properties of my project and attempted to add this library to my project. I read that this was included in the rt.jar file which was located at /usr/lib/jvm/java-6-openjdk/jre/lib/rt.jar
I was able to use the imports but it seems like it added a million libraries I am not using. Will this negatively effect my application? What is the correct way to add just the one extension?

You don't. Android doesn't use Swing. You'll need to use Android's API to create your UI and perform text parsing. Consider android.text.Html as a simple way to strip HTML from a string.