constructor(){
super();
this.state={
data : [1,2,3,4,1,2,3,4,1,3,1,4,12,2,3,2]
};
}
componentDidMount(){setInterval(this.updateCanvas(),5000);}
updateCanvas() {
console.log(this.props.newData);
let data = this.state.data.slice();
let length = data.length;
console.log(length);
data.push(20);
this.setState({data:data},()=>{console.log(this.state.data);});
}
我试图每5秒将一个新值推送到状态，但状态立即改变。我怎样才能达到我想要的效果？
答案 0 :(得分：3)
状态立即更改，因为您正在通过向其添加括号来调用您在此行上立即传递给setInterval的回调方法：
setInterval(this.updateCanvas(),5000);
//---------------------------^
// Adding these to function will invoke it
解决方案是将引用传递给没有括号的函数（并且它们不会立即调用它）
setInterval(this.updateCanvas,5000);
答案 1 :(得分：1)
从this.updateCanvas（）中删除该括号。 即 setInterval（this.updateCanvas，5000）;}
第一个将立即执行该功能，而第二个将其作为设定间隔
的函数传入答案 2 :(得分：0)
为什么不起作用？
实际上有两个问题：
您需要将函数传递给<html>
<head>
<title>PARTICLES</title>
<script src="http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<script>
$(document).ready(function(){
var d = document, $d = $(d),
w = window, $w = $(w),
wWidth = $w.width(), wHeight = $w.height(),
credit = $('.credit > a'),
particles = $('.particles'),
particleCount = 0,
sizes = [
15, 20, 25, 35, 45
],
colors = [
'#f44336', '#e91e63', '#9c27b0', '#673ab7', '#3f51b5',
'#2196f3', '#03a9f4', '#00bcd4', '#009688', '#4CAF50',
'#8BC34A', '#CDDC39', '#FFEB3B', '#FFC107', '#FF9800',
'#FF5722', '#795548', '#9E9E9E', '#607D8B', '#777777'
],
mouseX = $w.width() / 2, mouseY = $w.height() / 2;
function updateParticleCount () {
$('.particle-count > .number').text(particleCount);
};
$w
.on( 'resize' , function () {
wWidth = $w.width();
wHeight = $w.height();
});
$d
.on( 'mousemove touchmove' , function ( event ) {
event.preventDefault();
event.stopPropagation();
mouseX = event.clientX;
mouseY = event.clientY;
if( !!event.originalEvent.touches ) {
mouseX = event.originalEvent.touches[0].clientX;
mouseY = event.originalEvent.touches[0].clientY;
}
})
.on( 'mousedown touchstart' , function( event ) {
if( event.target === credit.get(0) ){
return;
}
mouseX = event.clientX;
mouseY = event.clientY;
if( !!event.originalEvent.touches ) {
mouseX = event.originalEvent.touches[0].clientX;
mouseY = event.originalEvent.touches[0].clientY;
}
var timer = setInterval(function () {
$d
.one('mouseup mouseleave touchend touchcancel touchleave', function () {
clearInterval( timer );
})
createParticle( event );
}, 1000 / 60)
});
function createParticle ( event ) {
var particle = $('<div class="particle"/>'),
size = sizes[Math.floor(Math.random() * sizes.length)],
color = colors[Math.floor(Math.random() * colors.length)],
negative = size/2,
speedHorz = Math.random() * 10,
speedUp = Math.random() * 25,
spinVal = 360 * Math.random(),
spinSpeed = ((36 * Math.random())) * (Math.random() <=.5 ? -1 : 1),
otime,
time = otime = (1 + (.5 * Math.random())) * 1000,
top = (mouseY - negative),
left = (mouseX - negative),
direction = Math.random() <=.5 ? -1 : 1 ,
life = 10;
particle
.css({
height: size + 'px',
width: size + 'px',
top: top + 'px',
left: left + 'px',
background: color,
transform: 'rotate(' + spinVal + 'deg)',
webkitTransform: 'rotate(' + spinVal + 'deg)'
})
.appendTo( particles );
particleCount++;
updateParticleCount();
var particleTimer = setInterval(function () {
time = time - life;
left = left - (speedHorz * direction);
top = top - speedUp;
speedUp = Math.min(size, speedUp - 1);
spinVal = spinVal + spinSpeed;
particle
.css({
height: size + 'px',
width: size + 'px',
top: top + 'px',
left: left + 'px',
opacity: ((time / otime)/2) + .25,
transform: 'rotate(' + spinVal + 'deg)',
webkitTransform: 'rotate(' + spinVal + 'deg)'
});
if( time <= 0 || left <= -size || left >= wWidth + size || top >= wHeight + size ) {
particle.remove();
particleCount--;
updateParticleCount();
clearInterval(particleTimer);
}
}, 1000 / 50);
}
});
</script>
<style>
html, body {
background: #fff;
width: 100%;
height: 100%;
overflow: hidden;
cursor: default;
-webkit-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
font-family: 'PT Sans', sans-serif;
}
.title {
font-size: 10vw;
font-weight: 700;
text-align: center;
margin-top: 15%;
color: #444;
}
.subtitle {
font-size: 4vw;
color: #777;
font-weight: normal;
text-align: center;
margin-top: 0;
}
.credit {
position: absolute;
bottom: 5px;
width: 100%;
display: block;
text-align: center;
color: #777;
}
.credit > a {
color: #777;
}
.particle-count {
display: block;
text-align: center;
margin: 25px 0;
}
.particles > .particle {
border-radius: 100%;
background: transparent;
position: absolute;
background-size: 100% 100%;
background-repeat: no-repeat;
}
.particles > .particle.smaller {
width: 5px;
height: 5px;
}
.particles > .particle.small {
width: 10px;
height: 10px;
}
.particles > .particle.normal {
width: 15px;
height: 15px;
}
.particles > .particle.big {
width: 20px;
height: 20px;
}
.particles > .particle.bigger {
width: 25px;
height: 25px;
}
</style>
</head>
<body>
<h1 class='title'>PARTICLES!</h1>
<h4 class='subtitle'>Click / Touch Anywhere</h4>
<div class='particle-count'>
<span class='number'>0</span>
Particles
</div>
<span class='credit'>
Created by
<a href='https://twitter.com/Shawn_Sauce' target='_blank'>Shawn G.</a>
</span>
<div class='particles'></div>
</body>
</html>
。 setInterval method除了函数外，它是第一个参数。使用setInterval时，将传递调用的方法setInterval(this.updateCanvas(),5000);的返回值。由于该方法没有返回任何内容（未定义），实际得到的是this.updateCanvas()。
您必须将该函数绑定到组件实例的window.setInterval(undefined, 5000);。由于this方法使用updateCanvas，例如this，
将this.setState()绑定到updateCanvas并在this中调用：
传递setInterval箭头功能，并在内部调用setInveral：
updateCanvas或
将方法绑定到组件实例componentDidMount(){
setInterval(() => this.updateCanvas(),5000);
}
：
this