unity_keyboard_overlay.cs

// On Android, every Activity can respond differently to the software keyboard: scrolling to fit, just resizing, overlaying, etc.
// http://developer.android.com/training/keyboard-input/visibility.html
// The C# code below adjusts Unity's current Android Activity to make the keyboard overlay the game, with no size adjustments.
// It is equivalent to calling getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_NOTHING) in Java.

// Helped method needed for proper UI thread calls (required when accessing context views)
private static void runOnAndroidUiThread(Action target) {
    using (var unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer")) {
        using (var activity = unityPlayer.GetStatic("currentActivity")) {
            activity.Call("runOnUiThread", new AndroidJavaRunnable(target));
        }
    }
}

// Wrap it
private static void setSoftInputModeOverlay() {
    runOnAndroidUiThread(setSoftInputModeOverlayInThread);
}

// Actual logic
private static void setSoftInputModeOverlayInThread() {
    int SOFT_INPUT_ADJUST_NOTHING = 0x00000030; // WindowManager.LayoutParams.SOFT_INPUT_ADJUST_NOTHING
    using (var unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer")) {
        using (var activity = unityPlayer.GetStatic("currentActivity")) {
            using (var window = activity.Call("getWindow")) {
                window.Call("setSoftInputMode", SOFT_INPUT_ADJUST_NOTHING);
            }
        }
    }
}

// Finally, call it
setSoftInputModeOverlay();

Ah, I think I understand the problem better now.

When you said it was resizing, I assumed the whole game canvas was resizing to fit the smaller area provided by the keyboard. That's what the code snippet (instructing it to overlay) was set to fix. But when I tested it seemed to be fine:

But now that I've played around with it, I believe I misunderstood you. I think I know what you mean: when you hide the navigation completely, AND open the keyboard, it does force a small resize.

It works like this: when the software keyboard is shown, the navigation bar is always enforced. It is used to close the keyboard, I suppose. But it also means that if the navigation bar is set to "invisible", then instead of just showing it above the contenbt, it forces it to completely visible, thus resizing.

There's two ways to fix it.

1. Set the navigation bar to "translucent over content" or "visible over content" instead. This makes the keyboard display without resizing. When the keyboard closes, you need to set it to invisible again.

Or

1. Naturally listen to events and circumvent the system to always reset that flag. Haven't done this yet, but there's a discussion about this here at StackOverflow.

Let me see if there's a quick/easy fix that makes sense to add to this library.

Edit: nevermind that. I finally got it the way I originally thought you described. It's the full software resize. Sorry about the misunderstanding. Let me investigate it.