How to implement Picke in mobile effects-JS Tutorial-php.cn

Written in front

Following the previous research on mobile effects, this time let’s take a look at How to implement Picke in mobile effectsThe implementation principle of the selector

Swiper of mobile effects

See the code here: github

How to implement Picke in mobile effects

##1. Core analysis

1.1 Basic HTML structure

<!--     说明：    
1. 类 How to implement Picke in mobile effects-3d 是为了提供3d视角，如果不需要可以去掉    
2. 类 How to implement Picke in mobile effects-slot-absolute 在3d视角中需要加上，因为下面相对定位的 How to implement Picke in mobile effects-items 是要相对父容器进行    transform的，如果不加，就会造成位移不正确    3. DOM中所有的style样式都是在初始化的时候加上的--><p class="How to implement Picke in mobile effects How to implement Picke in mobile effects-3d">
    <p class="How to implement Picke in mobile effects-items">
        <p class="How to implement Picke in mobile effects-slot How to implement Picke in mobile effects-slot-absolute" style="flex:1;">
            <p class="How to implement Picke in mobile effects-slot-wrapper" id="wrapper" style="height: 108px;">
                <p class="How to implement Picke in mobile effects-item How to implement Picke in mobile effects-selected" style="height:36px;line-height: 36px">1981</p>
                <!-- ... -->
                <p class="How to implement Picke in mobile effects-item" style="height:36px;line-height: 36px">1999</p>
            </p>
        </p>
    </p>
    <p class="How to implement Picke in mobile effects-center-highlight" style="height:36px;margin-top:-18px;"></p></p>

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1.2 Initializing DOM

Because the

How to implement Picke in mobile effects in the Ele.me source code is generated using the v-for instruction, Therefore, I simply use javascript to simulate the generation of DOM.

var el = document.querySelector(&#39;#wrapper&#39;);
var animationFrameId = null;
var currentValue;
var itemHeight = 36;
var visibleItemCount = 3;
var valueIndex = 0;
var rotateEffect = true;
var datas = [&#39;1981&#39;, &#39;1982&#39;, &#39;1983&#39;, &#39;...&#39;, &#39;1999&#39;];// 如果支持3d视角，则给<p class="How to implement Picke in mobile effects"></p>加上类"How to implement Picke in mobile effects-3d"// <p class="How to implement Picke in mobile effects-slot" style="flex:1;">加上类"How to implement Picke in mobile effects-slot-absolute"if (rotateEffect) {
    var How to implement Picke in mobile effects = document.querySelector(&#39;.How to implement Picke in mobile effects&#39;);
    var How to implement Picke in mobile effectsSlot = document.querySelector(&#39;.How to implement Picke in mobile effects-slot&#39;);
    How to implement Picke in mobile effects.classList.add(&#39;How to implement Picke in mobile effects-3d&#39;);
    How to implement Picke in mobile effectsSlot.classList.add(&#39;How to implement Picke in mobile effects-slot-absolute&#39;);}// 限定容器高度el.style.height = `${visibleItemCount * itemHeight}px`;// 生成DOMvar html = &#39;&#39;;datas.forEach(function(data, index) {
    html += `<p class="How to implement Picke in mobile effects-item" style="height:36px;line-height:36px;">${data}</p>`;});el.innerHTML = html;// 激活当前itemvar How to implement Picke in mobile effectsItems = document.querySelectorAll(&#39;.How to implement Picke in mobile effects-item&#39;);How to implement Picke in mobile effectsItems[valueIndex].classList.add(&#39;How to implement Picke in mobile effects-selected&#39;);

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1.3 Initialization event

Generally speaking, the events of

How to implement Picke in mobile effects

also include sliding start, sliding, and sliding end. Because it is a mobile device after all, sliding is inevitable. This time, the sliding event is encapsulated in the source code, compatible with the

PC terminal, and eliminates the impact of dragging and selection. Let’s take a closer look at the analysis. `

/**  * draggable.js  * 只是起到一定的兼容性 * 实质和直接调用 el.addEventListener(&#39;touchstart&#39;, startFn); 并没有多大差别 */// 滑动开始// touchstart 和 mousedown 可见对PC端的兼容// onselectstart/ondragstart 直接return 可见排除了拖动和选择element.addEventListener(supportTouch ? &#39;touchstart&#39; : &#39;mousedown&#39;, function(event) {
    if (isDragging) return;
    document.onselectstart = function() { return false; };
    document.ondragstart = function() { return false; };

    // ...});// 滑动结束var endFn = function(event) {
    // 注销事件
    if (!supportTouch) {
        document.removeEventListener(&#39;mousemove&#39;, moveFn);
        document.removeEventListener(&#39;mouseup&#39;, endFn);
    }
    document.onselectstart = null;
    document.ondragstart = null;

    isDragging = false;

    if (options.end) {
        options.end(supportTouch ? event.changedTouches[0] || event.touches[0] : event);
    }}

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If
DOM

follows your sliding on the mobile phone screen, the method is similar, it is nothing more than recording the starting position at the beginning of sliding. Calculate the displacement in real time, and after the sliding is completed,

DOM will slide to the position where it should slide. For this point, please refer to the previous article Swiper for mobile effects. This article has the same method. Here we focus on the difference

// 滑动开始的执行事件方法start: function(event) {
    dragState = {
        range: getDragRange(),
        // ...
        startTranslateTop: translateUtil.getElementTranslate(el).top
    };}

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There are two methods, the first
getDragRange

and the second

getElementTranslate(el ).

The function of the first function is to obtain the minimum and maximum displacement that

can slide, which will be used in the sliding end event arrive. Regarding how to calculate, here is a brief mention. When you slide down, the maximum cannot exceed the top of the middle
item. This is why itemHeight * Math.floor(visibleItemCount / 2) , and when sliding upward, the maximum cannot exceed the bottom of the middle item, -itemHeight * (valuesLength - Math.ceil(visibleItemCount / 2)), just think about it carefully.
The second function is to obtain the
value of the current
How to implement Picke in mobile effects as the basis for the next sliding calculation. In fact, it feels like this is quite troublesome, because the translate value will definitely be calculated in touchend. We only need to save the last sliding movement value each time, instead of doing it every time. Get it from DOM.

/** * translateUtil * 对浏览器对前缀支持的一些判断 * 检测浏览器对3d属性的支持情况 * 获取当前的translate值/清空How to implement Picke in mobile effects的translate值/移动How to implement Picke in mobile effects * 对于浏览器的检测方面，这也算是一个比较好的工具类 */var docStyle = document.documentElement.style;var engine;var translate3d = false;// 浏览器判断if (window.opera && Object.prototype.toString.call(opera) === &#39;[object Opera]&#39;) {
    engine = &#39;presto&#39;;} else if (&#39;MozAppearance&#39; in docStyle) {
    engine = &#39;gecko&#39;;} else if (&#39;WebkitAppearance&#39; in docStyle) {
    engine = &#39;webkit&#39;;} else if (typeof navigator.cpuClass === &#39;string&#39;) {
    engine = &#39;trident&#39;;}// css前缀var cssPrefix = {
    trident: &#39;-ms-&#39;,        // IE
    gecko: &#39;-moz-&#39;,         // FireFox
    webkit: &#39;-webkit-&#39;,     // Chrome/Safari/etc...
    presto: &#39;-o-&#39;           // Opera}[engine];// style前缀var vendorPrefix = {
    trident: &#39;ms&#39;,
    gecko: &#39;Moz&#39;,
    webkit: &#39;Webkit&#39;,
    presto: &#39;O&#39;}[engine];var helpElem = document.createElement(&#39;p&#39;);var perspectiveProperty = vendorPrefix + &#39;Perspective&#39;;var transformProperty = vendorPrefix + &#39;Transform&#39;;var transformStyleName = cssPrefix + &#39;transform&#39;;var transitionProperty = vendorPrefix + &#39;Transition&#39;;var transitionStyleName = cssPrefix + &#39;transition&#39;;var transitionEndProperty = vendorPrefix.toLowerCase() + &#39;TransitionEnd&#39;;if (helpElem.style[perspectiveProperty] !== undefined) {
    translate3d = true;}// 讲一下这个正则// \s*(-?\d+(\.\d+?)?)px 这是一个单元，匹配这样的 -23.15px, 剩下的应该就好理解了var regexp = /translate\(\s*(-?\d+(\.\d+?)?)px,\s*(-?\d+(\.\d+?)?)px\)\s*translateZ\(0px\)/ig;

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Next look at the sliding

drag: function(event) {
    // 加上 dragging 类是为了清除过渡效果，在swiper中也有同样的应用
    el.classList.add(&#39;dragging&#39;);

    dragState.left = event.pageX;
    dragState.top = event.pageY;

    var deltaY = dragState.top - dragState.startTop;
  
    // 计算当前的滑动位移
    var translate = dragState.startTranslateTop + deltaY;

    // 滑动元素
    translateUtil.translateElement(el, null, translate);
    velocityTranslate = translate - prevTranslate || translate;

    prevTranslate = translate;

    if (rotateEffect) {
        updateRotate(prevTranslate, How to implement Picke in mobile effectsItems);
    }}

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See the above code There is a
velocityTranslate

. This value has a magical effect. I didn’t know it at first. Later, I found out that it was used after the sliding was completed, and then I realized that it represents a displacement value of a velocity. What is velocity? Just like when you slide quickly, you always hope that it can slide with inertia. This value multiplied by an inertia value can get an inertial displacement. Look at the code in

end.

end: function() {
    // 添加过渡
    el.classList.remove(&#39;dragging&#39;);
    // 惯性值
    var momentumRatio = 7;
    var currentTranslate = translateUtil.getElementTranslate(el).top;
    var duration = new Date() - dragState.start;

    var momentumTranslate;
    if (duration < 300) {
        momentumTranslate = currentTranslate + velocityTranslate * momentumRatio;
    }

    // 加上惯性速率之后的位移值
    console.log(&#39;momentumTranslate&#39;, momentumTranslate);

    dragRange = dragState.range;

    setTimeout(function() {
        var translate;
        if (momentumTranslate) {
            translate = Math.round(momentumTranslate / itemHeight) * itemHeight;
        } else {
            translate = Math.round(currentTranslate / itemHeight) * itemHeight;
        }

        // 取得最终的位移值，
        // 必须为itemHeight的倍数
        // 在范围的最大值和最小值中取
        translate = Math.max(Math.min(translate, dragRange[1]), dragRange[0]);
        translateUtil.translateElement(el, null, translate);

        // 计算得出当前位移下应该对应的实际值
        currentValue = translate2Value(translate);

        // 3d效果
        if (rotateEffect) {
            planUpdateRotate();
        }
    }, 10);

    dragState = {};}

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This is the implementation process of the entire
How to implement Picke in mobile effects

. It can be used without the

3d effect. Let’s take a look at how to achieve the 3D effect. There is an initial initialization in doOnValuesChange.

[].forEach.call(items, function(item, index) {
    translateUtil.translateElement(item, null, itemHeight * index);});

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sets a displacement value based on the index for each
item

. At this time, the positioning of each

item is They must be absolute, so that they are next to each other after the displacement. Otherwise, there may be a space of itemHeight in the middle. 3D

The most critical point in the effect is how to calculate the flip angle. A constant object is defined in the source code:

var VISIBEL_ITEMS_ANGLE_MAP = {
    3: -45,
    5: -20,
    7: -15};

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You can see that when there are only 3 visible elements, the highlighted part is relative to the
X

axis Parallel, the previous

item must be rotated 45 degrees clockwise around the X axis, and the next item must be rotated 45 degrees counterclockwise around the X axis Spend. In addition, there is a section of code that is particularly convoluted. According to my understanding, it is as follows:

// 当前item相对于顶部原本应该有的位移值var itemOffsetTop = index * itemHeight; // 滑动过程中，相对于最开始的位置滑动的位移值var translateOffset = dragRange[1] - currentTranslate;// 当应该有的位移值和滑动的位移值相等的时候，也就说明了当前的`item`被选中// 也就是说此时当前的角度为0var itemOffset = itemOffsetTop - translateOffset;var percentage = itemOffset / itemHeight;var angle = angleUnit * percentage;if (angle > 180) angle = 180;if (angle < -180) angle = -180;rotateElement(item, angle);

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If you think it is too convoluted, there is actually no need to follow his approach. We only need to find a way to determine whether each
item

is in the previous or next position relative to the currently selected

item, and we can calculate the angle based on this. 2. Summary

I have read so much about the

How to implement Picke in mobile effects

component in Ele.me. Overall, it is very similar to the sliding one in

swiper Similar, the key point is to calculate the final displacement value to slide to the correct position according to the displacement value. As for how to calculate the value, in fact, everyone's implementation may be similar, and there is no need to follow the source code. You can Add your own understanding appropriately, so that you may be more comfortable writing code. This is just my personal understanding, and I hope it can provide some help to myself and everyone else.

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