Question

我目前正在开发Electron.js应用程序，但遇到了异步问题。我在三个if语句中依次执行三个函数（downdloadFile（）），但它们异步运行；我已经尝试过使用async / await，但是没有用。这是我的代码：

ipcMain.on('play',(event,payload) => {
        launcherConfig.savedRam = payload.savedRam;
        launcherConfig.savedMaxPermSize = payload.savedMaxPermSize;
        if(payload.selectedPacket) {
            //FIRST IF
            if (!fs.existsSync(launcherDir + "\\natives")) {
                downloadFile("http://soulnetwork.it/launcher/natives.zip", launcherDir + "\\natives.zip", true, 'natives');
            }
            //SECOND IF
            if (!fs.existsSync(launcherDir + "\\bin")) {
                downloadFile("http://soulnetwork.it/launcher/bin.zip", launcherDir + "\\bin.zip", true, 'bin');
            }
            //THIRD IF
            if (launcherConfig.installed_modpacks.includes(payload.selectedPacket)) {
                launchMinecraft(payload.selectedPacket);
                saveConfig();
            } else {
                downloadFile(`http://soulnetwork.it/launcher/modpacks/${payload.selectedPacket}.zip`, launcherDir + "\\modpacks\\" + payload.selectedPacket + '.zip', true, payload.selectedPacket, launchMinecraft);
                launcherConfig.installed_modpacks.push(payload.selectedPacket);
                saveConfig();
            }
        }
}

function downloadFile(file_url , targetPath, showProcess, packetName, callback){
// Save variable to know progress
var received_bytes = 0;
var total_bytes = 0;

var req = request({
    method: 'GET',
    uri: file_url
});

var progressWindow = null;

if(showProcess){
    progressWindow = new BrowserWindow({width: 300, height: 60, title: `Downloading ${packetName}`,icon: '../public/images/sn.png'})
    progressWindow.setProgressBar(0.0);
    progressWindow.loadURL('file://' + __dirname + '/views/download.ejs');
    progressWindow.setMenu(null);
}

var out = fs.createWriteStream(targetPath);
req.pipe(out);

req.on('response', function ( data ) {
    // Change the total bytes value to get progress later.
    total_bytes = parseInt(data.headers['content-length' ]);
});

req.on('data', function(chunk) {
    // Update the received bytes
    received_bytes += chunk.length;
    if(showProcess)
        showProgress(progressWindow,received_bytes, total_bytes);
});

req.on('end', function() {
    if(showProcess)
        progressWindow.close();
    if(targetPath.includes('.zip')){
        var zip = new archiver(targetPath);
        zip.extractAllTo(targetPath.substr(0,targetPath.length-4-packetName.length));
        fs.unlinkSync(targetPath);
    }
    if(callback)
        callback(packetName);
    console.log("RETURN");
    return;
});
}

使用回调系统会产生很多麻烦，而且这也是多余的，我希望能找到其他解决方案。谢谢您的时间！

Answer 1

当前console.log("RETURN")所在的位置可以解决downloadFile返回的Promise。然后，您可以简单地等待if分支中的调用（并将async回调传递给ipcMain当然）。

采用更简单形式的结构如下所示

function doJob () {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log('RETURN')
      resolve()
    }, 2000)
  })
}
// ipcMain.on('play', async (event, payload) => { ... })
(async () => {
  if (true) {
    await doJob()
  }
  if (true) {
    await doJob()
  }
})()

Answer 2

我可以看到您在所有三个时间里都对launcherDir产生了影响！即使在操作失败的情况下，它也会始终执行第一个进程，即如果正在检查则最后一个进程 launcherDir +“ \ natives” +“ \ bin”还是这是期望的行为，否则我认为您所有的if都会失败

电子上的异步问题

2 个答案: