画布计时器的settimeout调用功能
[英]settimeout call function for canvas timer
问题描述
I wrote this code and I have problem with setTimeout call function for delay 
我写了这段代码，我对setTimeout调用函数有延迟的问题
This is a timer but setTimeout doesn't work every second 这是一个计时器，但setTimeout不能每秒工作
Why? 为什么？
<head>
<script>
function timer(sec) {
var c = document.getElementById("arcTimer");
var ctx = c.getContext("2d");
ctx.clearRect(0,0,200,200);
ctx.lineWidth = 20;
ctx.strokeStyle = "#0066CC";
ctx.beginPath();
ctx.arc(100,100,75,-0.5*Math.PI,sec*Math.PI);
ctx.stroke();
if ( sec >= 1.5 ) {
sec = -0.5;
}
setTimeout(timer(sec+0.03),1000);
}
</script>
</head>
<body onLoad="timer(-0.5);">
<canvas width="200" height="200" id="arcTimer" ></canvas>
</body>
Thanks 谢谢
2 个解决方案
解决方案1
1 已采纳 2013-10-13 21:41:46
The code 编码
setTimeout(timer(sec+0.03),1000);
... calls the timer function and passes its return value into setTimeout , exactly the way foo(bar()) calls bar and passes its return value into foo . ... 调用 timer函数，并将其返回值传递给setTimeout ，就像foo(bar()) 调用 bar并将其返回值传递给foo 。 Since your timer function (implicitly) returns undefined , and setTimeout doesn't do anything when you pass it undefined , that calls timer (immediately) and then does nothing. 由于您的timer函数（隐式）返回undefined ，而setTimeout在您传递undefined时不执行任何操作，因此（立即）调用timer ，然后不执行任何操作。
If you want to schedule a call to timer with sec+0.03 as its argument, create a function that does that: 如果要安排以sec+0.03作为其参数的timer调用，请创建一个执行该操作的函数：
setTimeout(function() {
timer(sec+0.03);
}, 1000);
解决方案2
0 2013-10-13 21:45:33
this line is wrong: setTimeout(timer(sec+0.03),1000); 这行是错误的：setTimeout（timer（sec + 0.03），1000）; the first parameter is undefined, not a function. 第一个参数是不确定的，不是函数。
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