<item
    android:id="@+id/action_search"
    android:actionLayout="@layout/my_search_view"
    android:icon="@drawable/ic_search_white_24px"
    android:title="Search"
    app:actionViewClass="android.widget.SearchView"
    android:digits="0123456789 qwertzuiopasdfghjklyxcvbnmABCDEFGHIJKLMNOPQRSTUVWXYZ"
    app:showAsAction="always|collapseActionView" />

EditText editText = (EditText) searchView.findViewById(android.support.v7.appcompat.R.id.search_src_text);
editText.setKeyListener(DigitsKeyListener.getInstance("0123456789"));

EditText editText = (EditText) searchView.findViewById(android.R.id.search_src_text);
editText.setKeyListener(DigitsKeyListener.getInstance("0123456789"));

android:digits="abcdefghijklmnopqrstuvwxyz1234567890 "

yourEditText.setKeyListener(DigitsKeyListener.getInstance("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890 "));

yourEditText.setKeyListener(DigitsKeyListener.getInstance("abcdefghijklmnopqrstuvwxyz1234567890 "));

yourEditText.setKeyListener(DigitsKeyListener.getInstance("ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890 "));

private void addFilterToUserName()
    {

        sign_up_display_name_et.setFilters(new InputFilter[] {
                new InputFilter() {
                    public CharSequence filter(CharSequence src, int start,
                                               int end, Spanned dst, int dstart, int dend) {
                        if(src.equals("")){ // for backspace
                            return src;
                        }
                        if(src.toString().matches("[a-zA-Z 0-9]+")){
                            return src;
                        }
                        return "";
                    }
                }
        });
    }