Show soft keyboard even though a hardware keyboard is connected

You need to override the InputMethodService method onEvaluateInputViewShown() to evaluate to true even when there is a hard keyboard. See onEvaluateInputShown() and the Soft Input View section of InputMethodService. Try creating your own custom InputMethodService class to override this method.

EDIT: The source for onEvaluateInputShown() should help. The solution should be as simple as creating your own class that extends InputMethodService and overriding this one method, which is only a couple of lines long. Make sure to add your custom service to your manifest as well.

From Source:

"Override this to control when the soft input area should be shown to the user. The default implementation only shows the input view when there is no hard keyboard or the keyboard is hidden. If you change what this returns, you will need to call updateInputViewShown() yourself whenever the returned value may have changed to have it re-evalauted and applied."

public boolean onEvaluateInputViewShown() {
     Configuration config = getResources().getConfiguration();
     return config.keyboard == Configuration.KEYBOARD_NOKEYS
             || config.hardKeyboardHidden == Configuration.KEYBOARDHIDDEN_YES;
}

Here are the possible configurations you can check for. Configuration.KEYBOARD_NOKEYS corresponds to no hardware keyboard. This method returns true (soft keyboard should be shown) if there is no hardware keyboard or if the hardware keyboard is hidden. Removing both of these checks and simply returning true should make the software keyboard visible even if a hardware keyboard is attached.

Try (not tested):

public boolean onEvaluateInputViewShown() {
     return true;
}

Since this return value will not change, you won't need to call updateInputViewShown() yourself. If you modify this method differently, be sure to remember this detail.

If your app has the WRITE_SECURE_SETTINGS permission (available to system apps or Android Things apps) it can set the show_ime_with_hard_keyboard system setting which will enable soft keyboard even if a hard keyboard is plugged:

Settings.Secure.putInt(getContentResolver(), "show_ime_with_hard_keyboard", 1);

The soft keyboard can have unpredictable behaviour on different platforms. First in your code, ensure you have an editable input control. Eg, if you have an EditText, you could use:

((InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE))
    .showSoftInput(myEditText, InputMethodManager.SHOW_FORCED);

However, you can just show and hide it whenever you want using:

//show keyboard:
getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);
//hide keyboard :
 getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);

You could also add any of these events inside OnCreate or some other method of the controls.

If however for some reason any of the above fails, your best option might be to use an alternative keyboard, e.g. Compass Keyboard,

OR

You could even build yours:

See an example of a keyboard implementing the inputmethodservice.KeyboardView

You might also want to take a look at the GingerBread Keyboard source.