Cordova SQLite插件承諾JavaScript鏈

Question

大家好，我想在一次迭代中調用3個諾言，然后在它們完成之后再進行一次迭代，再進行一次調用。 誰能幫我解決這個問題？

for(i=0;i<$scope.CurrentES.Issues.length;i++){
    app.Logger($scope.CurrentES.Issues[i])
    var promiseEvidence = $cordovaSQLite.execute(db, queryEvidence, [$scope.CurrentES.Issues[i].Evidence.Id]).then(function(result){
    app.Logger(result.rows.item(0).ImageID);
    app.Logger(result.rows.item(0).SupportingDocumetID);
    app.Logger(result.rows.item(0).QuoteID);
    var promiseImageLib = $cordovaSQLite.execute(db, queryImgLib, [result.rows.item(0).ImageID]).then(
        function (r) {
            if (r.rows.length != 0) {
                var img = r.rows.item(0);
                issue.Evidence.ImageLibary.Id = img.id;
                issue.Evidence.ImageLibary.ServerID = img.ServerID;
                issue.Evidence.ImageLibary.Conclude = img.Conclusion;
                issue.Evidence.ImageLibary.ImageTitle = img.Title;
                issue.Evidence.ImageLibary.Image = img.Image;
            }
        }, function (e) {
            app.Logger(e);
        });
        var promiseSupp = $cordovaSQLite.execute(db, querySupp, [result.rows.item(0).SupportingDocumetID]).then(
            function (r) {
                if (r.rows.length != 0) {
                    var sup = r.rows.item(0);
                    issue.Evidence.SupportingDocument.Id = sup.id;
                    issue.Evidence.SupportingDocument.ServerID = sup.ServerID;
                    issue.Evidence.SupportingDocument.Link = sup.Link;
                    issue.Evidence.SupportingDocument.Title = sup.Title;
                    issue.Evidence.SupportingDocument.Quoatation = sup.Extract;
                }
            }, function (e) {
                app.Logger(e);
            });
            var promiseQuote = $cordovaSQLite.execute(db, quesryQuote, [result.rows.item(0).QuoteID]).then(
                function (r) {
                    if (r.rows.length != 0) {
                        var quot = r.rows.item(0);
                        issue.Evidence.Quote.Id = quot.id;
                        issue.Evidence.Quote.ServerID = quot.ServerID;
                        issue.Evidence.Quote.Quoatation = quot.QuoteLegend;
                        issue.Evidence.Quote.Attributed = quot.QuoteText;
                    }
                }, function (e) {
                    app.Logger(e);
                });
                $q.all([promiseImageLib,promiseSupp,promiseQuote]).then(function(r){
            })
        });
        var isDone = $q.all([promiseEvidence]).then(function(r){

    })
}

Answer 1

考慮這一點的一種好方法是，您的諾言鏈的構建與它們的執行無關。 一旦有了適當的心理模型，就很容易進行推理了。

讓我們將其分解為幾個步驟，然后從那里構建代碼。

執行異步代碼並允許操作在完成后發生：

function doSomeAsyncWork(){
   var promise1 = foo();
   var promise2 = bar();
   var promise3 = blah();

   return $q.all([promise1, promise2, promise3]);
}

重復此代碼N次，但順序重復。 在第一次迭代運行之后。

function doWorkNTimes(n) {
 var lastPromise;

 for (var i = 0; i < n; i++) {
     //After initial promise, keep
     // chaining them together
     if (lastPromise) {
       lastPromise = lastPromise.then(function(items) {
         return doStuffAsync(i);
       });
     } else {
       lastPromise = doStuffAsync(i);
     }
 }

 return lastPromise;
};

這是一個工作示例，稍微復雜一些，但應該說明這一點。

 (function() { 'use strict'; function getRandomInt(min, max) { return Math.floor(Math.random() * (max - min)) + min; } function promiseController($q, $timeout) { var vm = this; vm.results = []; vm.numTimes = 3; vm.isBusy = false; vm.isDone = true; vm.doWork = function(times) { vm.results.splice(0); vm.isBusy = true; vm.isDone = false; doWorkNTimes(vm.numTimes || 1) .finally(function() { vm.isBusy = false; vm.isDone = true; }); }; function doWorkNTimes(n) { var lastPromise; for (var i = 0; i < n; i++) { (function(i) { if (lastPromise) { lastPromise = lastPromise.then(function(items) { return doStuffAsync(i); }); } else { lastPromise = doStuffAsync(i); } lastPromise.then(function(items) { //console.log(items); vm.results.push(items); }); }(i)); } return lastPromise; }; function doStuffAsync(i) { var prom1 = createPromise(i), prom2 = createPromise(i), prom3 = createPromise(i); return $q.all([prom1, prom2, prom3]); } function createPromise(i) { var timeout = getRandomInt(200, 2000); return $timeout(function() { var item = { iteration: i, executionTime: timeout }; //console.log(item); return item; }, timeout); } } angular.module('promise-sample', []) .controller('promiseController', promiseController); }()); 

 <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css"> <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.0-beta.4/angular.min.js"></script> <div class="container" ng-app="promise-sample" ng-controller="promiseController as ctrl"> <div class="row"> <div class="col-xs-6"> <div class="form-group"> <label>Number of Iterations</label> <input type="number" class="form-control" min="0" max="10" ng-model="ctrl.numTimes" /> </div> <div class="form-group"> <button type="button" class="btn btn-primary" ng-click="ctrl.doWork()">Run {{ctrl.numTimes}} Times</button> </div> </div> <div class="col-xs-6"> <table class="table table-striped" ng-repeat="set in ctrl.results"> <thead> <tr> <th>Run</th> <th>Time</th> </tr> </thead> <tbody> <tr ng-repeat="item in set"> <td>{{::item.iteration}}</td> <td>{{::item.executionTime}}</td> </tr> </tbody> </table> </div> </div> </div>