HTML5 mobile development-code examples for scrolling and inertial easing

1. The following are three ways to implement scrolling: 1) Using native cssattribute overflow: scroll p id= parent style = overflow:scroll; pid='content'content area/p /p Notice: There is a bug in android, it will roll back after scrolling To reach the top content area, the solution is to use the latter two methods to achieve 2) js programming implementation idea: compare the position changes before and after the finger moves on the screen to change the content element content

　1. Scroll

The following are three implementation methods:

1) Use the native css attribute overflow: scroll

<div id="parent" style="overflow:scroll;>
    <div id=&#39;content&#39;>内容区域</div>
</div>

Notice:

There is a bug in android, and it will roll back after scrolling To reach the top content area, the solution is to use the latter two methods to achieve

　2) js programming implementation

Idea: compare the position changes before and after the finger moves on the screen to change the position of the content element content

The first step: Set the parent's overflow to hidden, set the content's position to relative, and top to 0;

The second step: Monitor the touch event

var parent = document.getElementById('parent');

parent.addEventListener('touchstart', function(e) {
    // do touchstart
});
parent.addEventListener('touchmove', function(e) {
    // do touchmove
});
parent.addEventListener('touchend', function(e) {
    // do touchend
});

The third step Step: Implement rolling code

/**
 * 这里只实现垂直滚动
 */
var parent = document.getElementById('parent');
var content = document.getElementById('content')
var startY = 0; // 初始位置
var lastY = 0; // 上一次位置

parent.addEventListener('touchstart', function(e) {
    lastY = startY = e.touches[0].pageY;
});
parent.addEventListener('touchmove', function(e) {
    var nowY = e.touches[0].pageY;
    var moveY = nowY - lastY;
    var contentTop = content.style.top.replace('px', '');
    // 设置top值移动content
    content.style.top = (parseInt(contentTop) + moveY) + 'px';
    lastY = nowY;

});
parent.addEventListener('touchend', function(e) {
    // do touchend
    var nowY = e.touches[0].pageY;
    var moveY = nowY - lastY;
    var contentTop = content.style.top.replace('px', '');
    // 设置top值移动content
    content.style.top = (parseInt(contentTop) + moveY) + 'px';
    lastY = nowY;
});

Step 4: Optimization

The above code runs much better on a mobile phone than on a PC

For the optimization part, please see:

　3) Use iScroll4 framework

　var scroll = new iScroll('parent', {
　　hScrollbar: false,
　　vScrollbar: true,
　　checkDOMChanges : true
　　});

　2. Inertial easing

Idea: Take the average speed v of the finger swiping on the screen in the last period of time, and let v press one Decrementfunctionchanges until it cannot move or v<=0

/**
 * 这里只实现垂直滚动
 */
var parent = document.getElementById('parent');
var content = document.getElementById('content')
var startY = 0; // 初始位置
var lastY = 0; // 上一次位置

/**
 * 用于缓动的变量
 */
var lastMoveTime = 0;
var lastMoveStart = 0;
var stopInertiaMove = false; // 是否停止缓动

parent.addEventListener('touchstart', function(e) {
    lastY = startY = e.touches[0].pageY;

    /**
     * 缓动代码
     */
    lastMoveStart = lastY;
    lastMoveTime = e.timeStamp || Date.now();
    stopInertiaMove = true;
});
parent.addEventListener('touchmove', function(e) {
    var nowY = e.touches[0].pageY;
    var moveY = nowY - lastY;
    var contentTop = content.style.top.replace('px', '');
    // 设置top值移动content
    content.style.top = (parseInt(contentTop) + moveY) + 'px';
    lastY = nowY;

    /**
     * 缓动代码
     */
    var nowTime = e.timeStamp || Date.now();
    stopInertiaMove = true;
    if(nowTime - lastMoveTime > 300) {
        lastMoveTime = nowTime;
        lastMoveStart = nowY;
    }
});
parent.addEventListener('touchend', function(e) {
    // do touchend
    var nowY = e.touches[0].pageY;
    var moveY = nowY - lastY;
    var contentTop = content.style.top.replace('px', '');
    var contentY = (parseInt(contentTop) + moveY);
    // 设置top值移动content
    content.style.top =  contentY + 'px';
    lastY = nowY;

    /**
     * 缓动代码
     */
    var nowTime = e.timeStamp || Date.now();
    var v = (nowY - lastMoveStart) / (nowTime - lastMoveTime); //最后一段时间手指划动速度
    stopInertiaMove = false;
    (function(v, startTime, contentY) {
        var dir = v > 0 ? -1 : 1; //加速度方向
        var deceleration = dir*0.0006;
        var duration = v / deceleration; // 速度消减至0所需时间
        var dist = v * duration / 2; //最终移动多少
        function inertiaMove() {
            if(stopInertiaMove) return;
            var nowTime = e.timeStamp || Date.now();
            var t = nowTime-startTime;
            var nowV = v + t*deceleration;
            // 速度方向变化表示速度达到0了
            if(dir*nowV < 0) {
                return;
            }
            var moveY = (v + nowV)/2 * t;
            content.style.top = (contentY + moveY) + "px";
            setTimeout(inertiaMove, 10);
        }
        inertiaMove();
    })(v, nowTime, contentY);
});

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