DOM（十）使用DOM设置单选按钮、复选框、下拉菜单

1.设置单选按钮

单选按钮在表单中即<input type="radio" />它是一组供用户选择的对象，但每次只能选一个。每一个都有checked属性，当一项选择为ture时，其它的都变为false.

先贴沙漠化一个例子：

<script type="text/javascript">
        function getChoice() {
            var oForm = document.forms["uForm1"];
            var aChoices = oForm.camera;
            for (i = 0; i < aChoices.length; i++) //遍历整个单选项表
                if (aChoices[i].checked) //如果发现了被选中项则退出
                    break;
            alert("相机品牌是：" + aChoices[i].value);
        }

        function setChoice(iNum) {
            var oForm = document.forms["uForm1"];
            oForm.camera[iNum].checked = true;
        }
    </script>
    <form method="post" name="uForm1" action="addInfo.aspx">
        相机品牌：
        <p>
            <input type="radio" name="camera" id="canon" value="Canon">
            <label for="canon">Canon</label>
        </p>
        <p>
            <input type="radio" name="camera" id="nikon" value="Nikon">
            <label for="nikon">Nikon</label>
        </p>
        <p>
            <input type="radio" name="camera" id="sony" value="Sony" checked>
            <label for="sony">Sony</label>
        </p>
        <p>
            <input type="radio" name="camera" id="olympus" value="Olympus">
            <label for="olympus">Olympus</label>
        </p>
        <p>
            <input type="radio" name="camera" id="samsung" value="Samsung">
            <label for="samsung">Samsung</label>
        </p>
        <p>
            <input type="radio" name="camera" id="pentax" value="Pentax">
            <label for="pentax">Pentax</label>
        </p>
        <p>
            <input type="radio" name="camera" id="others" value="其它">
            <label for="others">others</label>
        </p>
        <p>
            <input type="submit" name="btnSubmit" id="btnSubmit" value="Submit" class="btn">
        </p>
        <p>
            <input type="button" value="检测选中对象" onclick="getChoice();">
            <input type="button" value="设置为Canon" onclick="setChoice(0);">
        </p>
    </form>

单选按钮在表单中即<input type="radio" />它是一组供用户选择的对象，但每次只能选一个。每一个都有checked属性，当一项选择为ture时，其它的都变为false.
从以上代码中看出，id和name是不同的，一组单选按钮中它们的name是相同的，只有一个被选中。id则是绑定<label>或者其它选择作用的。

其中代码中：检查被选中对象的代码是（当某一项的chcked值为ture时，遍历结束）

var oForm = document.forms["uForm1"];
            var aChoices = oForm.camera;
            for (i = 0; i < aChoices.length; i++) //遍历整个单选项表
                if (aChoices[i].checked) //如果发现了被选中项则退出
                    break;
            alert("相机品牌是：" + aChoices[i].value);

2.设置多选框

与单选按钮不同，复选框<input type="checkbox" />可以同时选中多个选项进行处理，邮箱中每条邮件之前的复选框就的典型的运用

<script type="text/javascript">
        function checkbox() {
            var str = document.getElementsByName("hobby");
            var objarray = str.length;
            var chestr = "";
            
            for (j = 0; j < objarray; j++) {
                if (str[j].checked == true) {
                    chestr += str[j].value + ",";
                }
            }
            if (chestr == "") {
                alert("请先选择一个爱好～！");
            } else {
                alert("您先择的是：" + chestr);
            }
        }

        function changeBoxes(action) {
            var oForm = document.forms["myForm1"];
            var oCheckBox = oForm.hobby;        
            for (var i = 0; i < oCheckBox.length; i++) //遍历每一个选项
                if (action < 0) //反选
                    oCheckBox[i].checked = !oCheckBox[i].checked;
                else //action为1是则全选，为0时则全不选
                    oCheckBox[i].checked = action;
        }
    </script>

    <form method="post" name="myForm1" action="addInfo.aspx">
        喜欢做的事：
        <p>
            <input type="checkbox" name="hobby" id="ball" value="ball">
            <label for="ball">打球</label>
        </p>
        <p>
            <input type="checkbox" name="hobby" id="TV" value="TV">
            <label for="TV">看电视</label>
        </p>
        <p>
            <input type="checkbox" name="hobby" id="net" value="net">
            <label for="net">上网</label>
        </p>
        <p>
            <input type="checkbox" name="hobby" id="book" value="book">
            <label for="book">看书</label>
        </p>
        <p>
            <input type="checkbox" name="hobby" id="trip" value="trip">
            <label for="trip">旅游</label>
        </p>
        <p>
            <input type="checkbox" name="hobby" id="music" value="music">
            <label for="music">音乐</label>
        </p>
        <p>
            <input type="checkbox" name="hobby" id="others" value="其它">
            <label for="others">其它</label>
        </p>
        <p>
            <input type="button" value="全选" onclick="changeBoxes(1);" />
            <input type="button" value="全不选" onclick="changeBoxes(0);" />
            <input type="button" value="反选" onclick="changeBoxes(-1);" />
            <input type="button" value="提交"  onclick="checkbox()" />
        </p>
    </form>

复选框原理利用checked属性布尔值进行确定，全选和不全选可以采用0和1的方式传递参数。

3.下拉菜单

下拉菜单<select>是比较常用的表单元素。当它的下拉为单选时，和单选按钮<input type="radio" />功能一样，当下拉菜单为多选时multiple="multiple时，功能相当复选框，但所占面积远小于复选框。

下拉菜单的常用属性

i.下拉菜单获取单选值

<script language="javascript">
        function checkSingle() {
            var oForm = document.forms["myForm1"];
            var oSelectBox = oForm.constellation;
            var iChoice = oSelectBox.selectedIndex; //获取选中项
            alert("您选中了" + oSelectBox.options[iChoice].text);
        }
    </script>

    <form method="post" name="myForm1">
        <label for="constellation">星座：</label>
        <p>
            <select id="constellation" name="constellation" >
                <option value="Aries" selected="selected">白羊</option>
                <option value="Taurus">金牛</option>
                <option value="Gemini">双子</option>
                <option value="Cancer">巨蟹</option>
                <option value="Leo">狮子</option>
                <option value="Virgo">处女</option>
                <option value="Libra">天秤</option>
                <option value="Scorpio">天蝎</option>
                <option value="Sagittarius">射手</option>
                <option value="Capricorn">摩羯</option>
                <option value="Aquarius">水瓶</option>
                <option value="Pisces">双鱼</option>
            </select>
        </p>
        <input type="button" onclick="checkSingle()" value="查看选项" />
    </form>

 ii.下拉菜单为多选时，取值

<script type="text/javascript">
        function checkMultiple() {
            var oForm = document.forms["myForm1"];
            var oSelectBox = oForm.constellation;
            var aChoices = new Array();
            //遍历整个下拉菜单
            for (var i = 0; i < oSelectBox.options.length; i++)
                if (oSelectBox.options[i].selected) //如果被选中
                    aChoices.push(oSelectBox.options[i].text); //压入到数组中
            alert("您选了：" + aChoices.join()); //输出结果
        }
    </script>

        <form method="post" name="myForm1">
            <label for="constellation">星座：</label>
            <p>
                <select id="constellation" name="constellation" multiple="multiple" style="height:180px;">
                    <option value="Aries">白羊</option>
                    <option value="Taurus">金牛</option>
                    <option value="Gemini">双子</option>
                    <option value="Cancer">巨蟹</option>
                    <option value="Leo">狮子</option>
                    <option value="Virgo">处女</option>
                    <option value="Libra">天秤</option>
                    <option value="Scorpio">天蝎</option>
                    <option value="Sagittarius">射手</option>
                    <option value="Capricorn">摩羯</option>
                    <option value="Aquarius">水瓶</option>
                    <option value="Pisces">双鱼</option>
                </select>
            </p>
            <input type="button" onclick="checkMultiple()" value="查看选项" />
        </form>

 iii.通用取值（下拉单选和多选的情况）

<script language="javascript">
        function getSelectValue(Box) {
            var oForm = document.forms["myForm1"];
            var oSelectBox = oForm.elements[Box]; //根据参数相应的选择下拉菜单
            if (oSelectBox.type == "select-one") { //判断是单选还是多选
                var iChoice = oSelectBox.selectedIndex; //获取选中项
                alert("单选，您选中了" + oSelectBox.options[iChoice].text);
            } else {
                var aChoices = new Array();
                //遍历整个下拉菜单
                for (var i = 0; i < oSelectBox.options.length; i++)
                    if (oSelectBox.options[i].selected) //如果被选中
                        aChoices.push(oSelectBox.options[i].text); //压入到数组中
                alert("多选，您选了：" + aChoices.join()); //输出结果
            }
        }
    </script>

    <form method="post" name="myForm1">
        星座：
        <p>
            <select id="constellation1" name="constellation1">
                <option value="Aries" selected="selected">白羊</option>
                <option value="Taurus">金牛</option>
                <option value="Gemini">双子</option>
                <option value="Cancer">巨蟹</option>
                <option value="Leo">狮子</option>
                <option value="Virgo">处女</option>
                <option value="Libra">天秤</option>
                <option value="Scorpio">天蝎</option>
                <option value="Sagittarius">射手</option>
                <option value="Capricorn">摩羯</option>
                <option value="Aquarius">水瓶</option>
                <option value="Pisces">双鱼</option>
            </select>
            <input type="button" onclick="getSelectValue('constellation1')" value="查看选项" />
        </p>
        <p>
            <select id="constellation2" name="constellation2" multiple="multiple" style="height:120px;">
                <option value="Aries">白羊</option>
                <option value="Taurus">金牛</option>
                <option value="Gemini">双子</option>
                <option value="Cancer">巨蟹</option>
                <option value="Leo">狮子</option>
                <option value="Virgo">处女</option>
                <option value="Libra">天秤</option>
                <option value="Scorpio">天蝎</option>
                <option value="Sagittarius">射手</option>
                <option value="Capricorn">摩羯</option>
                <option value="Aquarius">水瓶</option>
                <option value="Pisces">双鱼</option>
            </select>
            <input type="button" onclick="getSelectValue('constellation2')" value="查看选项" />
        </p>
    </form>