From Gossip@caterpillar

Ajax Gossip: 連動下拉選項

好啦！我知道有人在說了，這個程式有夠無聊…XD

改一下！就是個不錯的範例了，例如連動方塊，唔！在Ajax in action中叫啥？Dynamic double combo？…

假設一個會去從資料庫中查詢資料的Java程式示意如下：

Bike.java

package onlyfun.caterpillar;
 
import java.util.Map;
import java.util.TreeMap;
 
public class Bike {
  private Map<String, String[]> bikes;
  
  public Bike() {
    bikes = new TreeMap<String, String[]>();
    bikes.put("2000", new String[] {"2000 T1", "2000 T2", "2000 T3"});
    bikes.put("2001", new String[] {"2001 A1", "2001 A2"});
    bikes.put("2002", new String[] {"2002 BW1", "2002 BW2", "2002 BW"});
    bikes.put("2003", new String[] {"2003 S320"});
    bikes.put("2004", new String[] {"2004 TA1", "2004 TA2", "2004 TA3"});
  }
  
  public String[] getYears() {
    String[] keys = new String[bikes.size()];
    int i = 0;
    for(String key : bikes.keySet()) {
      keys[i++] = key;
    }
    return keys; 
  }
  
  public String[] getBikes(String year) {
    return bikes.get(year);
  }
}

getYears()跟getBkies()分別表示產品的年份跟型號，這邊用Map模擬，實際上資料是來自資料庫的查詢。

一樣的，在dwr.xml中設定：

dwr.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 1.0//EN" 
 "http://www.getahead.ltd.uk/dwr/dwr10.dtd">
 
<dwr>
  <allow>
    <create creator="new" javascript="Bike" scope="application">
        <param name="class" value="onlyfun.caterpillar.Bike"/>
    </create>
  </allow>
</dwr>

我們會有個腳踏車年份與型號查詢頁面：

bike.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=BIG5">
<title>Insert title here</title>
  <script type='text/javascript' src='dwr/interface/Bike.js'></script>
  <script type='text/javascript' src='dwr/engine.js'></script>
  <script type='text/javascript' src='dwr/util.js'></script>
  <script type='text/javascript' src='bike.js'></script>
</head>
<body onload="refreshYearList();">
  年份：<select id="years" onchange="refreshBikeList();"></select><br/><br/>
  型號：<select id="bikes"></select><br/>
</body>
</html>

注意，在選完第一個年份後，會觸發onchange事件，接著第二個下拉選單會自動填上對應年份的型號，而不是按鈕按下，再去取得第二個下拉選單，然後refresh...blah...blah...

bike.js如下…

bike.js

function refreshYearList() {
    Bike.getYears(populateYearList);
}
 
function populateYearList(list){
    DWRUtil.removeAllOptions("years");
    DWRUtil.addOptions("years", list);
    refreshBikeList();
}
 
function refreshBikeList() {
    var year = $("years").value;
    Bike.getBikes(year, populateBikeList);
}
 
function populateBikeList(list){
    DWRUtil.removeAllOptions("bikes");
    DWRUtil.addOptions("bikes", list);
}

一樣很簡單…

看個無聊的畫面…XD