javascript - 如何使用 Promise 将异步 Angular 函数的值返回到调用方法中？

Question

我有一个填充了 for 循环的列表，我通过这种方式调用 assync 函数:

在我调用的 For 循环中

  row.SUCCES_RATE_SINCE = $scope.computeSuccessRateSinceStart(row);

被调用的函数

  // Calculate percentage of a whole from since
    $scope.computeSuccessRateSinceStart = function(row) {

        db = window.sqlitePlugin.openDatabase({name:"callplanner"});
        // GET APPT COUNT
        db.transaction(function(tx) {
        tx.executeSql(sqlQuery, [], function(tx,results){
            // init empty array for results
            for (var i=0; i < results.rows.length; i++){
                row = results.rows.item(i);
                //Udpate date for writeout
                //row.DATE = moment(row.DATE).format('ddd DD.M');
                console.log("row APPT count is " + JSON.stringify(row));
                apptCnt = row.APPT_CNT;
                convCnt = row.CONVERS_CNT;
                dailySuccessRateSince = apptCnt / convCnt * 100;
                console.log("Success rate since is " +dailySuccessRateSince);
                // THIS IS NOT WORKING
                return Math.round(dailySuccessRateSince);

            }
            });
        },function (e) {
                console.log("ERROR: " + e.message);
                $ionicLoading.show({
                    template: $translate.instant('ERROR_DATABASE'),
                    duration:1000
                });
        });

    };

问题是计算值总是返回 null(返回函数在值在范围内可用之前执行)。

我对 Angular 还很陌生，但我发现这个问题可以使用 promise 来解决。有人能给我一个如何正确返回值的例子吗？

非常感谢您的帮助。

编辑:

现在触发了调用的方法，但我无法将返回值传递给变量，如下所示:

var test = $scope.computeSuccessRateSinceStart(row).then(function(result){
     //ALERT WITH VALUE WORKS FINE
     alert("Result " + result);
     return result;
    });
    // THIS GIVES ME EMPTY ARRAY {}
    alert("Result " + JSON.stringify(test));

Answer 1

为什么不让你的方法始终返回一个 promise ，然后从 promise 中提取结果？

$scope.computeSuccessRateSinceStart = function(row) {
    var deferred = $q.defer();

    db = window.sqlitePlugin.openDatabase({name:"callplanner"});
    // GET APPT COUNT
    db.transaction(function(tx) {
        tx.executeSql(sqlQuery, [], function(tx,results){
            // init empty array for results
            for (var i=0; i < results.rows.length; i++){
                row = results.rows.item(i);
                //Udpate date for writeout
                //row.DATE = moment(row.DATE).format('ddd DD.M');
                console.log("row APPT count is " + JSON.stringify(row));
                apptCnt = row.APPT_CNT;
                convCnt = row.CONVERS_CNT;
                dailySuccessRateSince = apptCnt / convCnt * 100;
                console.log("Success rate since is " +dailySuccessRateSince);
                // THIS IS NOW WORKING:
                deferred.resolve(Math.round(dailySuccessRateSince));
            }
        });
    }, function(e) {
        console.log("ERROR: " + e.message);
        deferred.reject(e);
    });

    return deferred.promise;
};

用法:

$scope.computeSuccessRateSinceStart(row).then(function(result){
    // THIS GIVES THE VALUE:
    alert("Result " + JSON.stringify(test));
    return result;
}, function(e) 
    $ionicLoading.show({
        template: $translate.instant('ERROR_DATABASE'),
        duration:1000
    });
});