Question

我想限制在第二个列表框中多次添加同一个项目，我想我非常接近它。请帮忙

<script type="text/javascript">
    function CopyFile() {
        var firstListBox = document.getElementById('<%= lstFirstBox.ClientID %>');
        var secondListBox = document.getElementById('<%= lstTarget.ClientID %>');
        for (var i = 0; i < firstListBox.options.length; i++) {
            if (firstListBox.options[i].selected) {
                for (var j = 0; j < secondListBox.options.length; j++) {
                    if (firstListBox.options[i].selected == secondListBox.options[j]) {
                        alert("Multiple selection will not allow");
                    }
                    else {
                        var newOption = document.createElement("option");
                        newOption.text = firstListBox.options[i].text;
                        newOption.value = firstListBox.options[i].value;
                        secondListBox.options[secondListBox.options.length] = newOption;
                        firstListBox.options[i].selected = false;
                    }

                }

            }
        }
        return false;

    }
</script>

Answer 1

我给你写了一个例子。以下html页面有两个选择和一个按钮。如果您在第一个选择中选择一个选项并按下该按钮，该选项将被复制到第二个选择，除非它已经存在。在最后一种情况下，它会提醒一条消息。尝试一下，将其粘贴到文件中（例如“test.htm”）并在浏览器中打开。

<!DOCTYPE html>
<html>
    <head>
        <script type="text/javascript">
            function tryToCopy() {
                var select1 = document.getElementById("select1");
                var select2 = document.getElementById("select2");
                var optionToBeCopied = select1.options[select1.selectedIndex];
                var contains = false;
                for(var i = 0, ceiling = select2.options.length; i < ceiling; i++) {
                    if(select2.options[i].value == optionToBeCopied.value) {
                        contains = true;
                        break;
                    }
                }
                if(contains) {
                        alert("duplicate options are not allowed.");
                } else {
                    var option = document.createElement("option");
                    select2.appendChild(option);
                    option.value = optionToBeCopied.value;
                    option.text = optionToBeCopied.text;
                }
            }
        </script>
    </head>
    <body>
        <select id="select1">
            <option value="" selected="true"></option>
            <option value="a">a</option>
            <option value="b">b</option>
        </select>
        <select id="select2">
        </select>
        <input type="button" value="tryToCopy" onclick="tryToCopy()"/>
    </body>
</html>

Javascript限制多次向第二个列表框添加相同的项目

1 个答案: