javascript动画系列第四篇——拖拽改变元素大小

Posted 2020-08-09

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目录

[1]原理简介 [2]范围圈定 [3]大小改变[4]代码优化

前面的话

　　拖拽可以让元素移动，也可以改变元素大小。本文将详细介绍拖拽改变元素大小的效果实现

 

原理简介

　　拖拽让元素移动，是改变定位元素的left和top值实现的。而拖拽改变元素大小，则还需要改变元素的宽高

 

范围圈定

　　我们把改变元素大小的范围圈定在距离相应边10px的范围内

　　左侧边界L = obj.offsetLeft + 10

　　右侧边界R = obj.offsetLeft + obj.offsetWidth - 10

　　上侧边界T = obj.offsetTop + 10

　　下侧边界B = obj.offsetTop + obj.offsetHeight - 10

<div id="test" style="height: 100px;width: 100px;background-color: pink;">测试文字</div>
<script>
test.onmousemove = function(e){
    e = e || event;
    //元素边界确定
    var L0 = this.offsetLeft;
    var R0 = this.offsetLeft + this.offsetWidth;
    var T0 = this.offsetTop;
    var B0 = this.offsetTop + this.offsetHeight;
    //范围边界确定
    var L = L0 + 10;
    var R = R0 - 10;
    var T = T0 + 10;
    var B = B0 - 10;
    //范围确定
    var areaL = e.clientX < L;
    var areaR = e.clientX > R;
    var areaT = e.clientY < T;
    var areaB = e.clientY > B;
    //左侧范围
    if(areaL){
        this.style.cursor = ‘w-resize‘;
    }
    //右侧范围
    if(areaR){
        this.style.cursor = ‘e-resize‘;
    }
    //上侧范围
    if(areaT){
        this.style.cursor = ‘n-resize‘;
    }    
    //下侧范围
    if(areaB){
        this.style.cursor = ‘s-resize‘;
    }    
    //左上范围
    if(areaL && areaT){
        this.style.cursor = ‘nw-resize‘;
    }    
    //右上范围
    if(areaR && areaT){
        this.style.cursor = ‘ne-resize‘;
    }    
    //左下范围
    if(areaL && areaB){
        this.style.cursor = ‘sw-resize‘;
    }    
    //右下范围
    if(areaR && areaB){
        this.style.cursor = ‘se-resize‘;
    }    
    //中间范围    
    if(!areaL && !areaR && !areaT && !areaB){
        this.style.cursor = ‘default‘;
    }
}
</script>

大小改变

　　处于左侧范围时，改变元素的left和width值

　　处于右侧范围时，改变元素的left值

　　处于上侧范围时，改变元素的top和height值

　　处于下侧范围时，改变元素的height值

　　[注意]元素改变前的状态是指按下鼠标的瞬时元素的状态

<div id="test" style="height: 100px;width: 100px;background-color: pink;position:absolute;top:100px;left:200px;">测试文字</div>
<script>
//共享mousedown事件的变量，设置为全局变量
var EW,EH,EX,EY,disL,disH;
test.onmousemove = function(e){
    e = e || event;
    //元素边界确定
    var L0 = this.offsetLeft;
    var R0 = this.offsetLeft + this.offsetWidth;
    var T0 = this.offsetTop;
    var B0 = this.offsetTop + this.offsetHeight;
    //范围边界确定
    var L = L0 + 10;
    var R = R0 - 10;
    var T = T0 + 10;
    var B = B0 - 10;
    //范围确定
    var areaL = e.clientX < L;
    var areaR = e.clientX > R;
    var areaT = e.clientY < T;
    var areaB = e.clientY > B;
    //左侧范围
    if(areaL){this.style.cursor = ‘w-resize‘;}
    //右侧范围
    if(areaR){this.style.cursor = ‘e-resize‘;}
    //上侧范围
    if(areaT){this.style.cursor = ‘n-resize‘;}    
    //下侧范围
    if(areaB){this.style.cursor = ‘s-resize‘;}    
    //左上范围
    if(areaL && areaT){this.style.cursor = ‘nw-resize‘;}
    //右上范围
    if(areaR && areaT){this.style.cursor = ‘ne-resize‘;}
    //左下范围
    if(areaL && areaB){this.style.cursor = ‘sw-resize‘;}
    //右下范围
    if(areaR && areaB){this.style.cursor = ‘se-resize‘;}
    //中间范围    
    if(!areaL && !areaR && !areaT && !areaB){this.style.cursor = ‘default‘;}
    //如果改变元素尺寸功能开启
    if(test.clientChange){
        //处于左侧范围
        if(areaL){
            this.style.left = e.clientX - disL + ‘px‘;
            this.style.width = EW + EX - e.clientX + ‘px‘; 
        }
        //处于右侧范围
        if(areaR){this.style.width = EW + e.clientX - EX + ‘px‘;}
        //处于上侧范围
        if(areaT){
            this.style.top = e.clientY - disH + ‘px‘;
            this.style.height = EH + EY - e.clientY + ‘px‘;
        }
        //处于下侧范围
        if(areaB){this.style.height = EH + e.clientY - EY + ‘px‘; }                
    }
    test.onmousedown = function(e){
        e = e || event;
        //记录鼠标按下时的宽高及鼠标clienX、clientY值
        EW = this.offsetWidth;
        EH = this.offsetHeight;
        EX = e.clientX;
        EY = e.clientY;
        //记录鼠标按下位置距离元素左侧的距离
        disL = EX - L0;
        //记录鼠标按下位置距离元素上侧的距离
        disH = EY - T0;
        //开启改变元素尺寸功能
        test.clientChange = true;
    }
    test.onmouseup = function(e){
        //关闭改变元素尺寸功能
        test.clientChange = false;
    }    
}
</script>

代码优化

　　与拖拽移动元素一样，拖拽改变元素大小也存在同样的问题

　　问题一：文字及图片具有原生的拖放行为，通过取消默认行为可解决。IE8-浏览器不支持，使用全局捕获来实现IE兼容

　　问题二：拖放过快，鼠标移动速度快于mousemove触发速度时，鼠标脱离元素，使后续事件无法发生。把mousemove事件加在document上，即可解决

　　问题三：元素大小改变需要有范围限制

<div id="test" style="height: 100px;width: 100px;background-color: pink;position:absolute;top:100px;left:200px;">测试文字</div>
<script>
test.onmousemove = function(e){
    e = e || event;
    //元素边界确定
    var L0 = this.offsetLeft;
    var R0 = this.offsetLeft + this.offsetWidth;
    var T0 = this.offsetTop;
    var B0 = this.offsetTop + this.offsetHeight;
    //范围边界确定
    var L = L0 + 10;
    var R = R0 - 10;
    var T = T0 + 10;
    var B = B0 - 10;
    //范围确定
    var areaL = e.clientX < L;
    var areaR = e.clientX > R;
    var areaT = e.clientY < T;
    var areaB = e.clientY > B;
    //左侧范围
    if(areaL){this.style.cursor = ‘w-resize‘;}
    //右侧范围
    if(areaR){this.style.cursor = ‘e-resize‘;}
    //上侧范围
    if(areaT){this.style.cursor = ‘n-resize‘;}    
    //下侧范围
    if(areaB){this.style.cursor = ‘s-resize‘;}    
    //左上范围
    if(areaL && areaT){this.style.cursor = ‘nw-resize‘;}
    //右上范围
    if(areaR && areaT){this.style.cursor = ‘ne-resize‘;}
    //左下范围
    if(areaL && areaB){this.style.cursor = ‘sw-resize‘;}
    //右下范围
    if(areaR && areaB){this.style.cursor = ‘se-resize‘;}
    //中间范围    
    if(!areaL && !areaR && !areaT && !areaB){this.style.cursor = ‘default‘;}
    test.onmousedown = function(e){
        var that = this;
        e = e || event;
        //取消默认行为
        if(e.preventDefault){
            e.preventDefault();
        }
        //IE8-浏览器阻止默认行为
        if(that.setCapture){
            that.setCapture();
        }
        //记录鼠标按下时的宽高及鼠标clienX、clientY值
        var EW = this.offsetWidth;
        var EH = this.offsetHeight;
        var EX = e.clientX;
        var EY = e.clientY;
        //记录鼠标按下位置距离元素左侧的距离
        var disL = EX - L0;
        //记录鼠标按下位置距离元素上侧的距离
        var disH = EY - T0;
        document.onmousemove = function(e){
            var thatL,thatW,thatT,thatH;
            e = e || event;
            //处于左侧范围
            if(areaL){
                thatL= e.clientX - disL + ‘px‘;
                thatW= EW + EX - e.clientX + ‘px‘; 
            }
            //处于右侧范围
            if(areaR){thatW= EW + e.clientX - EX + ‘px‘;}
            //处于上侧范围
            if(areaT){
                thatT = e.clientY - disH + ‘px‘;
                thatH = EH + EY - e.clientY + ‘px‘;
            }
            //处于下侧范围
            if(areaB){thatH = EH + e.clientY - EY + ‘px‘;}
            //范围限定
            if(parseInt(thatW) < 60){thatW = ‘60px‘;}    
            if(parseInt(thatH) < 60){thatH = ‘60px‘;}
            //赋值
            if(thatW != undefined){that.style.width = thatW;}
            if(thatH != undefined){that.style.height = thatH;}
            if(thatT != undefined){that.style.top = thatT;}
            if(thatL != undefined){that.style.left = thatL;}            
        }
           document.onmouseup = function(e){
            //关闭改变元素尺寸功能
            document.onmousemove = null;
            //释放全局捕获
            if(that.releaseCapture){
                that.releaseCapture();
            }
        }
    }
}
</script>

源码查看