How do I negate color of views in one go?

Question

Before asking this question, I have researched a bit on it and also looked for similar questions on SO, none of which seemed to answer it.

I am planning to provide visual accessibility feature in my android app where users will be able to negate the color of UI in one go(lets say a simple button to negate the colors).

There are few exceptions though. There are few views(say action bar) whose color is better to be fixed even if user chooses to negate the color, for readability.

I can think of few options to achieve the same:

1. Maintain two copies of each layout xml - one with normal colored views and one with negated colored views. Now, whenever user chooses to negate the colors, just load the corresponding xml in java.
2. Maintain two copies of color of each view in color.xml. Define them under two separate themes. Now set the corresponding theme based on what user wants.

Challenges:
Scalability: Given that the app is already using hundreds of views, hundreds of XML, and it is going to be using more and more views in future updates, how can I take care of that?

Questions:
1. Which option would be better for this keeping scalability in mind.
2. Is there any other way of doing the same?
3. Is there any android API which gives the negated color of a view?

Answer 1

Seems to me that the best approach is to maintain a normal theme and a negated theme in your app and then depending on the users setting, change themes at runtime.

There is a catch with this approach which is that you have to setTheme before setContentView in your activity. Which means that you can't reflect the changes immediately after the user has clicked a button. That being said, this is the best solution in my opinion as it scales nicely and you can probably have a BaseActivity that all your activites inherit from which can have the check to set your theme.

setTheme(userBlackTheme? android.R.style.Theme_Dark : android.R.style.Theme_Light);
super.onCreate(savedInstanceState); //IMPORTANT: setTheme is before the super call!!!
setContentView(R.layout.main);

If you have a button on the screen and want to do this, then you should be able to swap out all the style attributes on your Views and replace them with Dark attributes. Meaning, while you won't change your theme, you can change the attributes of each of your Views to be those of your dark theme.

You would then have to recursively loop through all your Views and depending on the class of the View change it's attributes to a Dark/Light.

public void recursiveLoopChildren(ViewGroup parent) {
    for (int i = parent.getChildCount() - 1; i >= 0; i--) {
        final View child = parent.getChildAt(i);
        if (child instanceof ViewGroup) {
            ((ViewGroup) child).setBackgroundColor(useDarkTheme? Color.BLACK : Color.WHITE);
            recursiveLoopChildren((ViewGroup) child);

            // DO SOMETHING WITH VIEWGROUP, AFTER CHILDREN HAS BEEN LOOPED 
        } else { 
            if (child instanceof TextView) {
                ((TextView) child).setTextColor(...);
            } 
        } 
    } 
} 

In short, you probably want to implement both of these, with option 1 all new activites will use a dark theme with option 2 when you click on the change theme button, your current activity will be changed. OR... when the button to change the theme is clicked, reload the current activity, not as elegant to the user, perhaps you can reload the same activity with a dark theme and fade it in above the light theme and then call finish() on the light theme providing a nice transition while simplifying your life. Hope this helps.