如何在 Leap Motion 框架中获取元素？答案

【问题标题】：How to get element in Leap Motion frame?如何在 Leap Motion 框架中获取元素？
【发布时间】：2014-06-26 08:41:41
【问题描述】：

这就是我试图通过 WebSocket 从 Leap Motion 设备的框架中获取特定元素的方式。

var webSocket = require('ws');
ws = new webSocket('ws://127.0.0.1:6437');

ws.on('message', function(data, flags) {
    var frame = JSON.parse(data);
    var id = frame.hands;
    var pos = id[0];
    console.log(pos);
});

JSON 对象看起来像这样：Leap Motion Sample Frame

我收到了这个错误。

Sanjeet-Suhags-MacBook-Pro:LeapJS sanjeetsuhag$ node index.js

/Users/sanjeetsuhag/Developer/Node/LeapJS/index.js:7
    var pos = id[0];
                ^
TypeError: Cannot read property '0' of undefined
    at WebSocket.<anonymous> (/Users/sanjeetsuhag/Developer/Node/LeapJS/index.js:7:14)
    at WebSocket.emit (events.js:98:17)
    at Receiver.self._receiver.ontext (/Users/sanjeetsuhag/Developer/Node/LeapJS/node_modules/ws/lib/WebSocket.js:697:10)
    at Receiver.opcodes.1.finish (/Users/sanjeetsuhag/Developer/Node/LeapJS/node_modules/ws/lib/Receiver.js:397:14)
    at Receiver.expectHandler (/Users/sanjeetsuhag/Developer/Node/LeapJS/node_modules/ws/lib/Receiver.js:384:31)
    at Receiver.add (/Users/sanjeetsuhag/Developer/Node/LeapJS/node_modules/ws/lib/Receiver.js:93:24)
    at firstHandler (/Users/sanjeetsuhag/Developer/Node/LeapJS/node_modules/ws/lib/WebSocket.js:673:22)
    at process._tickCallback (node.js:419:13)

怎么了？谢谢。

【问题讨论】：

标签： javascript node.js leap-motion

【解决方案1】：

如果没有检测到手，hands 数组为空，只需将代码更改为：

ws.on('message', function(data, flags) {
    var frame = JSON.parse(data);
    var id = frame.hands;
    if (id.length === 0)
        return;
    var pos = id[0];
    console.log(pos);
});

【讨论】：