This one is very gray zone in Android development but this is a flow that you can try. You must bind imm to some view and it is preferable that view is editable (like EditText widget) or you will have all kind of problem's. This is just example code that you can put in onClick method or something like that.
view.requestFocus();
InputMethodManager imm =(InputMethodManager)getSystemService(Context.INPU T_METHOD_SERVICE);
imm.showSoftInput(view, 0);