textarea如何实现高度自适应？

Posted 2020-10-04 加菲猫and大白

 

转自：http://www.xuanfengge.com/textarea-on-how-to-achieve-a-high-degree-of-adaptive.html

 

今天需要些一个回复评论的页面，设计师给的初始界面就是一个只有一行的框。然后当时就想这个交互该怎么实现比较好，然后想起了新浪微博的做法：点击评论，默认显示一行，当输入的文字超过一行或者输入Enter时，输入框的高度会随着改变，直到输入完毕。顿时觉得这个细节做得挺不错的，可以效仿下。下面分享2种实现textarea高度自适应的做法，一种是用div来模拟textarea来实现的，用CSS控制样式，不用js；另一种是利用JS控制的（因为存在浏览器兼容问题，所以写起来比较麻烦）；

方法一：div模拟textarea文本域轻松实现高度自适应

demo演示地址：http://www.xuanfengge.com/demo/201308/textarea/demo1.html

因为textarea不支持自适应高度，就是定好高度或者是行数之后，超出部分就会显示滚动条，看起来不美观。

而用DIV来模拟时，首先遇到的问题是：div怎么实现输入功能？

可能我们还是第一次见到这个属性contenteditable，如一个普通的block元素上加个contenteditable="true"就实现编辑，出现光标了。如

<div contenteditable="true"></div>

contenteditable属性虽是HTML5里面的内容，但是IE似乎老早就支持此标签属性了。所以，兼容性方面还是不用太担心的。

CSS代码

 .textarea{

    width: 400px;

    min-height: 20px;

    max-height: 300px;

    _height: 120px;

    margin-left: auto;

    margin-right: auto;

    padding: 3px;

    outline: 0;

    border: 1px solid #a0b3d6;

    font-size: 12px;

    line-height: 24px;

    padding: 2px;

    word-wrap: break-word;

    overflow-x: hidden;

    overflow-y: auto;

 

    border-color: rgba(82, 168, 236, 0.8);

    box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1), 0 0 8px rgba(82, 168, 236, 0.6);

}

 

 HTML代码

 <div class="textarea" contenteditable="true"><br /></div>

CSS代码中，因为IE6不支持min/max，所以做了hack，其他的也好理解。

 

方法二：文本框textarea根据输入内容自适应高度

demo演示地址:http://www.xuanfengge.com/demo/201308/textarea/demo2.html

这个写法是用原生JS写的，考虑了很多兼容性问题，完全和新浪微博的回复效果一样的功能。有兴趣的童鞋可以仔细分析下代码。

CSS代码

 #textarea {

    display: block;

    margin:0 auto;

    overflow: hidden;

    width: 550px;

    font-size: 14px;

    height: 18px;

    line-height: 24px;

    padding:2px;

}

textarea {

    outline: 0 none;

    border-color: rgba(82, 168, 236, 0.8);

    box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1), 0 0 8px rgba(82, 168, 236, 0.6);

}

JavaScript代码

 /**

* 文本框根据输入内容自适应高度

* @param                {HTMLElement}        输入框元素

* @param                {Number}                设置光标与输入框保持的距离(默认0)

* @param                {Number}                设置最大高度(可选)

*/

var autoTextarea = function (elem, extra, maxHeight) {

        extra = extra || 0;

        var isFirefox = !!document.getBoxObjectFor || ‘mozInnerScreenX‘ in window,

        isOpera = !!window.opera && !!window.opera.toString().indexOf(‘Opera‘),

                addEvent = function (type, callback) {

                        elem.addEventListener ?

                                elem.addEventListener(type, callback, false) :

                                elem.attachEvent(‘on‘ + type, callback);

                },

                getStyle = elem.currentStyle ? function (name) {

                        var val = elem.currentStyle[name];

 

                        if (name === ‘height‘ && val.search(/px/i) !== 1) {

                                var rect = elem.getBoundingClientRect();

                                return rect.bottom - rect.top -

                                        parseFloat(getStyle(‘paddingTop‘)) -

                                        parseFloat(getStyle(‘paddingBottom‘)) + ‘px‘;        

                        };

 

                        return val;

                } : function (name) {

                                return getComputedStyle(elem, null)[name];

                },

                minHeight = parseFloat(getStyle(‘height‘));

 

        elem.style.resize = ‘none‘;

 

        var change = function () {

                var scrollTop, height,

                        padding = 0,

                        style = elem.style;

 

                if (elem._length === elem.value.length) return;

                elem._length = elem.value.length;

 

                if (!isFirefox && !isOpera) {

                        padding = parseInt(getStyle(‘paddingTop‘)) + parseInt(getStyle(‘paddingBottom‘));

                };

                scrollTop = document.body.scrollTop || document.documentElement.scrollTop;

 

                elem.style.height = minHeight + ‘px‘;

                if (elem.scrollHeight > minHeight) {

                        if (maxHeight && elem.scrollHeight > maxHeight) {

                                height = maxHeight - padding;

                                style.overflowY = ‘auto‘;

                        } else {

                                height = elem.scrollHeight - padding;

                                style.overflowY = ‘hidden‘;

                        };

                        style.height = height + extra + ‘px‘;

                        scrollTop += parseInt(style.height) - elem.currHeight;

                        document.body.scrollTop = scrollTop;

                        document.documentElement.scrollTop = scrollTop;

                        elem.currHeight = parseInt(style.height);

                };

        };

 

        addEvent(‘propertychange‘, change);

        addEvent(‘input‘, change);

        addEvent(‘focus‘, change);

        change();

};

HTML代码（写在body里面的）

 <textarea id="textarea" placeholder="回复内容"></textarea>

    <script>

        var text = document.getElementById("textarea");

        autoTextarea(text);// 调用

    </script>