Resolving Promises Asynchronously in angularjs

My code:

$q(function (resolve) {
    var imageUploadResults = [];
    fileUploadService.uploadImage($scope.filesUpload, "/api/mailbox/uploadAttachFile", function (result) {
        console.log(result);
        imageUploadResults.push(result.LocalFilePath);
    });
    $scope.mail.Files = imageUploadResults;
    resolve($scope.mail);
}).then(function (mail) {
    console.log(mail);
    apiService.post("/api/mailbox/sendMail", mail, sendMailSucceed, sendMailFailed);
});

Expect:
I want to add value to mail.Files finish,then call apiService.post()
Actual:
But it execute apiService.post() with mail.Files value is [].
When apiService.post() execute finish mail.Files return value.length > 0.

------Answers-----

1.

Without knowing exactly which library you are actually using, it seems clear to me that fileUploadService.uploadImage() is asynchronous.
The function that you give as an argument is a callback and there is no guarantee that it would be executed "on time". In your case the path is added to imageUploadResults after the moment where you set $scope.mail.Files.
you should set $scope.mail.Files and call resolve in your callback function.

$q(function (resolve) {
    var imageUploadResults = [];
    fileUploadService.uploadImage($scope.filesUpload, "/api/mailbox/uploadAttachFile", function (result) {
        console.log(result);
        imageUploadResults.push(result.LocalFilePath);
        $scope.mail.Files = imageUploadResults;
        resolve($scope.mail);
    });
}).then(function (mail) {
    console.log(mail);
    apiService.post("/api/mailbox/sendMail", mail, sendMailSucceed, sendMailFailed);
});

2.

When you assigned $scope.mail.Files = imageUploadResults; and resolved resolve($scope.mail); there are no guarantee that fileUploadService.uploadImage finished request and saved imageUploadResults.push(result.LocalFilePath);
Possible solution is to add resolve($scope.mail); right after imageUploadResults.push(result.LocalFilePath); in function passed to fileUploadService.uploadImage