How to hide navigation bar permanently in android activity?

Do this.

public void FullScreencall() {
    if(Build.VERSION.SDK_INT > 11 && Build.VERSION.SDK_INT < 19) { // lower api
        View v = this.getWindow().getDecorView();
        v.setSystemUiVisibility(View.GONE);
    } else if(Build.VERSION.SDK_INT >= 19) {
        //for new api versions.
        View decorView = getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;
        decorView.setSystemUiVisibility(uiOptions);
    }
}

This works 100% and you can do same for lower API versions, even if it's a late answer I hope it will helps someone else.

If you want this to be permanent, just call FullScreencall() inside your onResume() method.

Snippets:

FullScreenFragment.java

HideNavigationBarComponent.java

---

This is for Android 4.4+

Try out immersive mode https://developer.android.com/training/system-ui/immersive.html

Fast snippet (for an Activity class):

private int currentApiVersion;

@Override
@SuppressLint("NewApi")
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);

    currentApiVersion = android.os.Build.VERSION.SDK_INT;

    final int flags = View.SYSTEM_UI_FLAG_LAYOUT_STABLE
        | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
        | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
        | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
        | View.SYSTEM_UI_FLAG_FULLSCREEN
        | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;

    // This work only for android 4.4+
    if(currentApiVersion >= Build.VERSION_CODES.KITKAT)
    {

        getWindow().getDecorView().setSystemUiVisibility(flags);

        // Code below is to handle presses of Volume up or Volume down.
        // Without this, after pressing volume buttons, the navigation bar will
        // show up and won't hide
        final View decorView = getWindow().getDecorView();
        decorView
            .setOnSystemUiVisibilityChangeListener(new View.OnSystemUiVisibilityChangeListener()
            {

                @Override
                public void onSystemUiVisibilityChange(int visibility)
                {
                    if((visibility & View.SYSTEM_UI_FLAG_FULLSCREEN) == 0)
                    {
                        decorView.setSystemUiVisibility(flags);
                    }
                }
            });
    }

}


@SuppressLint("NewApi")
@Override
public void onWindowFocusChanged(boolean hasFocus)
{
    super.onWindowFocusChanged(hasFocus);
    if(currentApiVersion >= Build.VERSION_CODES.KITKAT && hasFocus)
    {
        getWindow().getDecorView().setSystemUiVisibility(
            View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_FULLSCREEN
                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY);
    }
}

If you have problems when you press Volume up or Volume down that your navigation bar show. I added code in onCreate see setOnSystemUiVisibilityChangeListener

Here is another related question:

Immersive mode navigation becomes sticky after volume press or minimise-restore