# PDListBox.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    package org.apache.pdfbox.pdmodel.interactive.form;

    import java.io.IOException;

    import org.apache.pdfbox.cos.COSDictionary;
    import org.apache.pdfbox.cos.COSName;

    /**
     * A scrollable list box. Contains several text items, one or more of which shall be selected as the
     * field value.
     *
     * @author John Hewson
     */
    public final class PDListBox extends PDChoice
    {
        /**
         * @see PDField#PDField(PDAcroForm)
         *
         * @param acroForm The acroform.
         */
        public PDListBox(PDAcroForm acroForm)
        {
            super(acroForm);
        }

        /**
         * Constructor.
         *
         * @param acroForm The form that this field is part of.
         * @param field the PDF object to represent as a field.
         * @param parent the parent node of the node
         */
        PDListBox(PDAcroForm acroForm, COSDictionary field, PDNonTerminalField parent)
        {
            super(acroForm, field, parent);
        }

        /**
         * This will get the top index "TI" value.
         *
         * @return the top index, default value 0.
         */
        public int getTopIndex()
        {
            return getCOSObject().getInt(COSName.TI, 0);
        }

        /**
         * This will set top index "TI" value.
         *
         * @param topIndex the value for the top index, null will remove the value.
         */
        public void setTopIndex(Integer topIndex)
        {
            if (topIndex != null)
            {
                getCOSObject().setInt(COSName.TI, topIndex);
            }
            else
            {
                getCOSObject().removeItem(COSName.TI);
            }
        }

        @Override
        void constructAppearances() throws IOException
        {
            AppearanceGeneratorHelper apHelper;
            apHelper = new AppearanceGeneratorHelper(this);
            apHelper.setAppearanceValue("");
        }
    }