promise.then()和promise.catch()不在节点程序中工作

Question

我正在尝试显示一个实时流，由opencv4nodejs读取，并由人脸识别模块处理。这里的问题是，promise.then()不能工作。甚至没有在相应的条件下捕获()。(我是节点和承诺的新手。)预期工作流程：

读取帧从摄像头(通过cv.read) ->保存到缓冲区(由cv.imwrite) ->读取帧从缓冲区(由fr.loadImage) ->进程(由detector.locateFaces) ->显示->重复处理。

const fr = require('face-recognition');
const cv = require('opencv4nodejs');
const events = require('events');

const detector = fr.FaceDetector()
const cap = new cv.VideoCapture(0);
const win = new fr.ImageWindow()
const eventEmitter = new events.EventEmitter();

function process(){
    console.log('process');
    return new Promise(function(resolve,reject){
        console.log('promise');
        var frame = cap.read();
        cv.imwrite(`${__dirname}/buffer/img.jpg`, frame);
        if(frame != null)
            resolve('resolve');
        else
            reject('Problem While reading');
    });
}
eventEmitter.on('read',function(string){
    console.log('event call');
    var promise = process();
    promise.then(function(string){
        console.log(string);
        const image = fr.loadImage(`${__dirname}/buffer/img.jpg`);
        const faceRectangles = detector.locateFaces(image);
        win.setImage(image);
        fr.hitEnterToContinue();
    }).catch(function(err){
        console.log(err);
    });
});
while(true){
    console.log('emit');
    eventEmitter.emit('read','abcd');
}
/*****expected output should be*****
emit
event call
process
promise
resolve
/*****getting output*****
emit
event call
process
promise
*/

Answer 1

const fr = require('face-recognition');
const cv = require('opencv4nodejs');
const events = require('events');

const detector = fr.FaceDetector()
const cap = new cv.VideoCapture(0);
const win = new fr.ImageWindow()
const eventEmitter = new events.EventEmitter();

function process(){
    console.log('process');
    return new Promise(function(resolve,reject){
        console.log('promise');
        var frame = cap.read();
        cv.imwrite(`${__dirname}/buffer/img.jpg`, frame);
        if(frame != null)
            resolve('resolve');
        else
            reject('Problem While reading');
    });
}
eventEmitter.on('read',function(string){
    console.log('event call');
    var promise = process();
    console.log(promise);
    promise.then(function(string){
        console.log(string);
        const image = fr.loadImage(`${__dirname}/buffer/img.jpg`);
        const faceRectangles = detector.locateFaces(image);
        console.log(faceRectangles);
        win.setImage(image);
        // fr.hitEnterToContinue();
        eventEmitter.emit('read','abcd');
    }).catch(function(err){
        console.log(err);
    });
});
eventEmitter.emit('read','abcd');

更改:1)从eventEmitter.emit('read','abcd'); 2中删除while循环)在promise.then()中递归地发出事件--我观察到，在连续发射事件时，promise.then()不能工作，所以我在promise.then()中发出事件，所以现在它很好地工作。

Answer 2

由于您正在使用eventEmitter，所以您的代码应该如下所示：

const fr = require('face-recognition');
const cv = require('opencv4nodejs');
const events = require('events');
const Promise = require('bluebird');

const detector = fr.FaceDetector()
const cap = new cv.VideoCapture(0);
const win = new fr.ImageWindow()
const eventEmitter = new events.EventEmitter();

function process(){
    console.log('process');
    return new Promise(function(resolve,reject) {
        console.log('promise');
        var frame = cap.read();
        cv.imwrite(`${__dirname}/buffer/img.jpg`, frame);
        if(frame != null)
            resolve();
        else
            reject('Problem While reading');
    });
}
eventEmitter.on('read',function(string){
    console.log('event call');
    var promise = process();
    promise.then(function(string){
        console.log(string);
        const image = fr.loadImage(`${__dirname}/buffer/img.jpg`);
        const faceRectangles = detector.locateFaces(image);
        win.setImage(image);
        fr.hitEnterToContinue();
    }).catch(function(err){
        console.log(err);
    });
});
while(true){
    console.log('emit');
    eventEmitter.emit('read','abcd');
}