Android EditText默认数字键盘，能输入字母和数字

<EditText
android:id="@+id/limit_edittext"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="@dimen/dimen_basic4"
android:ellipsize="end"
android:hint="哈哈哈"
android:singleLine="true" />

EditText editText = (EditText) findViewById(R.id.limit_edittext);
String digists = "0123456789abcdefghigklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
editText.setKeyListener(DigitsKeyListener.getInstance(digists));